A A Malyutin

Risky intensity peaks resulting from nonlinear holographic imaging.

A study of the maximal intensity peaks due to nonlinear holographic images of obstacles such as obscurations or phase defects in a high-power laser system is presented. It is shown that the interference of the high-power plane wave and the converging image wave results in the formation of intensity maximums in the vicinity of the image plane, the values of which significantly exceed the intensity in the image plane itself. For round obstacles, analytical expressions that describe magnitudes and locations of the maxima depending on the radius and the type of obstacle are given. A procedure of numerical modeling that allows estimation of the influence of beam size, medium thickness, type, size, and shape of obstacles onto the properties of nonlinear images is described. It is demonstrated that for a given combination of the nonlinear medium and the high-power beam parameters, there is an intrinsic size of obstacles that is most harmful for the laser system components.

Efficiency of an Li–Nd–La phosphate glass laser at low pump energies. Free lasing

An investigation was made of the free-lasing regime in a high-concentration Li–Nd–La phosphate glass pumped in the energy range 1–15 J. A laser efficiency of 2.9% was obtained for a pump energy of 14.5 J. Estimates were made of the intracavity losses and the maximum attainable efficiency was determined. An investigation was made of the laser performance in the giant pulse regime and at pulse repetition frequencies of up to 25 Hz.

Interferometric diagnostics of femtosecond laser microplasma in gases

The laser plasma formed in gaseous media due to their optical breakdown under tightly focused femtosecond laser pulses has been experimentally investigated. Pump-probemicrointerferometry is chosen to perform spatial and temporal diagnostics of the plasma. Time dependences of the laser plasma electron density are obtained. It is shown that in breakdown of different gases (air, nitrogen, argon, and helium) at different pressures (in the range from 1 to 10 atm) the electron concentration continues to increase during ∼1 ps when the laser irradiation is over. This effect is related to the impact ionization of the plasma by the hot electrons formed in interaction of intense femtosecond laser pulses with matter. The results of theoretical simulation of the post-ionization processes are presented.

Spectrotemporal technique for enhancement of resolution in studies of ultrashort pulses

A new technique is proposed for the characterization of ultrashort optical pulses. The technique includes a simple mathematical treatment of the time-resolved spectrum of the signal that is obtained using an image converter camera. The theoretical description of the technique and several numerical examples modeling the ultrashort pulse reconstruction are presented. The dependence of the reconstruction result on the noise level is evaluated. It is shown that the temporal resolution of the technique can be up to two orders of magnitude higher than that for the used electro-optic device.

Ultrafast Space‐time and Spectrum‐time Resolved Diagnostics of Multicharged Femtosecond Laser Microplasma

We present the review of the recent experimental studies of fundamental mechanisms of femtosecond laser plasma formation and evolution performed in A. M. Prokhorov General Physics Institute of Russian Academy of Sciences. The main object we dealt with was the micro‐sized plasma produced in gases with high intensity (up to 5×1017 W/cm2), tightly focused (to a few microns in diameter) IR and UV femtosecond laser pulses. The main attention in the experiments was paid to the initial stage of microplasma formation and evolution characterized by strong laser‐plasma coupling resulting in efficient ionization and heating of the medium, distortion of laser beam, and nonlinear spectral conversion of laser radiation to the continuum and laser harmonics. Using a precise pump‐probe micro‐interferometric technique the dynamics of plasma was studied with femtosecond time‐resolution in a wide density range—from a minimal detectable electron concentration (1019 cm−3) to the almost total (down to nuclei) ionization of ions...

TIME CHARACTERISTICS OF A RING LASER WITH A BLEACHABLE FILTER

A theory of the development of mode locking in a ring laser is given. Equations are obtained for the relationship between, the forward and reverse waves in the course of bleaching of a nonlinear filter. The equations are compared with the time characteristics of the forward and reverse waves in a ring laser determined experimentally with an image-converter camera. It is shown that the time characteristics of the forward and reverse waves are strongly correlated when the concentration of the bleachable absorber is high, but this correlation becomes weaker with decreasing concentration of the absorber.