We demonstrate real-time and ultrabroadband THz time-domain spectroscopy in a compact optimized system. The system is based on a femtosecond fiber laser at 1560 nm as pump source and optical rectification and detection in organic electro-optic DSTMS crystals. Terahertz time-domain spectroscopy with a spectrum extending beyond 20 THz with a maximum bandwidth 70 dB has been reached with this system. We present spectroscopic measurements of various biomedical and pharmaceutical substances in transmission and reflection geometry at frequencies up to 20 THz.
Intense Terahertz radiation in organic crystals is typically generated by optical rectification of short wavelength infrared femtosecond lasers between 1.3 and 1.5 μm. In this wavelength range high energy ultrashort pump sources are hardly available. Here we present results on powerful THz generation by using DAST and DSTMS pumped directly by the widely used and well-established Ti:sapphire laser technology, emitting at 0.8 μm. This approach enables straightforward THz generation by optical rectification. We present systematic studies on
nIR-to-THz conversion efficiency, damage threshold, and on the emitted THz spectrum and field strength.
Characterization and optimization of KNbO3 crystals for photorefractive applications over an extended spectral range is described. Intrinsic properties are used to describe the refractive index response to space-charge field gratings. Extrinsic properties that are important for the photorefractive effect, such as absorption, photoconductivity, charge transport, and trapping, are discussed. Some results on the extended IR response of crystals doped with Fe, Ni, Cu, Ce, Mn, and Co are presented. Post growth annealing at temperatures of 400 to 900°C in a controlled atmosphere is shown to modify the charge-transport parameters, therefore also modifying the response time of photoinduced refractive index changes.