Table of contents

An experimental investigation was made of the influence of the motion of a ruby laser rod, relative to standing waves in the resonator, on the kinetics of the emission spectrum. Two main types of change in the emission spectrum resulted from the motion of the ruby rod: In one case the emission frequency periodically increased and in the other it periodically decreased. A possible mechanism of these effects was considered. A kinematic modulation of the intensities of the individual modes, which appeared because of the scattering of light on inhomogeneities in the ruby rod, was also observed.

An investigation was made of the exposure dependences of the parameters of reflection holograms of a mirror recorded in opposite beams of He–Ne laser radition (λ₀ = 632.8 nm) on Agfa Gevaert 8E75 photographic plates. The holograms were treated in Metinol–U and D–19 developers, fixed, and bleached in a solution of K₃Fe(CN)₆ and KBr. The diffraction efficiency of the bleached holograms was 20–25% when the width of the diffracted radiation spectrum was about 20.0 nm (at the 0.5 level of the maximum amplitude). The wavelength of the diffracted radiation maximum shifted by 5–8% in the direction of shorter wavelengths for exposures corresponding to the efficiency maximum. When the shrinking of the emulsion was eliminated, the efficiency increased considerably (to 40%). Holograms with a high brightness of the reconstructed image and a satisfactory noise level were obtained after exposures of ~0.2 mJ/cm².

Stimulated emission was obtained from mixtures of CO molecules with inert gases (He, Ne, Ar, Kr) expanding supersonically in a planar nozzle 4 cm long (the expansion ratio at the edge of the nozzle was 100). The influence of the nature of the inert gas and of the initial pressure of the mixture on the output power of the stimulated radiation was investigated. The effects observed in the CO gasdynamic laser could be explained by considering the vibration-vibrational (ν–ν) and vibration-translational (ν–T) processes as well as the rotation-translational interaction.

A new method was used in the determination of the refractive index of the active medium of a photodissociation laser at its emission wavelength and at the wavelength of a helium-neon laser. It was found that the refractive index increased with time and with the pressure of the active medium C₃F₇I. The measurement method could be employed in a study of the homogeneity of the active media of lasers at their emission wavelengths.

An experimental study showed that uniaxial compression (about 3000 kgf/cm²) accelerated the gradual degradation of gallium arsenide diodes. This was interpreted with the aid of a dislocation model in which centers of accelerated degradation were attributed to originally present dislocations that were multiplied by climb and slip processes. It was suggested that the climb of dislocations was activated by nonradiative recombination of electron-hole pairs.

It is shown theoretically that the Stokes components can be phase-matched in dispersion-free media if the stimulated Raman scattering occurs in a resonator transparent at the pump frequency or if the signal is amplified. The frequency pulling effects and the stability of single-frequency stimulated emission of N Stokes components in high-Q resonators are discussed.

Measurements were made of the ratio of the luminescence energies of Nd³⁺ in bands corresponding to the transitions ⁴F_3/2→⁴I_9/2, ⁴F_3/2→⁴I_11/2; ⁴F_3/2→⁴I_13/2,and ⁴F_3/2→⁴I_15/2. The radiative probabilities of these transitions were determined and the radiative lifetime of the ⁴F_3/2 metastable state of Nd³⁺ was found for silicate glasses LGS–24, LGS–28, and LGS–247. The kinetics of decay of the metastable level was found in a range of luminescence intensities representing a factor of 10³. When the concentration of neodymium was 2 wt.%, the final stages of the decay were exponential and the constant was nearly equal to the radiative lifetime. The results of measurements carried out on these silicate glasses were compared with those obtained for glass of ED–2 type.

The emission frequency of a laser with an active negative feedback was scanned. An interferometer with a piezoelectric ceramic element was used to control the frequency during stimulated emission. The frequency jumps during scanning were considerably smaller than under free-oscillation conditions and this was attributed to the elimination of the inhomogeneity of the population inversion.

The optoacoustic method was used in recording the absorption in order to determine the saturation energy of gases. The sensitivity of the method was 5×10^–9 J/cm, which made it possible to carry out measurements in gases with low laser radiation absorption coefficients (down to 10⁻⁶–10⁻⁸ cm⁻¹).The saturation energy of CO₂ measured with a CO₂ laser was in good agreement with a theoretical estimate. The saturation energy of SF₆ (traces of this compound were present in argon at a pressure of 1 atm) was also determined. It was found that the method employed could be used to determine the populations of vibration-rotational sublevels.

Photoinitiated stimulated emission was obtained from a mixture of CS₂ and SO₃. The output energy was higher and the optimal pressure of CS₂ considerably lower than in the case of the CS₂+O₂ mixture. A qualitative explanation was provided of this increase in the efficiency of CS₂.

Longitudinal modes emitted by a high-pressure cw CO₂ laser were selected with an Al diffracting film placed inside the resonator. The width of the transfer function of this selector was determined. It was found experimentally that the emission frequency could be tuned within a wide range by scanning the film and one of the resonator mirrors.

It was found experimentally that the output power of an He–Ne laser ( λ = 0.63 μ) increased resonantly when the discharge current was modulated at a frequency f_m≈60 kHz. This was attributed to a redistribution of the electrical properties of the gas-discharge plasma as a result of an artificial excitation of striae in the discharge. The possibility of using this phenomenon in the control of the output power of gas lasers was considered.

The results are given of calculations of the output power of a thermally excited CO₂ laser. The influence of the initial pressure and temperature of the gas mixture on the specific power characteristics is discussed.

An investigation was made of an electro-optic device for optical recording of images in a lead magnoniobate crystal. The characteristics of this device with photoconducting CdS and ZnS films were determined (these films were selected so as to obtain the desired voltage distribution in a multilayer system). The device ensured a high image contrast and a strong modulation under low voltages and for low recorded light intensities.

The dependence of the quantum efficiency of fluorescence on the intensity of pumping with the fourth harmonic of neodymium laser radiation (265 nm) was determined for solutions of several organic compounds (paraterphenyl, PPD, α–NPD, α–NPO, etc.). The reduction in the quantum efficiency with rising pump intensity was attributed to an induced absorption at the pump wavelength. A qualitative comparison was made of the intensity of the induced absorption and laser characteristics of the investigated compounds.

A description is given of the construction and power supply of a sealed copper vapor laser generating pulses at a repetition frequency of 6–10 kHz and producing an average power of 2 W.

Stimulated emission was obtained from an optically pumped gallium arsenide laser with a distributed feedback. The feedback was produced by a diffraction grating formed on the surface of a p –type GaAs layer prepared by the diffusion of zinc into an n –type substrate. The grating was in optical contact with the active layer and its period satisfied the Bragg condition for a guided mode within the gain band of the laser. For the selected Bragg scattering order, the radiation was extracted at right angles to the grating surface. The far-field distribution consisted of a single lobe with a divergence of 5–20', which corresponded to the emission from one to five randomly distributed modes whose frequencies depended on the position of the excited region in the laser.

A simple model is proposed for the description of pulsations (spiking) of the radiation emitted by a solid-state laser. The model is based on rate equations with random forces. When the noise level reaches a certain small critical value, the emission becomes quasiperiodic. Spiking is observed at a higher noise level. Experimental results obtained in studies of the amplitude stabilization are interpreted.

An experimental investigation was made of the intraresonator generation and control of the second harmonic in a cw YAG:Nd laser. A lithium niobate crystal, located inside the resonator, was used to generate the second harmonic and to modulate the resonator losses. In this way, simultaneous modulation of the first and second harmonics was achieved inside the resonator of the YAG:Nd laser.

The spectrum of atmospheric air was investigated inside the resonator of a dye laser tunable in the range 587–600 nm. Some of the spectral lines were identified. It was estimated that the use of this method increased the sensitivity of the absorption recording process by a factor of 10⁵.

Efficient mode conversion (~70–90%) was achieved and investigated in a multimode thin-film corrugated waveguide. The corrugations were nonsinusoidal so that modes could be converted using different orders of the spatial harmonics of the corrugation grating, tuning only slightly the grating in respect of the angle. The dependences of the mode conversion efficiency on the length of the grating were determined. The experimental results were compared with the theory.

A method for the determination of the energy center and diameter of a laser beam is considered using the probability theory.

Measurments were made of the excess pressure which appeared in laser pump cavities due to flashes of pulse-discharge lamps. It was found that the amplitude of the pressure pulses was independent of the ultraviolet component of the pump lamp radiation. It was concluded that pressure pulses reaching ~1 atm or higher could be one of the causes of the damage of laser pump cavities.

An analysis was made of the load characteristics of pulse-discharge lamps of 1.6 mm diameter producing flashes of 10⁻⁶–10⁻³ sec duration. It was found that the nominal flash energy of commercially available lamps could be increased considerably by altering the filling. This made it possible to increase the pump radiation power by a factor of 3–5 and to raise correspondingly the laser output power shortening at the same time the pulse duration to (1–2)×10⁻⁴ sec. Equations are given for estimating the maximum loads of lamps under "hard" operation conditions.

It was found experimentally that the stimulated Raman scattering thresholds depended on the direction of the wave vector and direction of the pump polarization relative to the crystallographic axes. The lowest threshold was 30% below the damage threshold in the pumping with an ordinary wave perpendicular to the [1100] plane of an Iceland spar crystal.

Stimulated emission was obtained from Ho³⁺ ions (⁵I₇→⁵I₈ transition) in a new single-component self-activated system with aluminum holmium garnet crystals grown by the Czochralski method. The thresholds of the λ= 2.129 and 2.122 laser emission at 90 °K were 9 and 14 J/cm, respectively. The absorption and luminescence spectra were used in the derivation of the Stark splitting scheme of the ⁵I₇ and ⁵I₈ terms. The lifetime of the ⁵I₇ term was determined (τ≈10 msec).

Stimulated emission was obtained from Tu³⁺ ions in YAlO₃ crystals doped with 1.0 at.% Tu and 0.1 at.% Cr. The stimulated radiation was generated by the ³F₄→³H₅(λ₁)→³H₅→³H₆(λ₂) cascade at wavelengths λ₁ = 2.34 μ and λ₁=1.93 μ and the threshold was 3.5 J/cm at 90 °K. A scheme of radiative and nonradiative transitions between the terms was constructed. The absorption and luminescence spectra recorded at 4.2 °K were used to derive the Stark splitting scheme of the ³H₄ and ³H₆ terms of the thulium ion.

Solutions of complex organic compounds were used as the active medium in a high-power laser with an output energy of 27 J and an efficiency of 0.7%. The duration of the output pulses was 102 μsec. The angular and energy characteristics of the output radiation were determined. A strong influence of the homogeneity of the active solution on the stimulated emission was observed.

A calculation is given of the distribution of illumination in selective vision zones formed by a holographic screen. It is shown that the actual distribution of illumination in the zones is governed by the initial distribution and by the distribution of illumination in the projected image. It is demonstrated that images whose dimensions are governed by the acuity of the human eye can be projected on such a screen. The results are in agreement with the experimental data obtained by projection on a small part of a screen.

A description is given of an amplifier with a stored energy of over 700 J intended for a short-pulse iodine laser. The pump radiation was derived from the thermal wave of an electric discharge in the active substance.

A study was made of the dependence of the relative reflection of the λ = 10.6 μ radiation on the concentration of aqueous solutions of salts, alkalis, and acids. The experimentally determined intensity of reflection from the surface of a solution was found to be in one-to-one correspondence with the concentration. This method could be used in long-distance measurement of the concentration of solutions including aggressive substances and in long-distance probing of water basins.

Experimental studies were made of some methods for enhancing the sensitivity of an infrared radiation detector by up-conversion of the radiation frequency. In one such method use was made of the intraresonator spherical focusing of a laser pump beam in a nonlinear crystal. The pump laser was operated under slow Q -switching conditions. The converted radiation was recorded by gating a photomultiplier which was used as a photon counter. In this way it was possible to record a signal of 5×10⁻¹⁴ W power.

The duration of picosecond pulses was shortened by suppressing the spectral narrowing. This was done by placing a suitably tuned mode selector inside the resonator. Pulses of 2.5 psec duration were observed with a Pikokhron scanning image converter.

The electron-beam-controlled method was used in the excitation of pure carbon dioxide gas at atmospheric pressure and pulse laser emission was obtained. This emission appeared near the threshold during the afterglow stage. When the rate of pumping of the upper laser level was increased, the delay time of the output radiation pulses relative to the discharge current became less than the duration of the discharge current pulses. This also reduced the duration of the output pulses. The specific energy characteristics of the discharge, output characteristics of the laser radiation, efficiency, and duration of output pulses were determined for different discharge parameters.

A non-self-maintained gas discharge was used to excite the active medium of a cw carbon dioxide laser. Preionization was produced by an electron beam of 150 keV energy. The specific output power from a mode volume was 3 W/cm and the efficiency was 7%. A study was made of the influence of the processes occurring in the cathode region on the stability of the discharge and on the energy characteristics of the laser.

The results are given of an investigation of the energy characteristics of an electron-beam controlled CO₂ laser with a working volume of 10 liter kept at a gas pressure of 1 atm. A cold-cathode electron gun was used to generate the electron beam which preionized the active medium. A study was made of the operation of the electron accelerator in the case of different systems of supplying the voltage to the electron gun. Measurements were made of the magnitude, duration, and uniformity of the electron-beam current which passed through Ti and Al foils on its way to the discharge chamber. The parameters of the output radiation of the laser were determined.

The dependences denoted by + in Figs. 4 and 5 apply to an Ne²⁰+Ne²² mixture with 50% of Ne²⁰, whereas the dependences denoted by O and • represent mixtures containing 91% and 99.8% of natural Ne, respectively.

The title should be corrected to read "in an optical fiber."

A pumping system, using low-inductance pulse-discharge lamps and a rectangular cell for rhodamine 6G, was developed. The lamp efficiency in various spectral ranges was investiagated in detail. The efficiency of the enclosure was deduced from the expansion of the dye. When the enclosure efficiency was about 0.2 and the lamp efficiency in the pumping region of rhodamine was close to 16%, the laser output energy was 50 J and the laser efficiency was 0.3% for pump pulses of about 20 μsec duration.

A new parameter, called the holographic efficiency, was introduced for estimating the performance of holographic materials under real experimental conditions. The efficiency of several mass-produced and new photographic materials was determined at different spatial frequencies. The results gave information about the relative influence of the diffraction processes on the holographic efficiency of photographic materials due to variation of the amplitude transmission, surface relief, and Bragg diffraction.

The results are given of an investigation of the luminescence and absorption spectra in the region of th stimulated transitions involving the ground and excited states in Y₃Al₅O₁₂:Cr³⁺ crystals. The dependence of the threshold population of the metastable level on the spectral losses at the emission frequency was studied. It was found that the stimulated emission from Cr³⁺ ions in Y₃Al₅O₁₂ crystals was possible only at low temperatures.

A signal due to the crossing of levels in zero magnetic field was observed in the λ=361 nm (5³D₃–5³P₂ transition) spontaneous radiation from the lower laser level of a Cd I pulse laser. The level-crossing signal had a profile close to the difference between two Lorentzian profiles, one of which was due to the decay of the upper laser level and the other to the decay of the lower laser level. The lifetimes of these levels and the cross sections of the depolarizing collisions with neon were determined.

An analysis is made of the stimulated emission due to electron transitions in the Xe₂ molecule as a result of excitation by the electron-beam-controlled method. A numerical solution is obtained of the transport equation for the electron energy distribution function in high-pressure xenon subjected to a static electric field. The excitation rates of electron levels of Xe are calculated. The computed efficiency of the conversion of the pump energy into radiation may reach 65–75%. Theoretical estimates are obtained of a population inversion and gain in the vacuum ultraviolet as a result of electron-beam-controlled excitation. In an experimental study, stimulated emission at λ=172.5 nm was obtained as a result of pumping with a fast-electron beam. An investigation was made of the spectral and energy characteristics of the spontaneous and stimulated radiation. The efficiency of electron-beam pumping of Xe compressed to 16 atm was ~15%. The energy input into the gas in an electron-beam-controlled method was measured. The degradation of the active medium was investigated in the two cases of the excitation by the electron-beam-controlled method and the pumping with an electron beam.

A study was made of the effects of focused 200–W CO₂ laser radiation (power density 1×10⁵ W/cm²) on rock crystal, agate, opal, sandstone, and quartzite. The two main damage mechanisms were considered: One was the brittle fracture due to phase transitions in a quartz and the other was the thermal decompositon accompanied by low-temperature sublimation of water and silica. The latter process was followed by further heating of a jet of matter and formation of a melted surface zone on opal and sandstone, and partly on agate. In all cases the absorption of radiation and heating were due to the Si–O valence vibrations.

A method is suggested for the calculation of the nonlinear susceptibility corresponding to the generation of second and third optical harmonics in atomic gases. The method is based on the use of the Green's function of an atomic optical electron in the computation of the composite matrix elements. The results are given of a numerical calculation of χ(–3ω;ω,ω,ω) and χ(–2ω;0,ω,ω) for hydrogen, alkali atoms, and inert gases at the frequencies of ruby and neodymium laser radiations and their second harmonics. A two-photon resonance in the generation of the third harmonics is considered.

The results are given of a machine calculation of wave fronts and the associated angular distribution of the radiation emitted by a laser with certain types of inhomogeneity in the active medium. The optimization of the parameters of a telescopic resonator and the correction of wave fronts are considered.

A superregenerative amplification scheme was used to obtain unidirectional stimulated emission from a ruby ring laser under free-oscillation and Q-switched conditions. The duration of external control pulses was either t_c > L/c or t_c < L/c. The carrier frequency of giant pulses could be tuned within a range of 0.25 nm when the spectrum was 6×10^–5 nm wide. Reproducible generation of short high-coherence light pulses was achieved.

Cholesteric liquid-crystal films, whose color changed as a result of heating, were used in a thermophotographic study of changes in the output parameters of cw infrared lasers. Photographs of the mode radiation structure and its variation with time were obtained. The time dependences of the coordinates of the center of the beam, power density, and divergence were determined in this way.

Stimulated emission from Al_xGa_1–xSb solid solutions, excited by an electron beam and cooled with liquid nitrogen, was observed for the first time. This emission was observed throughout the direct-gap range of compositions and the emission wavelength was within the range 1.1–1.6 μ. The dependence of the forbidden-band width E_g on the solid-solution composition x was determined and the point of transition from the direct- to the indirect-gap structure was found (x_c≈0.25, E_gc≈1.145 eV). A discrepancy between the experimental results and a graphical determination of the dependence E_g(x) was due to the influence of donor levels (E_d≈20 meV) below the indirect L minimum. The parameters of a sealed electron-beam-pumped laser made of such a material were determined.

An investigation was made of the processes which accompanied the passage of high-power laser radiation (λ=1.06 μ ) through an argon plasma generated in a plasmatron. Interaction of a laser beam of over 10⁷ W/cm² power density with a plasma whose initial temperature was 9500 °K and in which the electron density was ~10¹⁶ cm^–3 produced a perturbed region whose expansion during the first 10 λsec was of detonation type and which changed subsequently to a slow-combustion regime maintained throughout the passage of the laser beam. The plasma temperature rose to 19000 °K in the perturbed region although the absorption of the laser radiation was less than the experimental error (κ_λ≤0.04 cm^–1).

A theoretical analysis is made of some of the general problems encountered in the design of large-diameter optical telescopes with interferometric control and automatic alignment of the surface of a segmented primary mirror. Conditions are found for the rigidity of the construction of the segment supports which would make it possible to dispense with the control and alignment at right angles to the optic axis of the telescope. The rigidity requirements are found to be fully acceptable also for the telescopes operated in the terrestrial atmosphere and these requirements are independent of the telescope size.

Specific systems for interferometric laser control of the surface of a segmented telescope mirror are considered in the case when thermal deformations of the mirror segments can be ignored. The conditions are found under which a spherical wave of the control radiation can be regarded as plane and this makes it possible to simplify considerably the control and automatic alignment system. An estimate is obtained of the precision of measurement of the displacements of the mirror segments which ensures the required quality of the image at the telescope focus.

The results are given of calculations and an experimental investigation of the influence of the reflection of the output on the frequency and power of a single-frequency carbon dioxide laser. It is shown that, in the case of weak reflection, the dependences of the frequency and power on the distance from a reflecting object are sinusoidal and the maximum change in the frequency is proportional to the amplitude reflection coefficient of this object. In the case of strong reflection, the frequency exhibits a hysteresis and this results in hopping of the emission frequency from one branch of the frequency curve to another. The power may be modulated by 100% under these conditions.

Radiative characteristics of a laser plasma are considered. It is shown that a considerable proportion of the absorbed laser energy may be converted into resonance lines of multiply charged ions. Two methods for the utilization of resonance x-ray radiation in the population inversion in a two-component plasma are discussed. In one method, the resonance radiation of one component in the dense core of the plasma is used for selective resonance pumping of some level in the other component in the outer rare region. In the second method, the radiation of ions in the outer layer is used to photoionize ions in the inner core; this produces conditions analogous to those in a supercooled plasma and a population inversion is established. In all cases, the gain may be of the order of 10³ cm^–1.