The field of lightwave communications is undergoing a revolution brought about by recent achievements in optical amplifier technology. Erbium-doped fiber amplifiers (EDFAs) permit a variety of system architectures that facilitate greater access to the vast transmission capacity inherent in optical fibers, thereby providing significantly increased networking functionality and operational flexibility for both terrestrial networks and undersea-cable systems, all potentially at lower cost than at present. The features of EDFAs specific to the various applications include: high saturation power as transmitter power amplifiers, low-noise operation as receiver preamplifiers, a wide gain spectrum for amplifying a large number of wavelength-division-multiplexed (WDM) signals, and linear gain for analog amplification. Equally important, their simple construction utilizing reliable semiconductor pump lasers will allow system planners to design communications networks having substantially enhanced reliability. It can be said that lightwave communications is now passing from a replacement phase to a revolutionary phase, and the fiber optical amplifier is the catalyst in this transformation.

High average power Nd-YAG lasers in the multi-kilowatt are reviewed. The different configurations multi-rod, multi-slab, tube in various resonator set-ups are discussed in detail with respect to maximum output power, efficiency, and beam quality. The 3 kW-Nd-YAG laser under investigation in the lab and the planned 5 kW system are briefly presented.

Research activities on optoelectronic devices in China are reviewed with emphasis on quantum well semiconductor lasers, DFB laser diode and wideband tunable narrow-linewidth external cavity laser diode, laser diode pumped solid state and single crystal fiber lasers, doped fiber ring laser, semiconductor and doped fiber amplifiers, optical modulators, switches and bistable devices.

A novel industrial CO₂ laser is presented, based on a proprietary combination of rf excitation, conductive cooling, and a specially fitted resonator, conforming with the size and shape of the discharge. This design results in the most compact laser-head of the kilowatt class that is available on the market. The current model, ICCL 1000, generates about 1200 watts, in a high quality beam suitable for metal-cutting applications.

An enhanced turbulence fast axial flow CO₂ laser has been developed. The new helical cascaded metal discs discharge tube formed by hard anodized aluminum discs promises higher hold-off voltage, larger effective active volume, and good thermal conduction. The specific laser power has attained 1100 W/m for 2.1 cm tube diameter. Theoretical calculation of the effects of turbulent flow on the radial distribution of electron density, gas temperature, and small signal gain are presented.

CO₂ lasers have been used in industry mainly for such things as cutting, welding, and surface processing. To conduct a broad spectrum of high-speed and high-quality applications, most of the developments in industrial CO₂ lasers at the ILT are aimed at increasing the output power, optimizing the beam quality, and reducing the production costs. Most of the commercial CO₂ lasers above 5 kW are transverse-flow systems using dc excitation. The applications of these lasers are limited due to the lower beam quality, the poor point stability, and the lower modulation frequency. To overcome the problems we developed a fast axial- flow CO₂ laser using rf excitation with an output of 13 kW. In section 2 some of the results are discussed concerning the gas flow, the discharge, the resonator design, optical effects of active medium, the aerodynamic window, and the modulation of the output power. The first CO₂ lasers ever built are diffusion-cooled systems with conventional dc excited cylindrical discharge tubes surrounded by cooling jackets. The output power per unit length is limited to 50 W/m by those lasers with cylindrical tubes. In the past few years considerable increases in the output power were achieved, using new mechanical geometries, excitation- techniques, and resonator designs. This progress in diffusion-cooled CO₂ lasers is presented in section 3.

High-power lasers are characterized by high gains and large apertures. This leads to multimode operations of most high-power lasers (longitudinal and transverse), which in turn results in the complicated spatiotemporal modal behavior and the partial coherence of high-power laser beams. In section 2 we present some experimental results which show that the characterization of high-power laser beams using the beam quality such as K^* and M² is not sufficient and the application results are dependent on the intensity profile, its propagation and intensity fluctuations. According to the spatial coherence of the laser beam the average intensity distribution along the propagation can change distinctly. This is especially true in the case of laser beams from unstable resonators. To characterize high-power laser beams the propagation of the intensity profile has to be described. As shown in section 3 the propagation of the intensity profile is determined if the mode coherence coefficients (MCCs) are known. Furthermore, temporal local fluctuations notorious with high power lasers impair all applications, notably those with high processing speed and high process quality. Therefore, to correlate the application results to the laser beam performances the information about the intensity fluctuation is necessary. In section 4 we discuss a method to characterize the local intensity fluctuation. Finally, the main results are summarized in section 5.

Radiation from two new kinds of rare-gas fluoride ionic excimers, Ar²⁺F^- and Kr²⁺F^- was observed near 125 nm and 148 nm in experiments. Detailed radiation processes and kinetics are analyzed theoretically and experimentally.

In this paper, we consider the physics of slab laser discharges and in particular, the conditions for the avoidance of the alpha-to-gamma discharge instability at high power densities, and their implications for the design of waveguide slab lasers. The specific power extracted from multimode slab lasers has been observed to vary inversely with electrode separation, d and values to 30 kW.m^-2 have been achieved. In addition, multi-hundred watt cw power output has been observed at pressures of half an atmosphere without the use of high helium concentrations. For small values of d, the beam profile in the transverse direction is that of a fundamental waveguide mode, so the design of resonators for high quality output beams reduces to a 1-dimensional problem. As a consequence of the low losses associated with hollow waveguide propagation in the transverse direction, it is possible to achieve efficient, high power laser outputs while employing an unstable resonator configuration in the lateral dimension, despite the comparatively low gain of the cw carbon dioxide laser. We report the achievement of high quality laser beams from such resonators at power levels in excess of 1 kW from a sealed diffusion-cooled device. A second design of resonator has been demonstrated, in which a single high order waveguide mode in the lateral (wide) dimension of the slab is selected using a new mode control technique, which is based upon intra-cavity coherent imaging and depends on the exploitation of the Talbot effect. Results obtained with this all-waveguide resonator are presented.

A slab waveguide CO₂ laser excited by microwave has been constructed to obtain the output in identical phase locking coherence in far-field. In the first part of this paper, the construction of a microwave excited waveguide resonator is determined. Calculations on the design of a slab CO₂ optical waveguide are shown in the second part, while theoretical estimate of output is given in the third part. Finally, the experiment is reported.

In this paper, an rf excited waveguide CO₂ laser with a supermode output has been experimentally studied. At a distance over 4 meters, a stable far field distribution with a suppressed single peak has been obtained without using any of the optical focusing elements.

High frequency excitation is increasingly substituting for dc discharge excitation of the high power CO₂ laser, in general, a great quantity of helium is applied in a common high power CO₂ laser. In order to reduce the operation cost of CO₂ laser, a helium-free transverse flow CO₂ laser excited by high frequency has been researched. In this paper, some of the investigations of discharge characteristic and output characteristic are presented. It is shown that, under our experimental condition substituting Ar for He in the CO₂ laser, the maximum input discharge power density is stable up to about 21 W/cm³, the output laser power and photoelectric efficiency are 600 W and 13%.

The influence of electrode on laser gas stability of the CO laser by several kinds of metal materials is investigated. These materials are aluminum, phosphorus copper, OFHC copper, silver copper, stainless steel, nickel, and tantalum. From the analysis of the adhesion on the surface of the electrode after discharge, we get the information about the surface variation, and this can be the basis according to which we can select suitable electrode material. We find that tantalum is a relatively good electrode material for the CO laser.

The present ways and new ways for finding VUV/XUV lasers are briefly reviewed and comments made. This paper concentrates on describing the author's experiments, theoretical works, and results on the two new ways, cluster laser (or Excister laser) and high-order harmonical laser.

A new free electron laser concept has been developed which is capable of providing high power optical beams with novel polarization states. It is possible to generate azimuthally polarized radiation with properly chosen electron beam and wiggler field parameters in a free electron laser. The radiation can be easily converted into a radially polarized beam which is suitable for providing a high longitudinal electric field for next-generation particle accelerators.

In this paper we have analytically researched the degradation of the super-radiance power in an optical klystron due to the energy spread and the emittance of the electron beam.

Although operational for over twenty years, diode pumped solid state lasers have, for most of their existence, been limited to individual diodes pumping a tiny volume of active medium in an end pumped configuration. More recent years have witnessed the appearance of diode bars, packing around 100 diodes in a 1 cm bar which have enabled end and side pumped small solid state lasers at the few watt level of output. This paper describes the subsequent development of how proper cooling and stacking of bars enables the fabrication of multi kW average power diode pump arrays with irradiances of 1 kW/cm peak and 250 W/cm² average pump power. Since typical conversion efficiencies from the diode light to the pumped laser output light are of order 30% or more, kW average power diode pumped solid state lasers now are possible.

The dynamics of a two-element nonlinear-coupled laser array are briefly reviewed. It is pointed out that if the pump of the laser array reduces to zero for a time period shorter than the population decay time, then the system reduces to two coupled equations for the relative intensity and relative phase. It is well-known from the Poincare-Bendixson theorem that such an autonomous system of dimension two (without detuning) cannot exhibit chaos. By creating two evanescent-coupled lasers in a Nd:YAG etalon using diode end-pumping, the coupling strength between the two laser elements in the array can be continuously varied by adjusting the position of the pumping beams. This allows the observation of the phase locking process over a wide range of coupling strength. We have found that the locking is as fast as the on-set of lasing without undergoing a transition state as along as the coupling is strong enough to ensure such locking. The instantaneous locking is also independent of the coupling strength once the coupling is strong enough to ensure phase locking. New interpretation of phase locking process for a phase locked laser array is provided.

In order to improve the laser efficiency of LD end-pumped solid state lasers, it is important to optimize the mode matching between laser cavity mode and pumping beam mode. In our experiments a CCD array camera is used to measure the 3-D distribution of pumping beam transformed by matching optics, and by measuring the output laser beam parameters, the intracavity mode parameters of the solid state lasers also are determined. The result is useful for designing LD end-pumped solid state lasers.

The operation of an efficient, cw, TEM₀₀ mode Nd:YAG laser end-pumped by a laser diode has been achieved. The maximum output was 0.65 W. A 51% slope efficiency and 40.6% overall optical efficiency were obtained. Coupling optics and laser configuration are described in this paper.

An LD pumped YAG-KTP intracavity frequency doubling laser has been developed. A cw linearly polarized green laser at 532 nm is obtained. The pumping threshold, output power, and slope efficiency are 12 mW, 2.5 mW, and 5%, respectively. The influence of the states of pump light on transverse modes of the frequency doubling laser has been studied. The experimental methods and results are reported briefly.

The first modified neodymium yttrium aluminum borate (M-NYAB) self-doubling laser pumped by LD has been designed. The properties of the lasers are much better than those of NYAB self-doubling lasers pumped by LD. All of the M-NYAB self-doubling lasers pumped by LD can operate in TEM₀₀ mode and the pumping threshold is less than one-third of that of LD pumped SFD laser with NYAB. The pumping threshold, maximum output power, and slope efficiency are 3.6 mW, 29 mW, and 4.8%, respectively.

We report on the first laser diode pumped Nd:YVO₄ fundamental and second harmonic lasers made in China. The threshold pumping power of the LD-pumped Nd:YVO₄ fundamental laser is 4.5 mW. The cw 1064 nm output power is 64 mW with slope efficiency of 10.7%. The threshold pumping power of the LD-pumped Nd:YVO₄ intracavity frequency doubling laser with KTP doubler is 12.5 mW. Nineteen mW of fundamental-mode 532 nm green laser were measured with a slope with a slope efficiency of 3.2$%. Experiment setups and results are discussed.

The pulse width of a Q-switched diode laser pumped solid-state laser is compressed by the technique of gain switching for the first time. The experimental results are in agreement with the calculated values. Relations between pulse duration, peak power, and step jumping pump are discussed in detail.

In this paper, we report the influence of cavity QED effect on the fluorescence spectra of Nd- glass microspheres. The relative magnitude of the spikes and the background in spectra are analyzed. The cavity QED enhancement of spontaneous emission rate is estimated to reach 16 times.

In this paper, a detailed theoretical analysis is made about the beating frequency phenomenon of laser temporal profile induced by multi-mode oscillation in a laser resonator. Various possible temporal profiles of laser output are plotted by computer. The numerically calculated results are compared and in good agreement with experimental photographs.

A type II noncritically phase-matched LiB₃O₅ optical parametric generator pumped by a 30 ps 355 nm laser pulse is reported. 482.6 - 415.9 nm tunable wavelengths with linewidths as low as 0.15 nm, the highest pump-to-signal energy conversion efficiency up to 37.6%, and 6.33 mJ 211 MW peak-power single pulse have been achieved. Optical parametric process is a well-known way used to generate a high power tunable laser. The development of both the new nonlinear crystals such as (beta) -BaB₂O₄(BBO)¹ and LiB₃O₅(LBO)² and the high peak-power (GW) coherent sources have provided a good experimental situation.

The influences of lateral magnification M and optical interval (Delta) on the output of 1.54 micrometers intracavity Raman laser are studied, by using matrix optical methods, and the results are confirmed experimentally.

Based on the F-P interferometer with a radial variation, a mirror with a radial reflectivity variation is achieved by means of constructive interference in the center and destructive interference on the edge. The principle of the variable reflectivity mirror (VRM) is described. Errors are analyzed and estimated. A practical technique for developing the VRM is introduced. Experimental results of using the variable reflectivity output coupler in a Nd:YAG laser is reported.

We review the progress that has been made at Shanghai Institute of Optics and Fine Mechanics (SIOFM) on the Li-like recombination x-ray lasers and present the recent results on short wavelength Li-like x-ray laser gain experiments conducted at LF12 High Power Laser Facility. Also presented are the time behaviors of ASE emission in the Li-like x-ray lasers.

A theoretical investigation has been undertaken to study mode distribution in an x-ray laser (XRL) cavity comprised of mirrors with incident angle dependent reflectivities. Numerical solutions of integral equations are obtained for nonuniform cavities of rectangular plane mirrors and circular plane mirrors. Curves for field distribution and phase shift are given for different mirror geometries and different modes. Comparisons between XRL cavity and usual optical cavity are made.

Various optical thin films of metal oxides and ITO have been deposited by low voltage reactive ion plating technique. Analysis of the resulting thin films shows that their microstructures are evidently improved.

Since it has many outstanding properties, chemical vapor deposition (CVD) diamond thin film should be an excellent optical coating, but it has not been widely used because its surface is too rough. For reducing the surface roughness we tried different ways to process the substrates, choose optimum film growing conditions, polish the surface by ion beam and cover it with diamond-like-carbon (DLC) films. It has been shown that with the appropriate process, we can reproducibly get pretty smooth surface with roughness less than 250 angstroms and the transmittance of a silicon substrate, single side coated with diamond film, approaches 66% at wavelengths around 6 micrometers , which means the light scattering of the sample has been reduced to less than 1%.

The preparation and performance of AlNxOy solar energy selective absorptive film used in a vacuum tube and a flat-plate collector are described in this paper. The absorptive film with (alpha) equals 0.94, 310 degree(s)C equals 0.136 is deposited on Al substrate using single target metal Al reactive sputtering technology.

In this paper, we summarize crystal physical, spectroscopic, and laser characteristics of Ti:sapphire. We report the recent results of our study on the residual infrared absorption of the crystals, tunable lasers, and frequency doubling of the lasers. The recent development of various Ti:sapphire lasers in the world is briefly reviewed.

We report here the preliminary experimental results of a gain-switched Ti:sapphire laser in which some characteristics of the output pulses were investigated. In these experiments the minimum laser pulsewidth of 1.2 ns has been obtained and pulsewidth can be varied from 5 ns to 27.5 ns continuously under certain experimental conditions.

Quasi-continuous wave titanium-doped sapphire laser pumped by frequency doubled YAG laser was investigated. The maximum average output power is 2.7 W with 11.2 W pump power, and the tuning range is 750 to 870 nm by using one set of cavity mirrors. The rate equations of this type of laser were also developed. Theoretical predictions are confirmed by experimental measurements.

The Q-switching run and mode-locking run of laser self-frequency-doubling from 1.06 micrometers to 0.53 micrometers have been realized for the first time in self-active and self- frequency-doubling NYAB crystal pumped by an xenon flash lamp. Several MW/cm² giant pulse outputs at a 0.53 micrometers wavelength and a 0.53 micrometers ultrashort pulse chain of 0.22 mJ energy and 220 ps in duration were obtained, respectively. Meanwhile, the single green light pulse output energy and pulse duration were measured under the conditions of different resonator lengths and pumpings, and the ways of improving the green laser output peak power are proposed. The possibility of obtaining a total-solid NYAB mode-locked laser is discussed.

We present research on an Nd:YAG Q-switched laser with VRM optical resonator. High beam quality can be obtained efficiently by choosing an optimum profile, central reflectivity of VRM, and a magnification of an unstable resonator. Up to 100 mJ TEM₀₀ mode output pulse (10 ns pulsewidth) can be obtained with (phi) 5 X 50 mm Nd:YAG rod. A new viewpoint about perturbation stability of the resonator is also discussed in this paper.

In order to obtain a good beam quality from a high power, high repetition rate Q-switched Nd:YAG laser, a complete understanding of the thermally induced birefringence is necessary. We advanced a method by using a computer to simulate the photoelastic effects inside the Nd:YAG working material and developed a set of graphs on thermally induced birefringence via different electrical input power (e.g., 1, 2, 3, 4 kW) and different values in (e.g., 3, 4, 5, 6 mm) diameter of the YAG rod. The simulated results indicate the optimum way of thermal birefringence compensation under different pumping and cooling conditions.

On the basis of the GaAs photoconductor characteristic of the decrease resistance with the increase of irradiation, we first developed a high precision and ultrafast positive and negative feedback circuit. By using these techniques, we have made a novel method of mode-locking, automatic mode-selecting, Q-switching, and realizing synchronizing outputs of two independent pulse oscillators, the jitter is no more than +/- 1 ns.

GaAs used in a passively mode-locked Nd:YAG laser is demonstrated to be influential on pulse shortening and chirp production. Additional pulse shortening is partly due to the induced self-diffraction of colliding light pulses in GaAs. The frequency shift and chirp arising from the nonlinear refractive index induced by free-carrier generation in GaAs have also been investigated. Experiments on pulse compression from 23 ps to < 10 ps and showing the downchirp produced in pulse are finished.

A phenomenon of Q-switching due to stimulated Raman scattering in methane and the experimental studies of some features of methane Raman laser with stimulated Raman scattering for Q-switching are presented. The output energies from 0.21 to 4.9 mJ per pulse have been obtained with a pulse width of 6 ns at 1.54 micrometers .

In conventional DFB semiconductor lasers, the distributed feedback of optical wave is provided by the periodic perturbation of waveguide index along the laser axis. This index- coupled DFB laser has a troublesome problem of producing a pair of longitudinal modes having equal threshold gain. Kogelnik and Shank predicted that this threshold degeneracy could be removed if the optical feedback was provided by the periodic perturbation of gain coefficient. The attempt to apply the gain coupling mechanism to DFB semiconductor lasers was started in 1988 by the present authors. In these four years it has been elucidated that the gain-coupled DFB semiconductor lasers have many advantages such as excellent single mode nature, reflection insensitivity, and low-chirping short optical pulse generation capability. In this talk various kinds of the gain-coupled DFB lasers developed so far and their main features are introduced and reviewed.

Improved characteristics of gain-coupled distributed feedback (DFB) semiconductor lasers are obtained by optimizing the duty cycle of the absorptive grating and using an absorptive conduction-type-inverted grating. Low threshold current cw operation is achieved at 10 mA lower than lasers without conduction-type-inverting. Furthermore, improved linear oscillation and a narrow linewidth are demonstrated. For gain-coupled DFB semiconductor lasers based on absorptive gratings, ultralow chirping operation under gain switching conditions is obtained for the first time.

Various semiconductor laser material system and device structures which have led to the ultralow threshold current (<EQ 1 mA) operation are reviewed with an emphasis on the quantum well (QW), especially strained QW, structures. To date, cw threshold current as low as approximately 1 mA for as cleaved lasers and 0.35 mA (pulsed 0.25 mA) for high reflectivity coated lasers are realized. These low threshold lasers also display excellent dynamic behavior, a direct current modulation bandwidth of 4.6 GHz at a bias current of only 1 mA above threshold has been demonstrated.

In a practical quantum well structure, the separate confinement heterostructure is usually employed to confine the optical field in the waveguide and the injected carriers in the quantum well region. The fundamental Fermi-Dirac statistics results in that, in addition to the carrier population in the quantum well region, there is also a significant carrier population in the optical confining region (referred to as the state-filling effect in the quantum well structure). The differential gain depends on the rate of increase of the quasi Fermi energies with respect to the increase of injected carrier density. The presence of upper subbands with large density of states tends to clamp the Fermi energies thus leading to a degradation in the differential gain. The state filling effect also significantly affects the amplitude-phase coupling and the spectral linewidth of quantum well lasers as a direct consequence of its influence on the differential gain.

In this paper, light amplification and frequency modulation of an InGaAsP/InP bistable laser are investigated experimentally. The lowest light power for switching the device on was about 2 (mu) w, and optical digital gain was larger than 30 dB with switch on time being less than 100 ps and switch off time less than 0.5 ns. Based on the rate equation, theoretical analysis shows that the width and height of an injected pulse plays an important role in switch operation and determines the delay time during switch on process along with the level of the current bias. In 3-terminal operation of the device, with the `on' pulse applying to the absorption region, the delay time can be reduced and a modulation frequency over 2 GC is expected.

A novel wavelength-tunable semiconductor laser is proposed, where use is made of a chirped grating. Threshold conditions of this chirped grating tunable (CGT) distributed feedback (DFB) laser with three electrodes have been numerically studied on the basis of coupled-mode equations with transfer-matrix forms. It has been found that the DFB lasers with gratings properly chirped may have enhanced single-mode continuous tunability. A preliminary experimental result has shown a 7.3 nm tuning range in a GaAlAs/GaAs CGT DFB laser.

The laser source with good performance is very important in the optoelectronics field. In this paper, a dual-wavelength laser source with single mode and high stability is introduced. The paper content consists of structure, principle, features, and performances.

By employing both multi-quantum barrier (MQB) and strained InGaP active layer including strained multi-quantum well (MQW) into a 670 nm region visible (red) laser diode, cw output power of 60 mW in a fundamental transverse mode oscillation even at 100 degree(s)C has been realized.

In this presentation, the valence band mixing effect in strained quantum well structures based on the multiband effective mass theory is first presented. By using the envelope function approximation and the direct variation method, the valence band structures of some strained III-V semiconductor quantum well systems which are of interest to photonic applications are discussed. With the knowledge of the electronic wave functions and the energy band structures, optical gain behaviors of the strained quantum well systems are analyzed using the density matrix theory. The polarization dependence of the optical gain in strained layers is discussed in association with the dipole moment between the conduction band and the valence band. It is shown that biaxial compressive strain can reduce the asymmetry between conduction band and heavy-hole band masses, thus resulting in the reduction of laser threshold current as well as losses due to Auger recombination in semiconductor lasers.

Quaternary alloys of semiconductor compounds are suitable materials for wide-spectrum optoelectronic applications. The most important property of these efficient luminescent materials is the opportunity to fit the lattice parameter in some range to a given value corresponding to another crystalline material. This leads to the method to construct defect-free and stress-free heterojunctions, which was used for the preparation of a number of laser and LED devices. Quaternaries of InGaAsP, InGaSbAs, InSbAsP, PbSnTeSe, and other alloys were introduced into practical usage particularly in diode laser devices. The alloy InGaAsP appears to be one of the most widely used in optoelectronic applications at present as it covers ranges near 1.3 and 1.55 micrometers wavelengths of fiber-optic communication. For the spectral range near 2 micrometers the alloy InGaSbAs seems to be most attractive, and cw-operating diode lasers at room temperature were demonstrated at 2.0 - 2.4 micrometers . The alloy PbSnTeSe was used to obtain a longest wave of diode laser emission 46 micrometers . Quaternaries played an important role in the development of the semiconductor optoelectronics during the last two decades.

Optoelectronics research has been established at OES/ITRI since 1981. The R&D program started from compound semiconductor crystal growth. The major contribution is the development of a modified horizontal Bridgman method for growing GaAs single crystals. In the area of optoelectronic devices, both liquid phase epitaxy (LPE) and the metalorganic vapor phase epitaxy (MOVPE) are used to fabricate most of the light emitting diodes (LED), laser diodes (LD), and photodetectors (PD). The light sources with emitting light wavelength from visible 0.65 micrometers to 1.3 micrometers were made. Detectors, such as Si PIN and InGaAs PIN were developed. We are focusing on a new material system, i.e., AlGaInP. The LED and LD at the wavelength of 0.67 micrometers were grown by MOVPE. The threshold current is about 60 mA for a ridge-waveguide laser.

We report the results of a novel method for frequency-tracking and locking of the diode laser using the transmission spectrum of a Faraday anomalous dispersion optical filter (FADOF) as our frequency discriminator. A frequency stability of better than 2.1 X 10^-10 for 100 ms <EQ (tau) <EQ 10 s was obtained, and continuous frequency scans of more than 2 GHz were made by changing the intensity of the magnetic field of the FADOF from 70 G to 220 G.

Travelling wave rate equations have been used to study the optical bistability of the two- segment laser diodes. Closed form solutions for photon flux inside the cavity have been deduced and some aspects of the bistable lasers discussed.

The experimental value of the modal reflectivity of a semiconductor amplifier with AR coatings determined from the recorded spontaneous emission spectrum changes with the passband width of the grating monochromator used. It is found that the measured reflectivity becomes smaller as the passband width becomes larger, and takes its minimum periodically when the passband width is equal to multiples of the mode spacing of the diode. Under certain circumstances the measured value may be orders of magnitude different from the true reflectivity. In order to achieve a reliable measurement, the passband width should be kept less than 1/5 of the mode spacing of the diode.

Analog optical fiber communication requires linear modulators with low third order intermodulation and harmonic distortions in order to realize sufficient dynamic range. We report here a novel design of the directional coupler modulator which has used passive serial feedforward mechanism to effectively compensate nonlinear distortions. Low frequency testing has demonstrated that, for an optical modulation depth of 30% per channel, the third order intermodulation distortion is more than 30 dB lower than that of the conventional directional coupler or Mach-Zehnder modulators. Harmonic distortions are reduced substantially at the same time. Operation at rf and microwave frequencies is limited by the transit time effect.

Advances in conventional technologies are reviewed first. The contributions of various components, namely optical amplifiers, external modulators, tunable and narrow-linewidth lasers, high-sensitivity and high-speed detectors, and dispersion-shifted fibers, to the realization of higher speed and longer span fiber communications are discussed. The effect of techniques such as time-division and wavelength-division multiplexing, coherent detection, and dispersion compensation is explored. Optical soliton transmission is then reviewed as an alternative technology. Finally, mid-infrared communications based on new fluoride fibers and associated transmitters and receivers are considered. The author's opinions on the prospects for each approach, in the context of their limitations, are presented.

We review the reduction of losses in Y-branch waveguides using the phase-front accelerator (PFA) design. The use of the PFA design helps not only in reducing the junction loss significantly, but also in achieving faster settling lengths, multi-branch equal power dividers, and in improving the range of power splitting ratios in integrated optical proportional beam splitters.

Theoretical and experimental investigations of the nonlinear refractive index in an erbium- doped fiber are reported. We also show that an optical switch based on twin-core erbium- doped fiber can be constructed and operated at low input optical power, in the order of 1 or 2 mW. The transient response of this fiber also is examined. The switching speed can be improved by using a signal power at a wavelength close to the resonant wavelength between the excited state and the ground state.

Using a comprehensive model proposed by the author, it is found that the amplified spontaneous emission (ASE) propagating opposite to the pump beam causes depression to pump and signal evolution near to the pump input end of a high-gain erbium-doped fiber amplifier (EDFA). In a m-stage cascaded EDFA chain, the S/N ratio is inversely proportional to m, and the gain may decrease with increasing m if the signal wavelength markedly deviates from the ASE peak wavelength.

Focal shift of the zone plate is completely different from the corresponding circular and annular apertures. Focal powers of the zone plate are constant under some conditions but for the latter they are always variables. Astigmatism for a zone plate is also investigated. The sagittal focal surfaces are unchanged but the tangential focal surfaces are changed as a function: cos²(Theta) , besides, it has neither spherical aberration nor coma. They are also completely different from conventional imaging devices.

A method for measuring a distributed external pressure field along an optic fiber is discussed, which is based on the principle of mode-coupling of polarization-maintaining fiber and optical path compensation in the interference of two beams from a broadband light source. A modified Mach-Zehnder interferometer is used to process the optical signal representing the distributed pressure information, and a polarization light heterodyne detecting technique is used to improve the signal-to-noise ratio and to eliminate the influences of light source fluctuation and background light. For the automatic measurement of the distributed pressure information, an A/D and interface circuit is designed. Under the control of the microcomputer, the arm of the interferometer with an optical path scanning setup scans a distance corresponding to the length of the fiber, then the information of the pressure field is obtained. The experimental results have shown that the measuring system has a high measurement accuracy and a rather large pressure measuring range (10 g/mm - 500 g/mm).

For an extremely large-capacity asynchronous transfer mode (ATM) system, it is required to develop photonic switching devices with high-speed and broadband capabilities. System requirements for photonic devices are presented. Recent research topics on integrated semiconductor switching devices including space- and frequency-division switches are also described.

A new master recorder with UV Ar laser ((lambda) equals 351.1) has been developed to study high density optical recording for a future optical video disc system, in combination with high resolution photoresist process. High CNR of 63 dB was demonstrated in 4-times density recording using a read-out optical system with He-Cd laser ((lambda) equals 441.6 nm).

For more than twenty years, SONY has participated in the development of CCD image sensors. This paper has been written in order to gauge the prospects for the future, introduce SONY's CCD history and recent technical trends.

Progress of optical data storage technology and application systems, which have been obtained in recent years at Tsinghua University, are reviewed. In this paper, the new multifunction optical drive, miniaturizational optical head, high speed precise seeking system, automatic exchange disk system (jukebox), controller interface adapter, data compression technology, and various application systems are reported.

This paper presents a new optoelectronic hybrid numerical system for the parallel processing of algebra polynomial evaluation. Free-space optical perfect shuffle interconnection network is adopted in our systems. Optical interconnection networks can make the operating time the minimum, which is proportional to log₂N.

The light-harvesting protein in the purple membrane of halobacterium halobium, called bacteriorhodopsin, has been proposed as an erasable holographic storage medium. It has demonstrated recording properties superior to those of conventional materials, with switching times on the order of picoseconds. It has been shown capable of storing both amplitude and phase holograms, or a combination thereof, with diffraction efficiencies on the order of 7%. While this is lower than in some silver halide applications, other properties, such as its virtually infinite shelf life and its diffraction limited resolution of 5000 l/mm, are outstanding compared to conventional materials. There are many holographic applications of bacteriorhodopsin, such as spatial light modulation, optical associative memory, and high speed interferometry. Each of these applications requires the temporary storage of an image during processing, with rapid erasure and re-exposure. Through its change in absorption spectrum, its large variation in refractive index, and its response to external voltage, it is capable of modulating both phase and amplitude. This is important in pattern recognition architectures, for example. Also, because it is self-developing and recyclable, the use of bR in aero-optic applications allows the recording of high speed interferometric `movies' of short- lived events, superseding the archaic one-shot silver halide plates which are still used in such applications today.

As neuroprostheses are reduced in size, and as they are implanted in younger individuals with increasing life expectancies, the demands on the biomaterials used to protect them from the hostile extracellular environment are increased. Thus, implantable electronic packages must meet stringent quality assurance specifications, which dictate that both gross (approximately 10^-4 atm cc/sec) and fine (approximately 10^-8 atm cc/sec) leak testing must be performed on even very delicate packages. For such devices, Van der Lugt Optical Correlation (VLOC) Techniques offer the potential of superseding conventional leak testing methodologies, in that working with light is cleaner, faster, more sensitive, and eliminates the disadvantages of tracer gas introduced through backfilling or `bombing.' This paper briefly presents VLOC techniques, coupled with a discussion of basic leak theory. The ability of the method to detect and to estimate the size of leaks down to 10^-6 atm cc/sec is demonstrated, and a comparison is made between VLOC techniques and conventional helium leak testing methodology in terms of accuracy, speed, efficiency, and total cost.

In this paper, the random function optimization method has been put forward by the authors. The local extreme value problem has been overcome. In the design work of magneto optic pick-up lens, by use of the method mentioned above, it becomes possible to get much better results. Some design problems of magneto optic pick-up lenses are discussed.

The conditions for laser beam welding of aluminum alloys and measures for increasing the weld penetration depth are discussed. The mechanisms of creating pores and cracks are thoroughly analyzed and several countermeasures are proposed.

By using micro-computer controlled stepmotor, we made the laser beam scan in accordance with the pattern of the thick-film element, and measured its resistance at the same time. The resistance value precision can reach 10^-4.

In this paper a presentation of some study results on the use of artificial neural networks (ANN) in the laser materials processing area is given. It is shown that ANN has the ability to catch process variable relationships by a training process using a small set of data and then generating seemingly more information. Some basics about ANN are given. Also, two cases of experimentation are presented which are used as case studies for the ANN analysis and are taken from the laser transformation hardenting process and the laser cladding process. After a discussion of how to set up a network structure, the ANN analysis results are presented for hardening and cladding.

In order to enhance the fretting resistance of austenitic stainless steel, a 2 kW cw CO₂ laser was used to remelt the flame sprayed Ni-Cr-B-Si coating on a substrate of 1Cr18Ni9Ti. The laser remelted coating showed excellent fretting resistance for over 500 hrs in our previous vibration test. In this paper, the microstructures and chemical compositions of the coating were studied by means of x-ray diffraction (XRD) and scanning electron microscope (SEM) analysis. The results show that the homogeneous and dense coating includes two main microconstituents: hard precipitate CrB of Hv1100 - 1400 and tough solid solution of Hv590. The formation of these microstructures and the effect of laser power density on it also were discussed. It is proven that the precipitation of hard phases and the forms of solid solution are greatly related to the input power density and the cooling rate after laser remelting.

This paper reports rapidly solidified amorphous by 10 kW cw CO₂ laser glazing Fe₄₀Ni₃₆Cr₂Si₈B₁₄ and Fe₄₀Ni₄₀P₁₆B₄ alloys, previously prepared by melting the above alloys onto mild carbon steel substrates in a vacuum furnace. The process variables of laser glazing were investigated. The surface layers of laser glazing have been examined by scanning electron microscope (SEM), transmission electron microscope (TEM), and x-ray diffraction (XRD). An amorphization layer was achieved by laser glazing. A large-area amorphous layer has also been obtained by laser overlapping glazing, but a recrystallization was produced in the overlapped area.

In this paper we show that PL intensity of porous Si is critically dependent on the behavior of the thermal treatment of porous Si, prepared by anodization, which was carried out in 20% HF solution at a current density of 50 mA/cm², then annealed at 450 degree(s)C for 20 minutes. The PL results show that the PL intensity of porous Si annealed was degraded by more than an order of magnitude. Some samples made by the same method were covered with Si₃N₄ or SiO₂, no noticeable degradation of their PL intensity was found. The increase of bandwidth and the shift of PL peak positions were also observed. Obviously, the dielectrics, covering porous Si, prevent the degradation of PL whose mechanism is also discussed.

Laser glazing of flame sprayed coatings of METCO Ni25 and Ni45A on mild and 1Cr18Ni9Ti stainless steel substrates is used on some valves in chemical plants. The surface residual stresses of these coatings can be detected using the x-ray diffraction method. It indicated that the residual stress condition of the treated coatings was affected by different parameters under laser processing. Based on this stress analysis, the optimum parameters, including coating composition, coating thickness, spot size, scanning speed and overlapping coefficient of laser beam, and pre-heating temperature of the parts before laser processing, were obtained.

TH coating, a new kind of pretreatment coating for laser strengthening on the surface of metal, is presented and its mechanism is studied. The results of the experiment show that TH coating can produce a deeper laser-strengthening layer which has a smooth and clean surface and lower roughness in comparison with phosphatic coating and graphitic carbon coating when it is applied to laser surface strengthening of metal.

Recent work from this research group has investigated and characterized a plasma formed by an ArF excimer laser at a metal surface. The ArF excimer laser plasma has the potential to replace conventional plasma (e.g., inductively coupled plasma, direct current plasma, etc.) for spectrochemical analysis. This paper describes the formation and instrumentation used to characterize and evaluate the plasma. Space and time resolved studies using emission measurements were obtained for copper and lead targets. Results are presented which show that the two metals gave quite different sizes of plasma. The plasma formed with copper extending 2 mm, and that with lead extending 5 mm above the metal surface. Excitation temperature of the plasma was calculated using the Boltzmann method and found to be in the range 11,200 to 17,200 degree(s)K for copper and 11,700 to 15,300 degree(s)K for lead. The effect of pressure over the range 10 - 760 torr and atmosphere (air, argon, and helium) on the shape and line-to background ratio and temperature of the plasma created above the surface of a copper target also is discussed.

Three kinds of plasma sprayed coatings on nuclear valves of FRAMATOME, which are the cobalt-based Stellite, the nickel-based Eutroloy, and the iron-based Cenium, were remelted with a 5 kW CO₂ laser. The aim is to build-up a fine homogeneous metallurgical structure onto the hardface, with a uniform thickness and free of cracks in order to improve the wear and galling properties of the coatings. It was concluded from the experimental results that for plasma sprayed Stellite coating, satisfactory results can be obtained by carefully selecting the process parameters, preheating of the substrate is not needed; and for the Eutroloy coating, preheating of the substrate is necessary to get rid of cracking during laser remelting. Laser remelting is not an adequate process for Cerium coating because it is very difficult to avoid cracks on the remelted layer.

Recently the interest in cladding one material on another is greatly increasing because of the fact that engineers and designers are becoming more and more aware of the advantages afforded by the many advanced surfacing techniques. Among many cladding processes, laser cladding is one of the latest developments. Because of the high optical reflectivity and thermal conductivity, laser surface treatment of aluminum alloys still seems to be difficult, especially for cladding some wear resistant material with a high melting point onto them. So far, few successful cases have been reported in the literature. The aim of this study is to investigate the feasibility of laser cladding of Stellite and Silica on aluminum substrate in order to develop the potential application of aluminum alloys in the tribological field. The blown powder laser cladding technique was used in this study. The aluminum substrate used was AlCu4SiMg (H15). The powders used were Stellite 6 and pure silica. To clad Stellite on aluminum substrate, there exists a lot of difficulties. The main problems are: (1) the cladding track is very likely to peel off; and (2) the cladding track is prone to cracking, especially when overlap treatment is used. Because there exists no direct metallurgical bonding between aluminum and cobalt, the only way to bond Stellite and aluminum together is to sandwich it in with intermetallic compounds. So, an alloying zone is essentially needed, and some dilution is unavoidable. The elementary experiments for cladding silica on aluminum substrate seem to be successful. A uniform cladding bead of silica on aluminum has been obtained. This is a prospective future for applications of aluminum in the area where thermal conductivity and electrical isolation are both required.

In this paper rare gas fluoride ionic excimers, Ar²⁺F^- and Kr²⁺F^-, are studied theoretically and experimentally as candidates of VUV/XUV laser media. First, potential curves of rare gas fluoride ionic excimers were calculated with the aid of the improved Rittner potential which involved parameters corrected by ab initio calculation. Transition parameters of ionic excimers were also obtained. Then radiations from Ar²⁺F^- near 125 nm and Kr²⁺F^- near 148 nm were obtained for the first time, these results are in good agreement with our calculations.

In this paper, we review the microscopic description for nonlinear optical processes originating from populated electronic excited states and examine an enhancement mechanism for third order optical processes. For a general case, we consider the third order (formula available in paper) excited state susceptibilities for linear chains that have been previously well-studied for their ground state nonlinear optical properties. We see that for a given frequency, enhancement can occur in the excited state (formula available in paper) and the origin and mechanism of the enhancement can be directly understood in terms of new virtual excitation processes. In section III, we summarize a recently completed experimental study of enhanced excited state third harmonic generation in conjugated structures.

The theory of a self-pumped phase conjugator (SPPC) for speedily amplitude-modulated beams is presented by combining DFWM theory of speedily amplitude-modulated beams in photorefractive (PR) crystal with the model of two interacting regions for SPPC. The field expression of phase conjugate beam is given. For the special case of code modulation the phase conjugate reflectivity is calculated. The experimental result using code modulation shows that SPPC is endowed with the ability of processing speedily modulated information in the temporal domain.

In the transient interaction between the laser and the material, because of the medium memory effect, the transient response of the stimulated Raman scattering (SRS) to the pulse train of high power laser is different from the effect of the single pulse. This paper discusses the SRS of the pulse laser. The gain expression of Stokes field is given. It can be seen that as the interval T increases, the Stokes's gain decrease. When the pulse number N is large enough, the gain of the Stokes pulse arrives at the steady-state value. The memory effect is the most important fact, influencing the gain of the Stokes field. At the edge of each pulse there is the Stokes field.

The third-order optical nonlinearity of a newly synthesized Buckminster Fullerene charge- transfer complex is investigated. The measurement was made at 1064 nm in a toluene solution by 50 picoseconds degenerate four wave mixing. The third order hyperpolarizability is measured to be 4.9 X 10^-31 esu and nonlinear optical temporal response less than 50 picoseconds is determined.

A novel polymer film doped with natural active chloroplastin was formed by spin coating backings. The nonlinear refractive index of this composite polymer was measured by picosecond laser pulses. Comparing our experimental setup for measuring nonlinear refractive index and the response time of our samples with the original Z-scan system proposed by M. Sheik-Bahae et al., we added a variable time delay path and a tunable probe beam into this system to implement the measurement of the response time and spectra of n₂. The nonlinear refractive index and response time of the polymer film ((alpha) equals 1.29 cm^-1) is about 4.9 X 10^-8 esu and 85 ps. When we put a F-P filled with the polymer film into a nanosecond pulse laser path, we observed optical bistability phenomena. The rising time was less than 1 ns and the recover time was about 2.5 ns. Analyzing and comparing the nonlinearities of chloroplastin derived from heat effects and (pi) -electron transition, we found that the heat effects, reorientation, and redistribution of the chloroplastin molecule can be neglected and the large optical nonlinearities of the film were of electronic origin.

A simple experimental method is proposed to measure the time sequence by using a Boxcar Averager, in which the time-resolved spectrum of every pulse is measured independently, and it is used on UV dye laser excited Na₂ molecules.

Seventeen two-photon transitions for neon have been observed in the 580 - 635 nm spectral region for use in the spectroscopic study of its higher excited levels, which are not accessible by one-photon absorption. To compare the two and one-photon absorption signals being originated from the lower level, an effort was made to record single-photon optogalvanic spectrum in the available wavelength region. The dependence of the optogalvanic signal on the laser power has also been studied. The optogalvanic signals were obtained from a commercial neon-filled hollow-cathode lamp, which was irradiated with pulsed dye laser pumped with N₂ laser.

A newly observed laser induced collision (LIC) and anti-stokes frequency up-conversion process in He/Ne mixture is reported. The fluorescence emission line of Ne at 486.7 nm can be enhanced 3 - 4 times by applying both discharge and optical excitation. The result shows that the LIC process can be a major competitive process in the two step excitation process. Both experimental description and theoretical analyses are given.

Multiple diffraction rings are observed after a pulse laser beam passes through an absorbing dye LB film. The theoretical analysis, based on the model of transverse self-phase modulation, is also given. The saturated nonlinear refractive index n₂ is estimated to be 2.0 X 10^-8 cm²/W from the number of rings induced in the LB films. The main contribution to this larger nonlinearity is believed to be from laser-induced transformation between H-aggregates and monomers of molecules in the LB films.

Although LIDAR (light detection and ranging) technique has been used to probe the atmosphere before the invention of lasers, remote measurement of several important atmospheric parameters, which require high spectral resolution, is only recently being done. After a brief overview on lidar technique for atmospheric parameter measurements, I discuss the ongoing efforts for atmospheric probing using a high-spectral-resolution lidar system at Colorado State University.

Super Tracking Theodelite-1 (STT-1) is a precision instrument measuring trajectory and attitude of flying targets using a laser, an infrared and a video tracking system, and a laser ranging system. The tracking accuracy is better than 60 arc seconds. The real time angular measuring accuracy is better than 15 arc seconds. The ranging accuracy is 1 m. The instrument can record the target picture on film with a high speed synchronous camera. The overall arrangement, tracking systems, and measuring results are described.

This paper describes a method to use the optic fiber network to control the signal frequency and phase independently from the subarray modules in the phased array antenna.

Development of laser 3-D imaging is reviewed briefly in this paper. The stress is on the state of the art semiconductor laser and its potential use in 3-D imaging systems. Three methods of ranging, i.e., IM-PM, pulsed TOF, and FM-CW, are analyzed. We confirmed that it is necessary to use constant fraction discrimination (CFD) technique and high resolution timing technique in a pulsed system for obtaining high resolution ranging. The calculation of distance of reliable ranging and needed sample rate of 3-D imaging have been made. The approaches to implement high speed, high resolution counter circuitry are discussed. Ranging experiments were done using a pulsed diode laser with pulse duration of 70 ps, peak power of 1 W, and repetition rate of 200 KHZ, a Si APD with a response time of 370 ps was also used to detect the return signal, and a range counter with a time resolution of 66 ps was used to measure the distance. The experimental results show an excellent range accuracy of 1 to 2 cm in the wide dynamical range of signal amplitude.

In this paper we discuss the heterodyne receiving technology at the band of 10.6 micrometers for single and double tubes and compare the two receiving methods. For an acousto-optic modulation receiving system, we have analyzed the collimation alignment and matching technology of signal optical field. The structure and design of the antenna are also analyzed. Furthermore, the frequency stabilization is analyzed for a double-tube heterodyne system. On the condition of seim-all-weather, the outer field experiments have been taken out, and the terminal signal to noise (S/N) ratio is proven to be better than approximately 50 dB for the analogue FM/FM (electric FM/optical FM) and digital FM/FSK (electrical FM/optical frequency shift key) systems. The terminal bit error rate is better than 10^-8. It's very important to develop the technology for 10.6 micrometers laser heterodyne detection.

Theoretical analysis and experimental results of a two-wavelength pulsed laser ranging system are presented. In the system, a short Q-switched pulsewidth Nd:YAG laser and its second harmonic wave are used, MCP/PMT and APD are used to detect 0.53 micrometers and 1.06 micrometers , respectively, and a multichannel analyzer with CFD is used to measure the time interval of the two returning waves. The main factors that affect the precision of the ranging system include the second harmonic generation of the laser with modes instability and the transit time jitter of the detectors, target character affects the waveform, but for several ns pulsewidth laser wave, this is negligible. Experiment data expressed that the synthetical transit time jitter rms value of the two detectors is about 100 ps. Our ranging experiment revealed that with a consequent average of 50 measurements to a distance of several hundred meters the rms precision of the time interval of 0.53 micrometers and 1.06 micrometers is about 30 ps, and the rms precision of the ranging system can reach 10 cm.

This article reports the application of laser range imaging radar in the measurement of mechanical vibration frequency and the mode distribution, and the periodic motion of the mechanical parts such as a piston rod. The principle of the laser range imaging radar is based on the phase shift of the reflected amplitude modulated laser beam. The mechanical vibration frequency up to 20 KHZ and the minimal retrieved amplitude (or the motion displacement) of 0.5 mm have been achieved with the laser modulating frequency of 40 MHZ. With appropriate modulating frequency, this laser range system can measure the mechanical vibration amplitude, or the moving displacement, from 10^-1 mm up to 10² mm, or even higher to the order of meters, which will be useful to measure the vibration and the periodic motion of machines and their parts for field test.

The principle of infrared angular measurement is introduced. Theory analysis of error sources, calculating methods, and measurement of system accuracy are discussed in the paper.

A birefringent filter for detecting faint laser signal under the sunlight background is presented. it consists of five Lyot elements. Every element is of the configuration of wide field of view. The filter device is characteristic of narrow bandwidth, wide field of view, and tunable transmission wavelength. The bandwidth is 0.19 nm, the transmission wavelength is 532.07 nm, and the wavelength is tunable with the half wave plate. The tunable range is 4 nm and the tuning fineness is 0.075 nm per degree. The free spectral range is 6.5 nm and the transmittance of the filter is 31.2%. Furthermore, the optimum design of combination of the Lyot elements is discussed. The influence of different constructional errors on the performance of the filter device is analyzed as well.

In this paper, the filtering characteristics of Cs atomic filter were theoretically and experimentally investigated, especially the influence upon the Cs atomic filter's properties with Ar buffer gas.

The transmission theory of laser polarization is presented in this paper. The transmission matrix of laser polarization in optical systems --H matrix is derived. The transmission theorem of laser polarization --H theorem of z parameter is founded. Transmission properties of the laser polarization through some usual optical systems are analyzed.

Barium titanate is one of the photorefractive crystals. It has extremely large electro-optic coefficients (r₄₂ equals r₅₁ equals 1640 pm/v) which give rise to an efficient photorefractive effect. It has wide applications in volume hologram storage for high capacity optical memories, real-time information processing, real-time holography and interferometry, coherent light amplification, integrated optics, and laser applications. The growth from two different TiO₂ sources and fabrication in oxygen partial pressure between 1 and 10^-17 atm for commercial BaTiO₃ crystals are discussed. The optical constants of barium titanate crystals from the UV to the far infrared were compiled from various literatures, and the results are presented. Single domain barium titanate crystals exhibit unusual scattering and fanning phenomena. Some models which contribute to this effect are described, and an analysis related to the experimental observations is presented. The changes in response (writing) time, decay (storage) time, and diffraction efficiency of barium titanate crystals as a function of temperature ranging from room temperature to about 100 degree(s)C were measured by non-degenerate four-wave mixing and self-pumped phase conjugate experiments. These results also are discussed.

The quest for more efficient nonlinear optical materials of increased optical quality is being spurred by the development of optical communication systems that require ultrafast broadband optical signal processing functions. Conversely, nonlinear optical phenomena enlarge traditional spectroscopic approaches to encompass more complex and informative multiphotonic pathways. In this stimulating context, organic nonlinear materials have been recognized as forefront candidates for investigations of fundamental and applied natures involving in a joint effort chemists, material scientists, and optical physicists. After reviewing the molecular engineering foundations of the domain, specifically with respect to an efficiency-transparency trade-off, we concentrate on a more specific case that embodies, from the definition of the molecule, all the way down to applied physics end goals, the key-concepts and methodological tools in the field. This is the paradigmatic case of N-4-Nitrophenyl-(L)- Prolinol (NPP) which, after almost a decade of efforts involving crystal growth and ultrafast time resolved spectroscopy, has recently reached sufficient quality to lead to optical parametric oscillation. Stable coherent tunable oscillation in the near IR from 0.9 to 1.7 micrometers has thus been demonstrated for the first time in an organic molecular crystal with specific advantages as compared to mineral candidates and room for further performance improvements. We recall in conclusion that new molecular and crystalline pathways are still opening-up, such as based on molecular nonlinearities of octupolar origin or organo-mineral crystals.

Coupling amplification of Stokes seed beam in a light guide filled with high pressure H₂, excited by an unfocused laser beam during multi-reflection is reported. The amplification coefficient is about 5.5 and the quality of the amplified beam is the same as or better than that of seed beam.

The full quantum treatment on the three-mode interaction in an optical parametric oscillator (OPO) is presented. The simultaneous resonance of three nondegenerate modes in the OPO cavity has been experimentally demonstrated. Reductions in photocurrent noise of 30% relative to the vacuum noise level are obtained for frequency offsets near 2 MHz.

The laser output power of the dimer of O₂(¹(Delta) _g) has been estimated theoretically. The dimer of O₂(¹(Delta) _g) was generated by microwave (2.450 GHz) exciting high pure oxygen. The laser oscillation of the dimer of O₂(¹(Delta) _g) was realized at 656.3 nm for the first time, and the laser power was as high as 100 (mu) w, which corresponded to theoretical estimation in order of magnitude. In addition, the divergent angle measured was about 37.3 mrad.

The combined effect of diffraction, anomalous dispersion and nonlinear refraction under both symmetric and unsymmetric initial conditions is studied by using a variational approach and numerical simulation. It is shown that the compression parameter B_o which strongly depends on the initial condition and the nonlinear interplay strength, plays an important role. When B_o > 0, the beam width and pulse width blow up vibrantly as z yields (infinity) . When B_o < 0, the pulse collapses oscillatorily and simultaneously both in space and time.

Dynamic orientation of anisotropic molecules in a gas-phase medium under the action of laser pulses of a duration shorter than the rotation relaxation time has been studied both theoretically and experimentally. The effect was observed in the VUV third-harmonic generation in naphthalene vapor. The peculiarities of nonlinear optical UV and VUV generation (by frequency mixing of Nd-laser radiation) in the vapors of some compounds are studied.

This paper is aimed at discussing the basic principles of light-induced drift (LID) and estimating the characteristic of the effect, produced by quasi-black-body radiation. Many astrophysical objects as well as laser-produced plasmas may be described by that model in the first approximation. The feasibility is analyzed of converting the radiation of the most efficient cw laser (a technological CO₂ laser) via laser-produced plasma into a broad-band radiation to be used as a source of LID of a wide range of substances.

The paper studies the process of photostimulated aggregation of ultradispersoidal silver particles into fractal clusters observed in some colloidal solutions irradiated by different types of pulsed and continuous-wave lasers and by a nonmonochromatic light. A photoaggregaton mechanism has been proposed, based on mutual charging of different-size particles in a conducting medium when the Fermi potentials become equal because of their dimensional dependence.

We have recently made several improvements to the Nova laser at the Lawrence Livermore National Laboratory to enhance its capability for conducting research on both the indirect- drive and direct-drive approaches to inertial confinement fusion (ICF). For indirect-drive ICF, we have been working on the Precision Nova project to increase the ten beam output at the third-harmonic wavelength (0.351 micrometers ) to 40 kJ (30 TW power), to obtain instantaneous power balance to 5 - 10% among the beams, and to improve the centroid pointing precision on target to 30 micrometers rms. This paper discusses improvements to the frequency converters and the use of spectral chirp to reach the goals for the energy and power levels. It also discuses our power balancing technique, diagnostics capabilities, and the status of the beam pointing improvements. For direct drive studies, we have implemented on a single beam, 80 cm diameter random phase plates and a version of smoothing by spectral dispersion to achieve a smooth beam at the second harmonic wavelength (0.527 micrometers ). The phase plates were fabricated by a unique sol-gel process and our temporal smoothing technique utilizes a special cross-phase-modulation oscillator. We report the smoothing levels and smoothing rates that we have achieved and briefly discuss the target physics research being done with this smoothed beam.