Andrei A Sychev

Ultrashort-pulse generation in a passive-mode-locked YAG:Nd laser by means of the resonator-loss-unloading method

The method of generating ultrashort pulses of extreme duration by the controlled resonator-loss unloading of pulsed solid-state lasers with a passive shutter was proposed. The conditions of prolonged maintenance of the threshold operation mode up to the bleaching point of the passive shutter were determined on the basis of calculation of the kinetics of generation. The method was realized for an YAG:Nd laser, and intense ultrashort pulses were obtained with a duration ≈12 ps corresponding to the maximum width of the generation spectrum of a nonselective resonator.

Laser diagnostics of the Bubston phase in the bulk of aqueous salt solutions

Stable gas nanobubbles in the bulk of NaCl aqueous solutions and clusters of these nanobubbles have been investigated at different ion concentrations by four independent laser techniques (phase microscopy, dynamic light scattering, optical breakdown, and measurement of angular dependences of the light scattering matrix). The results obtained by these radically different techniques are in good agreement. It is found that the nanobubble size is practically constant and amounts to approximately 100nm in the range of ion concentrations 10−6<C <1M. It is shown that a necessary condition for nanobubble nucleation is the saturation of solution with dissolved air. It is revealed that nanobubble clusters form a thermodynamically nonequilibrium phase with a lifetime of several months.

Multiphoton optical breakdown in water under picosecond laser pulses

The phenomenon of optical breakdown in highly purified (free of external impurities and bubstons) water under picosecond laser excitation was experimentally investigated. Narrow-band UV flashes were revealed. This effectmakes it possible to distinguish themodes of optical breakdown occurring either through multiphoton ionization of water molecules or via impact ionization at heterogeneous seeds.

Parametric Interactions in Highly Purified Water in Intense Optical Radiation Field: Degassing Effect

Excitation of optical breakdown and four-photon parametric processes in water in a pump field at a wavelength of 1.064 μm with pulse duration of 20 ps was experimentally studied. It was shown that degassing and helium washing of a water sample result in optical breakdown suppression; in this case, the processes of the four-photon parametric interaction are excited most efficiently. This effect is explained by the fact that pump self-focusing in water degassed and washed by helium is regular under given experimental conditions.