Yuri V. Senatsky

Generation of radially and azimuthally polarized beams in Yb:YAG laser with intra-cavity lens and birefringent crystal

We demonstrated the operation of cw diode-pumped Yb:YAG laser in radial or azimuthal polarized (RP or AP) beams using a combination of birefringent uniaxial crystal (c-cut YVO4 or α-BBO) and lens as intra-cavity elements. RP and AP doughnut modes (M2 = 2-2.5, polarization extinction ratio 50-100:1) with output power up to 60 mW were generated. Apart from doughnut modes, RP or AP ring-like off-axis oscillations and multi-ring beams with mixed RP and AP were also observed at the output of this laser scheme. Using intra-cavity short focus lenses with spherical aberrations AP or RP modes of higher orders was obtained. Mechanism of mode selection in the laser is discussed. The large variety of beams with axially symmetric polarizations from the output of the proposed laser scheme may find applications in different fields.

Measurements of nonlinear refractive indices in ceramic laser media

At the recent years a technology of ceramic laser media on the base of crystals with a cubic symmetry has been developed. The perspective of the usage of ceramic materials in many different applications including high-power short pulse lasers stimulates the work on the systematic study of the properties of these new laser media. In this report a nonlinear refractive index, n2, was studied for several garnet and sesquioxide laser ceramics using Z-scan method. This technique with a “top-hat” probe beam intensity distribution was used. Nonlinear indices in the range of (2-6)x10-13 were measured for YAG, Y2O3, Lu2O3, and Sc2O3 ceramic samples. These data together with the laser and spectroscopic parameters of several Nd3+ and Yb3+ doped crystals of a cubic symmetry were used to estimate in the complex the properties of laser ceramics for the application in high-power pulsed-repetitive laser-drivers for inertial confinement fusion (ICF) program. A high heat conductivity of ceramic materials is a profitable characteristic for this application as compared to glasses which are used now for experiments in ICF at single shots regime. Compared to single crystals, ceramic elements provide laser designers with a variety of new design options for the projects of laser-drivers. The usage of ceramic active elements with low and increased n2 values in the channels of a powerful laser facility is discussed.

High-order mode selection in Yb:YAG ceramic laser

Selection in various families of axi-symmetric modes (Laguerre-Gaussian, cylindrical vector and Bessel-like modes with near-diffraction free propagation properties) in an Yb:YAG ceramic laser by manipulating the cavity stability conditions of a lens resonator is reported.

Transformation of the ytterbium laser spectrum with pulsed selective pumping

The Yb-doped crystals and glasses present promising active media for high power lasers. These media are typical of broad gain linewidths -- near 10 nm for Yb:YAG and 100 nm for glasses. The experiments have been performed on pumping Yb- doped YAG and glass samples in a cavity by Nd:YAG laser at 0.94 micrometer. The pumping intensity was 105 divided by 106 W/cm2, stored energy density, 1 - 2 J/cm3. For Yb:YAG simultaneous oscillations have been produced at transitions near 1.03 and 1.05 micrometer. The spectral width for both bands reached 3 nm. There was established a competitive character of lasing at these transitions displayed in opposite amplitude modulation of the corresponding oscillation envelopes. The laser spectrum transformation using the interconnection of 1.03 and 1.05 micrometer transitions is discussed. When pumping the Yb-doped silicate glass there were registered the spectra near 1.03, 1.04 and 1.06 micrometer with the total width over 40 nm. A method of the laser spectrum transformation based on the stored energy transfer over inhomogeneously broadened emission line is proposed for Yb glasses. The expected range of the spectrum transformation makes several tens of nm, the transfer rate 103 - 104s-1. The obtained results are of interest for the creation of pulse-repetitive laser sources with the spectrum varying from shot to shot.

Flashlamp-pumped Yb-laser for an average-power operation

An Yb,Nd-doped flashlamp pumped crystal laser for an average-power operation is discussed. Excitation transfers from Nd3+ to Yb3+ ions in garnet offer stored energies near 1 J/cm3, pulse repetition rate of 1 Hz.

Smoothing of the inversion profile in Nd- and Yb-doped solid state laser elements

In connection with an elaboration of selective pumping techniques for solid-state laser-drivers a stored energy formation in solid state media under absorption of a narrow-band pumping radiation has been considered. The calculations demonstrate the possibility of the inversion profile smoothing in the slab-like Nd- and Yb-doped active elements pumped from excited levels of activators or sensitizers ions. A possibility of the Nd:glass and iodine lasers usage to carry out modelling experiments on selective pumping at several kJ energy level is discussed.