Shanghai Optics and Machinery Institute has made progress in the research of new terahertz sources based on Yb lasers

Recently, the State Key Laboratory of Intense Field Laser Physics of the Chinese Academy of Sciences Shanghai Institute of Optics and Fine Mechanics has made new progress in generating intense field terahertz waves based on Yb laser pumped organic crystals. The relevant research results were published in Applied Physics Letters under the title "Efficient strong field THz generation from DSTMS crystal pumped by 1030nm Yb laser".

Compared to 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 frequency band. In previous studies, infrared ultra short pulse lasers with wavelengths ranging from 1200 to 1700nm were generally used to pump organic crystals for better phase matching and higher terahertz conversion efficiency. However, obtaining high-energy ultra short laser pulses in this band requires frequency conversion using techniques such as OP (CP) A, which not only greatly reduces energy conversion efficiency and system stability, but also increases equipment cost and complexity. In recent years, ultrafast Yb lasers have received attention from the scientific and industrial communities due to their advantages in low cost, high power, and miniaturization. The use of Yb laser to directly drive crystals to generate terahertz waves provides ideas for the development of integrated terahertz sources, as well as opportunities for the development of related scientific research and application fields.

This study elucidates the phase matching conditions for the generation of terahertz waves by organic crystal optical rectification pumped by ultra short pulse lasers, and analyzes the dependence of terahertz frequency, coherence length, etc. on the pumped laser. The research team utilized Yb laser pumped organic crystal DSTMS to generate strong field terahertz. By designing phase matching in the terahertz band and optimizing conditions such as pump laser pulse width and power density, a single pulse energy of 0.4 is obtained μ J. A strong field terahertz wave with a peak field strength of 236 kV/cm, covering a frequency spectrum of 0.1-6 THz, and a laser terahertz wave energy conversion efficiency of 0.22%. The above relevant experiments have verified the feasibility of Yb laser pumping organic crystals to generate milliwatt level high-power strong field terahertz waves, providing a new integrated terahertz light source scheme for scientific research and application promotion in related fields.

Relevant work has been supported by the national key research and development plan, the National Natural Science Foundation of China, and the Chinese Academy of Sciences instrument and equipment development project.

Figure 1. Generation and characterization of strong field terahertz waves (a) Experimental optical path; (b) Terahertz time-domain waveform and spectrum (illustrated as terahertz focal spot).

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

Source: Shanghai Institute of Optics and Mechanics