Wavefront-reversing Mirror Research Articles

The structure of the Stokes' fields reflected in SBS in a light guide

The calculation of gain increments and the spatial structure of the scattered Stokes' radiation is carried out on the basis of a proposed theoretical method. The so-called rotated modes are shown to be trapped into a spatial resonance with the central reversed mode. These spatial configurations are discovered experimentally with the help of an interferometer with wavefront-reversing mirrors based on stimulated Brillouin scattering. The rotated modes are concentrated in a so-called 'background pedestal' for which the divergence theta /sub b/ increases with the gain increment at the longitudinal correlation length Gamma /sub c/. For a fixed Gamma /sub c/ the relationship between the energy of the Stokes' signal reproducing exactly the spatial structure of the pump radiation and the energy of the background pedestal varies randomly from one laser pulse to another, resulting in a strong dispersion of the energy of the Stokes' waves measured in both interferometer arms.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Influence of transient variations of the refractive index on the operation of a laser interferometer with a wavefront-reversing mirror

An optical interferometer with a wavefront-reversing mirror is considered. This mirror contains a layer with a time-dependent refractive index. The dependence of the phase shift of the beams returning to the input of the interferometer on the rate of change of the refractive index is determined.

Characteristics of an interferometer with stimulated Brillouin scattering mirrors

An interferometer with wavefront-reversing mirrors based on stimulated Brillouin scattering was used to investigate the spatial structure of the Stokes radiation. A Stokes wave formed as a result of stimulated Brillouin scattering in a light pipe included fields with configurations reversed relative to the pump radiation and propagating not exactly backward but at certain angles. These fields were concentrated in a background pedestal for which the divergence increased on increase in the gain increment Γc at the correlation length. For a fixed Γc the relationship between the energy of the Stokes signal (reproducing exactly the spatial structure of the pump radiation) and the energy of the background pedestal varied randomly from pulse to pulse, resulting in a strong dispersion of the energy of the Stokes wave measured in both interferometer arms.

Influence of the angular selectivity on imaging properties of a four-wave wavefront-reversing mirror

An experimental investigation was made of the angular selectivity of a wavefront-reversing mirror based on a degenerate four-wave interaction and of the influence of this selectivity on the quality of an image formed by the reversed wave in a scheme with an object in one of the pump beams.

Energy characteristics of a round-trip CO2amplifier

An investigation was made of the energy characteristics of a round-trip CO2 amplifier intended for operation with a wavefront-reversing mirror. A quantitative comparison is made between the results obtained and the theory of amplification based on the steady-state two-level model of an active medium with a homogeneously broadened line. It is shown that this theory is applicable to the amplification of a typical CO2 laser pulse both when a single saturation parameter is introduced for the whole pulse and when the pulse shape is taken into account.

Investigation of the characteristics of a wavefront-reversing mirror utilizing a photorefractive strontium barium niobate crystal

An experimental investigation was made of the time and energy characteristics of a wavefront-reversing mirror with a self-intersecting laser beam using a strontium barium niobate crystal as the nonlinear medium. A study was made of the dependence of the reflection coefficient R of the wavefront-reversing mirror and of the reversed beam formation time τ on the length of the wave vector of the induced grating and the refractive index. It was found that in a certain range of wave vector lengths, the reflection coefficient showed a sharp drop. A theoretical explanation of the observed dependences was based on calculations of the strength of the coupling of the light waves in the medium. The dependences of R and τ on the intensity and divergence of the laser beam were studied. The conditions for conservation and erasure of the refractive index grating in the crystal were investigated.

Investigation of a hypersonic wavefront-reversing mirror operating in a master-oscillator-amplifier configuration

An investigation was made of a wavefront-reversing mirror utilizing hypersonic vibrations in a master-oscillator-amplifier configuration with a strong signal wave and weak reference waves. Preferential amplification of the Stokes reference wave was found to occur for large values of the incremental gain in the interaction region, so that the reflection coefficient of the signal did not exceed 20%. The method of spatially separating the interaction and saturated gain regions and the use of polarization decoupling devices made it possible to reduce the transfer of the signal energy to the Stokes reference wave and to raise the signal reflection coefficient to 50% or higher.

Copper vapor laser with a wavefront-reversing mirror induced in the active medium

A study was made of the operation of a copper vapor laser and a resonator with a dynamic wavefront-reversing mirror induced in the active medium by a four-wave interaction with pump waves excited in an auxiliary resonator. Radiation with a diffraction-limit divergence was generated in a resonator with a convex second mirror. The energy, time, and spectral characteristics of lasing were determined.

Copper vapor laser with a self-pumped wavefront-reversing mirror

A report is given of the first operation of a copper vapor laser with a self-pumped wavefront-reversing mirror based on a four-wave interaction with the active medium and free of additional devices for the self-excitation of the laser. The steady-state energy characteristics are calculated and an analysis is made of the condition for the occurrence of cw lasing. It is shown that in the case of the degenerate four-wave interaction such cw lasing is possible only in the case of some saturation of the medium at a frequency coinciding with the center of the gain profile of the medium.

Suppression of an opposite wave in pumping a four-wave wavefront-reversing mirror by a CO2laser with an unstable resonator

An experimental investigation was made of optical systems in which polarizers eliminated the influence of an opposite wave on the angular characteristics of the radiation emitted by a laser with a telescopic resonator. The feasibility and advantages of the use of an unstable resonator were analyzed for a generator of reference waves in systems for a degenerate four-wave interaction at the wavelength of 10.6μ.

Two-pass compact laser amplifier made of a gadolinium scandium gallium garnet crystal doped with Cr3+and Nd3+

A compact laser amplifier utilizing a gadolinium scandium gallium garnet crystal doped with Cr3+ and Nd3+ was constructed and investigated. Efficient operation of such an amplifier with a wavefront-reversing mirror of titanium tetrachloride was demonstrated. The diffraction-limit divergence of the beam was achieved at the exits from the laser when the repetition frequency of the light pulses was up to 10 Hz.

Lasers with wavefront-reversing mirrors (review)

The principles of construction of lasers with wavefront reversing (WFR) mirrors are considered. Descriptions are given of methods for the determination of the transverse and longitudinal mode structures in such lasers. The advantages and shortcomings of various systems with WFR mirrors are reviewed. A comparison is made of the various systems with one another and with conventional mirrors. The future trends and the main lines of further research are forecast.

Stimulated Brillouin scattering mirror in the form of a multimode optical fiber in a four-pass neodymium phosphate glass laser amplifier

A multimode optical fiber was used as a wavefront-reversing mirror in a four-pass laser amplifier utilizing neodymium phosphate glass.

Noise of four-wave hypersonic wavefront-reversing mirrors under absolute instability conditions

A calculation is made of the noise of four-wave hypersonic wavefront-reversing mirrors under absolute instability conditions. An analysis made using the approximation of a constant field of the pump waves in the absence of wave mismatch shows that the sensitivity of such mirrors deteriorates on increase in the excess above the instability threshold. Estimates are made of the lowest power of weak signal waves at which it is still possible to separate the reversed signal from the background of the noise in the nonlinear medium of the wavefront-reversing mirrors.

Laser with a wavefront-reversing mirror andQswitching by stimulated Brillouin backscattering

An investigation was made of the spectral, temporal, and spatial characteristics of the radiation emitted by a YAG:Nd laser with a wavefront-reversing Brillouin mirror, obtained in the resonator stability range. The radiation pulses were found to be shortened while the energy was practically unaffected (it was at least 80% of the initial value).

Oscillation modes in a resonator with a self-pumped wavefront-reversing mirror

An investigation is made of the oscillation modes and natural frequencies of a resonator with a self-pumped wavefront-reversing mirror (SWM). An integral equation describing the transverse mode structure is derived for a resonator with an SWM and a Gaussian profile of the reflection coefficient. The parameters of the lowest oscillation mode are also found for this resonator. The advantages of a resonator with an SWM are identified and it is suggested that resonators of this kind may find extensive applications in systems for the formation of highly directional optical radiation.

Waveguide resonator with wavefront-reversing mirrors

A study is made of the properties of waveguide resonators with wavefront-reversing mirrors, of the spatial structure of radiation in such resonators, and of resonator mode losses. It is shown that wavefront reversal can ensure that the resonator modes are identical with the waveguide modes and that their losses and selectivity are due to the losses in the waveguide and are independent of the dispersion of the phases of the waveguide modes.

Investigation of a two-pass CO2amplifier for operation with a wavefront-reversing mirror

It was demonstrated experimentally that for a pulse duration of ~ 1 μsec the amplifying properties of the active medium in photoionization CO2 lasers can be estimated using the steady-state approximation formulas. The gain and the saturation parameter, averaged over the pulse duration, were measured for a number of P branch CO2 lines including the 10P(8) and 10P(10) lines for which the maximum reflection coefficient was achieved using a wavefront-reversing mirror and a four-wave interaction in SF6. A study was made of a two-pass CO2 amplifier intended for operation with a wavefront-reversing mirror and providing a gain of ~ 104 with an output energy of 60 J.

Energy characteristics of a laser with a wavefront-reversing mirror utilizing a degenerate four-wave interaction in a medium with a local response

The output characteristics of a laser are calculated for the case of a frequency-degenerate four-wave interaction of light in media with a local nonlinearity. Nonmonotonic dependences of the output radiation intensity on the interaction constant are predicted, as well as the existence of regions of bistable and multistable solutions. The results are generalized to the case of a resonator formed by a four-wave mirror and a conventional reflector, and filled with an additional active medium.

Fields of resonators with a wavefront-reversing mirror and an inhomogeneous optical medium

The problem of finding the dominant oscillation mode of a resonator with a wavefront-reversing mirror and an optical medium exhibiting extremely random inhomogeneity is solved analytically for large Fresnel numbers. The average characteristics of random fields formed in statistical media using a wavefront-reversing mirror are also determined. Various approaches to the computation of these characteristics are discussed.