Low temperature near-field scanning optical microscopy on infrared and terahertz photonic-crystal quantum cascade lasers

Abstract

We report the development of a scattering-type near-field scanning optical microscope (sNSOM) which operates at temperatures down to 100 K with a scanning range of up to $400\mu \text{m}$ . We have used this sNSOM to map the electromagnetic near-field on mid-IR and terahertz (THz) surface emitting quantum cascade lasers with photonic-crystal resonators. Mid-IR devices operate at $\text{λ}=7.5\mu \text{m}$ (40 THz) while THz devices operate at $\lambda \approx 110\mu \text{m}$ (2.7 THz). The near-field images—in agreement with numerical calculations—demonstrate an instrument resolution of 100's nm.