Triple wavelength-switchable lasing in yellow-green based on frequency mixing of self-Raman operation

Abstract

An efficient Nd:YVO<sub>4</sub> crystal self-Raman laser combined with second-order nonlinear frequency conversion is demonstrated to achieve an switchable output of three wavelengths in the yellow-green band. In order to improve the thermal effect and increase the length of Raman medium, a three-stage diffusion-bonded YVO<sub>4</sub>/Nd:YVO<sub>4</sub>/YVO<sub>4</sub> crystal is designed for high power and efficient self-Raman laser operation. Selective frequency mixing mechanisms between the fundamental wave and the first Stokes wave using the LiB<sub>3</sub>O<sub>5</sub> (LBO) and BaB<sub>2</sub>O<sub>4</sub> (BBO) crystals are comparatively studied by temperature tuning and angle tuning, respectively. Considering the frequency mixing conversion efficiency and a relatively fast wavelength switching, the BBO crystal with critical phase matching is selected as the second order nonlinear optical crystal for frequency conversion. It only needs to fine-tune the phase match angle of BBO crystal within 1.4°, and thus successfully realizing all second harmonic and sum frequency generation between the fundamental wave and the first Stokes wave. Therefore the efficient-switchable output of the three wavelengths of 532 nm green light, 559 nm lime light and 588 nm yellow light is obtained. Under the incident pump power of 19.5 W and the pulse repetition rate of 60 kHz, maximum average output power of 4.37 W at 532 nm, 2.03 W at 559 nm, 3.43 W at 588 nm are achieved. The conversion efficiency values of the corresponding pump light to visible light are 22.4%, 10.4% and 17.6%, respectively. The corresponding pulse widths are 36 ns, 12.2 ns and 12.7 ns, respectively. The results show that the selective frequency mixing of self-Raman operation is an efficient approach to achieving the wavelength-switchable emission in visible waveband. This wavelength-switchable laser source has important applications in the areas of laser therapy, visual display, spectral imaging and biological medicine.