S M Vatnik

Efficient thin-disk Tm-laser operation based on Tm:KLu(WO 4 ) 2 /KLu(WO 4 ) 2 epitaxies

A diode-pumped thin-disk laser based on Tm:KLu(WO4)2/KLu(WO4)2 epitaxies is realized. The emission is in the 1850-1945 nm spectral range for Tm-doping between 5 and 15 at. %. The maximum slope efficiency of 47% with respect to the absorbed power obtained with 5 at. % Tm:KLu(WO4)2/KLu(WO4)2 corresponds to a maximum output power of ~6 W in cw operation.

Thermal lensing in Nm-cut monoclinic Tm:KLu(WO4)2 laser crystal

The thermal lensing effect is characterized in slab-shaped monoclinic Tm:KLu(WO4)2 crystal cut for light propagation along the Nm optical indicatrix axis (the light polarization is E???Np). The optical power of the thermal lens was measured directly by a modified probe beam technique. Alternatively, it was calculated on the basis of measured material parameters, including the thermal expansion coefficients along the optical indicatrix axes (?p?=?3.1, ?m?=?11.1 and ?g?=?13.1(10?6?K?1)) and the principal thermo-optic coefficients (dnp/dT?=??13.3, dnm/dT?=??5.9, dng/dT?=??9.0(10?6?K?1) at 1.95??m). The two methods are in good agreement and confirm the defocusing action of the thermal lens; the ?effective? thermo-optic coefficient ? for Nm-cut crystal is ?2.1???0.5???10?6?K?1. The fractional head load ?h for slab-shaped Tm:KLu(WO4)2 crystal is 0.33???0.03 (as determined from ISO-standard laser calorimetry).

Quasi-continuous wave and continuous wave laser operation of Eu:KGd(WO4)2 crystal on a 5D0 → 7F4 transition

We report on the first demonstration of quasi-continuous wave (quasi-CW) and real CW room-temperature lasing on the 5D0 → 7F4 transition of Eu3+-doped material using a 25 at.%Eu3+ : KGd(WO4)2 crystal pumped into the 7F1 → 5D1 transition by a diode-end-pumped Nd3+ : KGd(WO4)2/KTP green laser at 533.6 nm. The maximum CW output power of this laser at 702.3 nm is 5.3 mW with 1.4% green-to-red conversion efficiency. In quasi-CW operation mode with a 10% duty cycle, the peak power of ms long pulses reaches ~54 mW, which corresponds to the optical conversion efficiency of 3.5%.

Laser operation and computation of thermal stress in endpumped 1.1 at.% Nd-doped yttrium aluminium garnet rods with sub-millimetre diameters

Laser operation of a fibre-like 1.1 at.% Nd-doped yttrium aluminium garnet rod with a diameter of 0.34 mm and a length of 4.7 mm has been demonstrated. The fibre was end pumped with 0.5 W of continuous-wave radiation from a laser diode emitting at 808 nm. The measured laser thresholds are in a reasonable agreement with theoretical estimations. The distributions of temperature and stress in the crystal fibre were calculated with finite-element simulations showing that the fibre can be pumped up to a power of 40–50 W without fracture caused by thermal stress. The advantages and disadvantages of the proposed laser rod design are discussed.

Red Eu,Yb:KY(WO4)2 laser at ~702 nm

In this letter, laser operation is demonstrated with a Eu,Yb: KY(WO4)2 crystal on the 5D0 → 7F4 transition of the Eu3+ ion. When pumping into the 7F1 → 5D1 absorption band by a diode-pumped Nd3+:KGd(WO4)2/KTP laser power-scaled at 533.6 nm up to a watt-level, we achieved 2.5 mW of the continuous wave (CW) red output at ~702.1 nm. At quasi-CW pumping with a duty cycle of 10%, the peak power of the ms-long pulses arrived at ~19 mW, corresponding to a green-to-red conversion efficiency of 0.8%.

Crystal growth, characterization and thin disk laser operation of KLu1−xTmx(WO4)2/KLu(WO4)2 epitaxial layers

Epitaxial samples of KLu1−xTmx(WO4)2/KLu(WO4)2 (x up to 0.15) have been obtained by the Liquid Phase Epitaxy (LPE) method. The lattice mismatch between the epitaxial layer and the substrate is small enough to allow the growth of good quality, well-oriented, single crystalline epilayers as evidenced by the 2θ scan of the (0k0) reflections and the rocking curve of the (040) reflection. Electron probe microanalysis shows an increase of 1021Tm3+ at cm−3 in a 2.5 μm interval at the substrate/layer interface. The main morphologies observed in the epilayers are steps and growth spirals. The laser operation around 2 μm, realized with epitaxial layers of 15 at% Tm doping and three different thicknesses, in a thin disk laser configuration with only two pump passes through the epitaxial layer, demonstrates maximum average output power as high as ∼1.4 W corresponding to a slope efficiency of 40%.

Synthesis of ceramic active Nd:YAG laser medium

The research results on the synthesis of highly transparent YAG ceramics and the generation of radiation in samples are reported. The possibilities of the synthesis of highly transparent ceramics from nanopowders in the garnet stoichiometry (Nd3+:Y3Al5O12) and a mixture of nanopowders (Nd3+:Y2O3, Al2O3) are studied. Data on phase transformations in compacts fabricated from both types of nanopowder obtained from results of calorimetric and X-ray analyses are presented. It is shown that a higher transparency (∼83%) is achieved in samples synthesized from a mixture of powders. According to the optical microscopy of the extinction centers in ceramics, it is established that a lower transparency compared to the theoretical one (83.8%) is caused by the dispersion by pores that appears near large agglomerates of particles. Experimental results on continuous lasing at the 1.064-μm wavelength with a power of 3.8 W and a slope efficiency of 19.1% in the ceramic sample with the best transparency are reported.

Fabrication and Properties of Neodymium-Activated Yttrium Oxide Optical Ceramics

About new technology of production of transparent ceramics including laser synthesis of nanopowders, their magnetic pulsed compaction and vacuum sintering is reported. The results of investigations of the synthesized samples of transparent ceramics made from neodymium-activated yttrium oxide are presented. It has been shown that in a 1.1 mm thickness sample with optical loss coefficient α1.07μm = 0.03 cm−1 laser generation at λg ∼ 1.08 μm with a slope efficiency of 15% at laser diode pumping at a wavelength of 807 nm has been obtained.

Highly efficient Ho:KY(WO4)2 thin-disk lasers at 2.06 µm

The recent advances in the development of Holmium monoclinic double tungstate thin-disk lasers are reviewed. The thin-disk is based on a 250-μm-thick 3 at. % Ho:KY(WO4)2 active layer grown on a (010)-oriented KY(WO4)2 substrate. When pumped by a Tm-fiber laser at 1960 nm with a single-bounce pump geometry, the continuous-wave Ho:KY(WO4)2 thin-disk laser generates an output power of 1.01 W at 2057 nm corresponding to a slope efficiency η of 60% and a laser threshold of only 0.15 W. The thin-disk laser is passively Q-switched with a GaSb-based quantum-well semiconductor saturable absorber mirror. In this regime, it generates an average output power of 0.551 W at ~2056 nm with η = 44%. The best pulse characteristics are 4.1 μJ / 201 ns at a repetition rate of 135 kHz. The laser performance, beam quality and thermo-optic aberrations of such lasers are strongly affected by the Ho3+ doping concentration. For the 3 at.% Ho3+-doped thin-disk, the thermal lens is negative (the sensitivity factors for the two principal meridional planes are -1.7 and -0.6 m-1/W) and astigmatic. The Ho:KY(WO4)2 epitaxial structures are promising as active elements in mode-locked thin-disk lasers at ~2060 nm.

Holmium thin-disk laser at 2056 nm based on Ho:KYW/KYW epitaxy

Tm-doped monoclinic double tungstate crystals, KRE(WO<inf>4</inf>)<inf>2</inf> or shortly KREW, are suitable for efficient multi-watt thin-disk lasers emitting at ∼1.9 μm [1] due to the high available doping levels and high transition cross-sections of the Tm³+ ions. Holmium (Ho³⁺) ions are attractive for laser emission above 2 μm due to the ⁵I<inf>6</inf> ↔⁵I<inf>8</inf> transition which is of interest for medical applications. KREW crystals are very suitable for Ho³⁺ doping [2] as well and efficient inband-pumped bulk Ho:KREW lasers have been demonstrated [3]. In the present work, we report on the first Ho:KREW thin-disk laser.