Recent progress in single-crystal Fe:CdTe lasers

We present our recent results obtained with single-crystal Fe:CdTe lasers. In particular, different pumping schemes and operation temperatures are investigated. Our high-quality Fe:CdTe single-crystal has been grown using the physical vaportransport technology with simultaneous Fe²⁺-ions doping. When pumped by 40-ns pulses from a Q-switched Er:YAG laser at 2.94 μm, the Fe:CdTe laser produces up to 2 mJ of output energy at room temperature (RT), with a slope efficiency of 16 %. A spectral tunability in the range of 5.1–6.3 μm is achieved. The lifetime of the upper laser level is measured to be 530 ns at RT. When using a 4.1-μm Fe:ZnSe laser (40-ns pulses) as a pump source instead of Er:YAG, the efficiency of the Fe:CdTe laser is increased to 30 % and we obtain an output energy of 5.8 mJ at RT. Furthermore, a record 2300-nm smooth and continuous wavelength tunability over 4.5–6.8 μm is achieved. With the latter system we demonstrate the first application of the Fe:CdTe laser to intracavity absorption spectroscopy. The experimental spectrum of atmospheric H₂O shows good agreement with a calculated spectrum from the HITRAN database. The obtained sensitivity corresponds to an effective absorption path length L_eff = 10 m, being limited only by the laser-pulse duration. However, by applying longer pump-pulses, the sensitivity can be enhanced by up to seven orders of magnitude, thus enabling extremely sensitive spectroscopic measurements. Furthermore, an energy up-scaling of the laser output is demonstrated at 77 K. The increased upper-state lifetime of 68 μs facilitates pumping by 250-μs pulses of a 4.1-μm Fe:ZnSe laser, and our Fe:CdTe laser produces a record-output of 0.35 J at 77K, with a slope efficiency of 44 %.