Andrew Gallian

3.9–4.8 μm gain-switched lasing of Fe:ZnSe at room temperature

We report a room temperature Fe:ZnSe laser in gain-switched operation and tuning over the 3.9 - 4.8microm spectral range. Mid-IR emission of Fe2+:ZnSe was studied under three regimes of excitation: ordinary optical (2.92mum) excitation of 5T2 excited state of Fe2+; excitation via 5E level of Cr co-dopant (1.56mum); and excitation via photo-ionization transition of Fe2+ (0.532mum). The energy transfer from Cr2+ (5E level) to Fe2+ (5T2 level) under 1.56microm wavelength excitation was observed and resulted in simultaneous RT emission of Fe:Cr:ZnSe crystal over ultra-broadband spectral range of 2- 3 and 3.5-5mum. We also report the observation of mid-IR emission at 3.5- 5mum induced by 2+->3+->2+ ionization transitions of the iron ions in Fe:ZnSe.

Hot-pressed ceramic Cr(2+):ZnSe gain-switched laser.

The technology of hot-pressed Cr(2+):ZnSe ceramic preparation is reported. Comparative gain-switched lasing of hot-pressed ceramic and CVD grown Cr(2+):ZnSe samples with slope efficiencies up to 10% and output energies up to 2 mJ were demonstrated. This is a milestone in the development of future large scale mid-IR laser systems based on ceramic TM(2+):II-VI materials. This evolving technology has excellent potential as media for practical low cost, high power mid-IR laser applications.

Spectroscopic studies of molecular-beam epitaxially grown Cr2+-doped ZnSe thin films

Cr:ZnSe thin films were grown by molecular-beam epitaxy with the long-term goal of demonstrating a route for the development of transitional-metal-doped semiconductor lasers. Photoluminescence (PL) and PL lifetime measurements of doped thin films and bulk crystals indicate that Cr is incorporated in the optically active Cr2+ state up to levels of 5×1019cm−3. The shape of PL spectra and lifetime measurements of doped thin films compares favorably with that reported for bulk samples. A microcavity formed by film interfaces is responsible for differences in spontaneous emission observed between films and bulk crystals.

Middle-infrared electroluminescence of n-type Cr-doped ZnSe crystals

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.

Fe:ZnSe passive Q-switching of 2.8-μm Er:Cr:YSGG laser cavity

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).

Mid-Infrared Electroluminescence of Cr2+ Ions in ZnSe Crystals

We report the first observation of the room-temperature middle-infrared electroluminescence of n-type Cr doped bulk ZnSe crystals in the spectral range of 1800-2800 nm.

3.9-4.8μm gain-switched lasing of Fe:ZnSe at room temperature

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.

All solid state laser system, continuously tunable over 0.2-10 micron spectral range

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.

MBE GROWTH AND STUDY OF Cr2+:ZnSe LAYERS FOR MID-IR LASERS

MBE growth and photoluminescence study of thin films and bulk Cr2+:ZnSe are reported. We show that MBE provides optically active chromium in ZnSe and is viable for fabrication of optically and electrically pumped laser structures.

Parametrically amplified room temperature 4.3–4.7 μm gain-switched Fe:ZnSe laser

Parametric amplification of a 4.3-4.7 mum microchip gain-switched Fe:ZnSe laser radiation is reported. As an amplifier medium, we have used a 2.92-mum-pumped OPA based on ZGP crystal. The single-pass amplification factor of 2 was achieved.