On-chip mid-infrared and THz frequency combs for spectroscopy

Abstract

Frequency combs, spectra of phase-coherent equidistant lines often generated by mode-locked femtosecond lasers, have revolutionized time and frequency metrology [1,2]. In recent years, new frequency comb lasers, of a high compactness or even on-chip, have been demonstrated in the mid-infrared and THz regions of the electromagnetic spectrum. They include electrically pumped quantum cascade and interband cascade semiconductor devices, as well as highquality factor microresonators. These new comb generators open up novel opportunities for spectroscopy of molecular fingerprints over broad spectral bandwidths: their small form-factor promises chip-scale spectrometers, while their large line spacing simplifies the resolution of the individual comb lines with simple spectrometers and provides short measurement times, with an intriguing potential for time-resolved spectroscopy in the condensed phase. This Letter summarizes the recent advances in this rapidly developing domain of on-chip combs for broadband spectroscopy and discusses some of the challenges and prospects. While some review articles already provide a perspective into some aspects of chip-based frequency comb generators [3][4][5], of mid-infrared frequency comb synthesizers [6] and of the applications of frequency combs to spectroscopy [7], the growing and rapidly advancing interest in molecular sensing using quantum cascade and microresonator-based on-chip frequency combs motivates this Letter.

RF Injection of THz QCL Combs at 80 K Emitting over 700 GHz Spectral Bandwidth

“…Mid-IR and THz spectral regions are especially important in the fields of sensing and spectroscopy since many chemical species have strong absorption lines there. Such developments gave large momentum to the effort of integrating comb-based spectroscopy platforms onto chip-sized platforms [8]. Quantum cascade lasers [9] are intrinsically well suited to be applied for on-chip integration and a rapid development of QCL-based comb sources has been observed in the past few years.…”

QCL-Based Dual-Comb Spectrometer for Multi-Species Measurements at High Temperatures and High Pressures

“…Dual-comb spectroscopy could surpass conventional broadband spectroscopy for a wide range of applications as frequency comb technology progresses. There are other references [ 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 ] introducing different dual-comb spectroscopy techniques and applications in different fields, such as atmosphere monitoring, combustion, and biomedical studies. Here, we focus on dual-comb spectroscopy based on quantum cascade laser frequency combs (QCL-FC) due to their wide spectral coverage, high spectral resolution, fast time response, and a compact construction.…”

“…Here, we focus on dual-comb spectroscopy based on quantum cascade laser frequency combs (QCL-FC) due to their wide spectral coverage, high spectral resolution, fast time response, and a compact construction. QCL-FCs and their applications are discussed in the recent literature [ 40 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 ] and their operation / functionality is contrasted with other types of frequency combs in these references [ 44 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ].…”

Monitoring formaldehyde in a shock tube with a fast dual-comb spectrometer operating in the spectral range of 1740–1790 cm–1

“…As recently shown, near-IR dual-comb spectroscopy is well-suited for many major species in combustion diagnostics in single-pass arrangements [23]. With the development of compact and electrically pumped mid-IR QCL combs, the spectroscopically attractive MIR spectral range becomes increasingly accessible [24][25][26]. As a consequence, the field of QCL-based frequency-comb spectroscopy grows rapidly, resulting in a variety of promising applications [26][27][28], including recent shock-tube studies using a QCL DCS in the spectral range of 1200 cm −1 [26,28].…”