Advancements in High-Power Multi-Wavelength Femtosecond Laser Parametric Oscillators at Beijing's National Research Center for Condensed Matter Physics

Broadband tunable multi-wavelength femtosecond lasers have emerged as a significant focus in the field of ultrafast laser technology, primarily due to their diverse applications in areas such as time-resolved spectroscopy, biomedical imaging, laser radar, and environmental monitoring. However, the current limitations of laser gain media and their emission spectra restrict the output wavelength range of mode-locked laser oscillators, which in turn limits their tuning capabilities.

One effective method to achieve tunable ultrashort pulses is through the use of optical parametric oscillators (OPOs) that are synchronously pumped by mode-locked lasers. Despite their advantages, the output power of OPOs tends to be lower than that of traditional mode-locked lasers. The L07 research group at the Institute of Physics of the Chinese Academy of Sciences, in collaboration with the Beijing National Center for Condensed Matter Physics, has made significant strides in this area. They were the first in China to develop a femtosecond OPO and have since focused on expanding its wavelength range and enhancing its power output.

Utilizing laser wavelengths of 800 nm, 1030 nm, and 515 nm, along with various nonlinear crystals such as KTP, BBO, LBO, and BiBO for the parametric gain medium, the group has successfully conducted a series of femtosecond OPO operations. Notably, in collaboration with Xi'an University of Electronic Science and Technology, they employed the novel nonlinear crystal BiBO, achieving signal light wavelengths from 688 nm to 1057 nm and idler light wavelengths from 1150 nm to 1900 nm, with a peak average power output of 1.09 W.

Recently, a Ph.D. student named Meng Xiangyu, under the guidance of professors Wei Zhiyi, Wang Zhaohua, and Fang Shaobo, further advanced this research by utilizing KTA as the nonlinear crystal. This effort, in partnership with Xi'an University of Electronic Science and Technology, resulted in the successful generation of tunable femtosecond laser pulses from the visible spectrum to the mid-infrared range of 3.84 μm. This development led to a maximum output power of 2.3 W and a pulse duration of 129 fs, surpassing the average output power of conventional femtosecond Ti:Sapphire laser oscillators. The findings of this research were published in a recent edition of a scientific journal.

Additionally, the team employed the femtosecond OPO laser as a light source for collaborative experiments with the Suzhou Medical Institute of the Chinese Academy of Sciences. These experiments included two-photon microscopy imaging, scanning confocal microscopy, and two-photon stimulated emission depletion (STED) applications, resulting in high-resolution biological imaging.

The research was supported by various funding sources, including a special project by the Chinese Academy of Sciences, a major scientific instrument development initiative by the Ministry of Science and Technology, and several National Science Foundation projects.