High energy terahertz pulses from organic crystals: DAST and DSTMS pumped at Ti:sapphire wavelength

High energy terahertz pulses are produced by optical rectification (OR) in organic crystals DAST and DSTMS by a Ti:sapphire amplifier system centered at 0.8 microns. The simple scheme provides broadband spectra between 1 and 5 THz, when pumped by collimated 60 fs near-infrared pump pulse and it is scalable in energy. Fluence-dependent conversion efficiency and damage threshold are reported as well as optimized OR at visible wavelength.Comment: 8 pages, 6 figure

Generation of 1.5-octave intense infrared pulses by nonlinear interactions in DAST crystal

Infrared pulses with large spectral width extending from 1.2 to 3.4 μm are generated in the organic crystal DAST (4-N, N-dimethylamino-4′-N′-methylstilbazolium tosylate). The input pulse has a central wavelength of 1.5 μm and 65 fs duration. With 2.8 mJ input energy we obtained up to 700 μJ in the broadened spectrum. The output can be easily scaled up in energy by increasing the crystal size together with the energy and the beam size of the pump. The ultrabroad spectrum is ascribed to cascaded second order processes mediated by the exceptionally large effective χ2 nonlinearity of DAST, but the shape of the spectrum indicates that a delayed χ3 process may also be involved. Numerical simulations reproduce the experimental results qualitatively and provide an insight in the mechanisms underlying the asymmetric spectral broadening

High-energy terahertz pulses from semiconductors pumped beyond the three-photon absorption edge

A new route to efficient generation of THz pulses with high-energy was demonstrated using semiconductor materials pumped at an infrared wavelength sufficiently long to suppress both two- and three-photon absorption and associated free-carrier absorption at THz frequencies. For pumping beyond the three-photon absorption edge, the THz generation efficiency for optical rectification of femtosecond laser pulses with tilted intensity front in ZnTe was shown to increase 3.5 times, as compared to pumping below the absorption edge. The four-photon absorption coefficient of ZnTe was estimated to be β₄=(4±1)×10⁻⁵ cm⁵/GW³. THz pulses with 14 μJ energy were generated with as high as 0.7% efficiency in ZnTe pumped at 1.7 µm. It is shown that scaling the THz pulse energy to the mJ level by increasing the pump spot size and pump pulse energy is feasible

Intense sub-two-cycle infrared pulse generation via phase-mismatched cascaded nonlinear interaction in DAST crystal

Octave-spanning, 12.5 fs, (1.9 cycle) pulses with 115 mu J energy in the short-wavelength mid-infrared spectral range (1-2.5 mu m) have been generated via phase-mismatched cascaded nonlinear frequency conversion using organic DAST (4-N, N-dimethylamino-4 '-N '-methylstilbazolium tosylate) crystal. Such ultrafast cascading effect is ensured by the interaction of a pump pulse with the exceptionally large effective nonlinearity of the DAST crystal and experiencing nonresonant, strongly phase-mismatched, Kerr-like negative nonlinearity