Highly efficient THz generation by optical rectification of mid-IR pulses in DAST

We report on efficient THz generation in DAST by optical rectification of intense mid-IR pulses centered at (i) 3.9 mu m and (ii) its second harmonic at 1.95 mu m. Suppression of multi-photon absorption shifts the onset of saturation of the THz conversion efficiency to pump energy densities, which are almost an order of magnitude higher as compared to conventional pump schemes at 1.5 mu m. Despite strong linear absorption at 3.9 mu m, DAST exhibits a high optical-to-THz conversion efficiency, which we attribute to resonantly enhanced nonlinearity and advantageous phase matching of the THz phase velocity and group velocity of the driving pulse. At 1.95 mu m, we find that low linear and multi-photon absorption in combination with cascaded optical rectification lead to record optical-to-THz conversion efficiencies approaching 6%. The observed high sensitivity of the THz generation to the parameters of the mid-IR driving pulses motivates an in-depth study of the underlying interplay of nonlinear wavelength- and intensity-dependent effects.

Automated summary

Efficient THz generation in DAST is achieved through optical rectification of intense mid-IR pulses at 3.9 µm and its second harmonic at 1.95 µm. The high optical-to-THz conversion efficiency is attributed to resonantly enhanced nonlinearity and advantageous phase matching of THz and driving pulse velocities. The low linear and multi-photon absorption at 1.95 µm, combined with cascaded optical rectification, leads to record optical-to-THz conversion efficiencies nearing 6%.