Ultra-Low-Noise Frequency Comb at 2.3 μm

Since their inception a quarter of a decade ago, optical frequency combs have revolutionized the development of modern optics, finding countless applications in diverse fields ranging from ultraprecise metrology to attosecond science [1]. Rather than being limited to basic research, frequency comb technology has also had an unparalleled impact on very practical spectroscopic applications, including environmental sensing or biomedical investigations [2]. These fields typically require frequency combs operating in the mid-infrared spectral range, due to the abundance of characteristic molecular absorption features in this spectral range. Recently, it has been shown that lasers based on Cr:ZnS/Se gain media can be ideal candidates for frequency combs [3] with unprecedentedly low-noise performance [4], and, in combination with nonlinear frequency conversion, can spectrally cover the major part of the mid-infrared band [5].