Table of contents

Pulses of 0.3 J energy, 0.2–0.8 μsec duration, and 1.3 · 10^–3 cm^–1 spectral width were generated in a resonator with weak feedback.

A study was made of a single-mode ring ruby laser operating under free-oscillation conditions. The laser was used for recording holograms on photographic film of the Mikrat-VR type and on thin metal films.

A comparative study was made of the spatial and energy characteristics of a circulating-liquid laser operated at different velocities of flow v of the active liquid through the laser cuvette:

1) v = 0;

2) v ≠ 0,

laminar flow;

3) v ≠ 0,

turbulent flow.

The results are given of theoret ical and experimental investigations of light-sensitive films on which information was recorded by altering the shape of the film surface. Calculations are given of the brightness of the diffraction fringes as a function of the deformation of one- and two-dimensional gratings. The experiments were carried out on films of dichromated gelatin. The agreement between the theoretical and the experimental results was satisfactory.

The multiple recording of holograms in the same region of a light-sensitive surface is considered in the case of an extended reference-beam source. It is shown that such a reference beam makes it possible to achieve the multiple recording of holograms of extended sources employing small deflections of the reference beam. A description is given of experiments in which up to 50 holograms were recorded on the same plate.

The results are reported of experiments to which holograms were recorded on photosensitive polymers. Phase holograms could be recorded on these materials, which offered the advantage of a high diffraction efficiency. The holograms were recorded in a convergent beam (λ = 0.63 μ) which ensured a high density of recorded information and did not require high laser powers. The photosensitive polymer was sensitized to red light. The results are given of measurements of the sensitivity of the polymer and of the diffraction efficiency of the holograms. A photograph is included of the reconstructed image of a television test card.

A calculation is given of the longitudinal electrooptical effect in oblique-cutplates of lithium niobate. The dependence of the half-wave voltage on the angle between the direction of the incident beam and the optic axis of a crystal is derived. The calculated value of the half-wave voltage lies within the limits 2.3–2.5 kV and is in agreement with the experimental results.

It is shown theoretically that Bragg diffraction by two ultrasonic beams, traveling along mutually perpendicular directions in the same crystal, can be used for two-coordinate deflection of a light beam. A calculation concerning such a system was tested experimentally. The working medium was a -iodous acid which had a high acousto-optical Q factor.

An investigation was made of the conversion of an image from λ = 10.6 μ to λ = 0.65 μ by nonlinear optical methods in a crystal of proustite. A resolution of 10 lines/mm was achieved using a crystal 0.65 cm thick. The conversion efficiency was not less than 10^–5. The angular detuning of the signal beam was 0.170 rad.

Experimental investigations were made of the processes occurring during the high-temperature heating of plasma by ultrashort laser pulses focused onto the surface of lithium deuteride. The following methods were used in these experiments: schlieren photography of a plasma illuminated with ultrashort pulses; photography of an expanding plasma with an image converter; investigation of the time dependences of the reflection of laser pulses; determination of the electron temperature of a plasma from its x-ray emission. The principal processes which accompany the heating of a plasma by ultrashort pulses are considered theoretically within the framework of approximations based on experimental results.

A report is given of generation of laser radiation in the vacuum region by the excitation of condensed inert gases with an electron beam. Laser emission was achieved experimentally at λ = 1760 Å by the excitation of liquid xenon with a beam of 800 keV electrons. The threshold current density (30–50 A/cm²) was determined. The divergence of the emitted radiation (~7°) and the half-width of the stimulated line (~20 Å) were measured.

An investigation was made of the change in the duration of light pulses as a result of their transmission through media whose transparency increased under the influence of the transmitted light. A nonmonotonic reduction in the duration of a transmitted pulse was observed when the optical load density was varied. A dependence was obtained of the region of maximum narrowing of a light pulse on the optical load applied tobleachable solutions of various concentrations. It was also found that a metallized film illuminated with intense light exhibited an anomalous increase in its transparency. The observed effects were used as the basis of recommendations for procedures to be adopted in the generation of short pulses with steep leading edges. A neodymium-glass laser system, developed in accordance with these recommendations, generated pulses of 20 GW power and of 5–7 nsec duration with ~1 nsec leading edges.

Power resonances in the emission of a gas laser are considered in the case of spectral hole burning (a laser with a Fabry–Perot resonator) and of interaction between the oscillation modes at frequencies close to the center of a gain or absorption line (a laser with a ring resonator). In the second case, the resonances may be much narrower and have a higher contrast than the resonances in the emission of a laser with a Fabry–Perot resonator. Stabilization is reported for a helium–neon laser with a Fabry–Perot resonator, emitting a peak associated with the saturation of the absorption in methane.

A gas laser with nonlinear absorption, operating under quasitraveling wave conditions, is considered theoretically in the case of strong saturation of the absorption. The output power increases resonantly and the emission frequency is pulled strongly toward the center of an absorption line when the field frequency passes through the center of such a line. It is shown that, in contrast to the standing-wave case, the generation of a quasitraveling wave in a resonator makes it possible to obtain high peak powers and to achieve large values of the self-stabilization factor even in the case of strong saturation of the absorption and considerable differences between the saturation parameters of the amplifying and the absorbing media. This makes it possible to achieve, in principle, the condition of absolute selfstabilization of the frequency when a nonlinear pulling of the frequency into a power peak is maintained, even though the resonator frequency is detuned by an amount equal to the interval between the axial modes of a Fabry–Perot resonator. The conditions for achieving such operation are found and an example of a CO₂ laser with an absorption cell filled with SF₆ is considered.

An experimental investigation was made of the scattering of the light from a ruby laser by a cylindrical beam of 1–2 keV electrons of 10⁹–10¹⁰ cm^–3 density. The electron beam was subjected to a longitudinal magnetic field. A time-selective photon counter was used as the detector of the scattered radiation. An investigation was made of head-on and 90° collisions between the laser quanta and the electrons.

It is shown that the intensity of emission from a laser based on the stimulated Brillouin scattering effect can be increased by raising the pumping level, the pumping energy density, and the duration of the pumping pulses above their threshold values. An experimental investigation was made of a CS₂ Brillouin laser whose emission intensity was raised in this way, and an ether Brillouin laser whose emission intensity was not increased. The CS₂ laser was pumped with ruby laser pulses which satisfied the conditions necessary for an increase in the emission intensity. The CS₂ laser was found to have the following parameters: energy efficiency 2%, divergence of the output radiation

3 · 10^–4

rad, enhancement of the emission intensity by a factor of nine. The efficiency of the ether laser was 20%.

An investigation was made of a holographic memory device in which information was recorded in bulk on separate holograms. A method for ensuring the constancy of the spatial positions of the images reproduced from different holograms was developed. It was found that an image converter could be used effectively to amplify the brightness of the reconstructed image. A lithium niobate electrooptical deflector was used for switching the beam of light between 1024 discrete positions. Each hologram of about 1 mm diameter contained

5 · 10³

bits of information.

External spectrally selective elements were introduced into the resonator of an injection semiconductor laser in order to improve the spectral composition of the emitted radiation, and, in particular, to increase the output power in the single-mode operation. The following variants were investigated experimentally: a) a composite resonator; b) a resonator with an interference filter; c) two optically coupled Fabry–Perot resonators of different length. An external selective element always affected the emission spectrum of a semiconductor laser. A single longitudinal mode was obtained when the pumping level exceeded the threshold by an amount larger than in ordinary injection lasers. The output power under single-mode conditions ranged up to 0.5 W (in the case of a composite resonator). An investigation was made of the possibility of using an external element for varying the emission wavelength within the gain band of the semiconductor.

The results are given of a theoretical calculation of the energy characteristics of a laser with an unstable telescopic resonator. These results show that when the parameters of the resonator are optimal with respect to the efficiency, one can usually employ the standard equations of probability theory derived for a planar resonator. It is shown that these equations are inapplicable when the passive losses are considerable or when the laser threshold is exceeded appreciably. A simple method is suggested for estimating the efficiency of a laser in such cases.

The conditions for spatial coherence or noncoherence of a giant laser pulse are considered bearing in mind how the oscillation modes are affected by inhomogeneities in the permittivity or by changes in the permittivity due to the burning of holes in the population inversion. These conditions depend on the initial transverse distribution of the population inversion in the active rod and on the variation in the Q factor during the emission of laser radiation. The conditions were checked experimentally for a laser with a saturable filter excited under "soft" conditions.

An investigation was made of the generation of giant pulses in a ruby laser which did not contain any switching elements. The self-switching of the Q factor was achieved by the use of unstable configurations of the laser resonator.

An analysis is made of the generation of harmonics and of many-quantum processes (more than three quanta) in a specified field of laser radiation. Different statistics of the mode phases are considered and the absence of saturation effects is assumed. General relationships are derived for the calculation of the efficiency η_k of a nonlinear k-th order process in the case of arbitrary numbers of locked and nonlocked modes. It is shown that mode locking increases considerably the value of η_k. Precise values of η_k are found for third- and fourth-order processes in the case of mode locking and up to sixth order in the absence of such locking.

An investigation was made of the generation of the second, third, and fourth optical harmonics of the radiation emitted by a laser in which the active medium was neodymiumdoped yttrium aluminum garnet. The laser was operated under Q-switching fast-repetition pulse conditions. It was observed that the intensity of the fourth (ultraviolet) harmonic of λ = 266 nm was highly stable.

A discrete ten-stage system for beam deflection was developed on the basis of the electrooptical effect in lithium niobate. An Iceland spar crystal was used for static deflection. This system made it possible to deflect the beam in two planes between points forming a

32 × 32

matrix. The control voltage was 1 kV.

The absorption spectrum of Cr³⁺ ions in the magnesium spinel MgAl₂O₄ was determined for crystals excited by strong optical pumping, and for unexcited crystals. The absorption cross section of the ⁴A_2g level was found to be

2.5 · 10^–20

cm², which was an order of magnitude smaller than that for ruby. The spectrum obtained for the excited crystals consisted of five absorption bands with maxima at 250, 325, 390, 440, and 550 nm. The absorption cross section for the maximum of the first band was

~2 · 10^–18

cm². The absorption cross sections at the maxima of the other bands were

(1 – 2.5) · 10^–20

cm². An energy scheme for Cr³⁺ ions in MgAl₂O₄ was derived.