Silicon carbide--a high-transparency nonlinear material for THz applications.

Optical properties of 4H-SiC were measured using time-domain and Fourier transform spectroscopy in the range of 0.1-20 THz. A high-transparency region was found between <0.1-10 THz. Based on the obtained data and published results, the refractive indices for o-wave and e-wave were approximated in the form of Sellmeier equations for the entire transparency range. Phase matched frequency conversion was found to be possible at wavelengths from the visible through the mid-IR and further into the far-IR (THz) region beyond 17 µm. Extremely low absorption coefficient, high damage threshold, and the possibility of phase matching make this material highly suited for high power THz optics and generation.

Broadband two-stage frequency conversion of CO laser in AgGaSe(2) crystal.

For the first time, to the best of our knowledge, a broadband two-stage frequency conversion of multiline CO laser radiation was theoretically and experimentally demonstrated in a single AgGaSe2 crystal. The first stage is sum frequency generation of CO laser radiation. The second stage is concurrent difference frequency generation within 4.3-4.9 µm spectral range when mixing sum frequency radiation with the pump radiation in the same AgGaSe2 crystal. Internal sum frequency generation efficiency of multiline CO laser was up to 1%, while internal difference frequency generation efficiency was up to 0.065%.

Terahertz time-domain spectroscopy for textile identification.

A range of natural and artificial textiles are examined using terahertz time-domain spectroscopy. Different types of textiles are shown to have different terahertz optical properties, which may be employed for textile identification and to combat textile counterfeiting.

Cascaded carbon monoxide laser frequency conversion into the 4.3-4.9 µm range in a single ZnGeP2 crystal.

Collinear cascaded mid-IR frequency conversion in a single nonlinear optical crystal was accomplished. Concurrent collinear generation of the sum frequency of multiline fundamental band carbon monoxide laser radiation as a first frequency conversion cascade resulted in collinear difference frequency generation within the 4.3 to 4.9 µm spectral range when mixing this sum frequency radiation with the fundamental one as the second cascade in the same ZnGeP(2) nonlinear optical crystal.