Cavity-Enhanced Direct Frequency Comb Spectroscopy in the CH Stretching Region with Interband Cascade Lasers
Optical frequency combs provide the benefits of continuous-wave narrow-band lasers while maintaining broadband coverage. Being composed of many equally spaced frequency components, or comb teeth, allows for them to be efficiently coupled into enhancement cavities for trace gas detection. There has been a push to implement this in the mid-infrared in order to take advantage of strong fundamental vibrational bands. However, mid-infrared frequency combs based on non-linear optics are bulky, expensive, and technically challenging. Interband cascade lasers are semiconductor devices which have been demonstrated to be compact and efficient sources from 3-6 μm. They can also be designed to act as optical frequency combs, providing 1 THz of coverage in the CH stretching region. Although they lack the coverage of fiber based femtosecond lasers, their simplicity and portability opens new possibilities. We have investigated cavity-enhanced schemes with these devices, including Vernier spectroscopy which allows for the full comb spectrum to be measured in ~1 ms with comb-tooth resolution. We present these results and discuss possible applications for these novel devices.