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An introduction to current trends in the digital processing and manipulation of images is presented. The paper does not attempt a detailed survey of the field, but outlines instead the motivation behind it, and the relationships between the ‘disciplines’ such as image enhancement, pattern recognition and scene analysis involved with processing images. Selected examples are used to indicate the state of the art. Finally the typical configuration of an image processing system is described. The processing speeds of available digital processors are discussed, and the need for special purpose processors is emphasized.

In this paper the geometrical theory of pulse distortion and energy launching into multimode optical fibres is generalized when skew rays are taken into account.

Automatic pattern recognition is the subject of a large literature, much of it theoretical. The present review paper deals primarily with optical pattern recognition techniques, and concentrates on the principles of recognition rather than the detailed physics and technology of opto-electronic transduction. Mathematical, sequential, and interactive techniques are mentioned only briefly because they have already been well reviewed by various authors.

In this paper, the techniques of extended pulse stroboscopic holography and holographic subtraction have been applied to the study of periodic, non-sinusoidal vibrations represented by a Jacobian elliptic function. Fringe irradiance distribution in reconstructed images has been evaluated for the two cases. For this purpose we make use of an expression for the characteristic fringe function derived from considerations of the effect of motion on the coherence. It is shown that the above-mentioned techniques are more advantageous for the measurement of periodic, non-sinusoidal vibrations than in the case of pure sinusoidal vibrations.

This paper describes and reviews experimental results on both the processes involved in the establishment of ultrashort light pulses during their build-up from noise and in their subsequent growth and narrowing. Schemes for the improvement of the USP train are suggested.

An optical modulator inside a laser cavity, if driven at the cavity c/2L frequency or a harmonic, will produce a variety of mode-coupled short-pulse and FM-laser phenomena. This paper reviews the kinds of CW and transient mode-coupling phenomena hat can occur in CW lasers and in selected lower-power pulsed lasers using either an active optical modulator or in some cases passive saturable absorbers.

This paper is concerned with the investigation of a longitudinal electric field (1 V/cm) arising in a homogeneous piezo-electric crystal at a high level of optical excitation. The sign of the effect corresponds to free carrier drag (electrons — in the case of CdS) in the direction of light propagation. The magnitude of the effect and its kinetics have been related to the light intensity, temperature, crystal orientation and the distance between the fest points. The effect is assumed to be a result of generation of a phonon packet, referred to by the authors as an acousto-optical domain, and carrier drag by this domain. Calculations based on the Boltzmann kinetic equation for the electron distribution function give a reasonable phonon density inside the domain, necessary for generating the electric field observed. Estimates based on the calculated phonon density show considerable mechanical stresses to exist in the domain area. These can result in the destruction of the crystal when there is an increase in light intensity; so the effect observed can be directly related to the problem of optical strength.

A theory of spatial frequency domain filters is presented from the standpoint of leastsquare linear estimation. The general expression of this filter is obtained with few assumptions, thus allowing considerable flexibility in its application. Noise common to pictorial information usually can be described as a mutually exclusive process, whereas much of the available signal processing theory assumes additive noise. Types of pictorial noise discussed in this paper include the background of signal patterns, pattern obscurity, and image modulation due to the recording process. It is shown that the additive noise assumption is valid under certain conditions. The general filter is described in terms of spatial frequency estimates which are conveniently expanded for particular applications. A detection filter for determinative patterns is obtained and compared to the matched filter. A filter is derived to restore patterns degraded by noise and a linear distortion filter.

The development of techniques for the deposition of semiconductor layers has led, over the last decade, to intensive studies of heterojunction systems. In this paper an outline is given of those properties relevant to the production of photodetectors, illustrated by a summary of the classes of device so far prepared with notes on the way in which their performances differ from classical detectors.

This paper presents theoretical results concerning pulse-broadening in multimode fibres. All the calculations are based on the geometric optic hypothesis. The results are given for different kinds of input functions in the case of a loss-free guide and an energy equidistribution. Subsequently, material and interface losses are included. The influence of angle-dependent energy distributions is also investigated. For all these cases analytical expressions are obtained. Experimental results are presented: they are in good agreement with theory.

This paper deals with the usability of laser velocimeters in supersonic flow field studies. Problems of the optical setup stability are considered as well as possibilities of data acquisition and evaluation. It is demonstrated that dust particles always present in the air are well suited as tracers for the flow velocity. The behaviour of these particles is studied in a rapidly decelerated flow.

This paper describes the techniques that have been developed in attempts to photograph in detail the events occurring during the electrical breakdown of an insulating liquid. As the breakdown occurs at random times, it has been necessary to develop a means of synchronizing the recording system with this breakdown. The techniques discussed make it possible to photograph the discharge in the streak mode with a time resolution of only a few picoseconds.

Many studies on an optical ULM correlator have been carried out by various workers. Different types of correlation are usually produced, depending not only on the combinations of signals to be processed but also on the optical and electrical filters used in the detecting stage. This paper investigates the effects of these conditions on the performance of the optical ULM correlator in some detail on the basis of a unified analysis. It is also shown, by considering in the course of this analysis the propagation of a spatial coherence function, that the coherence property of light used for the illumination does not affect the correlation-output signal. Some experiments are performed concerned with the effect of spatial coherence, binary or intensity correlation and the linear response for correlation in the ULM correlator.

This paper offers a review of the contributions of German research groups in the field of fibre-optical communications until now. Since the latest publications are also taken into account which in part are not yet printed, a survey is given at the same time of current activities in this field in Germany.

Turbulent swirling water flow in a pipe has complex velocity distributions with special measurement problems tor experimental work. Some of these problems are described in the introduction to the paper along with comments on the basic characteristics of turbulent swirling flow.

This paper gives a unified theoretical analysis of Laser Doppler systems covering both the optical and electronic aspects, and applicable to all systems which have either a real or virtual fringe pattern. Previous experimental results by Greated for the Doppler spectrum are confirmed and in addition a fuller treatment of the low frequency part of the spectrum is presented.

In this paper a generalised result for theN-fold joint photoelectron counting distribution for independently modulated radiation is given. We extend the recent results of Diament and Teich, for the one-fold photoelectron counting distribution for light propagated through an atmosphere characterised by log-normal irradiance fluctuations, to theN-fold joint photoelectron counting distribution. An approximate solution for thisN-fold distribution is obtained, for detection intervals {Ti} «ta whereta is the characteristic time of the atmospheric turbulence. We present specifically the two-fold joint photocounting distribution for amplitude-stabilised laser radiation passing through such an atmosphere for several levels of turbulence and degrees of correlation. Cases including additive, independent, non-interfering Poisson noise are considered. Computer generated plots of the photocounting distribution are presented. For noise-free detection, the otherwise narrow-peaked photocounting distribution is seen to broaden markedly and shift its peak to lower counts as the turbulence level increases. Furthermore, a non-singular counting distribution is obtained for fully correlated detection. In the presence of additive noise and varying only the signal-to-noise ratio?, the probability surface is intermediate between that of the Poisson and that of the noise-free log-normal fading counting distribution. The peak, however, is observed to decrease and then again increase in magnitude as? ? 8, for correlated detection only. These results are expected to be of use in the study of atmospheric turbulence, as well as in the evaluation of certain stochastic functionals that occur in optical communication theory for the turbulent atmospheric channel.

Abstract: The van Cittert-Zernike theorem states that the spatial coherence over a space illuminated by an incoherent extended source is described by the Fourier transform of the intensity distribution over the source. The theorem is usually used in a restricted case of the spatial coherence in a plane parallel to the source plane and illuminated by an incoherent extended source of uniform intensity distribution. In this paper we re-examine the van Cittert-Zernike theorem by reviewing it in an original formulation and extend the theorem to the spatial coherence at any two points of a light field illuminated by an incoherent extended source having a non-uniform intensity distribution.

Abstract: The paper is based on C12O216 rotational constants and line frequency data gained from laser frequency measurements performed recently. Equations for transition frequencies and their standard deviations have been derived. A list is presented containing accurate 10.4 and 9.4 μm line frequencies and their relative and absolute standard deviations; also wavenumbers and wavelengths are given for each line. For transitions usually observed in CO2 lasers the relative standard deviations are on the order of a few megahertz, the absolute accuracy is about 25 MHz for the 10.4 μm band and about 18 MHz for the 9.4=μm band.

This paper describes a number of tunable infra-red lasers and techniques employing them for the detection and monitoring of gaseous air pollutants. Recent progress in the development of lasers that can be matched to characteristic infra-red absorption or emission lines of certain pollutants suggest wide potential application for sensitive specific monitoring. Examples to be described include highly-specific point-sampling,in situ source monitoring, ambient air monitoring, resonance fluorescence, and remote heterodyne detection.

This paper reviews the recent progress of the laser radar method, providing single-ended and range-resolved means for remote detection and analysis of various molecular species in the polluted as well as ordinary atmosphere, based on the existence of their Raman backscattering; simply called the laser-Raman radar method. A brief description is given of the operational principle including the basic concept and fundamental characteristics of this scheme, along with critical discussions of their advantages. The differential backscattering cross section and the spectral distribution of Raman scattering of molecular species present in the atmosphere are discussed and summarized from the practical view-point for providing molecular density evaluation and interference-free detection. After presenting experimental approaches of the laser-Raman scheme to show the feasibility of in-field monitoring and analysis of chemical species in various air conditions, the estimation of molecular concentrations is performed from observed Raman spectra. Analytical discussions on the minimum detectable concentration and the range detectivity are also presented to indicate the present capability and limitation of this laser-Raman technique. The potentiality for further progress in resonance Raman scattering for range-resolved measurement of dispersed pollutants in ambient air is pointed out.

Measurements are described on the operating parameters of 633nm He-Ne lasers, which are compared with the values calculated in the previous paper. A good overall agreement is obtained. Only for TEM00 lasers with several axial modes do slight deviations occur in the conditions for selecting TEM00 modes only.

This paper presents a theoretical investigation of the propagation and focusing of an electromagnetic wave in an inhomogeneous dielectric whose dielectric constant is given by?=?0(z)+F(r, z), whereZ-axis is the direction of propagation of the beam. The quantity F(r, z) may either be due to non-linear effects or due to inhomogeneity in the actual fabrication of the guide.

This paper is concerned with the application of opto-electronic signal processing to a certain class of interference-resistant communications techniques. The processing techniques are applicable to spread spectrum digital transmissions which are processed by a matched filter at the receiver. The analysis of optical delay line matched filters of the diffraction type is discussed. The analysis considers the basic ultrasonic light modulator, that is, the modulation of a light source by a sonic wave. The sonic wave may represent a received spread spectrum signal or received noise or a combination of both. Two ultrasonic modulators in cascade perform the desired correlation or matched filter function. The analysis considers the effects of intermodulation of signal and noise and also the effects of the beamspreading and attenuation of the sonic signal in the delay lines. Finally, the design of a matched filter having 40 dB process gain is presented together with an estimate of its communications performance.

This paper reviews some new spectroscopic techniques, broadly defined under the title of stimulated emission spectroscopy, which add to the information on activated crystals obtained by conventional luminescence and absorption techniques. Emphasis is placed on studies of the Stark structure of levels, and of the electron-phonon interaction. Experiments are included on lasers with dispersive resonators (prisms etc.), lasers with “combined active media”, and with “photon injection”. Also covered are high temperature (up to ~ 1000° K) spectroscopic analyses of stimulated emission, and multiplication and selfmultiplication (lasers based on non-linear crystals). Analysis of the temperature broadening and shifting of lines can be used to determine the effective Debye temperature for a given activator and a given medium. The kinetic studies have made possible estimation of the non-radiative de-activation time. Other measurements reveal the symmetry of activator centres through magneto-optical investigations. Spectroscopic analysis of the output of phonon lasers yields information on the phonon states of the crystal-matrix.

When using nitrobenzene Kerr cells and single element birefringent prisms in digital light deflectors one encounters the problem that the deflection pattern moves with a change of the operating temperature of the system. This paper describes how, by inverting the prism with the largest refracting angle, this effect can be eliminated while retaining the advantages offered by single element prisms. The operating temperature range is now of the order of 10° C compared with approximately 0.07° C for the conventional system.

The performance of a continuous HF chemical laser is presented in this paper. Population inversion was obtained by diffusion of H2 into a supersonic jet containing F atoms [H2+F ? HF(v)+H1 ?H=-31.7 kcal/mole]. A peak power of 630 W was obtained with an F atom flow rate of 0.040 mole/sec, and the efficiency of conversion of chemical energy to laser energy was 12%. The performance of a corresponding DF laser is also given. Major laser output is from 2-1 and 1-0 transitions for both lasers. Radiation is at 2.6 to 2.9µm and 3.6 to 4.0µm for the HF and DF lasers, respectively. The ratio of DF to HF laser power is 0.7 under similar flow conditions.

There is at present great interest in crystals which are suitable for efficient mixing at optical frequencies. Such a crystal should be acentric, have a wide transmission band, have a large non-linear coefficient and permit phase matching. Proustite possesses such properties [1], and this paper summarises the information that has been obtained to date at R R E on these properties and their use in “up-converting” 10µm radiation to the visible, on the available optical quality, on the electro-optic effect, and on electrical conduction in the crystal; some general observations on the type of damage caused to proustite by laser beams are given.

This paper describes a method for determining some important laser parameters from the fluorescence changes of an excited media induced by a resonant laser pulse. The parameters measured include stimulated emission cross-section, metastable level population and spectral relaxation rate. Results are reported for Nd3+ in silicate and phosphite glasses and in solution in POCl3 and SeOCl2.