PAM-XIAMEN can supply SiC crystals, more specifications are found in  https://www.powerwaywafer.com/sicsilicon-carbide-boule-crystal.html.

Mid infrared laser (3-5μm) has important applications in environmental monitoring, gas molecule recognition, coherent tomography, and other fields. Especially in recent years in the research of generating single attosecond pulses from high-order harmonics, due to the fact that periodic level mid infrared femtosecond lasers can obtain higher harmonic order cutoff energy, they are expected to obtain shorter attosecond pulses and higher time resolution. However, limited by the laser gain medium, it is currently difficult to directly obtain femtosecond lasers in the mid infrared band at room temperature. Therefore, the widely used solution is based on nonlinear crystal laser parametric oscillation and amplification technology. In 2013, researchers have found that semi insulating 4H-SiC crystals have high transmittance in the 2.5-5.6um mid infrared band. For the first time, this crystal was used to obtain a wide spectrum mid infrared laser output with a wavelength coverage of 3.9-5.6um using a differential frequency broadband femtosecond laser.

1. Characteristics of Silicon Carbideas a Nonlinear Mid-Infrared Material

Compared to commonly used mid infrared nonlinear crystals, 4H-SiC crystals have two major advantages:

Firstly, it has a very high damage threshold, thus it is expected to obtain higher parametric laser energy than crystals such as AgGaS2 and ZnGeP2;

Secondly, it supports an extremely wide parametric bandwidth. By systematically calculating the phase matching supporting role angle, noncollinear angle, walk off angle, parameter bandwidth, angular dispersion and compensation of femtosecond laser in SiC crystal during noncollinear parametric amplification. The mid infrared idle light with a bandwidth of more than 500 nm can be obtained theoretically.

Therefore, it can be used to generate the mid infrared ultrafast laser with periodic pulse.

2. Research on Mid Infrared Femtosecond Laser Generated by SiC Crystals

Based on the characteristics of 4H-SiC crystals and the development needs of mid infrared femtosecond lasers, researchers have switched to using L07 group’s self built femtosecond titanium sapphire laser amplifier as the pump laser, and A02 group’s newly grown high-quality 4H SiC crystals as nonlinear crystals. Through femtosecond laser parametric amplification research, broadband mid infrared laser output with significantly increased energy has been obtained.

In the experiment, they divided the laser output from the titanium sapphire amplifier into three parts (Fig. 1), with one part used to generate stable single filament white light supercontinuum; The other part, after frequency doubling, pumps the BBO crystal to amplify the wavelength 1um component in the white light supercontinuum; In the third part, while pumping the 4H-SiC crystal to further amplify the 1um signal light, a mid infrared idle frequency light with a central wavelength of 3.75um, single pulse energy of 17uJ, and energy stability better than 1.5% was obtained.

Fig. 1 Schematic diagram of the optical path of the mid infrared laser device

In the experiment, the optimal non collinear angle (2.3 °) obtained by theoretical calculation was used to achieve good group velocity matching between the signal light and the idle light in the crystal. An ultra wideband idle light spectrum with a half width of 550nm was obtained (Fig. 2), supporting a Fourier limit pulse of 56 fs. The experimental measurement results showed that the actual laser pulse width was 70fs. Compared to the results in 2013, not only has the single pulse energy increased by nearly two orders of magnitude, but the pulse width is also only about 6 optical oscillation cycles.

Fig. 2 Infrared laser spectrum and corresponding Fourier limit pulse graph

For more information, please contact us email at victorchan@powerwaywafer.com and powerwaymaterial@gmail.com.