Fig. 1. The THz SHG from organic crystals. (a) Schematic of the experiment. (b) The time-domain waveform of THz SHG from a DAST crystal (upper panel) and the corresponding THz pump waveform with a fundamental frequency of 2.4 THz (lower panel). (c) The time-domain waveform of THz SHG from a DSTMS crystal (upper panel) and the corresponding THz pump waveform with a fundamental frequency of 1.6 THz (lower panel). (d) The time-domain waveform of THz SHG from an OH1 crystal (upper panel) and the corresponding THz pump waveform with a fundamental frequency of 0.8 THz (lower panel). (e)–(g) The frequency spectra of THz SHG from different crystals with incident THz waves at fundamental frequencies of 2.4, 1.6, and 0.8 THz.

Fig. 2. The dependence of the generated second-harmonic field strength on the pump field strength. (a)–(c) The field strength of SHG from different crystals with the incident fundamental frequency of 2.4, 1.6, and 0.8 THz.

Fig. 3. The effective distance for SHG in crystals. (a)–(c) The effective distance for SHG in DAST, DSTMS, and OH1 crystals with varying thicknesses under different fundamental frequencies’ pumping. (d) The blue curves depict the simulated effective distance for SHG in DSTMS crystals of varying thicknesses under fundamental frequencies of 2.4, 1.6, and 0.8 THz, and the red dots represent the measured electric fields of SHG from DSTMS crystals with thicknesses of 300, 400, and 500μm under the three fundamental frequencies.

Fig. 4. Polarization dependence of SHG from DAST crystal at a pump frequency of 2.4 THz. (a), (b) The time-domain waveform of SHG measured in the x and y directions with the DAST rotation angle of φ. The color information represents the measured electric field strength of SHG. The bottom panels of the figure represent the variation of the peak electric field of the SHG with the rotation angle of φ.