Femtosecond Color Center Lasers near 2.8 µm with HgCdTe Multiple Quantum Well Saturable Absorber

Abstract

We have used HgCdTe multiple quantum well (MQW) saturable absorbers to passively modelock two color center lasers (CCL) near 2.8 µm. The KC1:Li CCL generates pulses as short as 120 fs and the RbC1:Li CCL generates pulses as short as 190 fs, which are the shortest pulses in the mid-infrared wavelength range. These CCL are the only direct laser source of sub-picosecond pulses in this wavelength range. Our results extend the semiconductor passive modelocking technique previously applied to the NaCI CCL system (1) to different wavelength range, saturable absorber material and laser systems. Both pulse durations are close to the 150 fs estimated LO phonon collision thermalization time for HgCdTe MQW (2) and are shorter than the 275 fs pulses obtained with the NaC1 CCL (1). The NaCl CCL used an InGaAs/InAlAs MQW saturable absorber that has a thermalization time of 200 fs. These results are consistent with the proposal that the pulses are generated by the fast saturable absorption due to the thermalization, through LO phonon collision, of a cold carrier distribution (1).

We have used a HgCdTe multiple quantum well saturable absorber to passively modelock KCl:Li and RbCl:Li color center lasers and generated pedestal free pulses as short as 120 fs near 2.8 µm.