Shanghai Institute Of Optics And Precision Machinery (SIPM) Makes Progress in Research Of New Terahertz Source Based On Yb Laser

Recently, the State Key Laboratory of Strong-Field Laser Physics of Shanghai Institute of Optical Precision and Mechanical Research (SIPMR), Chinese Academy of Sciences (CAS), has made new progress in generating strong-field terahertz waves based on Yb laser-pumped organic crystals. The related research results were published in Applied Physics under the title of "Efficient strong-field THz generation from DSTMS crystal pumped by 1030nm Yb-laser". published in Applied Physics Letters.
Compared with inorganic crystals such as ZnTe and LiNbO3, organic crystals such as DAST and DSTMS have higher nonlinear coefficients and lower absorption coefficients in the terahertz band. In previous studies, an infrared ultrashort pulsed laser with a wavelength of 1200 to 1700 nm was generally used to pump the organic crystals in order to achieve better phase matching and higher terahertz conversion efficiency. However, obtaining high-energy ultrashort laser pulses in this wavelength band requires frequency conversion using techniques such as OP(CP)A, which not only greatly reduces the energy conversion efficiency and system stability, but also improves the equipment cost and complexity. In recent years, ultrafast Yb lasers have been emphasized by the scientific research community and industry for their advantages in low cost, high power and miniaturization. The generation of terahertz waves with a Yb laser directly driving a crystal provides an idea for the development of an integrated terahertz source, and brings an opportunity for the development of related scientific research and application fields.
This study describes the phase matching conditions for generating terahertz waves by pumping organic crystal photo rectification with ultrashort pulse laser, and analyzes the dependence of terahertz frequency, coherence length, etc. on the pumping laser. The research team utilized Yb laser pumped organic crystal DSTMS to generate strong-field terahertz. By designing the phase matching of terahertz band and optimizing the pump laser pulse width and power density, the team obtained strong-field terahertz wave with single pulse energy of 0.4 μJ and peak field strength of 236 kV/cm, with a spectrum covering 0.1-6 THz, and the energy conversion efficiency of the laser-terahertz wave reached 0.22%. The above experiments have verified the feasibility of Yb laser-pumped organic crystals to generate milliwatt-level high-power strong-field terahertz waves, providing a new integrated terahertz light source solution for scientific research and application promotion in related fields.
This work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China, and the Instrumentation Development Program of the Chinese Academy of Sciences.

Figure 1. Generation and characterization of strong-field terahertz waves (a) experimental optical path; (b) terahertz time-domain waveforms and spectra (the inset shows the terahertz focal spot).

Fig. 2. Laser-terahertz wave phase matching (a) refractive indices of DSTMS crystals in the infrared and terahertz bands; (b) dependence of terahertz frequency, coherence length, etc., on the wavelength of the pump laser; (c) terahertz coherence length at the wavelength of the pump laser of 1030 nm; and (d) absorption characteristics of DSTMS crystals in the infrared and terahertz bands.