Dy-doped KPb₂Cl₅ and PbGa₂S₄ lasers for N₂O sensing at stand-off in 4.45  µm spectral region: a feasibility study [Invited]

Experiments on energy scaling and extending the wavelength tunability of Dy:PbGa 2 S 4 (PGS) and Dy:KPb 2 Cl 5 (KPC) lasers were undertaken. Both lasers demonstrated >1mJ output pulse energy at ∼4.4µm under diode laser pumping. Dy:PGS laser wavelength tunability was extended to 4.68 µm, which is the longest wavelength of laser oscillation ever reported for this crystal under 1.7 µm diode pumping. The longest wavelength of laser oscillation with Dy:KPC crystal was 4.46 µm. Modeling of Dy:KPC and Dy:PGS laser operation in Q-switching mode under direct diode-laser pumping was carried out. It was shown that under the pump energy fluence close to the damage threshold of the crystals, both Dy:KPC and Dy:PGS lasers are capable of producing Q-switch pulses with the energy/pulse duration of up to 1.7 mJ/11 ns (Dy:PGS) and 4.3 mJ/9 ns (Dy:KPC) at the wavelength of 4.45 µm. This spectral region is considered as one of the most suitable one for airborne observation of N 2 O gas in the atmosphere using the differential absorption LIDAR (DIAL) approach. Both crystals are therefore suitable for building a laser transmitter for the DAIL system, with Dy:PGS having some advantages over Dy:KPC due to superior thermo-optical parameters and to non-hygroscopicity.