Table of contents

A theoretical analysis is given of the influence of a resonance signal on the stability of a single-frequency traveling-wave laser. A one-dimensional model of a ring laser is used. It is assumed that the active medium of this laser has a homogeneously broadened luminescence line. The losses in the laser resonator are concentrated. It is also assumed that the external signal frequency coincides with the emission frequency and they are both equal to the central frequency of the luminescence line. It is shown that the critical value of the excess of the pump power over the threshold at which the single-frequency emission becomes unstable increases with rising intensity of the external signal but always remains finite.

The paraxial approximation is used in the development of a theory for the visualization of monochromatic infrared point images using a cylindrical pump wave. The theory is based on the application of the classical Green's functions. One of the possible waves of efficient visualization is considered in detail. Expressions are obtained for the converted image field and, in particular, for the plane of the best image along two mutually perpendicular directions. These expressions describe qualitatively the astigmatism of the visualized image field. Illustrative numerical calculations are given for LiNbO₃, LiIO₃, and Ag₃AsS₃. Experimental investigations are reported of the visualization, with the aid of a cylindrical pump wave, in LiNbO₃ and LiIO₃ crystals under degenerate conditions, i.e., in the frequency doubling regime. In particular, a study is made of the nature and degree of astigmatism of the visible image field. The experimental results are in satisfactory agreement with the theoretical predictions.

Explosive breakup of an overheated metastable liquid is considered in the case when intensive evaporation may occur from a free surface. It is shown that, in particular, a pulsating evaporation of an absorbing substance under the action of laser radiation may occur without a significant screening of the irradiated surface by the explosive evaporation products. If the depth of absorption of laser radiation in this substance exceeds the characteristic length of the steady-state temperature distribution influenced by the free surface, the process of explosive breakup of the metastable state at the maximum overheating temperature may sometimes have a fine structure manifested by high-frequency (≤10^–5 sec) pulsations. These pulsations should also be observed in the case of explosive breakup of the metastable state which occurs after a sudden removal of the pressure from the surface of a liquid previously heated under equilibrium conditions to a temperature close to the critical value.

A calculation is reported of the back-reflection coefficient R of a mirror and of the radiation scattered by a mirror. Two methods for measuring R are suggested.

A theoretical analysis is made of an axial image-multiplication system and some requirements realting to optical elements in such a systemt are specified. The quality of images obtained by this method is estimated in the specific case of the technological processes used in the manufacture of integrated circuits. Experimental results are reported on the generation of sets of images of drawings of integrated circuits.

An analysis is made of nonlinear nonstationary equations describing dynamics of the stimulated Raman scattering in optical resonators excited by external nonmonochromatic radiation. The threshold of the excitation of the stimulated scattering by nonmonochromatic radiation is found and its dependence on the dispersion of the active medium is deduced. Solutions are obtained for steady-state oscillations in a resonator and their characteristics are investigated as a function of the spectrum of the exciting radiation and of the dispersion of the active medium.

An analysis is made of the capture of electrons by excited states of an ion in collisions of atoms with multiply charged ions (Z 10). General expressions are obtained for the transition probabilities and cross sections of one-electron charge exchange and allowance is made for the strong coupling of the initial and final states of an atom + ion system. The capture cross section of an ion level with a binding energy exceeding the ionization potential of an atom is found to have two separate maxima along the energy scale. The total charge-exchange cross section in the range of energies of relative motion 1–10⁵ eV/nucleon is proportional to Z², where Z is the ion charge. The results of calculations are in quantitative agreement with the published experimental results. It is shown that the two-electron capture cross section is smaller than the one-electron cross section and that in the Z ≥ 10 range an unstable excited state of an ion decays preferentially by the emission of radiation.

An experimental and theoretical investigation was made of the amplification and stimulated generation of λ = 10.6 μ radiation (00⁰1–10⁰0 transition) in CO₂ pumped with a pulsed CO₂ laser emitting at λ = 9.6 μ (00⁰0–02⁰0 transition). A study was made of the dependencee of the gain on the pumped energy density for various values of pressure and temperature. The room-temperature gain at pressures up to 1 atm was 4×10^–4 cm^–1. The maximum value of the gain (2×10^–3 cm^–1) corresponded to p =100 mm Hg and T=400°K. The results obtained were in good agreement with the theory. The emission of 10.6 μ radiation as a result of λ = 9.6 μ optical pumping was achieved and investigated for the first time in a wide range of CO₂ pressures and temperatures of 80–600 mm Hg and 330–400°K.

An investigation was made of the laser action in compensated gallium arsenide doped with donors (Te or Sn) and acceptors (Zn). Such doping reduced considerably the threshold current density and the working voltage of electron-beam-pumped lasers. The lowest values of the threshold were 0.1 A/cm² at T≈85°K and 1.5 A/cm² at T≈300°K. The maximum efficiency reached 30% at T≈85°K and 21% at T≈300°K. A waveguide resonator structure ensured that these values of the threshold current and the efficiency were not affected when the electron energy was reduced from 50 keV to ~25 keV. A further redution of the electron energy to 9 keV caused the threshold current density to rise to 1.5 A/cm² at T≈85°K.

A theory is given of the operation of a detector element suitable for measuring the power of transmitted CO₂ laser radiation. The experimental results of a study of this element are also reported. The element consists of a double array of thin-wire (3.8 μ diameter) bolometers. When this detector is coupled to a suitable circuit, we can use it to measure power densities beginning from 5 W/cm² with an error of ±13%. The response time is 1 msec and the transmission coefficient of the detector exceeds 98%.

A theoretical analysis is made of the possible use of a multiply charged expanding plasma for laser action in far ultraviolet. It is shown that a plasma containing ions with low-energy resonance states (ΔE~kT_e) may cool strongly by the emission of lines. The populations of excited states in a lithiumlike ion Al XI is considered by way of example. It is shown that cooling and expansion of a plasma should result in a population inversion of the 4→3 transition (λ~150 Å) and the gain should 0.1–1cm^–1.

An analysis is made of the scattering and absorption of light by a hydrogenlike atom in the field of an electromagnetic wave which mixes resonantly an excited level (n = 2) with its neighbor (n = 3). The scattering and absorption cross sections are calculated as a function of the frequency of the wave and of the intensity of the electromagnetic field. The influence of low-frequency nonresonance field on the scattering and absorption of light by an atom in the ground state is considered. It is shown that the scattering (absorption and luminescence) spectra of a hydrogenlike atom may be frequency modulated by a low-frequency amplitude modulated field.

An analysis is made of the width and resolution of "competitive" power resonances in a ring gas laser with a nonlinearly absorbing cell in the resonator. It is shown that in the case of the Lorentzian profile of an inverted Lamb dip in a nonlinearly absorbing cell the resolution of competitive resonances is equal to the homogeneous linewidth in spite of the fact that the width of competitive resonances is much smaller than the homogeneous width (Lamb dip width). An analysis is made of the narrowing of the tip of the Lamb dip in the case of long-lived molecular levels and particularly of the field broadening of the narrowed tip. It is found that the resolution of competitive resonances in the case of a narrowed tip of a Lamb dip in a low-pressure gas cell may be much higher than the resolution governed by the time needed to cross a light beam by molecules with an average thermal velocity.

It is shown that the diffraction and self-focusing of laser radiation plays the dominant role in several types of characteristic damage observed in cylindrical active elements during the amplification of high-power light pulses. An analytic treatment is given of the Fresnel diffraction of a laser beam passing through apertures of different shape that are encountered in practice. An analysis is also made of the development of small perturbations of a laser beam which eventually damage the active element because they become self-focused against the background of a strong field. It is shown that "seed" perturbations may be waves diffracted by aperatures or secondary waves which appear due to the scattering of the principal wave by local inhomogeneities in the active element.

Possible ways of suppressing the harmful influence of the diffraction and self-focusing on a laser beam are considered. These methods include the use of apertures with piecewise-linear boundaries, apertures with a diffuse absorption edge and diverging beams, and the splitting of a continuous active medium into fragments (disks).

Parameters of a slit in an open resonator are optimized for efficient excitation of two-dimensional lens and aperture quasioptic lines. An equation for phase correctors is derived.

A long-term stability better than 10^–12 (averaging time 100 sec) was achieved for the emission frequency of a cw CO₂ laser, which was stabilized using narrow saturated-absorption resonances in an external low-pressure SF₆ cell. Narrow molecular resonances of OsO₄ were used as a second natural frequency standard. A nonlinear spectrometer with a stabilized CO₂ laser and an external OsO₄ absorption cell was found to be suitable for measurement of the energy of metastable osmium nuclei.

Magnetic bubble domains were detected using injection laser radiation. It was found that the number of domains that could be recorded at maximum contrast was 10⁴–10⁵. Possible ways of constructing logic and memory devices were suggested on the basis of the results obtained.

A description is given of an otpical pulse generator suitable for a wide-band pulse-code-modulated communication system. The generator includes a mode-locked helium-neon laser. The mode locking is due to loss modulation inside the resonator. Use is also made of the spontaneous mode locking, which makes it possible to reduce considerably the excitation power of a KDP modulator. Conditions ensuring stable generation of pulses are derived for the active mode locking and for the stabilized self-mode-locking.

An experimental investigation was made of the amplification of light and of coherent emission from a 10% N₂O+20% CO+70% He gas mixture. The amplification was recorded at λ = 10.6 and 10.9 μ at a distance of 15 mm from the nozzle edge. The maximum amplification was obtained when the velocity of the incident shock wave was ~ 1.9 km/sec, which corresponded to a deceleration temperature T₀ ~2100°K. In the presence of mirrors the mixture emitted coherent λ = 10.6 μ radiation under maximum-gain conditions.

A tunable (λ=720–970 nm) laser system utilizing organic dye solutions was built and investigated. The system comprised an oscillator with a dispersive resonator (diffraction grating) a prism telescope, and a single-pass power amplifier using the same dye solutions. The system was excited with a Q-switched ruby laser. When the excitation power was divided in the ratio 1:4 between the oscillator and amplifier, the gain of the system as a whole was 25. The width of the output spectrum was 1–4 Å. The radiation was emitted in the form of 0.25 J pulses of 20 nsec duration. The radiation power density reaching the grating was 0.6 MW/cm². The construction of the system should make it possible to increase the angular brightness of the radiation and to reduce the modulation of the spectral-energy tuning characteristic.

A geometric contribution to the active-medium gain is estimated for laser tubes of circular, rectangular, and elliptic cross sections. The gain averaged over an elliptic cross section is found to decrease with increasing ellipse eccentricity and this gain is intermediate between those obtained for circular and rectangular cross sections (the gain on the axis is assumed to be the same in all cases). A smoother distribution of the gain over elliptic and rectangular cross sections and lower diffraction losses suggest that tubes with these cross sections should be used in ring lasers.

An experimental study was made of the amplification of YAG: Nd laser radiation in neodymium glass (gain k = 50) and of subsequent conversion of this radiation into a stable fourth harmonic of 6.5 ±1.5 MW power.

Sources of distortion of the information obtained by active Raman spectroscopy are discussed. The case of a strong nonlinear coupling between pump waves due to the inverse Raman scattering is analyzed in detail. Active spectra are calculated for the case of inverse Raman scattering of a pump doublet which occurs when the nonlinear interaction length is increased. A criterion is derived of the strength of the nonlinear coupling between pump waves which ensures that the inverse Raman scattering does not distort the dispersion curves of the nonlinearity deduced from active spectroscopy data.

A description is given of a holographic system with a narrow reference beam. The system is based on a standard shadowgraph and it is used to study the flow of a gas from a reflecting nozzle in a shock tube. It is shown that one hologram can be used to reconstruct both shadow patterns and interferograms. Details of the holographic interferometer system are described and examples of its use are given.

A theoretical analysis is made of the possibility of selective predissociation of excited molecules by influencing the positions of paramagnetic molecular terms with a magnetic field.

A description is given of the construction of a continuously pumped electric-discharge laser using a N₂O–He–N₂ mixture. The optimal ratio of the components in the mixture was 1:4:2 for a constant flow velocity of 4 m/sec; this corresponded to an output power of 0.5 W. We studied the influence of xenon on the operation of this laser. A diffraction grating was used as a selective element to achieve stimulated emission of several rotational lines of the P and R branches of the 00⁰1–10⁰0 transition of the N₂O molecule in the wavelength range 10.4–11.0 μ.

A description is given of a method for recording high-density microholograms. Information recorded at a density of 10⁵ bit/mm² can be read using a semiconductor laser.

A description is given of several variants of a high-voltage pulse generator based on L C circuits. This generator can supply several loads simultaneously. The construction of a generator capable of producing pulses up to 200 kV is described. Such a generator can be used as a power source of high-current accelerators and for pumping various semiconductor and gas lasers.

A theoretical and experimental study was made of the time and optical characteristics of the reading of holograms with an integrated optoelectronic memory element. A semiconductor laser operating at room temperature was used as an optical radiation source.

An experimental investigation was made of the energy and spectral characteristics of single-pass parametric generation of light in an α-HIO₃ crystal pumped with ultrashort pulses. This crystal produced continuously tunable radiation (λ = 0.71–1.115 μ) of 2×10^–4 J energy. The angular structure of the parametric generation spectrum was determined.

An analysis is made of one of the possibilities of generating tunable radiation in the wavelength range λ=200–260 nm. The results are given of an experimental investigation in which such radiation was generated in the 216–226 nm range.

An investigation was made of the characteristics of a Q-switched laser utilizing a phosphate glass and producing pulses with a repetition frequency up to 5 sec^–1. The pulse duration was 15 nsec when the Q factor of the resonator was switched by an optomechanical modulator with a prism rotating at an equivalent angular velocity of 60,000 rpm.

A television image was projected onto a 6 m² screen by connecting a laser electron-beam tube to a standard television receiver.

The integrated intensity of frequency modulated laser radiation falls after passing through a Fabry–Perot interferometer tuned to the transmission maximum. The extent of this fall can be used to determine the frequency deviation. An experimental study has confirmed the feasibility of this method.

An experimental investigation was made of the frequency spectrum of the stimulated emission from an argon laser at λ=514.5 nm in the region of of anomalous competition with a line at λ=488 nm. The relationship between the frequency spectrum and the nature of the optical competition was determined. A mechanism explaining the anomalous interaction between these lines was put forward.

An investigation was made of the operation of a pulsed electron-beam-controlled CO laser with a working mixture kept at room temperature. It was found possible to build a large (10 liter) laser of this type. When the excitation duration was ~30 μsec, the output energy exceeded 100 J per pulse.

An experimental and theoretical investigation was made of an electron-beam-controlled CO₂ laser operating under conditions ensuring the maximum output energy. This energy exceeded 1000 J per pulse. Overheating of the active mixture and the development of electric discharges in the active region at high pump powers limited the specific output energy to 75–80 J·liter^–1atm^–1.

A theoretical analysis is made of the influecne of a magnetic field on the gain of a monochromatic traveling-wave field in a medium composed of charged two-level particles (ions). An expression is obtained for the traveling-wave gain, allowing for the drift of ions and weak saturation. It is shown that the drift results in the asymmetry of the gain profile.