A defunct technology of lead tungstate (PbWO4, PWO) crystal growth was re-established and improved at Crytur. It has been discovered that key to crystal quality is pretreatment of raw material and double crystallization, although time consuming, but very effective in optimizing the final product. Several important technological advances have been made to be able to industrialize and scale up the crystal production for the needs of the large-scale physics experiments. These crystals have been evaluated at the Jefferson Accelerator facility in Newport News, VA, and found to meet the stringent requirements of the future detectors for EIC, unlike PWO crystals grown by different methods by other suppliers. Comparison of the crystal performance conducted by JLAB will be shown.
Ho-doped yttrium aluminum perovskite Ho:YAP (Ho:YAlO3) is a promising material for the construction of high-power lasers, operating in 2.1 µm spectral region. We present the dependencies of key spectroscopic properties on Ho-doping concentration and on Ho:YAP crystal orientation. Three Ho:YAP crystals with various Ho-doping concentrations were grown by Czochralski method: 0.26 at.% Ho/Y, 0.45 at.% Ho/Y, 1.05 at.% Ho/Y. The uncoated samples were prepared in the form of polished wafers 2.8 mm thick with diameter up to 45 mm and in the form of an oriented cuboid (6 x 7 x 8mm). The detailed polarization resolved absorption spectra were measured with a high resolution in the range from 300 up to 6500 nm. The polarization resolved emission spectra were investigated in the range from 500 up to 3500 nm. The 5I7 upper-laser-level lifetime was measured using a confocal method. From the obtained data, the absorption cross-sections in all investigated spectral ranges were determined and the Judd-Ofelt analysis was performed. It was found that the Ho-doping concentration significantly influenced mainly the upper 5I7 laser level lifetime, which drops from 5.8 ms for the lowest doping to 4.7 ms for the highest tested Ho-doping. Using the oriented Ho:YAP cuboid (1.05 at.% Ho/Y), laser emission reaching the quantum limit under Tm-fibre excitation (1939 nm) was reached. By an appropriate choice of the Ho:YAP crystal orientation and reflectance of the laser output coupler, it was possible to achieve laser action at wavelengths of 2083, 2102, 2118, and 2130 nm, or to generate laser radiation at several wavelengths simultaneously.
Lasing of Tm3+-doped yttrium aluminum perovskite (Tm:YAlO3) microchip laser was investigated. A novel 1.7 μm in-band diode pumping was compared with traditional 0.8 μm pumping of thulium-doped lasers. The sample was b-cut (Pbnm) cylindrical microchip, 5 mm in length and 3 mm in diameter, with its planar surfaces polished and coated: HT for pumping wavelengths (T < 95 % at 1690 nm, T < 95% at 790 nm) and HR R < 99.8 % at 1900–2050 nm at the pumping end and R=97.5–98.5 % at 1900–2050 nm at the output end. The doping concentration was 4 at.% (Tm/Y). The sample was wrapped in an indium foil and held in a water-cooled (11°C) copper holder. For both pumping wavelengths, the sample was longitudinally pumped using a fiber (core diameter 400 μm, NA=0.22) coupled laser diode operating in QCW (25% duty cycle) and CW regime. Under the 1.7 μm diode (delivering up to 30 W at 1680 nm) pumping, obtained slope efficiency (with respect to absorbed power) was 57%. The highest obtained output power amplitude was 14.4 W in QCW and 9.4 W in CW. Under the 0.8 μm diode (delivering up to 20 W at 793 nm) pumping, obtained slope efficiency (with respect to absorbed power) was 58%. The highest obtained output power amplitude was 6.6 W in QCW and 6.9 W in CW. Laser emitted at 1988 nm under all pumping regimes.
We present the dependence of the main spectroscopic properties of Ho:YAG on Ho doping contraction estimated at room temperature. Five Ho:YAG crystals with various Ho-doping concentrations were grown by Czochralski method: 0.34 at.% Ho/Y, 0.51 at.% Ho/Y, 0.90 at.% Ho/Y, 1.61 at.% Ho/Y, and 1.98 at.% Ho/Y. Detailed absorption spectra with high resolution were measured in the range from 185 up to 6500 nm. The emission spectra were measured in the range from 500 up to 3500 nm under excitation in UV (450 nm) and IR (1862 nm) range. The 5I7 upper-laser-level lifetime was measured using the confocal method. From the measured transmission data, the absorption cross-sections in all investigated spectral ranges were determined. Using the absorption spectrum data, the Judd-Ofelt analysis was performed to reach nett spontaneous radiative lifetime of the 5I7 level. Based on these data and measured fluorescence spectra, the emission cross-sections for 2.1 μm laser band were determined together with non-radiative relaxation rates. It was found that the Ho-doping concentration significantly influenced mainly the upper laser level lifetime, which drops from 7 ms for the lowest doping to 5.8 ms for the highly doped Ho:YAG sample.
Crytur is a company with long tradition of growing and processing crystals for technical applications, with history reaching back to 1943. Recently we have developed Crystal Improved Growth (CRIG) method for production of large core-free single crystals of YAG. The diameter currently achieved is 140 mm (in case of undoped crystal), and the crystal weight is up to 10 kg. The method was used to grow un-doped YAG crystals, YAG:Ce crystals for large scintillating screens, and Yb:YAG and Nd:YAG for high power solid-state laser systems.
Large laser slabs were manufactured from Yb:YAG doped crystals for Diode-Pumped Solid State Laser (DPSSL) system Amos, which operates within Extreme Light Infrastructure in the Czech republic (ELI Beamlines). The dimension of the largest Yb:YAG laser slab produced is 120×120×8 mm, there is no visible stress under crossed polarizers and the wavefront distortion in the clear aperture region is smaller than λ/10 (λ=633 nm) in its Peak-to-Valley value. The edges of the slab are from diffusively bonded Cr:YAG cladding in order to suppress ASE (Amplified Spontaneous Emission).
In 2018 the performance of three sets of laser slabs (ø55x5 mm) with differently realized ASE suppression was characterized at cryogenic temperatures at HiLASE Centre in terms of small signal gain measurements as well as amplification test under 30 J pumping at 1 Hz and 10 Hz repetition rates. We provide data that show that the crystal slabs have comparable properties to the ceramic slabs (produced by Konoshima company, Japan) currently in use at HiLASE.