Characteristics Of Laser Radiation Research Articles

Continuous tuning of radiation frequency in fibre and waveguide lasers by a controllable Bragg grating

A method for fast radiation wavelength tuning is proposed for a single-frequency fibre laser. A diffraction grating written on a waveguide electrooptical modulator serves as the mirror of the external cavity and as the selector. The voltage supplied to the grating electrodes shifts the reflection band of the grating and hence tunes the emitted radiation range. The radiation frequency tuning within the grating reflection band is carried out by using an intracavity waveguide electrooptical cell. The spectral characteristics of laser radiation are calculated. It is shown that the tuning range of such a laser achieves 0.2 nm for a control voltage up to 5 V, the switching time being shorter than 0.7 ns.

Express Method for Control of Space–Energy Characteristics of Laser Radiation Using Al-VO 2 -D (Dielectric) Thermochromic Materials

ВИ-1 and ВИ-2 visualizers of optical radiation are described, whose screen is based on film-type reversible Al-VO2–D thermochromic materials (D is a dielectric). By using a ВИ-2 visualizer, it is possible to perform the semiquantitative express analysis of the space–energy characteristics of pulse and continuous laser radiation at wavelengths of 0.3–10.6 μm.

Laser Propulsion at Ambient Vacuum Conditions.

The paper purpose is consideration of principal phenomena affecting a laser propulsion mechanism at ambient vacuum condition. The consideration is based on examination of a) conversion of laser pulse energy into a thermal energy of working gas, and b) conversion of the thermal energy into a kinetic energy of an exhaust gas of parabolic type lightcraft. If paraboloid is used like a laser jet engine unit, the process of laser energy explosion is realized at the conditions of strong variation of both radiation intensity and gas flow parameters within a parabolic type nozzle. It is shown that regimes of laser beam energy explosion, whichdepend on both laser radiation and working gas characteristics, affect strongly an amplitude of thrust impulse generated, even though momentum coupling coefficient determined via laser energy deposition does not change sufficiently.

Effect of regular wavefront perturbations on the structural transformation of laser beams

The effect of a regular phase modulation on the dynamics of variation in spatial characteristics of laser radiation is studied. The conditions and processes of the transformation of phase aberrations to topological wavefront perturbations resulting in the appearance of edge and screw dislocations are considered. The relationship between the caustic and dislocation elements of the laser beam is discussed. It is shown that the phase modulation leads to the formation of narrow channels with an increased intensity inside the laser beam.

Fs-pulse synthesis using phase modulation by impulsively excited molecular vibrations

We report the temporal characteristics of laser radiation transmitted through impulsively excited SF6 and exhibiting sideband Raman lines. Even without special dispersion control we observed a sequence of compressed fs pulses following with the period of the excited A(1g) vibrational mode of SF6. The use of both negative and positive group velocity dispersion compensation for the temporal compression was found to be as appropriately efficient. The results prove our new concept of the ultrafast molecular phase modulator.

Transformation of the spectral density of intensity fluctuations of the pulsed radiation from a quasi-single-mode heterolaser in an optical fiber

The spectral density of intensity fluctuations of quasi-single-mode heterolaser radiation under pseudorandom pulsed modulation of the pumping current has been studied for the first time by numerical methods. In the limit of the second-order dispersion theory, the effect of the chromatic dispersion of an optical fiber on the noise characteristics of laser radiation (spectral density of fluctuations and signal-to-noise ratio in the operating range of the photodetector) was investigated. The effect of the laser parameters and modulation on the transformation of the intensity fluctuations in a fiber-optic communication line was studied.

Supersonic oxygen — iodine 1.4-kW laser with a 5 cm gain length and a nitrogen-diluted active medium

A compact chemical oxygen — iodine laser with a jet generator of singlet oxygen and a nitrogen-diluted active medium was developed. The maximum chemical efficiency equal to 24.1% was achieved for a chlorine flow rate of 39.2 mmol s-1 , and the maximum output power equal to 1.4 kW was obtained for a chlorine flow rate of 75 mmol s-1 . The following specific energy characteristics of laser radiation were obtained: output power of 5 kW per one litre of the reactor volume of the jet generator of singlet oxygen, paraxial intensity of 100 W per one square centimetre of the cross sectional area of the stream of the active medium in the resonator, and an output power per unit volume evacuation rate of 2.7 W (litre s-1)-1.

A TEA CO2 laser with a peak radiation power of 100 MW

A high-power pulse-periodic TEA CO2 laser is used as a component of a long-range mobile differential absorption lidar. In order to reach the ultimate peak generation power, a system for laser excitation with a supply voltage of ±40 kV and efficient preionization was developed, allowing the laser to operate at high pressures of gas mixtures of various compositions. Energy, time, and spatial characteristics of laser radiation were studied. Laser pulses with an energy of >10 J and FWHM duration of ≈30 ns were obtained. The ultimate peak laser radiation power is 100 MW, and the maximum efficiency with respect to the discharge-consumed energy is 12.6%.

Characteristics of XeCl laser radiation from an unstable cavity with asymmetric radiation coupling-out

The divergence of the radiation from a repetitively pulsed electric-discharge transversely excited XeCl laser with an unstable cavity and asymmetric coupling-out of the radiation was studied experimentally. A cavity with convex mirrors made it possible to generate radiation with a near-diffraction divergence and to retain the energy at the level of 40% — 50% of the energy of a laser with a plane — plane cavity. The generation of a circular spot with a uniform intensity distribution by focusing a rectangular beam is described. Calculations and experiments are used to show that this phenomenon does not arise from diffraction and is not a result of the interaction of the laser radiation with the medium or with the target material.

Anomalous backscattering of high-power laser radiation by the flat surface of a solid

Results of measurements of the backscattering characteristics of high-power laser radiation at flat randomly rough surfaces of various materials are described for a wide range of radiation and surface parameters. It is observed that for probe radiation intensities in the range ∼103–107 W/cm2 and a pulse duration of ∼10−8 s the scattering pattern becomes anomalous under various additional conditions. The results are analyzed in accordance with the laws of structural conditionality, the qualitative boundary, abnormality, and alternation of nonequilibrium. Possible practical applications of the observed effect are discussed.

Polarization and intensity characteristics of scattered field by interacting particles in eye lens model

This article is concerned with the problem of calculating the polarization and spatial characteristics of laser radiation scattered by the eye lens. In calculation a complete general solution of the problem of interactive electromagnetic scattering by clusters of arbitrary configured non-identical spheres was used. The light scattering matrix (LSM), the image of a speckle structure of scattered radiation, the intensity distribution are received. The optical constants and dimensions of the particles varied in a range of values corresponding to the normal and pathological lens. The modelling results are compared with the previously reported experimental indicatrixes of the eye lens.

Pulsed lasers utilizing transitions in atoms and molecules

An examination is made of processes occurring in the active media of lasers utilizing organic compounds, metal vapors, and dense gases. The laws are established which govern the relationships between the laser radiation characteristics and the parameters of the exciting electromagnetic field. The particular features of the conversion of high-power radiation of exciplex lasers by organic compounds are studied. Original active-element designs are created. The results of experimental and theoretical investigations of the physics of lasers utilizing self-terminating transitions in metal vapors are presented. Questions are considered which are related to the possibility of raising their physical efficiency, increasing the laser pulse-repetition frequency and the practical lasing efficiency, and of controlling the energy characteristics of a copper vapor laser. A description is given of the kinetics of the most important plasma-chemical processes which occur in pulsed lasers utilizing dense gases. Their dependence on the method of creating the population inversion and on the gas composition is indicated. A detailed description is given of lasers prototypes constructed using organic compounds, metal vapors, and dense gases, of laser systems based on them, and of applications in ecological monitoring systems, navigational systems, medicine, and other fields.

Investigation and optimization of generation characteristics for an XeCl excimer laser–Compressed-hydrogen IRS-converter system

A comprehensive experimental investigation of the power and spatial characteristics of XeCl electricdischarge excimer laser radiation and the power characteristics of a single-pass compressed-hydrogen IRS laser excited by the focused flux of this radiation is performed. The existence of optimum laser-radiation pulse energies and divergences which ensure the maximum IRS-conversion to different Stokes components is established. It is shown that, to estimate the optimum conditions of IRS-conversion to the first Stokes component, use can be made of a simple model of the description of a multimode focused pumping flux.

A Study of the Main Dye Laser Radiation Characteristics for Different Temperature Regimes of the Active Element

A Study of the Main Dye Laser Radiation Characteristics for Different Temperature Regimes of the Active Element

Radiation characteristics of injection lasers based on vertically coupled quantum dots

We have studied injection lasers based on InGaAs/GaAs vertically coupled quantum dots (QD) grown by molecular beam epitaxy. The threshold current density decreases by one order of magnitude down to 90 A cm−2(300 K) with an increase of the number of QD stacks (N) up to 10. ForN≥ 3 lasing occurs via the QD ground state up to room temperature. Differential efficiency increases withNup to 50%. No change in range of high temperature stability of threshold current density (Jth) was observed, while the characteristic temperature (T0) measured at 300 K increases from 60 to 120 K. Using InGaAs-AlGaAs QD with higher localization energy allowed us to decreaseJthdown to 60 A cm−2and to increase the differential efficiency up to 70%.

Phase locking of a semiconductor diode array in an external cavity

Theoretical investigations are reported of the characteristics of high-power lasers with the active medium in the form of a semiconductor diode array. The selectivity of a Talbot cavity, of a cavity with an aspherical output mirror, and of a semiconfocal cavity is studied as a function of the array parameters. Estimates are obtained of the sensitivity of the laser radiation characteristics to fluctuations of the array parameters. It is shown that the dependence of the selectivity of an aspherical cavity on these parameters is nearly the same as that of a Talbot cavity, but the fundamental mode propagates without radiation losses between the diodes and beyond the array edges. A semiconfocal cavity is more selective than a Talbot or aspherical cavity. When the number of diodes in a linear array exceeds 20, the losses of the second mode in a semiconfocal cavity grow to more than 80%. The efficiency of a laser with a semiconfocal cavity, calculated ignoring the diode efficiency, can reach 80–90%.

Лазерное управление процессами в твердом теле

The large amount of information carried by the energy, spectral, and space-time characteristics of a laser beam makes it feasible to use laser radiation to control the processes that occuring in solids. The influence of laser radia- tion with a wide range of deposited energies on a variety of processes is considered: these processes include crystal growth, formation of dissipative (spatial and temporal) defect struc- tures on the surface and in the bulk of a solid, instabilities in melts, materials fracture considered from the point of view of both selectivity and self-organisation. An analysis is made of the relationship between the nature and parameters of such structures, on the one hand, and the characteristics of laser radiation, on the other.

Photodissociation XeF laser operating in the visible and UV regions

The results of experimental and theoretical investigations of the photodissociation XeF laser operating in the visible and UV regions and pumped by the radiation of an open discharge initiated by an electric explosion of thin metal wires are reported. A detailed description of the laser design and experimental techniques is given. The analysis of the energy balance in the XeF laser on the basis of measurements of energetic parameters of laser radiation and the pump source are performed. The results of optical investigations of the active medium aimed at the study of the interaction of high-power fluxes of pump radiation with the absorbing active medium are presented. This interaction forms free-running bleaching and inversion waves in the active medium. Spectral, spatial, time, and energy characteristics of laser radiation on theB-X(λ=353 nm) andC-A(λ=480 nm) transitions of XeF are investigated. The instantaneous laser efficiency with respect to the electrical power feeding the pump source is shown to be about 1%. The specific energy of laser radiation on theC-A transition in the blue-green region was 8.5 J/liter for a total laser energy of 14.5 J. The specific energy of radiation on theB-X transition in the UV region was 16.5 J/liter for a total energy of 28 J.

Contactless transmission method for determining the energy characteristics of laser radiation

A contactless method is proposed for determining the energy distribution and the total energy of large-diameter laser beams propagating in air. The energy distribution is found from an analysis of interference fringes, and the compact expressions needed in this analysis are given. A crossed Mach—Zehnder interferometer is one of the most sensitive interferometers for laser pulses propagating in air when the absorption at certain wavelengths is minimal. The error of the proposed transmission method (25%) can be reduced by a single calorimetric calibration. The upper limit of the method is set by breakdown in air and by the self-induced transparency. The physical basis of the method is considered and main expressions for the defocusing of a beam in air are given. These expressions can be used to determine the energy distribution in a beam and its total energy.

The connection of the spectral, time, and energy characteristics of laser radiation with the phase-polarization wavelength selector

The connection of the spectral, time, and energy characteristics of laser radiation with the phase-polarization wavelength selector