Tunable Cr3+ lasers belong to the family of transition-metal vibronic lasers that includes Ni2+, Co2+, and V2+ doped in crystalline hosts such as MgF2, MnF2, ZnF2, and KMgF3, the Ti:Al2O3 crystalline host, or colquiriites (summarized in several publications1,2). These lasers exhibit broadband emission spectra, a relatively long lifetime of the upper lasing level, low nonlinear refractive indices, low thermal lensing, and low excited-state absorption. These characteristics make the transition-metal vibronic lasers unique sources for tunable lasers, capable of producing ultrashort pulses. Some of these lasers operate both in CW or pulsed operating modes, and over a wide temperature range-from ambient to cryogenic temperatures. This chapter mainly describes Cr3+-doped single crystals of the colquiriite fluoride family of the form LiAMF6 (A = Ca, Sr and M = Al, Ga, Cr). These Cr3+- doped crystalline lasers are efficient tunable solid state lasers; they can be operated in various configurations and geometries such as laser rods, a multipass zigzag slab, and in an oscillator-amplifier configuration. The systems are pumped either by a flashlamp or by visible AlGaInP diode lasers, with various geometries (transverse or longitudinal pumping). The pumping is usually at a wavelength of ~670 nm into the 4A2 → 4T2 absorption band of Cr3+.
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