Mid-infrared optical parametric generator with extra-wide (3–19-μm) tunability: applications for spectroscopy of two-dimensional electrons in quantum wells

Using a λ=2.8 µm pump makes it possible to take full advantage of notable nonlinear optical properties of the infrared crystals ZnGeP2, CdSe, and GaSe to achieve efficient mid-infrared frequency downconversion. Traveling-wave optical parametric generators with angular tuning were pumped by single 100-ps 2.8-µm Er,Cr:YSGG laser pulses. The continuous tuning range achieved was 3.9–10 µm (ZnGeP2), 3.57–4.3 and 8–13 µm (CdSe), and 3.3–19 µm (GaSe), with a quantum conversion efficiency of typically 10% and the lowest, to the author’s knowledge, threshold ever obtained for a traveling-wave optical parametric generator. A dual-wavelength optical parametric generator was used for nonlinear spectroscopy of intersubband transitions of conduction-band electrons, quantum confined in semiconductor quantum wells, as well as for the study of intersubband-based resonantly enhanced χ(2) in quantum wells.