D. V. Badikov

Optical properties of thallium mercury iodide

We investigated the growth conditions and obtained Tl4HgI6 nonlinear crystals of red and black phases. We also measured the dispersion of the black-phase crystal refractive indices and analyzed possible nonlinear three-frequency processes.

Laser action in bulk Cr:ZnSe crystals

Cr:ZnSe laser active material is one of the favourite possibility how to generate broadly tunable mid-infrared laser radiation at room-temperature. The aim of this study was to demonstrate and analyze pulsed as well as continuous-wave laser action in bulk Cr:ZnSe crystals grown by the floating-zone method or by the Bridgman method. The absorption spectra of Cr:ZnSe were measured to be from 1500 to 2000 nm, therefore various lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1658 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm), and diodepumped Tm:YAP laser (generated wavelength 1980 nm). In the first case, the Cr:ZnSe crystal grown by the Bridgman method was investigated. In the second case, the Cr:ZnSe crystal grown by the floating zone method was studied. In both cases, the homogeneity of the active Cr:ZnSe crystals was found reasonable good. The emission spectrum was from 2000 up to 2800 nm. The Cr:ZnSe laser generated radiation was broadly continuously tunable in the range from 2050 nm up to 2750 nm. The generated radiation beam spatial structure was close to TEM00.

Mid-infrared tunable laser based on the Cr:ZnSe active crystal

Broadly tunable mid-infrared laser sources operated at room-temperature are desired in many technological and medical applications. The aim of the project was to design and construct broadly tunable powerful Cr:ZnSe laser. The investigated Cr:ZnSe various shaped bulk crystals were grown by the Bridgman method or by the floating zone method. The absorption spectrum was measured to be from 1500 to 2000 nm and the emission spectrum was from 2100 to 2800 nm. Three different lasers were utilized for coherent longitudinal pumping of Cr:ZnSe laser, namely flashlamp-pumped Er:YAP laser (generated wavelength 1660 nm), diode-pumped Tm:YLF laser (generated wavelength 1912 nm) and diode-pumped Tm:YAP laser (generated wavelength 1980 nm). The constructed Cr:ZnSe laser operated in pulsed as well as in continuous-wave regime. In the first case the Cr:ZnSe crystal grown by the floating zone method was studied. The maximal output power in continuous-wave regime was 310 mW with the slope-efficiency 73% for the Tm:YAP laser pumping. In the second case the Cr:ZnSe prism grown by the Bridgman method which served simultaneously as laser active medium and intracavity dispersive element was investigated. For the Er:YAP laser pumping the maximal output energy was 20 mJ with the slope-efficiency 36%. The output radiation was tunable in the range from 2050 nm up to 2750 nm. For the Tm:YAP laser pumping the maximal output power in continuous-wave regime was 175 mW with the slope-efficiency 24%. The output radiation was tunable in the interval from 2220 nm up to 2680 nm. The generated radiation beam spatial structure was close to TEM00.

Some new approaches for development of mid-IR laser sources

Stimulated Raman scattering (SRS) in BaWO4 crystal under 1.56 μm pumping was investigated. Several (up to fourth) Stokes components were observed. Mid IR spectral range 2.75 µm and 3.7 μm radiation was obtained using BaWO4 crystalline Raman shifter. Under 1.318 μm pumping 4.3 μm and 4.7 μm oscillations in low phonon PbGa2S4:Dy3+ laser were obtained.

Cr:ZnSe laser pumped with Tm:YAP microchip laser

Cr:ZnSe laser coherently longitudinally pumped with Tm:YAP microchip laser was realised. The pumping laser consisted of Tm:YAP crystal (3x3 mm) with resonator mirrors deposited directly on its faces (on rear face the dielectric layer with high reflectance for 1998 nm wavelength and high transmittance for 790 nm pumping radiation wavelength; on output face the dielectric layer with reflectance 97% at 1998 nm wavelength). The maximal output power was 5.5 W and the generated radiation wavelength was 1998 nm. The main advantage of this pumping was stable and still output without relaxation spikes (non-spiking). The Tm:YAP laser radiation was collimated and focused by the set of two CaF2 lenses. The pumping beam spot diameter inside the Cr:ZnSe crystal was 300 μm. The Cr:ZnSe laser resonator consisted of flat rear mirror (HT at 1998 nm and HR at 2100 - 2900 nm) and curved output coupler (r = -150 mm, R = 95% at 2100 - 2700 nm). The maximal output energy of stable radiation was 4 mJ (pulse duration 10 ms, repetition rate 10 Hz). For wavelength tuning the Lyott filter (quartz plate under Brewster angle) was placed between the Cr:ZnSe crystal and output coupler. The generated radiation wavelength was continuously tunable from 2246 - 2650 nm.

Qualitative improvement in the lasing performance of PbGa{sub 2}S{sub 4} : Dy{sup 3+} crystals through Na{sup +} doping

We have studied the lasing properties of lead thiogallate crystals codoped with dysprosium and sodium ions. Sodium doping has been shown to have an advantageous effect on the optical and lasing properties of lead thiogallate crystals. At a pump pulse duration of 1.5 ms, output pulse energies up to 15 mJ have been obtained at a slope efficiency of up to 4%. Cascade lasing on two Dy3+ transitions, at 4.3, 4.5, 4.65, 5.2, 5.3 and 5.4 μm, has been demonstrated.

Dysprosium Doped Lead Thiogallate Laser

By Er:YAP 1.66 μm laser resonant pumping of Dy3+:PbGa2S4laser was investigated and compared with non-resonant Nd:YAG 1.32 μm one. The maximum energy obtained was 57 μJ with only negligible influence of the atmosphere.