The use of Fe:ZnSe polycrystals as passive Q-switches for the Er:Cr:YSGG laser operating at 2.8&mgr;m is introduced.
Fe:ZnSe samples with 1-7cm-1 coefficients of absorption were prepared using thermal diffusion of iron in CVD grown
polycrystalline ZnSe. A flashlamp pumped Er:Cr:YSGG laser with a variable (40 - 80% reflectivity) output coupler (OC)
was used as a test bed for passive Q-switching. Using a 90% initial transmission Fe:ZnSe placed at the Brewster angle
we obtained a single giant pulse lasing with a pulse duration of ~65 ns and a maximum output of 13 mJ under 30 J of
flashlamp pump. Multi-pulse (19 pulses) output was obtained with 85 mJ total output energy at a pump energy of 30 J.
The saturation curve of Fe:ZnSe was measured. Fitting this data with a theoretical model results in absorption crosssection
of 0.56 × 10-18 cm2, which is close to the value of the absorption cross-section obtained from spectroscopic
measurements (0.85 × 10-18 cm2 at 2.8 &mgr;m).
Absorption and luminescence properties of Fe:ZnSe and Fe:Cr:ZnSe crystals in the middle infrared spectral range were studied at room and low temperatures. Room temperature emission cross section of 5T2->5E transmission of iron ions was estimated from spectroscopic measurements. Middle infrared emission of Fe2+ in ZnSe was studied under three different regimes of excitation: direct optical (2.92 μm) excitation of 5T2 first excited state of Fe2+, excitation via 5E level of Cr co-dopant (1.56 μm), and excitation via photo-ionization transition of Fe2+ (0.532 μm). For the first time the energy transfer from Cr2+ (5E level) to Fe2+ (5T2 level) under 1.56 μm wavelength excitation was observed and resulted in simultaneous room temperature emission of Fe:Cr:ZnSe crystal over ultra-broadband spectral range of 2-3 and 3.5-5 μm. We also report the first observation of middle infrared emission at 4.5 μm induced by 2+->3+->2+ ionization transitions of iron ions in Fe2+:ZnSe. The first room temperature gain-switched lasing of Fe:ZnSe crystal at 4.4 μm wavelength was demonstrated. Room temperature tunable oscillation of Fe:ZnSe crystal over 3.9-4.8 μm spectral range was realized.
We report the study of middle-infrared electroluminescence of n-type, Cr doped bulk ZnSe crystals. n-type, Cr-doped
ZnSe samples were prepared in three stages. At the first stage, the undoped polycrystalline ZnSe samples were grown
by chemical vapor deposition. During the second stage, the doping of 1 mm thick ZnSe polycrystalline wafers was
performed by post-growth thermal diffusion of Cr. Finally, Cr:ZnSe wafers were annealed with Al2Se3 and ZnSe
powders in sealed vacuumed ampoules at 950°C for 96 hours. Comparison of the absorption spectra of the crystals
before and after thermal diffusion with Aluminum indicates the preservation of the desired Cr2+ ions. Ohmic contacts
for electrical measurements were formed by polishing the facets and wetting the surface of the crystals with In. The best
crystals demonstrated conductivity of up to 10-100 ohm*cm. The electroluminescence measurements were taken using
synchronous detection methods with an InSb detector. A pulse generator output (100V) at 5 kHz and a lock-in amplifier
were used to distinguish luminescence signals from other possible noise sources. We report the observation of middleinfrared
(2-3μm and 8μm) and visible (~600 nm) electroluminescence of n-type Cr doped bulk ZnSe crystals.
An efficient room temperature all-solid-state laser system continuously tunable in the 0.2 - 10 micrometers spectral range has been developed. It is based on the alexandrite laser pumped LiF:F2+** color center laser system. The alexandrite - LiF:F2+** color center laser combination system has been shown to be a suitable drive source for a number of efficient nonlinear processes, including harmonic, sum-frequency and difference-frequency generation.