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Refraction of light at an interface between a homogeneous dielectric and a two-dimensional photonic crystal is studied. Using the isofrequency method, various cases of refraction, including a change in the magnitude and direction of the wave vector of the incident wave, in the refractive indices of the media, and in the mutual orientation of the interface and the translation vectors of the photonic crystal, are investigated. Different types of refraction and the possibilities for realizing negative and multiwave refraction are considered.

Periodic arrays of air holes with diameters ranging from about 80 nm up to 400 nm are shown to modify intensity profiles of guided modes in photonic-crystal fibers, suggesting new ways of fiber dispersion engineering and modal birefringence control. Guided modes supported by such fibers provide a high efficiency of anti-Stokes frequency conversion for 100-fs pulses of a Cr: forsterite laser.

Numerical modeling methods were used in an investigation of the condition for active mode locking in gas lasers with inhomogeneous broadening of the gain profile. It is shown that a change in the loss modulation frequency gives rise to chaotic and regular instabilities of the output radiation. The characteristics of the resultant chaotic spontaneous oscillations are determined. Equations describing the dynamic model of a laser are derived allowing for trapping of resonant radiation from the upper active level.

A dynamic model is proposed for describing active mode locking in gas lasers with inhomogeneous broadening. Different dynamic regimes are investigated depending on the depth of modulation of the losses. It is shown that disruption of the mode locking regime is accompanied by the appearance of more complex dynamic states, both regular and random, the shape of each individual field pulse having a complex multihump structure which is a consequence of the coherent nature of the interaction of the electromagnetic field with the active medium.

A device is developed to locate both metallic and non-metallic (e.g., explosives, etc.) objects hidden under people's clothes. The device is based on receiving the radiothermal radiation from the surface of the person's body.

A model of the dynamics of a single-longitudinal-mode unidirectional ring laser with a homogeneously broadened medium is proposed. The model includes the transverse variation of the field and of the material parameters and is based on a treatment of the round-trip propagation of a beam in a nonlinear medium rather than on an expansion in terms of the empty-cavity modes. In particular, the case of adiabatically eliminated polarization and inversion is studied. A three-dimensional point mapping is obtained and analyzed. It is shown that this model describes stationary regimes with mode deformation and spatiotemporal (quasi-periodic or periodic) oscillations of both the beam parameters (beam radius and phase-front curvature) and the intensity on the axis.

Theoretical and experimental investigations were made of the influence of external modulation of the parameters on the characteristics of a ring gas laser with circular polarization of the radiation, operating in a single-mode regime well above the threshold. A report is given of the main results obtained on modulation of the gain, tuning, and magnitude of the frequency pedestal created by the application of an axial magnetic field to the active medium. A good qualitative agreement (and in the case of the static characteristics also a quantitative agreement) is obtained between the experimental results and theoretical calculations based on a large-signal theory. These results can be employed in simulation of technical fluctuations of the parameters of ring lasers with circular polarization of the output radiation caused by vibrations of the resonator, plasma fluctuations, etc.

It is shown theoretically that injection of an optically dense jet between two parallel planar streams establishes a dielectric gas waveguide which localizes light in a narrow reaction zone. It then becomes possible to use narrow inversion zones (with a thickness of the order of 10−2 cm) in cw chemical lasers without suffering the diffraction losses of light. This waveguide effect should make it possible to use gas streams at pressures 1 atm in chemical lasers. A fast chemical reaction, Ba+S2Cl2→S*2(B)+BaCl2, resulting in the emission of visible light is considered by way of example.