Cherenkov-type terahertz generation by optical rectification in KD2PO4 (DKDP) crystal

• Published in: Journal of applied physics 2023-12, Vol.134 (21)
• Main Authors: Bodrov, S. B., Abramovsky, N. A., Paramonov, G. S., Belyaev, S. N., Prokhorov, A. P., Stepanov, A. N., Bakunov, M. I.
• Format: Article
• Language: English
• Subjects: Applied physics; Broadband; Cerenkov radiation; Crystals; Femtosecond pulses; Frequency ranges; Luminous intensity; Optics; Sapphire; Terahertz frequencies; White light
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/5.0178255

The potential of KD 2PO 4 (or DKDP) crystal as a terahertz generator is demonstrated, despite its extremely strong terahertz absorption. By combining the Cherenkov radiation scheme and surface-emitting geometry, femtosecond Ti:sapphire laser pulses of ∼ 200 − 300  μJ energy were converted to broadband ( ∼ 4 THz bandwidth) terahertz transients with the efficiency of ∼ 8 × 10 − 6. The transients produced electro-optic signals of a ∼ 0.15 modulation depth and ∼ 10 3 dynamic range in a 1-mm thick ZnTe detector crystal. This suggests DKDP as a potential generator crystal for terahertz time-domain spectroscopy. From our measurements, we estimated the nonlinear coefficient d 36 ≈ 3 pm/V of DKDP for optical rectification, which is an order of magnitude larger than the value known from second-harmonic-generation experiments. At the same time, the obtained value of d 36 is an order of magnitude smaller than the value calculated from the clamped electro-optic coefficient r 63 for the MHz frequency range. At high pump intensities, we observed multiple filamentation of the pump beam and white light generation, spatially separated from terahertz generation.