Long-wave infrared and terahertz spectroscopy based on organic nonlinear crystals pumped at telecommunication wavelengths
Abstract
Megahertz repetition rate fiber lasers at 1.5 μm of wavelength have reached technological maturity and robustness that permits their integration into tablet-size self-starting devices with battery operation capabilities. When subsequently amplified by an erbium-doped fiber amplifier (EDFA), optical pulses with sub-20-fs durations and nanojoule energies can be obtained via in-fiber self-phase modulation and dispersive compression. While such sources are of relevance for many fields ranging from material processing to nonlinear microscopy, optical sensing offers more advantages at longer wavelengths. In our work, we explore the feasibility of frequency conversion of telecommunication-wavelength optical pulses using new organic nonlinear optical crystals in the nanojoule pulse energy regime for spectroscopy. In particular, we study the broadband terahertz (THz) emission and detection capabilities of PNPA ((E)-4-((4- nitrobenzylidene)amino)-N-phenyl-aniline) compared with DSTMS (4-N,N-dimethylamino-4'-N'-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate). Not only can the crystals be used for room-temperature broadband THz generation, but also detection via the optical Pockels effect - a linear change of the refractive index in the presence of an external electric field. This in turn lifts the requirement for cooled infrared detectors because a conventional uncooled InGaAs photodiode for near-infrared wavelengths can be used instead to detect far-infrared waveforms. Currently, we obtain a spectroscopic coverage of 2-25 THz but future improvements in application-tailored organic crystals should offer even broader optical bandwidths.
- Publication:
-
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series
- Pub Date:
- June 2024
- DOI:
- 10.1117/12.3022499
- Bibcode:
- 2024SPIE12994E..0DS