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Schematic viewgraph of the experimental setup for ultrabroadband terahertz generation.
(a) Phase spectra observed using the SPIDER setup after transmission through each plates having the indicated thickness. The intensity spectrum of the laser is also shown as the thin solid line. (b) Terahertz waveform generated from the -thick DAST crystal without plate for chirp compensation. The inset is the expansion of the data around 0.8 ps in order to show the high-frequency oscillation with the period of 8 fs. (c) Observed terahertz spectra from the DAST crystal. The spectra obtained with plates for chirp compensation whose thicknesses are 0 mm, 2 mm, and 4 mm. The terahertz spectrum generated using a -thick GaSe crystal with the same setup is also shown. The dotted line is the Fourier transform of the data shown in (b). The spectra above 210 THz are the low-energy tail of the laser itself.
(a) Polarization of three spectral components in the generated terahertz wave. Horizontal axis indicates the angle of the polarizer. The intensity of each spectral component is estimated from the difference of the intensities measured using several low-pass filters (230, 150, and 120 THz). (b) Coherent lengths calculated for the generation of the 180 THz component. Several polarization configurations with a large nonlinear susceptibility known in the literature are calculated. The intensity spectrum of the laser is also shown in a linear scale for reference.
Calculated spectra of the difference frequency generation in the DAST crystal. The spectra are multiplied with a constant to compare directly with Fig. 2. Note that the absorption of the DAST crystal and the dependence of the nonlinear coefficient on the wavelength are omitted.
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