Microresonator-based high-resolution gas spectroscopy

Abstract

In recent years, microresonator-based optical frequency combs have created up opportunities for developing a spectroscopy laboratory on a chip due to its broadband emission and high comb power. However, with mode spacings typically in the range of 10 -1000 GHz, the realization of a chip-based high-resolution spectrometer suitable for gas-phase spectroscopy has proven to be difficult. Here, we show mode-hop-free tuning of a microresonator-based frequency comb over 16 GHz by simultaneously tuning both the pump laser and the cavity resonance. We illustrate the power of this scanning technique by demonstrating gas-phase molecular fingerprinting of acetylene with a high-spectral-resolution of < 80 MHz over a 45-THz optical bandwidth in the mid-IR. Our technique represents a significant step towards on-chip gas sensing with an ultimate spectral resolution given by the comb linewidth. OCIS codes:(300.6340) Spectroscopy, infrared; (190.4975 Mid-infrared (Mid-IR) frequency combs[1] can enable broadband gas-phase spectroscopy[2, 3] with unprecedented measurement capabilities and new applications in medical diagnostics, astrochemistry, atmospheric monitoring, remote sensing and industry control. An optical frequency comb (OFC) [4,5] has a broad optical spectrum consisting of evenly spaced, spectrally sharp lines. The frequency of each comb line can be written as f m = f ceo + mf r , where f ceo is the carrier-envelope offset frequency and f r is the repetition frequency. Compared to tunable lasers, such broadband combs enable an accurate measurement of a large number of molecular absorption lines and species simultaneously in a complex environment [6]. The most widely used OFC is based on modelocked femtosecond lasers [4,7] and has been previously utilized for high-resolution spectroscopy [8,9]. Recently, there have been interest in the development of OFC sources in the mid-infrared (mid-IR) fingerprinting regime where the gas phase has strong fundamental vibrational transitions. However, the extension of OFC's into the mid-IR has proven to be challenging. Modelocked lasers emitting beyond 2.5 µm have not yet been demonstrated [1], and nonlinear optical techniques, such as difference frequency generation[10-12] and optical parametric oscillation [13][14][15][16], are often used to convert an OFC from the near-IR to the mid-IR with additional system complexities. In addition, the repetition rate of the OFC needed for gas-phase spectroscopy is on * Corresponding author: my2473@columbia.edu the order of 100 MHz especially for probing Dopplerbroadened absorption linewidths [17,18]. Therefore, detection techniques with high instrumental resolution are often required to resolve individual comb lines of a low repetition rate OFC. Comb-resolved molecular spectroscopy has been achieved using modelocked lasers in dual-comb systems [17][18][19][20] through long time averaging, high-resolution Fourier transform spectrometers (FTIR) [21] and VIPA-based spectrographs [9]. The generation of two OFC's with slightly different repetition ra...

Laser spectroscopy for breath analysis: towards clinical implementation

“…To reach the mid-IR wavelength range two main different approaches are most often used [78]: nonlinear frequency conversion such as optical parametric oscillation (OPO) or difference frequency generation (DFG) in combination with near-IR mode-locked lasers, or alternatively generating mid-IR comb directly from semiconductor lasers. Other approaches such as using microresonators to generate mid-IR combs are under development [79].…”

Dissipative Kerr solitons in optical microresonators

“…The observation of DKS in microresonators yields a merging of soliton physics and high-precision frequency comb applications, stimulating a renaissance in dissipative soliton research and enabling many technological applications. Soliton microcombs have already been applied succesfully to dual-comb spectroscopy in the near- (38)(39)(40) and mid-infrared (36), scanning comb spectroscopy (41), as well as the demonstration of a self-referenced comb for the counting of optical frequencies [both with (42) and without external broadening (43)]. Likewise, soliton microcombs have been used in massively parallel communication (44), in pairs at both the transmitter and receiver side, for low-noise microwave generation (45) as well as for chip-scale dual-comb-based light detection and ranging (LIDAR) (46,47).…”

Turn-key, high-efficiency Kerr comb source

“…Comb generation in microresonators enable integrated and robust platforms [1,2] that can be used for numerous applications such as spectroscopy [3][4][5][6], distance ranging [7,8], frequency synthesis [9,10], optical clocks [11], and data communications [12,13]. Recently, significant progress has been made in integrating microresonator combs by using low-power, electrically pumped sources [14][15][16], and by utilizing novel generation methods such as pump modulation [17,18] or thermal control of the resonances [19].…”