Marcel Stillhart

Generation of terahertz pulses through optical rectification in organic DAST crystals: theory and experiment

We present a combined theoretical and experimental investigation of the generation of few-cycle terahertz (THz) pulses via the nonlinear effect of optical rectification and of their coherent detection via electro-optic sampling. The effects of dispersive velocity matching, absorption of the optical and the THz waves, crystal thickness, pulse diameter, pump pulse duration, and two-photon absorption are discussed. The theoretical calculations are compared with the measured spectra of THz pulses that have been generated and detected in crystals of the highly nonlinear organic salt 4-N,N-dimethylamino-4′-N′-methyl stilbazolium tosylate (DAST). The results are found to be in agreement with the theory. By the selection of the optical pump wavelength between 700 and 1600 nm, we achieved several maxima of the overall generation and detection efficiency in the spectral range between 0.4 and 6.7 THz, with an optimum at 2 THz generated with 1500 nm laser pulses.

Optical properties of 4-N,N-dimethylamino-4 ′ -N ′ -methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate crystals at terahertz frequencies

We have measured the optical properties of 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium 2,4,6-trimethylbenzenesulfonate (DSTMS), a highly nonlinear organic crystal, in the terahertz (THz) spectral range. The conditions for efficient THz pulse generation through optical rectification of near-infrared pulses have been calculated and confirmed experimentally. The results show that DSTMS as a source of THz radiation is superior to 4-N,N-dimethylamino-4′-N′-methyl-stilbazolium tosylate (DAST), a well-investigated nonlinear material with one of the highest nonlinear susceptibilities known so far.

Improved emission and coherent detection of few-cycle terahertz transients using laser pulses at 1.5 μm

We present a comparative study of nonlinear optical materials for terahertz pulse generation by optical rectification and detection by electro-optic sampling, with the aim to find a material the is best suited for the use together with femtosecond lasers operating at a wavelength of 1.5 μm. Three crystals are identified that fulfill the condition that the optical group velocity matches the terahertz phase velocity: the organic salt DAST and the inorganic semiconductors GaAs and ZnTe, the latter showing velocity-matching with the second harmonic of 1.5 μm. A combined figure of merit for optical rectification and electro-optic sampling is derived. For the three materials under consideration, we find numerical values of 4300 (DAST):110 (GaAs):370 (ZnTe), in units of (pm/V)2. We also present experimental evidence that the performance of DAST is an order of magnitude better than those of the inorganic semiconductors, and we present spectroscopic data in the terahertz range of DSMOS, a chemical derivative of DAST that may in the future also be used for terahertz applications.

Highly efficient generation of THz pulses using laser pulses at telecommunication wavelengths

We demonstrate generation of few-cycle THz pulses through optical rectification in organic DAST crystals at telecommunication wavelength (1550 nm). An extremely high conversion efficiency is achieved through velocity-matching and the materialpsilas large nonlinear optical susceptibility.

Generation of THz and IR Radiation in DAST crystals

Short THz pulses are commonly generated through the optical rectification of ultrashort laser pulses in nonlinear optical crystals. Our purpose is to discuss the controllability of the THz spectrum emitted from the polar organic salt DAST (4-N,N-dimethylamino-4-N-methyl stilbazolium tosylate) and also the efficiency of the THz generation. It does not only depend on different experimental parameters such as duration of the laser pulse and crystal thickness, but is also affected by absorption and dispersion caused by several resonances of the crystal in the THz range.

Single-pass measurements of terahertz transients in a highly birefringent crystal

In this paper, we developed terahertz-induced lensing (TIL), a variation of electro-optic sampling that is not affected by birefringence.