D. A. Nikolaev

Down-conversion in ytterbium-doped NaGd(MoO4)2 crystals

A series of NaGd(MoO4)2 single crystals doped with various Yb3+ concentrations (from 0.5 to 30 at %) is grown. The optical absorption spectra of the crystals are measured within the range from 800 to 1200 nm and used to calculate the actual concentrations of Yb in the samples. The luminescence of crystals is studied under UV excitation. It is found that there exist two types of active centers that are not directly related to Yb3+ ions and exhibit broadband luminescence in the visible spectral region. In addition, UV excitation of crystal gives rise to Yb3+ luminescence in the region of 1 μm owing to nonradiative excited-state energy transfer from, probably, donor centers of the host to ytterbium. The character of the dependence of the UV-excited luminescence of Yb on its concentration in the samples, in comparison with the corresponding dependence measured under IR excitation, points to the occurrence of cooperative down-conversion in crystals with high ytterbium concentrations, which means that the excited-state energy of donors is simultaneously transferred to two Yb3+ ions. In other words, excitations are multiplied; i.e., the quantum yield of this down-conversion exceeds unity.

Efficiency of stone fragmentation by long pulses of a Q-switched Nd:YAG laser

The effect of long pulsed Nd:YAG laser (pulse duration 300 ns) with the fundamental and second harmonic wavelength on the fragmentation of different urological and gall stones has been investigated. With 200 and 400 micrometers fibers in a contact application, all types of stones could be fragmented with energies less than 120 mJ (400 micrometers fiber) or 45 mJ (200 micrometers fiber). By use of a double pulse-simultaneous application of second harmonic and fundamental radiation the efficiency of fragmentation could be increased and the energy threshold decreased.

Nd3+:GGG and Cr4+:GGG epitaxial films for neodymium lasers

An efficient technology was developed for growing the gadolinium gallium garnet (GGG) single-crystal films doped with Nd3+ or Cr and Ca ions. The films with thickness up to 100 µm have been grown by liquid-phase epitaxy method on undoped GGG substrates of small and big sizes (5–8 mm and up to 76 mm in diameter, respectively). The dependence of absorption, luminescence spectra and optical losses at the wavelength of 1 µm on growth temperature and melt-solution composition was studied. We demonstrated that Cr4+ centers have been implemented in epitaxial films and these films may be used as passive Q-switches for laser systems.

Comparative performance of infrared solid state lasers in laser lithotripsy

This paper describes the experimental investigation of the fragmentation processes of urinary stones by Cr,Nd:YSGG laser radiation (2.79 micrometers ). The laser operated in a pulse free-running regime with the pulse energy up to 1 J and pulse duration of 250-550 micrometers . It was shown that about 3 kJ of total radiation energy was required in order to ablate 1 g of urinary calculus. In those conditions, the stone substance was broken in a small fibrous-like dust. The maximum size of particles did not exceed 0.2-0.4 mm. The qualitative comparison of the stone ablation efficiency for the Cr,Er:YSGG laser, Cr,Nd:YSGG laser (1.06 micrometers ), and Cr,Tm,Ho:YSGG laser (2.09 micrometers ) was carried out.

Nd:GGG disk laser with coherent beam combining in Talbot laser cavity at multi beam diode pumping

The use of thin disk active elements [1] leads to essential decrease in negative influence of the thermal distortions on the output parameters of solid-state lasers. We may increase the output power from the single disk without suffering from thermal distortion while using the multi beam pumping. The purpose of our work was the realization of phase synchronization of several laser channels with a cavity utilizing Talbot effect.

Degenerated configuration of disk laser cavity at multi beam diode pumping

Application of active disks reduces thermally induced optical effects in powerful solid-state lasers significantly [1]. The next step to improve the quality of output laser emission together with increasing of the output power may be done while using multi beam pumping and degenerate laser cavity configuration [2]. The resonator should be designed to cover in series of all the pumped areas in the active disk with intracavity beam [2].

Transparent Cr:LiGaSiO 4 nano-glass-ceramics as the promising laser material

The fabrication technology of transparent Cr:LiGaSiO4 nano-glass-ceramics was optimized after the investigation of the crystallization dynamics of Cr-Li-Ga-Si-O precursors. The samples with increased Cr4+ content are obtained.

Study of heat release in Yb:GGG crystals with various Yb3+ ion concentrations using laser diode pumping

Heat release in Yb:GGG crystals with various Yb3+ ion concentrations was studied depending on the absorbed power of laser diode pumping. Initially, the heat release in Yb:GGG samples under study significantly (by a factor of 2–4) exceeded theoretically expected values. Additional annealing of samples in an oxygen atmosphere made it possible to significantly decrease the heat release in crystals to the theoretically expected value. Thus, it was shown that one of the major causes of the increased heat release in Yb:GGG crystals can be the presence of color centers in them.

Temperature distribution in disk active elements of lasers with longitudinal diode pumping

Experimental and computational data for determination of temperature profile in the region of crystalline laser disk pumping are presented. The analytical relations obtained link the values of temperature, pumping spot radius, and disk thickness and allow optimization of these parameters in the choice of laser construction. Good agreement between computational and experimental results is demonstrated on an example of an Nd:YVO4 crystal disk active element.

The growth and characterization of Nd:GGG and Cr/sup 4+/:GGG epitaxial films for solid-state lasers

Optically pumped solid-state lasers can benefit in a number of applications when using the waveguiding geometry in which pumping emission and lasing modes overlap well and pumping density is high. This paper presents the results of investigations of the gadolinium-gallium garnet (GGG) films grown by liquid phase epitaxy (LPE) method. We have studied spectral and lasing characteristics of the epilayers and the growing conditions influence to the film properties. Samples of epitaxial films of different composition starting from pure (undoped) GGG and then doped with Nd or Cr ions (with Mg or Ca codoping) were grown by LPE technique with 12-25 /spl mu/m thickness and 76 mm in diameter.