Laser diodes may find an application as pump sources for high-power solid-state laser drivers in the inertial confinement fusion (ICF) reactor because of their high efficiency, good matching to absorption pump bands, and the lower amount of heat deposited in the lasant as compared to conventional flashlamp pumping. The potential of a diode-pumped high-power solid-state laser system for ICF reactor is described. The laser fusion reactor driver will require a few mJ output at the wavelength of 0.35 micrometers , a 10% overall efficiency, and a 10 Hz repetition frequency. Using a diode-pumped regenerative amplifier, it is shown that the diode-pumped solid-state laser system will have a sufficiently high efficiency (over 10%), a long lifetime (laser diodes have a lifetime of over three years at 10 Hz operation), and a high repetition frequency (over 10 Hz, owing to its small thermal load to laser materials). The most likely candidates for such laser materials of the system are Nd: phosphate-glass, Nd: silica- glass, Ho, Tm: YAG-crystal, and Tm: YAG-crystal. Technical items to be developed with the system are also discussed.
We report on measurements of transient and steady-state pulse characteristics of an acousto- optically mode-locked titanium-doped sapphire laser. During the pulse evolution, oscillations in the pulse width and pulse energy are found. A steady state is reached after about 40 to 60 microsecond(s) . The steady-state pulse width is strongly influenced by the mode-locking loss as well as the intracavity bandwidth. Shortest pulses of typically 15 ps are obtained. The experiment is compared with results of a simple computer simulation.
The Air Force has played a leading role in the development of coherent semiconductor diode lasers since 1985. Because of their high efficiency and small size, these lasers have great potential for use in a variety of applications. In order to advance the technical base in the area of semiconductor lasers, the Air Force has awarded many development contracts as well as established a strong in-house modelling and characterization capability. This paper discusses the various techniques for achieving high-power, coherent, semiconductor laser sources. Among these are the use of broad area, single stripe sources, linear edge emitting arrays, surface emitting arrays, external cavities, and a phase conjugate master oscillator power amplifier system. The various techniques and their relative merits are discussed.
The basic principles for achieving population inversion and stimulated emission between light hole Landau levels in p-Germanium are discussed. An inversion between the Landau levels of the light hole subband of germanium is achieved when the crystal is subject to crossed electric and magnetic fields. This leads to stimulated far-infrared emission at the cyclotron resonance frequency. The emission spectrum consists of a single line which is linearly tunable with magnetic field between 65 cm-1 and 85 cm-1. The linewidth of the observed spectrum is about 0.2 cm-1 with an estimated output power of 200 mW. Lasing is found to depend critically on the orientation of the electric and magnetic field in respect to the crystallographic axis. By a comparison of absorption and emission spectra with band structure calculations including nonparabolicity corrections, the lasing transition was identified to be the n equals 2 to n equals 1 Landau level transition of the b-set light holes. Applications of the p-Ge cyclotron resonance lasers are discussed.
Experimental results of two-photon and three-photon excited luminescence in semiconductors and molecular crystals at room temperature are discussed. Dependence of two-photon luminescent intensity upon intensity of pumping light is analyzed for ZnSe samples. The power index of this nonlinear dependence for 532 nm excitation changes from 2 for 6 MW/cm2 to 3,6 for 30 MW/cm2 excitation intensity. The estimated optical gain coefficient reveals value up to 40 cm-1. Two-photon copper laser excitation of investigated molecular crystals and organic materials demonstrate luminescence from impurity and excitonic levels.
Free-electron lasers (FELs) are being developed for all infrared wavelengths and into the short millimeter wave region. The pulse structure and very large variation in output powers means that many different detectors are required. This paper summarizes the presently available detectors and discusses the use of less conventional devices such as submicrometer diameter Schottky barrier diodes and photon drag detectors.
In a fiber optic communication system, the receiver must have high gain and low noise. The latter is generated in the photodetector, the load resistor, and the preamplifier. The photodetector 'gain' can be improved by use of an Avalanche Photodiode (APD) in which an internal gain is obtained from the impact ionization multiplication process. If, however, the ionization rates of electrons ((alpha) ) and holes ((beta) ) have the same value, the noise associated to the multiplication process will be high, according to McIntyre theory. This means that most of the III-V semiconductors are unsuitable for APD with low noise because (alpha) and (beta) are about the same. One way to improve the noise performance of the III-V compound semiconductor APDs is to alter the ratio (beta) /(alpha) (or (alpha) /(beta) ) by the use of a multi-quantum well (MQW) structure in the multiplication region of the APD. For a GaAs/GaAlAs MQW superlattice there is a large difference between the conduction and the valence band discontinuities ((Delta) Ec and (Delta) Ev) at the GaAs-GaAlAs edges. (Delta) Ec higher than (Delta) Ev leads to (alpha) >(beta) : electrons have more ability than holes to impact ionize. The authors obtained from multiplication factors and noise measurements a ratio k-1 equals (alpha) /(beta) equals 8...10, which is similar to the value given by F. Capasso.
A set of programs to simulate a diffractive optics in various laser systems is developed. The codes are based on the efficient and general diffractive propagation computer program that employs FFT (FHT) techniques and the scheme of splitting the diffractive and gain-refractive steps of calculation. The codes include a new method of iterative calculation for the optical resonators loaded with active medium. This method solves the problem of the calculation's convergency in a case of several equal-loss modes and allows one to find the single mode's stability limits. The method is proposed to calculate continuous multimode lasing when neglecting a transverse-mode beating. The results of numerical simulation of several laser systems are reported: (1) the slave laser under the injection of an external signal (injection locked laser, 2-D code); (2) three-mirror resonators with active medium (3-D code); (3) two optically coupled lasers having unstable resonators (3-D code); (4) 1-D laser array in the Talbot cavity (self-imaging resonator 2-D code). Most suitable parameters of pointed optical schemes to achieve high efficiency and high beam quality can be found by using mathematical simulation.
A packaged subminiature external cavity laser with a linewidth of <70 KHz has been developed. The package has outside dimensions of 45 X 20 X 15 mm and is designed with a 10 mm cavity making it capable of direct modulation up to 2.4 Gbit/s. The wavelength is selected during manufacture to within the range 1510-1560 nm with an accuracy of 0.05 nm.
In multiphoton ionization mass spectrometry, the increase in laser pulse intensity leads to an additional absorption of photons by molecules, and the degree of fragmentation also increases significantly. A laser pulse is usually focused to interact with the molecular beam only once, and the laser power is then wasted. A novel device for increasing the laser pulse intensity in a multiphoton ionization mass spectrometer is put forward. By collecting and refocusing the laser pulse precisely onto the laser-molecules interaction region, the laser pulse intensity in this region is increased. By using two UV reflectors and a lens, the 0.3 ns delayed laser pulse is guided back to superimpose almost simultaneously onto the original pulse. UV optical fiber is used to guide the residual laser pulse out from the vacuum chamber. The accurate interaction between light pulses and molecules is obtained by monitoring this output laser pulse intensity. By using this device, the mass spectrum of benzene was produced, which showed a stronger fragmentation than was obtained with the usual method at the same laser power. This laser intensity enhancement device is of practical importance to applications where a strong local laser field is needed.
Construction of reliable, practical high-performance sources of picosecond and femtosecond light pulses. The proposed approach is to stabilize a passive mode-locking of solid-state lasers. Results of the authors' studies of spectral and radiation transverse spatial distribution instabilities are presented, and methods for their stabilization are suggested. Theoretical duration of generated subpicosecond and femtosecond pulses as a function of laser system parameters is found with due regard for nonlinearity and frequency dispersion of the refractive index for intracavity elements.
A new method is proposed for direct transformation of electronic energy of metastable species in inverse medium into energy of waveguide modes localized in a dielectric waveguide. Different waveguide configurations are examined. Numerical calculations show that transformation efficiency can be as high as 15-20%.
A 5 MeV FEL facility has been realized at the ENEA Research Center in Frascati, Italy. This facility is devoted to the testing of Cerenkov FEL devices and other compact FEL configurations. Power up to 50 W in 4 microsecond(s) pulse has been generated in a Cerenkov FEL at wavelengths ranging from 0.8 to 1.6 mm using different dielectric guides. Other planned activities include the testing of short-period undulators in a small size waveguide FEL designed to operate in the sub-millimeter region. Operating characteristics and predicted performance are presented.
The preparation of extremely high quality type IIa diamonds of varying isotropic composition is described. The quality of the diamond is measured by x-ray tomography and x-ray line widths. Changes in thermal conductivity, modulus, and optical properties as a function of isotropic composition are described.
A short review is presented of some present and possible future applications of free electron lasers (FELs) to the study of nonlinear optical (NLO) properties of condensed matter in the infrared spectral region. Emphasis is put on semiconductors, and in particular GaAs and related III-V systems, and recent work on organic semiconductors. Suggestions are also given for experiments in Ge and narrow gap semiconductors such as InSb and HgCdTe. The desirable (or, in some cases, essential) properties of the FEL for the particular experiment are emphasized. The following topics are addressed: bandgap (single and multiphoton) resonant processes; photoionization kinetics of semiconductors; the FEL as probe for far infrared (FIR) gain measurement; FIR second harmonic generation and nonlinear optics. For convenience these are taken in spectral order from the near and mid-infrared (mainly linac-based FEL) to FIR (mainly Van de Graaff-based FEL) applications.
In order to maintain and improve laser facility performances, several projects in R and D areas are supported. Some of these are briefly reviewed, and two programs are presented which could have some interest for ICF laser type systems and also for other systems.
Optically pumped molecular lasers have been developed for high-resolution spectroscopy in the wavelength range from 100 to 500 micrometers with a resolving power of >106. With more than 1,000 discrete laser lines, they cover the whole spectral range and offer high cw output power up to 50 mW, good signal-to-noise ratio, and high spectral purity. This paper summarizes the state of the art of optically pumped lasers and their use as local oscillators in a heterodyne spectrometer specially developed for airborne astronomy.
The new C02 laser has been developed for the high speed drilling and cutting process for sheet metals up to 16 mm thickness, with low operational costs.The new C02 laser is equipped with the newly developed acoustic filter and solid-state inverter power supply that have the fol lowing features: (1) To keep high quality glow-discharge under the laser gas flow, the acoustic filter has been newly applied to prevent the ripple of the laser gas pressure.Thus it is able to reduce fluctuations of the laser pulse power to within 10%. (2) The solid-state inverter power supply has been developed to make possible high response glow-discharge power.That creates a high peak pulse power, where the height of the laser pulse power is more than 4000w as well as twice cw laser power. The high speed drilling process using the high peak pulse power makes possible a driffing time of 5 secat 16 mm thickness and less than 0.5 sec at 9 mm thickness for mild steel.
In a Nd-glass microspherical cavity the spontaneous enhancement and inhibition emission processes have been observed in the optical region. The rate of the enhanced spontaneous emission is larger than the free-space values for some transitions, so that some lasing lines of Nd-ion in glass have been observed, since the large enhancements of the transition rates may modify the decay processes in the multilevel system of the Nd-glass medium. A simple theoretical discussion is given to explain the possible mechanism of the lasing in the 740 nm and 810 nm wavelength regions. The micropherical cavity laser may be used in studies of Nd- glass microcavity spectroscopy and nonlinear optics.
Computer analysis of the pure chemical H2-F2 amplifier with input laser radiation with sharp maximum at the front results in development of discharge, and initiating a chemical chain reaction by the electron impact is undertaken. As the calculations show when the peak intensity is equal to (2-5)X1011 W/cm2, the effective initiation of the H2-F2 amplifier takes place at high mixture pressure during several nanoseconds. Specific laser energy reaches the value 1000-2000 J/l.
The free-electron laser (FEL) amplification mechanism is discussed in this paper, including the influence of the electron beam quality (energy spread, emittance, stability) on the FEL performance. Considerations regarding the choice of the electron accelerator are presented, and some characteristic properties of the laser radiation are discussed. An overview of FEL- facilities for the infrared spectral region, which are being designed and built worldwide, is given.
The discovery of high-temperature superconductors (HTS) has opened new opportunities for applications of superconductors in optoelectronics. The HTS perovskites represent a new class of solid-state materials, exhibiting many very interesting and potentially useful electronic, optical, and electro-optical properties. They also operate in the 30-80 K temperature range, where refrigeration is cheap and the parameters of semiconducting devices are optimal. A review of the substrate materials and deposition techniques suitable for fabrication of high- quality epitaxial HTS films for electronic and optoelectronic applications is given. Laser processing techniques of HTS films are presented, with a special emphasis put on the laser writing method, which enable definition of superconducting and nonsuperconducting regions in the same epitaxial HTS film. Two possible approaches for the development of a complete optoelectronic system with the elements based on the HTS films and operational at liquid- nitrogen temperatures are presented. The first approach consists of manufacturing the devices made of conventional electro-optic materials and containing HTS transmission lines and electrodes. Design and properties of ultrafast HTS interconnects are discussed, and a new concept of the Mach-Zehnder-type YBa2Cu3O7-y-on-LiNbO3 optical modulator is introduced. The second, more futuristic approach, is to exploit contrasting properties of the oxygen-poor and oxygen-rich HTS phases to fabricate novel monolithic devices. Recent experiments are discussed which reveal intriguing optical properties of HTS films, and are most relevant for the development of all-HTS optoelectronics devices. Several practical devices, such as high-frequency modulators, ultrafast-pulse generators, and sensitive photodetectors are presented.