Wavefront-reversing Mirror Research Articles

Problem of suppression of interference losses in multichannel resonators with wavefront-reversing mirrors

An analysis is made of the optical losses in multichannel resonators with wavefront-reversing mirrors. The attention is concentrated on the losses due to interference between light beams that are passed through different resonator channels. The geometric-optics approximation is used to obtain the dependence of the interference loss factor on the resonator length and on the width of the frequency band of the wavefront-reversing mirrors. It is shown that the interference losses can be suppressed effectively for certain relationships between this band width and the resonator length.

Oscillation modes in resonators with mirrors performing partial wavefront reversal

A matrix approach is used to study the simultaneous influence of the frequency shift, and of amplitude and phase distortions arising in the course of partial wavefront reversal on the behavior of oscillation modes in a resonator with a wavefront-reversing mirror. It is shown that amplitude distortions associated with the finite transverse dimensions of such a mirror generate, in most systems employed in practice, oscillation modes typical of a stable resonator and the role of phase distortions and frequency shift then reduces to mode deformation. It is shown that if phase distortions are introduced into a wavefront-reversing mirror, it is possible to construct a resonator generating highly directional radiation in the form of the lowest transverse mode which is characterized by a large volume and is insensitive to intracavity phase distortions.

Polarization methods for improvement of the energy characteristics of wavefront-reversing mirrors

A theoretical and experimental investigation is reported of the feasibility of using a polarization method for decoupling of reference waves in a system incorporating threshold-free reflection and a Brillouin amplifier. Expressions are derived for the characteristic time taken for the establishment of scattering processes and for the spatial structure of the interacting waves. It is shown experimentally that this method can ensure a substantial improvement in the reflection efficiency whilst maintaining the quality of the wavefront reversal.

Calculations of fields in resonators with wavefront-reversing mirrors

It is shown rigorously that the problem of determining the oscillation modes of ring resonators with wavefront-reversing mirrors can be reduced to the determination of the oscillation modes of a certain equivalent resonator with ordinary mirrors. Methods of determining the parameters of an equivalent resonator are described and it is established that this can be both stable and unstable. The advantages of ring resonators with wavefront-reversing mirrors are noted.

Compensation for small-scale nonlinear distortions of optical beams using wavefront reversal

A statistical description of four-wave parametric scattering of complex optical fields is used to investigate interaction of high-power radiation with a transparent nonlinear distorting medium and a nonideal wavefront-reversing mirror. It is found that the regime involving compensation for nonlinear perturbations of the wavefront based on averaging these perturbations is unstable when the coefficients of energy reflection from the reversing mirror are high (of the order of or greater than unity). Possible conditions for suppression of this instability are discussed.

Influence of random inhomogeneities of the refractive index of a medium on the nature of fields in a laser resonator with wavefront-reversing mirrors

A study is made of the influence of random inhomogeneities of the refractive index of a medium on the nature of fields in a laser resonator with wavefront-reversing mirrors. This is done by analyzing the mutual coherence function of the fields. Solutions of the integral equation for the mutual coherence function are obtained for a resonator with mirrors which have a Gaussian transmission coefficient profile and with a medium which has a Gaussian correlation function of the refractive index fluctuations.

Calculation of the field in a laser resonator with a wavefront-reversing mirror

A solution is given to the problem of finding the fields in a resonator formed by two wavefront-reversing mirrors. It is shown that the resonator fields take the form of a Gaussian-Hermitian beam whose axis is generally inclined to the resonator axis.

Properties of a resonator with a wavefront-reversing mirror

The paraxial approximation is used to study the structure of the oscillation modes and normal frequencies of a resonator with a wavefront-reversing mirror. It is shown that when this resonator is filled with a linear and reciprocal medium, the fundamental oscillation mode has lower losses than the fundamental oscillation modes of any filled resonators formed by conventional mirrors of the same size. The absence of discrete normal frequencies in the resonator is noted.

Theory of resonators with wavefront-reversing mirrors

An analysis is made of the problem of determination of the oscillation modes in a plane-parallel resonator with one wavefront-reversing mirror. No restrictions are imposed on the dimensions of the mirrors forming the resonator. Expressions are obtained for the fields of the oscillation modes on the mirrors. It is shown that these fields are in the form of Gaussian-Hermitian beams with parameters depending on the ratio of the transverse dimensions of the mirrors.

Inaccuracy of reproduction of the spatial structure of a beam in a laser amplifying medium with a reversing mirror

An analysis is made of the influence of inhomogeneities of the gain and refractive index of an active medium of a double-pass amplifier with an ideal wavefront-reversing mirror on the accuracy of reproduction of spatial distributions of the amplitude and phase of the input signal. It is shown that if inhomogeneities of the refractive index are sufficiently small and an amplifier can be regarded as a thin lens (phase corrector), the wavefront of the output radiation is reversed relative to the wavefront of the input signal. If these conditions are not satisfied, reversal does not take place.

Possible use of resonantly excited media in wavefront reversal

A theoretical analysis is made of the conditions which a resonantly excited medium must have to act as a wavefront-reversing mirror. In the absence of saturation by the incident signal, the absorption cross section at the frequency of this signal should be considerably less than at the reversed-wave frequency. In the case of strong saturation it is preferable to use substances with narrow spectral lines. If a wavefrontreversing mirror is used to compensate distortions of the front of a wave during amplification, the necessary contrast of the reversed wave is a function of the gain and of the width of its profile.

Properties of resonators with wavefront-reversing mirrors

An analysis is made of the mode structure of a plane-parallel resonator with wavefront-reversing mirrors. An integral equation is derived for the oscillation modes of the resonator. It is shown that these modes are identical with those in a confocal resonator of the same length.