Temperature dependence and single-mode tuning behavior of Second Harmonic Generation in Quantum Cascade Lasers

Second harmonic generation (SHG) is reported in Quantum Cascade (QC) lasers with active regions that also support nonlinear cascades with large second order nonlinear susceptibility. SHG has been measured from 10 K up to 250 K heat sink temperature, with about 1 mW of nonlinear power at 10 K and about 50 nW at 250 K. The decrease of the second order nonlinear susceptibility with increasing temperature can mostly be attributed to the thermal broadening of the intersubband transitions. Single- mode and tunable SHG at 3.5 um wavelength has been measured from single-mode QC distributed feedback lasers operating at the fundamental pump wavelength of 7.0 um. Thermal tuning results in a tuning rate for the SHG emission of ~ 0.2 nm/K for temperatures above ~ 100 K.