Development of a 80MHz Kerr lens mode-locked 2.3 μm Cr:ZnS laser

Abstract

Lasers in the mid-infrared region are widely used in national defense, medicine, sensors, and basic science research. Cr-doped, broad bandgap II-VI semiconductor crystals have been shown to be effective as gain media for lasing in mid-infrared. In particular, Cr:ZnS is known to be suitable for high-power laser oscillation. In this work, a mode-locked Cr:ZnS laser operating at room temperature was developed. The gain medium was pumped using a 1567-nm Er:fiber pump laser. To increase pump efficiency, the gain medium was installed at a Brewster angle, and for the compensation of the astigmatism, the resonator was configured as an X-shaped cavity with a folding angle of 13.6 degrees. The length of the entire resonator was set to obtain the repetition rate of 80 MHz. For the pump of 3 W , the continuous wave laser output power was 290 mW. A pair of CaF2 prisms was installed on one arm of the resonator to compensate for the positive dispersion generated by the resonator. The spacing between the prisms was set to 100 mm to compensate for all the positive dispersion occurring in the resonator. Mode-locking operation was achieved by adjusting the positions of optical components in the resonator. The measurement of the output pulse train from the laser with a photodiode showed the repetition of 79.4 MHz. The measurement of the laser spectrum showed the spectral bandwidth of 45 nm centered at 2.28 m. Assuming the shape of the laser pulse of , the Fourier transform-limited pulse width was 120 fs.