Table of contents

It is suggested that the maximum useful output power of Q-switched lasers, limited by the damage threshold of the active element, can be increased by reducing the reflection coefficient of the exit mirror. An experimental check was carrier out on lasers in which the exit reflector was the end of an RL ruby rod of 10 mm diameter and 120–180 mm long. The useful power density obtained in this way ranged up to 170 MW/cm².

Experimental results were used as the basis for an empirical formula relating the threshold densities of the pulse-average power causing damage to the surface of optical glass with the duration of laser pulses in the range from tens of picoseconds to tens of milliseconds. An examination is made of the possibility of the same mechanism being responsible for the damage to glass surfaces caused by laser pulses of different durations.

The dependence of the threshold power density of laser radiation on the duration of interaction and diameter of the focal spot is calculated for solid transparent dielectrics. The calculation is made on the assumption that this dependence is governed by the development of an electron avalanche in absorbing inhomogeneities. The results obtained explain some of the experimental data.

A description is given of the construction of a pump-lamp enclosure with a diffuse reflector intended for a periodically operated laser. Parts of the enclosure were made of a reinforced rubber-like sealing material (Viksint U1–18), which ensured simplicity of construction and hermetic joints between various parts. A comparison was made of the optical properties of Viksint U1–18 and various diffusely reflecting materials. The characteristics of a laser utilizing such an enclosure were determined.

An investigation was made of the formation of dynamic holograms in media with a negative absorption coefficient. Recording and/or reconstruction of a wave front under these conditions resulted in an increase of the intensity of the light fluxes. When feedback was sufficiently strong, a dynamic hologram (recorded in an excited system by spatial modulation of the gain) generated radiation with a specified spatial-temporal spectrum.

A Gunn diode was used to modulate at about 1 GHz the radiation emitted by an injection laser with a double-sided heterostructure. An analysis of the operation of this system was made. It was found that one Gunn diode could modulate several tens of injection lasers. The output power and efficiency increased with the number of such lasers and the power rose faster than the number of the lasers.

A study was made of the spectra and other characteristics of the luminescence emitted by naphthalene single crystals containing ββ'-dinaphthylethylene and biphenylyl–β–naphthylethylene impurities. These crystals were excited by the third harmonic of a neodymium laser. Above the threshold the spectrum consisted of single-line radiation which was polarized and directional.

It was found experimentally that the action of resonant CO₂ laser radiation produced nonequilibrium populations of the vibrational levels of BCl₃. The average energy needed to reach high vibrational levels and dissociation threshold was less than the equilibrium (thermal) energy of the excitation process.

The use of a diffraction grating and a prism telescope in an organic dye laser improved considerably the selectivity and made it possible to operate at high energy levels. A polarization beam splitter was used in a longitudinal variant of pumping with laser radiation. The output frequency was continuously tunable in a wide range and the width of the spectrum was less than 0.1 cm^–1.

A laser projection microscope operating at λ = 1.5 μ was built. The investigated object was illuminated and the brightness of the image was amplified using the active medium of a pulse barium vapor laser. The image was visualized employing anti-Stokes phosphors based on yttrium oxychlorides activated with ytterbium and erbium. Images of some microscopic objects, illustrating the capabilities of the instrument, were obtained.

The example of an ultraviolet-emitting nitrogen laser was used in trying out two methods for reducing the divergence of superluminescent lasers: One involved introducing a periodic series of diaphragms in the discharge chamber and the other made use of a telescopic resonator. The characteristic features of these two methods were analyzed.

A description is given of a proposed system for continuous recording and reproduction of a holographic cine film. The system is based on the use of a uniformly moving photographic film and a reference wave formed by a diffuser.

A theoretical analysis is made of the polarization characteristics of the four-photon parameteric generation of stimulated radiation in gases. It is shown that the parametric threshold can be increased severalfold by selecting the optimal pump polarization and the most effective resonance levels.

Continuous tuning of the emission frequency of a CO₂ laser operating at 5 atm was obtained for the P and R branches of laser transitions in a combined range of about 45 cm^–1. This was achieved for a maximum energy of 0.1 J per pulse and a spectral line width of 0.05 cm^–1. .

A comparison was made of the results of measurements of the continuous attenuation in the 8–12 μ atmospheric "window" under natural conditions with the results of laboratory measurements of the attenuation of CO₂ laser radiation by pure water vapor. The results of the laboratory experiments converted to the thickness of the whole atmosphere were in good agreement with the results of measurements under natural conditions. A considerable contribution of the water vapor dimers to atmospheric absorption was confirmed.

An investigation was made of stimulated emission from a thin-film rhodamine B laser with a distributed feedback. This feedback was produced by a periodic variation of the film thickness. The stimulated emission occurred at the wavelength of 6118 Å and the emission line width was less than 3 Å .

An investigation was made of the temperature dependence of the two-photon absorption coefficient of mixed CdS_xSe_1–x single crystals. When the frequency of laser radiation (ω= 1.78 eV) approached the frequency of an exciton transition terminating inside an allowed energy band, the temperature dependence of the investigated coefficient was found to be governed by the temperature dependence of the transverse relaxation time of the intermediate exciton state.

An investigation was made of the dynamics of stimulated Raman scattering (SRS) in compressed hydrogen excited by a train of short pulses. The observed features of the SRS dynamics were attributed to the competition between the focusing influence of an SRS lens and the defocusing influence of a thermal lens generated as a result of relaxation of an excited state. The method employed made it possible to determine the polarizability of the vibrational state of the molecules excited by SRS.

A laser electron-beam tube was used to form a projection-television image in a system in which scanning with an electron beam across the laser screen produces the television line scan, and a rotating prism or mirror was used to provide the frame scan. Images of 1 m² area were obtained in green (λ = 500 nm) and red (λ = 620 nm) light. The advantages of this type of laser projector were: less stringent requirements in respect of the technology of fabrication of semiconductor screens and simplification of the system used to superimpose monochrome images to form a color image.

A laser with a single-stage amplifier using organic dye solutions was found to emit radiation continuously tunable in the range 400–1000 nm. The width of the emission line was 0.1 nm, this could be reduced to 0.01 nm when a Fabry–Perot etalon was used. The stability of the emission wavelength from one flash to another was within 0.1 nm and the precision with which a given wavelength was selected was 0.15 nm. The fundamental frequencies and second-harmonics of ruby and neodymium lasers were used for pumping purposes. The properties of the output radiation were determined.

Stimulated emission at the λ = 427.8 nm wavelength was obtained as a result of excitation of He+0.02–0.2 % N₂ mixtures by an electron beam ( W≈ 200 keV, I ≈ 3kA, j ≈ 50 A/cm², τ ≈ 50 nsec). The upper laser level N⁺₂(B²∑⁺_u) was populated by the transfer of energy from molecular helium ions. The observed stimulated violet radiation was due to the first negative band of the nitrogen ion (B²∑⁺_uυ'=0 → X²∑⁺_gυ''=1). The energy characteristics of the laser were determined as a function of the composition of the mixtures at pressures of 0–7 atm.

An investigation was made of the dependence of the electron temperature of a plasma, generated by heating a solid target with focused laser radiation, on the position of the focusing objective relative to the target surface. It was found experimentally that the position corresponding to the maximum electron temperature of the plasma did not represent exact focusing of the laser radiation on the target surface. The plasma heating process was most efficient when the focus of the objective was located ~ 100 μ above the target surface. A possible explanation of this result was considered.

Methods were developed for recording holograms and holographic interferograms in MnBi films by heating them with a flashlamp operating synchronously with an information-carrying laser beam. A model relationship was derived between the energies of the flashlamp and of the reference and subject beams of a YAG:Nd³⁺ laser used in two-exposure recording of a hologram in a magnetic film. Photographs were obtained of images reconstructed from a hologram and a holographic interferogram recorded in an MnBi film.

A theoretical analysis is made of the pulse generation of a second harmonic in a nonlinear crystal placed inside a Q-switched laser resonator. Allowance is made for the saturation of the nonlinear interaction and for the inhomogeneity of the longitudinal distribution of the intensity of the fundamental-frequency radiation in the active element. The following main results of a computer analysis are reported: "machine oscillograms" of isolated harmonic pulses often have a fine structure; for a given length of the nonlinear crystal there are, under certain conditions, two values of the pump energy which ensure optimal conversion; an increase in the pump energy causes a greater proportion of the total harmonic energy to be generated during the forward pass through the nonlinear crystal; phase-matching curves for the energy of harmonic single pulses are much wider and smoother than in the case of second harmonic generation outside the resonator.

An investigation was made of an electric-discharge CO₂ laser with a volume preionization by an auxiliary discharge through a a dielectric. A low-resistance circuit was used to supply the main discharge. Stimulated emission was observed at pressures up to 13 atm in the mixture. The spectral composition of the output radiation and the nature of its pulsations were investigated as a function of the pressure and composition of the mixture. Consideration was given to the possibility of constructing continuously tunable and highpower lasers on the basis of the method described.

The harmonic oscillator model is used in the derivation of general functions describing the distribution of molecules with excited vibrational levels formed as a result of chemical reactions. Allowance is made for the vibration-vibrational (v-v) exchange and vibration-translational (v-t) relaxation. Specific reactions are considered and it is shown that the formulas obtained can be used to calculate the population inversion density and unsaturated gain for any vibration-rotational transition of a laser-active molecule.

The results are given of an experimental investigation of the onset of evaporation and of the appearance of a plasma layer above a target irradiated with neodymium laser pulses of about 1 jusec duration. The targets were aluminum and bismuth in air, argon, and helium. The critical density of the radiation flux, below which no "flash" was observed for pulses of this duration, was determined for near-planar motion. The results obtained were compared with theoretical ideas and the results of other experiments.

A theoretical investigation is made of four-photon parametric interactions in a medium composed of threelevel atoms. The presence of the third level, associated with the doublet splitting of the excited state, gives rise to new regions of exponential parametric amplification. A study is made of the change in the value of the gain and its spectral range due to variation of the frequency of a strong wave participating in the parametric interaction.

A Raman spectrometer with a two-frequency laser excitation source is considered. It is proposed to use a sensitive optoacoustic detector with a condenser microphone to record the Raman gain. This spectrometer should make it possible to carry out high-resolution studies of lines due to the stimulated Raman scattering in gaseous media at low (10^–5 atm) partial pressures.

A tunable pulse GaAs injection laser was used in measurements of weak molecular absorption. The frequency was tuned by varying the applied hydrostatic pressure and current. The absorption sensitivity of an optoacoustic detector used in the study was 2.5×10^–12 J cm⁻¹ so that, when the energy of a laser pulse was 10⁻⁸–10⁻⁶ J, it was possible to record the absorption in gases at the 10⁻³–10⁻⁵ cm⁻¹ level. An experimental study was made of the second absorption harmonic of the HF molecules.

It was demonstrated that stimulated emission was possible as the result of several transitions in the spectrum of Be II. An experimental study was made of the stimulated emission due to the following ionic transitions in beryllium: 4F–3D at λ = 467.5 nm, 4S–3P at λ = 527.2 nm, and 3P–3S at λ = 1209.6 nm, all which occurred during the afterglow stage of a pulse discharge. It was established that the laser levels were pumped by charge exchange between helium or neon ions and beryllium atoms, and also due to recombination of doubly charged beryllium ions. It was found that the population inversion and the characteristics of stimulated emission were influenced strongly by inelastic collisions with slow electrons.

A numerical analysis is made of a kinetic model of the processes occurring in a pulse CO₂ laser excited by a non-self-sustained discharge. It is shown that the results of calculations are in satisfactory agreement with the experimental data in the range of pump powers covering long- and short-pulse regimes. The proposed model is used in the optimization of the parameters of this laser at atmospheric pressure in the specific pump power range 1–10³ kW/cm³. It is found that the optimal specific power, which produces the highest specific output energy in a pulse Q_out corresponds to high He concentrations in the gas mixture. The maximum value of Q_out(0.12 J cm⁻³ atm⁻³. for an efficiency up to 25%) is achieved at pump powers corresponding to discharge electron densities in the range (1–5)×10¹³ cm⁻³ and for pump pulse durations 5–10 μsec.

A theoretical analysis is made of the vibrational relaxation in a nonequilibrium stream in a gasdynamic laser utilizing CO+N₂+CO₂+H₂O mixtures. The dependence of the population inversion for the 00⁰1–10⁰0 transition in the CO₂ molecule on the concentration of CO is obtained. It is shown that under certain conditions it should be possible to construct a gasdynamic laser utilizing CO₂ transitions in nitrogen-free mixtures.

Approximate calculations are given of the feasibility of generation of directional x-ray pulses of up to 100 W power with a low relative line width. It is assumed that these pulses are generated as a result of the Compton scattering of laser photons by a relativistic high-density electron beam.

A theoretical analysis is made of the simultaneous influence of refractive index inhomogeneities and thermal nonlinearity of a medium on the broadening of a light beam. It is shown that the presence of a defocusing dielectric waveguide increases the broadening because of the scattering by random inhomogeneities. This effect is particularly important in the focusing of a beam in an absorbing medium.

An analysis is made of nonlinear interactions of arbitrarily polarized traveling waves in a double-mode ring gas laser with a two-isotope active medium (the isotope concentrations are assumed to be equal). A weak longitudinal magnetic field is assumed to be applied to the active medium. Derivations are given of the dependences of the interaction coefficients of the waves on the total angular momenta of the active levels, weak magnetic field, longitudinal dimensions and relative positions of tubes with the active medium, and positions of modes in the gain profile. It is shown that the interaction coefficients of opposite waves in the two-isotope case are η²=(γ_ab/ku)² (η²≪1) times smaller than in the one-isotope case. However, the interaction coefficients of the waves traveling in the same direction in a two-isotope gas medium are of the same order of magnitude as the corresponding coefficients for a one-isotope medium.

A description is given of a new experimental method for the suppression of strong and scalar (polarized) types of stimulated scattering of light and the excitation of tensor (depolarized) types. This method is based on elongation of the nonlinear interaction region in the direction of the electric vector of the exciting wave. The results are given of experiments in which the new method was used to study the temperature dependence of the shift of the stimulated scattering in the wing of the Rayleigh line when the stimulated Brillouin scattering was suppressed. Simple formulas are given for the design of such experiments. The advantages and capabilities of the proposed method are discussed.

Preliminary ideas are developed on the use of auxiliary optical pumping in a gasdynamic laser. The auxiliary pump source may be a second laser or the gasdynamic laser itself with a feedback in its optical channel. Such additional optical pumping may increase the gain of the medium and it may also allow reduction in the expansion ratio of a gas passing through a nozzle in a gasdynamic laser.

The general case of holographic recording of a vector field, based on the Weigert effect, is considered for an arbitrary polarization of the reference wave. An analysis is made of the nature of the changes in the polarization in the reconstructed images.

The variational problem of the optimal operating conditions in the gasdynamic carbon dioxide laser is solved in such a way as to maximize the gain for the P20(001)→(100) transition in the case of nozzles of arbitrary shape. A comparison is made with the results of optimization obtained for planar wedge-shaped nozzles. The optimal initial conditions (temperature, pressure, and composition) are found and the optimal nozzle shape is obtained for mixtures of carbon dioxide with nitrogen and helium. A continuous increase in the gain with rising pressure is predicted for optimal operation of the gasdynamic laser.

A solution is given to the electrodynamic problem of the spectrum and threshold of modes in a multilayer resonator in which the permittivity along the resonator axis is a piecewise-linear periodic function of the coordinate. This resonator is proposed for stable single-mode emission from semiconductor lasers.

A report is given of an experimental investigation of the optical parameters of planar microscopic waveguides prepared by the diffusion of PbO. A physical explanation is given of the experimental dependences of the phase delay coefficient and of the waveguide losses on the duration of diffusion and thickness of PbO film. It is shown that planar integrated-optics elements and devices can be made from diffused waveguides.

A quantitative analysis is made of several features of gasdynamic photorecombination lasers utilizing electronic transitions. The flow of a recombining gas through a supersonic nozzle is calculated in the sudden freezing approximation. Nonequilibrium dissociation, population inversion criteria, and the energy stored in inverted states are all considered. The dependences of the these quantities on the initial conditions, nozzle shape, etc. are analyzed.

An investigation is made of the influence of self-focusing on the shape of ultrashort light pulses passing through a stable two-component medium containing an inhomogeneous screen inside the resonator. In this system, the radiation losses decrease with increasing radius of the beam on the screen. It is shown that instantaneous self-focusing increases the contrast and produces a narrow peak at the maximum of an ultrashort pulse.

An investigation was made of the dependences of the intermodal beat frequency of a linear laser and of the difference frequency of a ring laser on the gain of the active medium and the losses in the resonator. These dependences made it possible to determine the reduction in the frequency pulling with increasing output power, relative to the total pulling. A determination of this reduction made it possible to compare the results of experiments carried out under different conditions. A comparison was made of the experimental results with the calculations.

A theory is developed of four-photon parametric frequency conversion in gases under two-photon resonance conditions. A study is made of the polarization characteristics of the process and of the conditions under which the conversion efficiency has its maximum value.

A theoretical analysis is made of the possibility of constructing a continuously tunable gas laser emitting radiation as a result of resonant optical pumping of a mixture of isotopic molecules by the radiation of a second laser. It is shown that a simple sealed laser can be built on this basis. The gain is calculated for binary and ternary mixtures of isotopic CO₂ molecules subjected to optical pumping with λ = 9.6 μ radiation emitted by a CO₂–N₂–He laser. It is shown that a gain of ~2×10⁻³ cm⁻¹ should be obtained as a result of optical pumping of an isotopic mixture of CO₂ molecules at a pressure of 1 atm at 400° K and this should be true both under pulse and continuous emission conditions. In the pulse case, the pump energy density should be 10 J/cm². In the continuous case, the same gain can be obtained using waveguides resonators of ~100 μ diameter when the pump power is twice the threshold value of ~70 W.

A theoretical analysis is made of the scattering of electrons by a strong standing wave with a slowly varying amplitude. It is shown that a consistent transition to the adiabatic limit is impossible unless higher orders of the perturbation theory are used. General expressions are derived for the scattering probabilities, which can be used in special cases to find the results of the perturbation theory or to pass the adiabatic limit. An analysis is given of the resonant scattering of electrons which appears when a third wave of similar frequency is added to the standing wave. The WKB time method is used to find expressions which govern the line profile and the resonant scattering probability.

An investigation was made of the influence of the substrate material, coating thickness, and conditions during evaporation and annealing on the optical strength of gold coatings illuminated with CO₂ laser pulses (interaction time ~ 100 nsec). It was found to be possible to prepare gold coatings whose optical strength was comparable with those of bulk metallic mirrors. Breakdown at the surface of a mirror could occur without causing any damage. Laser cleaning effect was also observed.

An analysis is made of the factors influencing the time (t' in which the stimulated emission threshold is reached in a CF₃I laser. The dependences of the time t' on the resonator losses L and on the CF₃I vapor pressure, applicable to a laser pumped by rectangular pulses of relatively slow amplitude, are used to derive the pressure dependence of the laser line width. The absolute value of this width is determined experimentally at pressures sufficiently low for the broadening to be of the Doppler type. The results obtained are used to calculate the pumping rate and quantum efficiency of the laser. The value of the latter quantity (0.9 ±0.18) demonstrates a high efficiency of recombination of the photodissociation products back into the original molecules. An experimentally verified approximation is used to develop a theory which yields the time dependence of the accumulation of metastable iodine atoms. The dependence t'(L) in the nonlinear range of high values of L is used to find the combination (k₁+ k₂)/k₅^1/2 of the rate constants of the reactions , which govern this nonlinearity. The combination is found to be 1.0±0.35×10^–6 cm^3/2·sec^–1/2. The results obtained indicate that the chemical pumping channels are ineffective in the case of CF₃I.