Super-octave longwave mid-infrared coherent transients produced by optical rectification of few-cycle 25-μm pulses

• Published in: Optica 2019-01, Vol.6 (1), p.111
• Main Authors: Vasilyev, Sergey, Moskalev, Igor S., Smolski, Viktor O., Peppers, Jeremy M., Mirov, Mike, Muraviev, Andrey V., Zawilski, Kevin, Schunemann, Peter G., Mirov, Sergey B., Vodopyanov, Konstantin L., Gapontsev, Valentin P.
• Format: Article
• Language: English
• Subjects: CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; Optics
• ISSN: 2334-2536; 2334-2536
• DOI: 10.1364/OPTICA.6.000111

Femtosecond laser sources and optical frequency combs in the molecular fingerprint region of the electromagnetic spectrum are crucial for a plethora of applications in natural and life sciences. Here we introduce Cr2+-based lasers as a convenient means for producing super-octave mid-IR electromagnetic transients via optical rectification (or intra-pulse difference frequency generation, IDFG). We demonstrate that a relatively long, 2.5 μm, central wavelength of a few-cycle Cr2+:ZnS driving source (20 fs pulse duration, 6 W average power, 78 MHz repetition rate) enabled the use of highly nonlinear ZnGeP2 crystal for IDFG with exceptionally high conversion efficiency (>3%) and output power of 0.15 W, with the spectral span of 5.8–12.5 μm. Even broader spectrum was achieved in GaSe crystal: 4.3–16.6 μm for type I and 5.8–17.6 μm for type II phase matching. The results highlight the potential of this architecture for ultrafast spectroscopy and generation of broadband frequency combs in the longwave infrared.