Nonlinear optics with intersubband transitions in high-band offset heterostructures

ABSTRACT We discuss peculiarities of the nonlinear optical processes utilizing intersubband nonlinearities in high band offset heterostructures formed by th ree nearly lattice matched binaries, InAs, GaSb, AlSb, and their alloys. We show that these materials offer unique benefits for nonlinear optics due to gr eat flexibility in designing optical interaction schemes in a wide frequency range and very large values of the nonlin ear susceptibilities even involving short-wavelength transitions. The resulting nonlinear conversion efficiency for the second-harmonic or sum-frequency generation is in the mW/W 2 range even for very short coherence lengths of the order of several P m. Keywords: quantum cascade laser, nonlinear optics, second-harmonic generation 1. INTRODUCTION High band offset antimonide-based heterostructures offer a number of unique benefits for nonlinear optics. The most important of them is, not surprisingly, the high band offset which allows one to accommodate nonlinear optical processes involving short-wavelength mid-IR and even near-IR radiation. Another advantage is very large values of the nonlinear susceptibilities associated with resonant intersubband nonlinearities. The dipole moments even for high-frequency transitions in the 600 meV range are of the order of 10 A. This combination makes these materials especially suitable for frequency up-conversion into 2-3 P m range by means of second-harmonic generation (SHG) or Anti-Stokes Raman scattering. Below we consider several sp ecific structures and calculate the nonlin ear frequency conversion efficiency.