Generation and beam shaping of THz radiation in an actively modulated nonlinear crystal

• Published in: Optics communications 2023-01, Vol.526, p.128950, Article 128950
• Main Authors: Kumar, Vikas, Varshney, R.K., Kumar, Sunil
• Format: Article
• Language: English
• Subjects: Angular steering; Beam-shaping; Optical rectification; Second-order susceptibility
• ISSN: 0030-4018; 1873-0310
• DOI: 10.1016/j.optcom.2022.128950

Broadband THz pulses can be generated by optical rectification of ultrashort visible or near-infrared laser pulses in a second-order nonlinear optical crystal. Here, we propose and demonstrate theoretically that THz beam-shaping and steering can be achieved by properly modulating the second-order susceptibility, χ(2) of a nonlinear crystal in its transverse plane. Different duty cycles of the periodic χ(2) -modulations provide the main control for the angular steering of the generated THz beam away from the direction of the undeflected beam from a uniform crystal. Zinc telluride crystal of thickness 1 mm is considered for the demonstration of the scheme in which optical rectification of 100 fs excitation pulses, centered at 800 nm, resulted in a THz beam of ∼0-3.5 THz bandwidth pulses. Angular steering of ∼7.4 degrees could be achieved in comparison to that of the undeflected THz beam case using a ZnTe crystal of the same thickness but without any periodic modulations of the nonlinear susceptibility. The THz power distribution around the central lobe of the deviated THz beam depends on the duty cycle of the modulation. Another consequence of the periodically χ(2)-structured nonlinear crystal is that the steered THz beam is focused at a particular point in the observation plane, hence, multiple splitting of the THz beam can be achieved by varying the number of modulation periods in the crystal. •A novel approach of THz beam shaping and steering during generation itself inside a nonlinear crystal by nonlinear susceptibility modulation. •Angular steering of ∼7.5 degrees is achieved in a nonlinear crystal thickness of 1 mm.•The beam shaping and steering is not limited to the bandwidth of the generated THz radiation.