Strong Light Beam Research Articles

A QUARTER CENTURY OF STIMULATED RAMAN SCATTERING

To round out a quarter century of SRS the timing of this writing (1986) requires a look ahead of only one year into the future. The proceedings of the 10th International Conference on Raman Spectroscopy present a picture of current activity. Further progress will be made in time-resolved spectroscopy with subpicosecond resolution, in the study of hyper-Raman and other higher order effects with CARS, in extension of resonant Raman excitation in the UV region of spectrum, and in the development of Raman laser sources. During past few years extensive theoretical investigations have been made for four-wave light mixing in the case of one or more very strong light beams. The perturbation approach for those fields ceases to be valid. If only one light field is strong, the usual approach is to make a transformation to a rotating coordinate system so that the strong Hamiltonian for this light field becomes time-independent. Very recently these techniques have been extended to the case of two or more strong fields. CARS-type experiments with strong beams are likely to receive more attention. Extrapolation of the current activities instills confidence in the vitality of stimulated Raman scattering for the foreseeable future.

A Quarter century of stimulated Raman scattering

Abstract

“X‐RAYING” HERBARIUM SPECIMENS WITH TRANSMITTED LIGHT, A NON‐DESTRUCTIVE WAY OF INVESTIGATING DRY PLANT MATERIAL

SummaryA strong light beam, transmitted through a herbarium specimen can often replace the somewhat risky softening of dried flowers. This method would be especially useful in the study of types and other material of special value.

New evidence for the mechanism of phototactic orientation ofEuglena gracilis

When rotated horizontally in a cuvette in a strong lateral light beam, the flagellateEuglena gracilis effectively corrects its course and shows negative phototaxis, provided the angular velocity does not exceed 200s−1. Faster rotations cannot be corrected effeciently. In two strong light beams of equal illuminance perpendicular to each other, the cells move along the resultant away from the light beams. Decreasing the illuminance of one beam causes increasing numbers of the organisms to orient with respect to the stronger light source. In two perpendicular low illuminance beams (>200lx), the population splits into two components moving towards either light source. The percentage of cells in each component depends on the relative illuminances. The results can be explained by the shading hypothesis combined with a dichroic orientation of the photoreceptor molecules perpendicular to the long axis of the cells. Externally applied electric dc fields have no effect on positive or negative phototaxis; this supports the hypothesis that electrical potential changes are not involved in the sensory transduction chain of photoorientation inEuglena.

Optical flip-flops and sequential logic circuits using a liquid crystal light valve

This paper is concerned with the application of optics to digital computing. A Hughes liquid crystal light valve is used as an active optical element where a weak light beam can control a strong light beam with either a positive or negative gain characteristic. With this device as the central element we have demonstrated the ability to produce bistable states from which different types of flip-flop can be implemented. In this paper we first present some general comments on digital computing as applied to optics. This is followed by a discussion of optical implementation of various types of flip-flop. These flip-flops are then used in the design of optical equivalents to a few simple sequential circuits such as shift registers and accumulators. As a typical sequential machine, a schematic layout for an optical binary temporal integrator is presented. Finally, a suggested experimental configuration for a optical master—slave flip-flop array is given.

Atomic velocity redistribution induced by a strong light beam and collisions

The velocity distribution of the two-level-atom populations induced by a strong laser beam in the presence of collisions is investigated. By means of a previously proposed method we have conducted numerical calculations using the collisional kernels introduced by Berman and co-workers. The obtained results indicate the importance of the collisions. Also the intensity of the light beam strongly influences the velocity distributions of the lower and upper state populations. In particular for large perturber density and large field intensity the broadening of the distributions approaches that of a maxwellian one. Distinct asymmetry of the total population is also noted.

A Comment on the Broadening of the Excitonic Molecule Band in CuCl

The broadening of the excitonic molecule band in CuCl is studied from the giant two-photon absorption (GTA) measurements by a weak linearly polarized probe light beam under the simultaneous excitation around the same GTA by another strong pumping light beam of the orthogonal polarization to the probe beam. The width of the GTA line monitored by the probe light remains almost constant less than 0.3 meV under the strong irradiation of the pumping light. It is pointed out that the broadened width of the GTA band which have been observed by the strong one monochromatic beam experiments is not associated with the mutual collision between the really produced excitonic molecules.

Light scattering from soap films

IF a strong light beam falls on the surface of a liquid, most of it will be reflected and refracted in certain directions, but a small part will be scattered in all other directions. This light scattering is caused by small surface ripples (corrugations) arising from thermal motion. The scattering intensity is proportional to kT/γ, where k is the Boltzmann constant, T the absolute temperature and γ the surface tension. In the case of a thin, free, liquid film (as found in soap bubbles), the scattered light also contains information about the interaction forces between the two film surfaces. According to the theory of Vrij1, the second derivative, d2F/dh2, of the interaction free energy, F, between the two film surfaces, with respect to the film thickness, h, can be obtained in this way.

Mixing and flow in ducted turbulent jets

The aerodynamic flow pattern of a confined, turbulent jet can differ profoundly from that of a free jet, most pronouncedly so in the massive recirculation of downstream gases which occurs under the operating conditions of many industrial furnaces. This paper reports on a study of furnace mixing patterns as represented in the cold by a round jet of oilfog-marked airissuing axially into a cylindrical duct fed by a uniform stream of clear air. Investigation of the fields of mean and fluctuating concentration was made possible by applying the recently developed scattered light technique of illuminating the space-point of interest with a strong light beam and measuring the intensity of 90°-scattered light. The technique has been refined to the point where the signal can be representative of a cubical volume element as small as 0.5 mm on a side. Emphasis was on the aerodynamic flow regime in which appreciable recirculation occurs. A mapping of the field of mean velocity was made with impact tubes. Velocity fluctuations were not measured as such, but indirect evidence was obtained from a mapping of the field of mean static-pressure defect in the jet. The sol-scattered-light technique itself yielded the fields of mean concentration of nozzle fluid, γ¯, and r.m.s. fluctuating concentration, (γ′2¯)12; lateral and longitudinal correlation coefficients and spatial scales of concentration fluctuations; and the wave-number spectrum of concentration fluctuations.