Sergey N. Smetanin

Self-Q-switching at phase conjugation in active media

Self-Q-switching of the Nd:crystal (Nd:YAG, Nd:GGG) and the Nd:glass multiloop lasers (phosphorus GLS-22) with self- pumped phase conjugation (SPC) in active media is investigated experimentally and theoretically. A possibility to realize single-mode single-frequent self-Q-switched laser radiation as repetitive giant pulse trains of 50 W average and 100 kW peak power with no Q-switcher is shown. Temporal dynamics of self-Q-switching and the mechanism of its occurrence on gain gratings are investigated with a help of the rate equations.

High power Nd:YAG laser with self-pumped phase-conjugate loop cavity and repetitive pulsed diode-matrix side-pumping

The joule-range high-beam-quality Nd3+:YAG laser oscillation in the multiloop self-pumped phase-conjugate cavity without an output coupling mirror at four-wave mixing of intracavity beams directly in the 110-mm long Nd3+:YAG rod with 12.6 kW diode side-pumping is developed and studied. The oscillation efficiency of up to 18 % and average power of up to 22 W were achieved in the optimized geometry of the laser cavity at the 13.9 kW pumping with repetition rate of up to 20 Hz and pulse duration of up to 475 μs. The laser generated a single high-intensive 200-ns giant laser pulse (or series of such pulses with microsecond period at increased pumping) oscillated at self-Q-switch on gain gratings with relatively narrow linewidth of about 2 GHz followed by low-intensive free-running wideband lasing. We also realized a passive Q-switch by the F2-:LiF and Cr4+:YAG crystals with oscillation of pulse trains and also 30-ns single-pulse oscillation with an individual pulse energy of up to 60 mJ and peak power of up to 4 MW at narrowed laser spectra down to 1.7 GHz.

Powerful neodymium lasers with the self-phase-conjugation

The powerful neodymium lasers with the self-phase-conjugation (SPC) and passive Q-swither are submitted. It is shown, that the application of a LiF:F2- crystal as Q-swither and SPC-mirror simultaneously, and also a Sagnac interferometer as end reflector of the cavity allows to increase efficiency and quality SPC-radiation. High power and spatial laser characteristics are obtained: Nd:YAG laser -- 114 W average power at 0.5 mrad beam divergence; Nd:YAP laser -- 51 W average power at 1.2 mrad beam divergence; Nd:Glass laser -- 18 J in pulse train at 1 mrad beam divergence.

A method for controlling the phase locking of a multichannel laser system

The conditions leading to control over phase-locked oscillation in a set of three loop lasers containing self-pumped phase-conjugate gain-grating mirrors by using a LiF: F2− passive Q-switch are studied both experimentally and theoretically. Cases of spatially uniform lamp pumping and high-efficiency spatially nonuniform transverse diode pumping are considered.

Principles of laser drilling with adapted control over the parameters of repeated laser pulses

Principles of laser drilling of deep holes with adapted control over the parameters of the multipulse laser irradiation are determined. In good agreement with earlier experimental results, the possibilities for increasing the depth and productivity of the laser treatment of deep cavities via controlled modulation of the Q-factor and active synchronization of the modes of a high-power single-mode YAG:Nd laser are substantiated theoretically.

Multi-channel laser system with phase locking by holographic gain gratings and small diameter deep hole drilling

A phase-locked three-channel Nd:YAG laser system based on phase-conjugate loop oscillators is designed and studied. The Nd:YAG laser system had three laser outputs as the self-Q-switched laser 100-mJ monopulses interfering with an interference pattern contrast tending to unity giving a sixfold interferential increase of the laser brightness. A new opportunity to apply the Nd:YAG laser systems based on phase-conjugate loop oscillators for drilling of the super-deep (up to 27 mm deep) holes of small 100-micron diameter for the most perspective metals, alloys and ceramics with different composition is shown.

Self-starting 100-W-average-power laser with a self-adaptive cavity

The numerical and experimental investigation of a self- starting Nd:YAG laser oscillator with a cavity completed by population gratings induced in the laser crystal by generating beams themselves are reported. The spatio- temporal characteristics of the laser comprising three Nd:YAG amplifiers and a saturable absorber were investigated. The generation of single mode beam with an average power of as large as 100 W and high quality was achieved.

Single-mode Nd:YAG laser with cavity formed by population gratings

Q-switched regimes of the nanosecond pulse-periodic Nd:YAG laser with dynamic cavity formed with participation of dynamics holographic gratings in laser elements have been investigated. A Sagnac interferometer was applied as a laser cavity mirror for angular selection of initial radiation. As a passive Q-switch, we used saturable absorber crystal LiF:F2-, which increased total intracavity diffraction efficiency of dynamic gratings completing the cavity. Self-pumped phase conjugation in Nd:YAG amplifier and LiF:F2- absorber provided adaptive properties of the cavity. The peak power of generated beam with diffraction quality exceeded 17.5 MW and the average power achieved 50 W.

Study of lasing on the 4F3/2 → 4I13/2 secondary transition of Nd3+ ions in a phase-conjugate Nd3+ : YAG laser

Lasing at a wavelength of 1.34 µm on the 4F3/2 → 4I13/2 secondary transition of Nd3+ ions in a phase-conjugate (PC) Nd3+ : YAG laser under four-wave mixing in a laser medium is theoretically and experimentally investigated. The influence of the amplified spontaneous emission at a wavelength λ = 1.064 µm on the parameters of phase-conjugate generation of the Nd3+ : YAG laser at λ = 1.34 µm under passive Q switching by a V3+ : YAG crystal using two-, three-, and four-loop open cavity schemes is analysed by mathematical simulation. It is shown that there is an optimal initial transmission of a passive Q switch (PQS), the value of which decreases with increasing number of cavity feedback loops. The generation in the Nd3+ : YAG laser at λ = 1.34 µm with an open PC multiloop cavity is experimentally obtained and studied for the first time. Emission in the form of a train of seven pulses with a total energy of 0.25 J and individual pulse energy and duration of 36 mJ and 150 ns, respectively, is obtained with an initial PQS transmission of 74 %. The angular divergence of the laser beam is found to be 0.7 mrad at quality factors and .

Phase Locking Control of the Multichannel Holographic Laser System with the Help of Passive Q-Switch

Method of phase-locking control of the multichannel laser system by use of a passive Q-switch is proposed. For the first time a phase-locked and Q-switched oscillation of the multichannel Nd:YAG-laser system is realized.