Recent results obtained in the field of storage ring free electron lasers are briefly summarized in this paper. The first operation of such a laser has been obtained in the visible range at Orsay in 1983. More recently coherent light in the U.V range has been produced from an optical klystron by harmonic generation using a Nd:YAG laser. PACS numbers : 42.60-v.

Frequency up-conversion by the anti-Stokes Raman laser process offers interesting perspectives for the generation of tunable uv-laser radiation. Systematic studies of the atomic Tl-system have led to small signal energy conversion efficiencies of more than 70 % and maximum output energies in the saturated regime of up to 5 mJ for the conversion of 535 nm into 377 nm radiation. In case of Tl the energy shift is about 7800 cm^-1. Considerable larger energy shifts are possible with realized novel anti-Stokes lasers using atomic Sn and Pb. Further aspects and possibilities of this conversion technique will be discussed.

Net gain and loss of the KrCl laser, excited in an UV-preionized transverse discharge, were measured in He and Ne based gas mixtures. A peak net gain of 0.15 cm^-1 and a loss of 0.05 cm^-1 have been observed in the 0.09% HC1/10.1% Kr/1.5% He/88.3% Ne mixture at a total pressure of 355 kPa and at a specific power loading of about 21 MW/cc. Smaller net gain and loss have been determined in the He based mix.

Operation of a corona-preionized TEA CO₂ laser with an active volume of 130 cm³ at repetition rates up to 100 Hz with helium-free gas mixtures is reported, resulting in average output powers in excess of 36 W.

The construction. (including hard-seal technology and the excitation ,fiethod) and performance (power, spectral mode, operating and shelf lifetime, high temperature performance, frequency stability and modulation) of radio-frequency excited. waveguide CO, lasers will be discussed.

A single mode, single line, CW ring-waveguide high gain, wideband power oscillator injection-locked by a highly stable CO2 waveguide master oscillator is presented for a CO₂ radar application. In the hybrid injection regime 14,5 Watts are extracted on the P(20) line under 350 mW of injection on P(18), with excellent frequency stability.

This paper presents a project of 0,5 TW four-beam CO₂ laser, as well as some selected constructions and results of its main elements investigations. It also includes some test results of the single-beam high power laser being started now on the basis of these elements.

Utilizing the model, in which the existance of two coupled photon beams in the resonator is taken into account, an analysis of the generation process in the laser with the pulsed transmission of the Q-switch is carried out. A wery good agreement between calculation and experimental results is achieved. The possibility of parameters controlling of the generated pulses is presented.

Nonreciprocal light transmission through a photorefractive medium is a consequence of the asymmetric self-diffraction at the photoinduced grating produced by two antiparallel beams. We report for the first time one way viewing experiment with KNbO₃ as the nonlinear, photorefractive medium. By illuminating the one way device with two antiparallel beams of equal intensity P = 10 mW (I = 19 W/cm4) the light transmission factors were 113% and 59% for the two beams, i.e. the transmissivity in the first case is larger than unity despite of an absorption constant of α = 1.5 cm^-lx The grating build-up time was 1.7 seconds at this power level and 0.1 second at 270 W/ce. The transmission asymmetry caused by the non-linear interaction between a beam and its own reflective from the back face of the crystal was investigated for several wavelengths X. We measured 57% and 27% for two antiparallel beams at X = 514.5 nm with an optimized crystal cut with light propagation direction 37' to the b-axis and perpendicular to the a-axis.

The cycling properties of photothermoplastics based on Staybelite Ester 10 can be improved to several thousands of recording cycles. It needs a chemical purification of as received Staybelite Ester 10 and the use of relatively thick thermoplastic and photoconductive layers. So it is possible to preserve both high diffraction efficiency and good cycling properties. Such devices are specially suited to variable beam steering and optical switching.

We report theoretical and experimental results on optical-feedback effects in single-mode semiconductor lasers with feedback levels varying from very low (<< 1% feedback power) to relatively high (1-5%) feedback.

In this paper we present an overview of the present state of the art in high-energy laser resonator design, with particular attention to solid state Nd:YAG lasers. A comparative review is made of the most common cavity configurations and a completely new resonator design is presented, which is a novel development of the unstable resonator concept.

High efficiency pulse compression using Raman induced cavity dumping has been studied theoretically and experimentally. Through stimulated Raman scattering the electromagnetic energy at a primary frequency is down-converted and extracted from a storage cavity containing the Raman medium. Energy storage may be achieved either at the laser frequency by using a laser medium inside the storage cavity, or performed at a new frequency obtained through an intracavity nonlinear process. The storage cavity may be dumped passively through stimulated Raman scattering either in an oscillator or in an amplifier. All these cases have been studied by using a ruby laser as the pump source and compressed hydrogen as the Raman scatter. Results differ slightly accordingly to the technique used, but pulse shortenings higher than 10 and quantum efficiencies higher than 80 % were obtained. This method could also be used with large power lasers of any wavelength from the ultraviolet to the farinfrared spectral region.

Lasing in N₂ and KrF at a wavelength of 337 nm and 248 nm, respectively, was achieved in a capacitively coupled discharge device having a cylindrical discharge volume. The dielectric electrodes are formed by a 3-mm bore through the diameter of a commercial doorknob capacitor. This electrode configuration provides a nearly unifOrm electric start field throughout the discharge volume. The scalability of this discharge device is discussed. Most capacitively coupled (CC) discharge lasers reported up to n?w4incorporate dielectric electrodes made out of flat or specially shaped slabs of BaTiO3 Recently, we described an extremely simple and compact CC discharge device with a new electrode design that produces a nearly constant electric start field in the discharge volume. Lasing in N₂ and in KrF at a wavelength of 337 and 248 nm, respecqvgly, could be achieved. The experimental results are reported in detail elsewhere ' and are summarized here briefly for convenience. Considering the scalability of this laser type, it can be shown that with this excitation technique lasers with a sizeable pulse energy output should be feasible.

A high energy density KrF laser pumped by a coaxial electron beam will be des5ribed. With a pumping pulse length of 250 ns (FWHM) and a current density of about 100 A/cm² a maximum output of 7.13J was obtained. The optical pulse width was 160 ns (FWHM) and the active volume 157 cm which means a specific energy of 46 J/L and an output power of 44 MW.

We present a simple method of intracavity frequency doubling based on critical phase matching with non-normal incidence. This method yields a large tuning range and avoids the beam displacements and cavity length changes usually encountered with critical phase matching inside the cavity.

Up till now the best performance of XeCl-lasers has been obtained by constructing systems with a low circuit inductance consisting of a waterline in series with a multi-spark gap. This multi-spark gap is required for obtaining a high voltage and therefore a high current rising speed. A serious disadvantage of a multi-spark gap however is, that it dissipates energy and contributes significantly to the total selfinductance of the system. We will discuss a construction, based on the corona-preionization technique, which functions as a system with multi-spark gap however without adding to the system self-inductance.

Combustion diagnostics techniques using lasers are described with special emphasis on laser-induced fluorescence, Raman and Coherent anti-Stokes Raman spectroscopy. Several examples from flame investigations are given illustrating the potential of these methods.

We measured the fluorescence spectrum of the Na-D lines in a sodium vapour cell filled with Ar gas, excited by an intense, nearly monochromatic laser near resonance. In this case the theory (dressed-atom model) predicts a line splitting dependent on the laser intensity.

A light scattering photometer is described with which one can measure periodicity in the intensity fluctuations of light, scattered from a dilute colloidal suspension. Using a specially designed sample cell, variations in the scattering when the system is subjected to pulsed electric fields can be recorded and interpreted to give the electrophoretic mobility for colloidal particles. Under conditions of direct optical transmission, transient optical birefringent effects can be measured and interpreted in terms of the electrical polarisability of the particles. These two parameters are of value in characterising the surface charges and hence the stability of the particles in their fluid environment. Illustrative data are given for asbestos sols.

A simple, low cost laser-Doppler flow monitor was developed. The instrument contains a diode laser two photodiodes, all integrated in a probe of small dimensions. The probe can be attached directly on or in tissue for the measurement of blood flow velocities. Out of two different prototypes, one prototype is described, together with test measurements.

An optoacoustic sensor for trace analysis in gases was constructed and experimentally tested. The crucial element in such systems, the highly sensitive electronic microphone, was replaced by a fiberoptic interferometer in the Mach-Zehnder configuration. The fiber of the sensing arm was wrapped onto a thin foil arranged close to the cylindrical walls of the acoustic cell. Thus the acoustical waves generated by the absorbed light were transferred to an elongation of the fiber. The cell was operated at one of its resonances. A sensitivity of ~ 50 ppb was evaluated for an input power of 500 mW radiation of an Ar-laser for the detection of NC^ in an inert buffer gas. Presently the minimum observable power is 7-10" 8 W/citiv/f!zl . Details on this device are described in 1 and 2 .

The possibility of analyzing two spectral lines by measuring the second-order factorial moment,n(2)(T), is studied. The results are compared with the ones obtained with a multichannel analyzer system.

The laser Raman spectra of somT HPD and of_FD in different solvents were investigated. These spectra extended from 570 cm to 1640 cm . Experiments showed that the solvents had a pronounced effect on these spectra. Some HPD had a strong curative effect, and the two Raman lines 1432 cm-1 and 1502 cm-1 , characterizing the u(C-C) + δ(C-H) and u(C=C) vibrations in the side-chain group, were observed.

Phase measurement techniques are becoming a useful tool for precision measurements. Spatial as well as temporal phase shift methods can be used. Optical testing, where computer analysis of interference fringes is becoming increasing important, will be discussed in connection with testing optical components,microprofilbs as well as for testing aspheric surfaces. In addition, methods using heterodyne techniques and real time holography will be described.

A simple and new device to balance a Mach-Zehnder fibre interferometer has been develo-ped. It consists in a thermo-optical phase shifter (TPS) whose normalised phase response (sensitivity) is about 10^-5 rad/m.K over an extremely large dynamic range (10³). The advan-tages of the TPS compared to the conventional piezoelectric cylinder are discussed and the mode of operation of the TPS is described.

In holographic interferometry, the phase difference governing the interference pattern appears to deviate slightly from the value that follows from the usual formula. This phase deviation 6 is a.o. due to the nonvanishing detector aperture. For the case that the detector is focussed on the object surface, we calculate this for double exposure holography. In many practical situations δ appears to be maximized by a function proportional to the longitudinal displacement and to the square of the angular detector aperture, while δ does not exceed the value of π usually. Related to holographical systems which can measure the phase differences very accurately, formulas are derived for δ in the paraxial as well as the non-paraxial situation. Since in the paraxial situation δ can be approximated accurately by a simple function of only two variables, the emphasis is laid on the question how accurately (S can be approximated by the paraxial formulas in the non-paraxial situation.

When we look at a fixed landmark on a distant hillside, sometimes the landmark is easily seen, yet on other occasions the same landmark is only just discernable. Your eyes have not changed nor has the distance between you and the landmark. The controlling factor which is dictating your viewing ability is the composition of the intervening atmosphere. This atmospheric composition is continually changing with the fluctuations of the prevailing meteorology. Despite the fact that it is known that prevailing meteorology affects performance the effect is seldom explored and when explored often made excessively complicated. A technique developed at the J Mc G Sowerby Research Centre within British Aerospace at Bristol allows the effects of meteorology to be rigorously, but yet simply evaluated.

A real-time Vander Lugt correlator for automatic recognition and tracking of targets from visible or thermal data is described. A modification to the classical system architecture was the use of difference-of-Gaussian spatial filtering, which provided greater tolerance to scale and aspect variations in targets. Incoherent-to-coherent conversion was achieved using a Hughes LCLV, and the results of a rigorous evaluation study of the device are discussed.

The vertical structure of the atmosphere, which is of invaluable interest to meteorologists, geo-physicists and environmental researchers, can be measured with LIDAR. A method has been proposed and applied to invert lidar signals from vertical soundings to height resolved scattering coefficients. In situ measurements have confirmed the applicability of this lidar technique. A fully computer controlled lidar system allows the study of the dynamic behaviour of the atmospheric mixing layer.

Vegetation remote-sensing is a quite new field for lidar investigations and only few results were shown in litterature. The potential of differential-reflectance and fluorescence lidars in the detection of some plant-characteristics was analyzed with a particular attention to water-stress, senescence and diseas. Both systems showed a good potential in vegetation remote-sensing: differential-reflectance lidars seem particularly interesting for senescence and disease monitoring, while fluorescence lidars seem particularly suitable for water-stress monitoring.

Two years evolution of the stratospheric aerosol loading are presented; this study started after the eruption of the volcano El Chichon. Measurements were carried out in Florence, Italy, from the end of April 1982 to today. The increase of stratospheric aerosols at our latitude up to December 1982-January 1983 and the following decay has been monitored. Scattering Ratio and Integrated Backscattering, from the tropopause to 28 Km height has been corn puted. Due to the characteristics of the IROE Lidar system short time fluctuations in the lidar signatures could be observed, obtaining information on stratospheric inhomogeneities and structures.

Second order factorial moment, n(2)(T), measurements of laser light scattered by binary mixtures of spherical and rodlike macromolecules allows to obtain the errors involved in the determination of their sizes and concentration ratio.

Pressure transients are observed in absorbing gases at low pressure in a non-resonant spectrophone. At very low pressure (transition saturated) the transient is negative on irradiation. Interpretation is given in terms of thermodynamics of laser driven systems. The local value of the partition function depends exponentially on the incident radiation's intensity. The observed depression on irradiation is the consequence of the law of mass action applied to inhomogeneously irradiated systems.

A lateral wave appears at an interface between two media when a bounded beam is incident in the denser medium at the critical angle. The evanescent penetration into the less dense medium offers a method of exploring the interface region and has been used to study weak absorption. In this paper, results relating to the effects of surface roughness and deposited film inhomogeneities are discussed.

An expansion of the angle characteristic for a rotationally symmetric, aspherical surface of 4th order is presented. It contains both odd and even order homogeneous functions of its variables. To emphasize the importance of angle characteristic expansions, the relationship between the angle characteristic and the Buchdahl quasi-invariant is enunciated. In order to improve, for a given finite aperture, the overall accuracy of predictions based on 3rd order aberration theory, the possible use of general 4th order surface equations for the representation of spherical surfaces is considered.

The self imaging (Talbot) effect is a diffraction phenomenon. Polychromatic illumination results in a blurring of the self-images. A chromatic system is presented that compensates this dispersion.

A computer program has been developed for the exact tracing of skew rays through a grating-spectrograph consisting of mirrors and reflection-gratings.

The NPL Centrax camera has been designed for ultra-precise work in close range photogrammetry. For this type of application it is seldom satisfactory to rely on natural object features, such as surface texture or edges, and in most cases specially designed targets are used to define the points being studied. If these targets are made small, symmetric and self-luminous, then it becomes a useful alternative to dispense with conventional photographic imaging and to redesign the lens so that the images which it produces, although larger than usual, have their positions sharply defined by a central diffraction pattern. These central patterns are referred to as "axicon images"; each of them contains a small bright spot surrounded by several concentric diffraction rings of almost regular spacing and gradually decaying intensity (Figure 1).

Many techniques have been suggested for diffraction-limited imaging of stellar objects from Earth-based telescopes. In this paper we review the methods that use the short-exposure images collected by Labeyrie's technique of stellar speckle interferometry [1,2]. These methods may be divided into two groups: those that use only the modulus of the Fourier transform of the object intensity (i.e. the quantity normally determined by speckle interferometry) and those that use the original short-exposure images. The latter methods, which include the shift-and add, Knox-Thompson, McGlamery and exponential filter techniques, show more promise in the case of astronomical imaging.

The development of the digital electronic computer was highly successful and its capabilities are still improving at a brisk rate. Are there any chances for digital optical computing? Indeed, there exist reasons to believe that an optical system can compete with electronic computing in some situations. We will analyze in the following first the basic aspects of optical computing and we will then describe as a laboratory example an optical, logical, parallel processor based on diffraction or scattering effects.

New results are presented which confirm the feasibility of detecting hidden diffracting structures by measuring the correlation of the far-zone scattered field. In particular, diffraction gratings were masked by random phase diffusers bonded to their surfaces, which precluded exploiting the usual temporal fluctuations which arise whenever the diffractor and diffuser are in relative motion. Instead, it was necessary to scan the quasistationary, broadly distributed speckle patterns spatially. Good agreement between the propagation theory for first-order field statistics and the experimental results was obtained with regard to the dependence on the geometric scanning parameters. Moreover, the dependence of the measured correlations on grating period and diffuser correlation length showed satisfactory agreement with the theory and allowed inferences to be made about nature of the diffuser statistics.

The paper presents a review of the Wigner distribution function (WDF) and of some of its applications to optical problems. The WDF describes a signal in space and spatial frequency simultaneously, and can be considered as the local spatial-frequency spectrum of the signal. Although derived in terms of Fourier optics, the description of a signal by means of its WDF closely resembles the ray concept in geometrical optics. The concept of the WDF is not restricted to deterministic signals; it can be applied to stochastic signals as well, thus presenting a link between partial coherence and radiometry. Properties of the WDF and its propagation through linear systems are considered; again, the description of systems by WDFs can be interpreted directly in geometric-optical terms. Three main categories of optical problems are considered, in which the concept of the WDF can be applied usefully. First, the application to geometric-optical systems, i.e., systems where a single ray remains a single ray. Second, the application to problems in which the signal appears quadratically, like in the case of partial coherence. Third, the application to problems where properties of the signal are discussed in space and spatial frequency simultaneously; the uncertainty principle in Fourier optics might be an example. The WDF approach is extremely useful when two or more categories are combined: for instance, the propagation of partially coherent light through geometric-optical systems, or the formulation of uncertainty relations for partially coherent light.

Optics is necessary to analyze and realize imaging processes, but it is also a possible tool in image processing. Since the concepts of coherent and incoherent optical image processing including the formalism of spacial frequency filtering, the laser, and holography, were developed, computer science went through revolutionary developments. The past and present situation of optical image processing is critically examined, and three subject to which we have recently contributed are used as illustrations. The first is the use of interference phenomena as spatial frequency filters, which can be a useful complement to the more conventional use of diffraction. The second is the use of white light illumination in spatial frequency filtering setups to obtain spatial frequency pseudocoloring. Finally, a texture discrimination experiment involving optical preprocessing by a set of interference spatial frequency filters Followed by computer classification is described.

The use of dead time effects to generate sub-Poissonion photo-electron counting statistics is discussed. An experiment is described in which dead times are introduced using an optical shutter triggered by photo-detection events. Although the triggering photo-electron train is sub-Poissonion and antibunched, the light sampled by a second detector gives rise to a super-Poissonion and bunched train of photo-elecrons. A second experiment is proposed which would generate truly sub-Poisson light (ie detector independent). This is based on the use of optical dead times in parametric fluorescence.

Anew architecture is described, for the real-time implementation of any discrete transform with incoherent light. Matrix-matrix products are performed using two 1-D acoustooptic spatial modulators with time-integration on a CCD camera. The operation can be iterated for N-D transforms, such as in multisensors image processing.

In optical information processing polarization and color may be introduced as orthogonal states in established measuring techniques. These signal independent states offer a great flexibility in information processing as for example frequency filtering in the space domain.

The permanent storage of true 3-D images in computer-generated rainbow holograms is proposed and tested. The procedure is of special interest in situations where image data are acquisitioned by computer like in tomography. A l-D Fourier transform lowers the requirement on memory space and allows short handling times. The spectra of different planes in depth of the object are repeated to form a hologram using a minimum of computation time but of a size sufficient for display. The spectrum of each object plane perpendicular to the optical axis is superposed with a quadratic phase factor. Full horizontal parallax is preserved. The reconstruction is accomplished in collimated white light.

The use of mosaic color filter arrays to derive a color video signal from a single solid-state image sensor is discussed. Special attention is required when designing schemes suitable for frame-transfer CCD's

An opto-electronic system for the evaluation of double-exposure and double-pulse holographic interferograms is presented. Video-electronic detection with quasi-heterodyne fringe interpolation (step-wise phase shifting) is employed and yields a resolution of 1/100 of a fringe. Automated quantitative determination of object shape and object deformation is possible in the same set-up.

An hologram can be recorded in BSO with picosecond beams. The necessary energy is the same than in continuous or nanosecond excitation, but the diffraction efficiency is far smaller. Rise and decay times for the hologram reading are measured. Long duration information storage has been proved.

Experiments have been done to extend the dynamic range of inverse filtering.by addition of a temporally invariant signal to the spectrum to be filtered. We obtained qualitative indications that this technique is feasible.

The effect has been discovered of light pulses contraction during their propagation in active neodymium glass fibres operating in regenerative amplification mode. It was demonstrated that the recombination of shortliving colour centres arising in silicate glass fibres fosters the shortliving of nanosecond pulses 2 times and their amplification by 4- -5 orders.

Intense ps-pulses are spectrally broadened after transmission through a singlemode fiber. The obtained spectra showed a strong sensitivity to the temporal symmetry and polarization of the input pulses.

The use of optical fibers in holographic set-ups allows the recording of holograms of objects which are not directly accessible to conventional optical technics. The problems for recording holograms through optical fibers are of the same nature as for producing optical fiber sensors. But the optimal use of the two technics corresponds to opposite conditions: sensors require a great sensitivity to phase variations while the hologram quality is disturbed by a very low variation. There are two possibilities of freezing the phases during the recording of the hologram: 1) in cwl.laser holography it is necessary to avoid any variation of physical parameters (temperature, pressure, electromagnetic field, vibrations, twisting, mechanical strain, air turbulence, etc...) influencing the phase or the polarisation of the light transmitted by the fiber; 2) use of a pulse laser with a very short time of emission. Unfortunately in this case non-linearity phenomena may occur in the fiber: reduction of the coherence length, light frequency variation. The focusing of the light beam may also ionize the air and damage the input face of the fiber. At last, the very high powers may destroy the fiber. In spite of those drawbacks holograms of small objects have been recorded through multi-mode and monomode fibers with the help of ruby and YAG lasers. A) Ruby laser: with a ruby laser giving a pulse of 20 mJ in 20 ns at 0.6943 pm the following set-ups have been tested: a) The object beam passes through a 1 mm-multimode step-index fiber; no fiber for the reference beam. b) Same arrangement for the object beam, the reference passing through a monomode fiber. The beamsplitter is located between the oscillator and the amplifier. B) YAG-laser: with a YAG-laser giving a pulse of 20 mJ in 20 ns at 0.53 pm the following set-ups have been tested: a) A 1mm-multimode step-index fiber in the object beam and a 133 pm-multimode step-index fiber in the reference beam. b) Same arrangement for the object beam and a monomode fiber in the reference beam. In each case single- and double-exposure holograms have been recorded. Some typical results are presented and discussed.

Optical amplification by stimulated Raman emission has been observed at five discrete wavelengths using a fibre Raman laser as both signal and pumping source to the amplifier. An amplification factor of 16 dB has been observed at 1.30 μm and 3 dB at 1.36 μm for a pump power of a few tens of milliwatts. RAMAN AMPLIFICATION IN OPTICAL FIBRES IN THE WAVELENGTH RANGE 1.06 TO 1.36 μm Stimulated Raman scattering in low loss optical fibre waveguides has attracted considerable attention owing to the high efficiency of generation of multiple Stokes frequency shifts. This effect has been utilised to provide a pulsed tunable source for fibre diagnostic measurements (1) , but the direct application of this mechanism for producing amplification of the transmitted signal in a fibre has only recently been investigated, with results showing substantial amplification in GeO2 doped SiO2 fibres at 1.064 μm (2), 1.24 μm (3), and 1.4 μm (4).

A new measuring method for the determination of diameter variations of optical fibres is presented in this paper. This microinterferometric method is based on the detection of the Fabry-Perot-like resonances observable in the intensity of laser light backscattered from a fiber when the diameter changes. Two illuminating laser beams with different, but well--determined angles of incidence are used and in case of varying diameter two corresponding photodetectors generate measuring (cosine) and reference (sine) signals. Monitoring the sign of the reference signal the direction of the diameter changes can be determined. A half period of the measuring signal corresponds to ~0,1 μm diameter variation thus the resolution is even better. Experimental results for thin (~14 μm) doubly-clad fibres are described and the allowable tolerances of the angles of incidence calculated by ray tracing analysis are also presented for thin and thick fibres.

Over the past few years there has been a rapid development in the use of optical techniques for communication and information processing. Most successful of these has been fibre-optics technology, now increasingly penetrating communications networks through-out the world. Other optics based technologies, currently being developed include: (i) acousto-optic devices (often in an integrated planar-waveguide format), for radar applications, etc.; (ii) Fourier optics techniques for image enhancement, etc., and (iii) nonlinear convolution or correlation systems, for pattern recognition, etc. These latter techniques all rely upon an analogue processing approach.

Nonlinear integrated optical devices based on second and third order nonlinearities of Ti:LiNbO3 waveguides are reviewed. Second harmonic and difference frequency generators as well as parametric amplifiers and oscillators are presented as efficient devices for frequency conversion of coherent radiation. Furthermore, third order devices for signal processing and optical logic applications are discussed.

The ability of phase conjugation to correct phase aberrations produced by distorting media has received much attention and most of the reported experiments involve passing a field through the distorting medium, phase conjugating the resulting distorted field and passing this back through the distorting medium. We present an analysis showing that two independent fields having the same plane wave spectra can be used to predistort a signal wave. By mixing in a slow non-linear medium one way correction of a thick distorting medium is possible.

In this paper we consider the conditions on relative beam powers and interaction region geometry necessary to obtain accurate correlation of two input images via degenerate four wave mixing in photorefractive materials. We also show how the correlation product may be 'weighted' to improve peak to background discrimination either by appropriately adjusting the beam intensities or by introducing an extra control beam. The discussion is supported both by experimental results and numerical simulations.

The nonlinear optical properties of the interface between glass and liquid crystal are reported Switching characteristics and optical hysteresis have beam studied.

Potassium niobate (KNb03) is well suited for efficient frequency doubling of near infrared laser light, due to its large nonlinear optical coefficients, d32 = (18.3 ± 0.3)pm/V and d31 = (15.8 ± 0.3)pm/V at λ = 1064 nm, and the possibility of noncritical 90° Type I phase-matching. Tunable second harmonic generation (λ = 420 to 475 nm) from low power (5 to 100 mW) cw and pulsed AlxGai_xAs and dye lasers has been demonstrated. Higher conversion efficiencies have been achieved by intracavity frequency doubling of a cw dye laser operating at wave-lengths around λ = 860 nm. The second harmonic of a pulsed Styryl-9 dye laser and a mode-locked Nd:YAG laser could be generated with efficiencies as high as 28% and 32% respectively. Efficient 90° phase-matched sum frequency generation of a Nd:YAG signal (λ = 1064 nm) and a ruby pump wave (λ = 694.3 nm) has been demonstrated. New accurate measurements of the non-linear optical coefficients of KNb03 at the wavelengths 1064 nm and 826 nm are presented.

The bifurcation structure of the transmitted light power for an electro-optic bistable device with delayed feedback has been investigated. We report a bifurcation scheme with hysteresis in the bifurcation points, so that we obtain different values of the bifurcation points when the bifurcation parameter is increas-ing and decreasing. This hysteresis phenomenon has been investigated experimentally and numerically, and we find that the time dependence of the bifurcation parameter is crucial to the bifurcation mechanism and to the critical values for which the transitions to period -2, period-4, etc. occur.

Stable and unstable states of a nonlinear silicon interferometer under external dc bias are investigated using Nd:YAG laser light excitation. Experimental results as well as calculations from a theoretical model reveal bi- and multistability and self-pulsing properties.

A new concept in light level detection. The basis is the use of hybrid optical bistable devices working in oscillatory mode. The obtained instabilities show a correspondence between their frequency and the laser light intensity.

The simplified band transport model of the photorefractive effect in which the material responds linearly to local changes in light intensity modulation ratio (fringe contrast) is examined in detail. The validity of the model for cosinusoidal grating formation is first discussed with reference to spatial frequency and time dependence. The "hopping" model of the photorefractive effect is then considered. It is shown that, although being physically distinct from the band transport model, the hopping model may be considered as a special case of the band transport equations. Results of a numerical simulation of the band transport model are presented which illustrate the validity of the linear in modulation approximation. The band transport model is then extended to describe non-plane wave interactions and include a tensor static permittivity. Features of this extended model are emphasised by some experimental results. These results show the effect of non uniform beam intensity profiles on apparent time constants as measured in four wave mixing experiments using photorefractive Bi12Siqo20

Attempts have been made to use an optical computer for the purpose of resolution enhancement by deconvolution in real-time echography. Phase holograms, obtained under special conditions will exhibit a prescribed dynamic range as a function of reference-beam level.

The need for developing an exact theory of surface scattering, formulated in terms of explicitly known, universal functions is discussed, and numerical examples of such a theory are given.

A numerical procedure is given for the reconstruction of the permittivity profile of a dielectric slab on a perfect conductor. Profiles not supporting guided modes are reconstructed from the complex reflection amplitude for TE-polarized, monochromatic plane waves incident from different directions using the Marchenko theory. The contribution of guided modes is incorporated in the reconstruction procedure through the Gelfand-Levitan equations. An advantage of our approach is that a unique solution for the permittivity profile is obtained without the use of complicated regularization techniques. Some illustrative numerical examples are presented.

An expansion of general stationary stochastic optical fields is presented. Each term of the series is seen to represent a recently defined new class of optical fields: the so-called spectrally quasi-factorizable fields. Results are applied to obtain an expansion of the elements of the coherence matrix of a general stationary partially polarized field in terms of factorizable functions.

A short survey of recent work on laser-produced metallic glasses and other metastable phases is presented. For details refer to the cited original publications.

The objectives of the five-year (1979-1983) Project on High Power Lasers supported by the Italian National Research Council and the major results on welding, cutting, drilling, surface treatments, and high-average-power laser development are presented.

Conventional laser processing of materials is essentially based on heat treatment which can take place in vacuum or in a nonreactive surrounding. Here, the high irradiance of the laser beam is used to induce structural transformations, such as removal of residival damage, recrystallization, amorphization, hardening, alloying etc., within the surface of the material. In micromachining such as drilling, cutting, shaping, welding etc., the material is melted and vaporized 1.

Hematoporphyrin-Derivative (HpD) is a photodynamic drug increasingly used in tumor photo-therapy. The chemical and biological bases of its tumor specificity are yet to be clarified. In this paper we present the results of fluorometric studies of HpD both at the cellular level and in solution, including time-resolved fluorescence measurements. The results of these studies were correlated with the effects of HpD observed in cells.

Fluorescence excitation spectra are recorded from HpD in living RUC-2 tumors implanted in rats. The experiments show that, compared with the excitation spectrum of HpD in solution, the Soret excitation band at 400 nm decreases with respect to the minor excitation bands at longer wavelengths. The excitation efficiencies at 503 nm and 625 nm are comparable with the efficiency at 400 nm. The differences in the in vivo and in vitro excitation spectra are caused by the wavelength dependent penetration depth of the excitation light due to absorption of blood and tissue.

Laser surgery and photoradiation therapy are still rapidly developing: they are therefore placing new requirements and conditions on the associated technology. Thus, optical fibers are often requested to have a particular output which matches the needs of the considered applications. Integral fibre tips are a very convenient solution to many optical systems. The fabrication techniques and the experimental characteristics of different kinds of fibre tips are described.

The goal of this communication was to report three works: 1.- Inmunological alterations of erythrocyte membrane by polarized light irradiation. 2.- Measurement of very weak haemagglutination using laser diffraction. 3.- An instrument developed to measure deformability of erythrocytes subjected to shear stress, by laser diffraction pattern analysis.

Third Purkinje image, formed with a coherent light, is used for roughness measurement of the eye lens anterior surface Isubcapsular lens epithelium) by applying Beckmann's scattering from rough surfaces theory. The contribution of this surface to the total intra-ocular scattering scattering has been estiwated. The relative contribution depends on the subject age. For midle aged subjects this surface contributes by a 1.5%.

The applicability of Raman scattering for the study of intact chromosomes and constituting compounds, such as DNA and its bases, has been investigated, using normal Raman and Surface Enhanced Raman microspectroscopy.

Contactmicroradiography produces an X-ray absorbance image of mineralized tissue slices. We use it to calculate the mineral content in tissue from the absorbance data of thin tooth sections as a function of depth in the tissue. This paper gives a complete analysis of the loss of detail caused by the microradiographic subsystems, describing this loss with the Modulation Transfer Function (MTF). Images (CuKaradiation) of thin test objects with a sharp edge were made on holographic film; an aluminium stepwedge was used to calibrate the film. Densitometric tracings of the images were fed into a microcomputer. The dose-density relation of the film was approximated by a 3rd degree polynomial using the stepwedge data. The resulting curve was used to convert the densitometric data of the slice into X-ray absorbance data. To filter out the film grain noise, 20 microradiograms were made of the same object and their edge scans were averaged. The resulting Edge Spread Function (ESF) was transformed into the MTF using standard techniques. Thus the MTF of the total method was obtained, using a 100 pm thick Al slab as object. The combined MTF of the densitometer together with the film was found with a 27 pm thick Cu slab as object, closely pressed to the film. The densitometer MTF was obtained using a knife edge as object in the densitometer. The results show that the total loss of spatial detail depends on the contributions of the X-ray projection geometry (projection subsystem), the film emulsion (film subsystem) and densitometer window width (densitometer subsystem). The MTF's of the individual subsystems were calculated from the measured combined MTF's assuming that the imaging subsystems are linear. After optimalization of the MTF's of the subsystems the maximum transmitted spatial frequency of the method was found to be 330 lines per mm.

This paper discusses the error made when measuring the color of translucent materials, using the same window for illumination and light collection. Two methods, based on large-window illumination and small-window collection are described.

Based upon a fluorescent coating and contouring technique, a video signal processing has been designed for real-time contouring with enlarged depth of field. Microscopic images with 5μm contour interval have been obtained.

To optimalize laser-parameters for therapy of port-wine stains temperature calculations have been performed on a skin model. The optimal values of these numerically evaluated variables are: wavelength λ= 415,577 or 540 nm., pulse-time t1 a few milliseconds and beam radius wi> 0.1 mm. Based on these theoretical results some experiments have been carried out which confirm the calculations. Thus laser-therapy for port-wine stains can be ameliorated.

Optical fiber illumination of a breast gives rise to a contrasted image where flaws conduct to a medical control for cancer inspection similar to other techniques and without any danger. Pseudocolor processing improves the technique.

This paper reports on experimental results of the photosensitized mechanism of HPD in cancer therapy. Human stomach cancer cells and Hela cells were chosen as the object of study. Two kinds of HPD were used being irradiated by either pulsed or CW laser light. The results showed that the main mechanism in photosensitized cancer therapy was singlet oxygen. The energy levels of HPD and HP were calculated and the photodynamic reaction process as well as it's corresponding physical model were discussed.

Following the suggestion of S.Y. Sokolov ( USSR ), a method and equipment has been developed whereby shortwavelength acoustic energy is used to produce magnified views of optically opaque samples non-destructively. The objective of this presentation is to acquaint the audience at this conference with the principle of operation and the application potential of the commercially available instrument based on this technique. The results also illustrate the synergy possible with the effective application of two modern technologies, i.e. acoustics and electro-optics. The acoustic waves reveal elasticity variations and hence provide new information on the observed sample's internal structure. The scanning focussed laser beam detects the acoustic information with high resolution and sensitivity.

A number of optical systems have been designed for use with flow-cells. The requirements are: sufficient optical acceptance for high signal-to-noise ratio, small cell volume for good analytical resolution, adequate path length for sensitivity to small concentrations, and minimum sensitivity to changes in refractive index and temperature of the sample.

A simple, inexpensive fibre optic temperature sensor based on the principle of the change in the fluorescence decay time of neodymium in glass with temperature has been developed.

Proposals are made for coherent processing of the signals from multiple element sensor arrays in order to obtain high resolution and high dynamic range. These proposals include time reversal, parametric reflection and inversion by a holographic method.

We started a research program to develop a new type of gamma camera. The basic idea is a synthesis of a BaF₂ scintillation crystal for the absorption of gamma rays and a wire chamber for the position-sensitive detection of the scintillation light emitted subsequently.