Radiation Wavefront Research Articles

Interferometer with a diverging lens for the investigation of laser radiation wavefronts

An interferometer was constructed for the analysis of laser radiation wavefronts. A lens optical component used in this interferometer was made by sintering and local compression of two glasses. The error in the determination of the wavefront topography of test radiation was less than 1/30 of its wavelength.

On the global behaviour of weak discontinuities in radiation gasdynamics

The nature of weak gasdynamic discontinuities has been studied by considering the interaction between the time dependent gasdynamic and the radiation fields. The effects of radiative transfer have been investigated using a quasi-equilibrium and quasi-isotropic hypothesis of a differential approximation which is valid over the entire optical depth range from the transparent limit to the optically thick limit. It is shown that the existence of the time dependent radiation field gives rise to a radiation induced wave which has a negligibly small effect on the non-relativistic flow properties of the gasdynamic field. The effect of the thermal radiation and initial wave front curvature on the non-linear breaking of weak discontinuities are discussed.

'Spekforms' — sintered components for shaping laser radiation wavefronts

Shaping of an image in the focal plane of an objective with the aid of a new optical component is proposed and implemented. This component ('spekform' in Russian) is made by sintering and hot moulding. Design and fabrication are reported of such 'spekforms' with the strongest optical inhomogeneity ranging from a fraction of a wavelength to hundreds of wavelengths. They are intended for the formation of axisymmetric and nonaxisymmetric outlines (line figures) and are capable of transforming radiation with an efficiency close to 100%.

Indirect measurements of the wavefront of semiconductor laser radiation

An algorithm similar to that proposed by Gerchberg and Saxton is discussed. It requires a knowledge of one-dimensional intensity distributions in two beam cross sections separated by a finite distance in order to reconstruct the phase. The results of a numerical reconstruction of the phase from experimental data are presented.

Minimization of the angular divergence of optical radiation transmitted by a nonlinear layer

An analysis is made of adaptive compensation for the self-interaction of optical radiation in order to minimize its angular divergence in the far-field zone. The compensation quality is governed by the functional of the effective width of the angular spectrum of the beam. A gradient method is used to control the radiation wavefront. Calculations are performed using the aberration-free and quasioptic approximations. The convergence, stability, and speed of the control algorithms and the efficiency of compensation for the angular divergence are analyzed as a function of the following: the nonlinear layer thickness, the nonlinear parameter, the choice of the initial beam focusing, and the control coefficient.

Suppression of stimulated enthalpy scattering of radiation from an iodine laser by introduction of quenching impurities into the active medium

Experiments demonstrated that the addition of water vapor to the active medium of an iodine laser made it possible to suppress effectively the stimulated enthalpy scattering and the associated instability of the radiation wavefront at the expense of a small loss in respect of the radiation energy. This opens up the possibility of a significant reduction of the divergence of the radiation emitted by these lasers.

Structure of the wavefront of coupled mode systems

Model experiments and theoretical investigations were used in a study of stimulated emission from diffraction-coupled two-beam modes. The radiation wavefront was found to suffer from perturbations due to screw dislocations of the phase.

Influence of dynamic deformation of the optical components on forming the radiation wavefront in a laser and in a master-oscillator–amplifier system

An experimental investigation was made of the dynamic deformation of metal laser mirrors under the action of radiation. Calculations were made of the influence of these deformations on the wavefront formation in a CO2 laser system consisting of a master oscillator and an amplifier. Quantitative data were obtained on the rise of a mirror surface as a function of the absorbed energy. The most dangerous size of mirror inhomogeneities for a laser (amplifier), causing the highest radiation energy losses within a selected angle was determined.

Dynamic chaos in the case of parametric interactions of light waves

An investigation is made of the spatial evolution of a system of constant-frequency light waves, each of which participates in two four-wave parametric interaction processes simultaneously. It is shown that the competition between the parametric processes may result in spatial chaos. The chaotic evolution regime is established if the wave amplitudes at the boundary of a nonlinear medium differ sufficiently from the values corresponding to an integrable limit, the existence of which depends on the symmetry of the system. The other condition for the appearance of chaos—strong interwave energy exchange—is obeyed when the parameters of the medium and of the radiation are of the same orders of magnitude as in the case of reflection accompanied by amplification in phase conjugation of a laser radiation wavefront on the basis of a degenerate four-wave mixing. The characteristic features of the appearance of a stochastic instability of a system of interacting light waves under experimental conditions are considered.

Correlation synthesis of a probe field in laser Doppler velocimeters with multimode fiber waveguides

Various configurations of a laser Doppler velocimeter with a synthesized probe beam are considered. The probe beam is formed by flattening the radiation wavefront at the exit from a multimode fiber waveguide with the aid of a correcting system including a spatial wavefront modulator and a flattening hologram. Measurements of the precision characteristics of the configurations are reported.

Deformation of the wave front of probe radiation in a refraction channel containing aberrations

Deformation of the wave front of probe radiation in a refraction channel containing aberrations

Stimulated Brillouin scattering of single-mode and weakly inhomogeneous beams

An investigation was made of stimulated Brillouin scattering of single-mode and weakly inhomogeneous beams. It was found that the Stokes beam profile was not similar to that of a Gaussian beam and it had a smaller angular divergence. In the case of weakly inhomogeneous pumping the conversion was efficient in a nonlinear region. The effects could be used for correction of the wavefronts of two-pulse laser radiation.

Efficiency of wide-aperture amplifiers with prism active elements

An investigation was made of the feasibility of constructing wide-aperture laser amplifiers from prism active elements made of neodymium-activated glass. Calculations were carried out and experiments confirmed the main energy characteristics of such amplifiers. The influence of thermooptic distortions on the laser radiation wavefront was negligible. The efficiency of storage of the excitation energy in such amplifiers was ~ 1.7% when the density of the inversion energy was ~ 0.5 J/cm3.

Instability of the radiation wavefront in pulsed CO2amplifiers

A theoretical investigation is reported of the evolution in space and time of a small-scale perturbation against the background of a smooth beam entering a pulsed CO2 amplifier. The ranges of the transverse frequency, longitudinal coordinate, and time in which the perturbation growth is exponential are determined. It is shown that the wavefront instability can be suppressed by amplification of the main beam and by the attenuation of sound.

Phase conjugation of CO2-laser radiation by a three-beam interaction

The distortion correction of a CO2-laser radiation wavefront is studied by using forward resonant parametric scattering in gaseous SF6 and retrace after retroreflection from a mirror.

Propagation of an intensity-modulated laser beam through a pulsed CO2amplifier

A theoretical study was made (by a self-consistent solution of the equations of vibrational kinetics, hydrodynamics, and quasioptics) of the influence of self-interaction of laser radiation on the transmission of a beam through a CO2 amplifier. It was found that for times exceeding the time for collisional decay of the upper active level the radiation wavefront becomes unstable in the presence of small-scale perturbations of the transverse structure of the beam. It was shown that the harmful influence of the self-interaction on the divergence can be weakened by raising the intensity of the incident beam and the gain of the amplifier.

Feasibility of radiation wavefront correction in the case of pulsed operation of a laser with a plane–plane resonator

It is shown that in the case of plane-plane resonator lasers with a short growth time of the lasing process the divergence of the output radiation can be reduced by correcting the wavefront with a positive lens. Experiments confirm a reduction in the divergence by a factor of about 2 in the case of a barium nitrate crystal Raman laser and a rhodamine 6G laser. The geometric-optics approximation is used for a II-shaped pump pulse of duration τ to demonstrate analytically that the correcting lens has a focal length F ≈ cτ near the lasing threshold.

Reversal of a radiation wavefront in six-photon parametric interaction in a nonmonochromatic pumping field

Reversal of a radiation wavefront in six-photon parametric interaction in a nonmonochromatic pumping field

Reversal of CO2laser radiation wavefront in a system of three interacting beams

A study was made of reconstruction of the wavefront of CO2 laser radiation in the course of forward resonance parametric scattering by gaseous SF6 and a reverse passage after reflection from a mirror.

Investigation of an unstable resonator with a perforated mirror

Theoretical and experimental investigations are reported of an unstable resonator with a perforated mirror used to couple out information on the phase structure of a radiation wavefront over the whole of its cross section inside the resonator. Estimates are obtained of the precision of determination of the wavefront which, for a given experimental error, makes it possible to determine the permissible size of perforations in the mirror. A numerical investigation is reported of the structure of the field inside a resonator with a perforated mirror when the active medium is subject to low-order aberrations. A report is given of an experimental study which confirms that, in principle, it is possible to use perforated mirrors in unstable resonators for obtaining information on the field structure necessary for the operation of systems with intracavity adaptation.