The influence of transverse mode locking in critical cavity configurations on the threshold pump power of diode end-pumped solid-state lasers was investigated both theoretically and experimentally for the large portion of the cavity stability region. An experimental study was performed for lasers based on Nd:YLF, Nd:YVO 4 , Nd:GdVO 4 and Nd:KGW crystals.

We describe a compact dual-wavelength (1.047 and 1.053 µm) diode end-pumped Q-switched Nd:YLE laser source which has a number of applications in demand. In order to achieve its dual-wavelength operation it is suggested for the first time to use essentially nonmonotonous dependences of the threshold pump powers at these wavelengths on the cavity length in the region of the cavity semiconfocal configuration under a radius of the pump beam smaller than the radius of the zero Gaussian mode. Here we demonstrate one of the most interesting applications for this laser: difference frequency generation in a GaSe crystal at a frequency of 1.64 THz. A superconducting hot-electron bolometer is used to detect the THz power generated and to measure its pulse characteristics.

Transverse mode locking in a diode end-pumped Nd:YAG laser with up to approximately 140 cm resonator length was investigated. It was found that for each resonator degeneracy, there are two degenerate lengths where the fundamental mode is very different from the Gaussian mode. Fundamental mode intensity patterns for these lengths expand in directions perpendicular to each other. Experimental results are in a good agreement with numerical calculations, taking into account active medium (AM) astigmatism and inhomogeneous gain. Optical powers of astigmatic AM can be found directly from measurements of degenerate lengths without using numerical modeling.

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We present modification of difference frequency generator of coherent THz radiation in a nonlinear GaSe crystal using dualwavelength diode-pumped solid-state Nd:YLF laser. Generation at the two wavelengths (1.047 and 1.053 μm) was carried out by equalization of the gains at these wavelengths near the frequency degeneracy of the transverse modes in resonator cavity, Qswitched by acousto-optical modulator. The main parameters of the device were measured: angular synchronism (width 0.6 degrees), polarization ratio (1:100), conversion efficiency (10 -7 ), pulse power (0.8 mW), frequency and width (53,8 сm -1 , 0,6 сm -1 ), pulse width and repetition rate (10 ns ,7 kHz). The method is promising for practical purposes.