Mid-infrared cross-comb spectroscopy

Abstract

Dual-comb spectroscopy has been proven beneficial in molecular characterization but remains challenging in the mid-infrared region due to difficulties in sources and efficient photodetection. Here we introduce cross-comb spectroscopy, in which a mid-infrared comb is upconverted via sum-frequency generation with a near-infrared comb of a shifted repetition rate and then interfered with a spectral extension of the near-infrared comb. We measure CO2 absorption around 4.25 µm with a 1-µm photodetector, exhibiting a 233-cm−1 instantaneous bandwidth, 28000 comb lines, a single-shot signal-to-noise ratio of 167 and a figure of merit of 2.4 × 106 Hz1/2. We show that cross-comb spectroscopy can have superior signal-to-noise ratio, sensitivity, dynamic range, and detection efficiency compared to other dual-comb-based methods and mitigate the limits of the excitation background and detector saturation. This approach offers an adaptable and powerful spectroscopic method outside the well-developed near-IR region and opens new avenues to high-performance frequency-comb-based sensing with wavelength flexibility.

High‐Power Mid‐IR Few‐Cycle Frequency Comb from Quadratic Solitons in an Optical Parametric Oscillator

“…In short, this work paves the way to realization of a compelling new source of ultrashort‐pulse frequency combs in the mid‐infrared region which can benefit numerous applications, for example, spectroscopy methods that require high‐power, broadband, and short‐pulse MIR frequency combs. [ 40,41 ] This work sheds new lights on soliton generation based on the quadratic nonlinearity and its potential in the MIR region. Recent advances in integrated quadratic platforms [ 33,38,43 ] promise on‐chip realization of such sources in the future.…”

“…In addition, we want to emphasize that the half‐harmonic signal of femtosecond degenerate OPOs are frequency combs that are intrinsically phase‐ and frequency‐locked to their pump combs, which is well‐established in previous works. [ 26,31,40 ] Very recently, we have used the OPO presented in this work as the comb source for a dual‐comb‐based spectroscopy experiment in the mid‐IR, [ 41 ] enabled by its comb character and intrinsic locking. Moreover, it is experimentally shown that the CEO frequency noise can be reduced by 6 dB through the half‐harmonic generation.…”

Compact mid-infrared dual-comb spectrometer over 3–4 μm via intra-pulse difference frequency generation in LiNbO3 waveguides

“…In comparison with bulk crystals, periodically poled LN (PPLN) waveguides with strong light confinement ensure high-efficiency nonlinear frequency conversion over a long interaction path. Therefore, PPLN waveguides allow low-power near-infrared (NIR) laser systems to perform efficient nonlinear processes and scale their spectra to the MIR region [11][12][13][14] . MIR sources based on LN waveguides have small size and low power consumption, making them ideal for the construction of integrated MIR frequency comb equipment.…”

Broadband Up‐Conversion Mid‐Infrared Time‐Stretch Spectroscopy

“…will benefit from high data refresh rate (>1 MHz) and short measurement time (<1 μs), which remain challenging for conventional techniques, such as stroboscopic spectroscopy and Michelson-type Fourier-transformed infrared spectroscopy (FTIR). [16,17] Dual-comb-type FTIR, [18] without moving parts, may access the sub-μs region using optical combs of large line-spacing, [19][20][21][22][23][24][25][26][27] which, however, requires high phase coherence [28][29][30][31] for heterodyne detection and suffers from limited bandwidth and signal-to-noise ratio (SNR) due to the multiplex penalty. [18] Pump-probe spectroscopy (or similar timeresolved techniques) offers ps to fs temporal resolution but is limited to investigating reversible or repetitive events.…”