Abstract
Dual-comb spectroscopy is a powerful spectroscopic tool with ultrahigh-resolution, high-sensitivity properties, which opens up opportunities for the parallel detection of multi-species molecules. However, in its conventional form, highly stable laser combs with sophisticated control systems are required to perform dual-comb spectroscopy. Here, a passive mutually coherent dual-comb spectroscopy system via an optical-optical modulation method is addressed, where all fast phase-locking electronics are retired. Without post computer-based phase-correction, a high degree of mutual coherence between the two combs with a relative comb-tooth linewidth of 10 mHz is achieved, corresponding to a coherent time of 100 s. To demonstrate the performance and versatility of the system, the dual comb spectrometer is applied to record the mode-resolved single molecular spectra as well as parallel detected spectra of mixed gases including CO2, CO and C2H2 that well agree with the established spectral parameters. Our technique exhibits flexible wavelength tuning capability in the near-infrared region and can be potentially extended to the mid-infrared region for more applications.
Highlights
Laser frequency comb spectroscopy with enhanced measurement speed, sensitivity, and precision has been used in various applications [1, 2], including distance metrology [3], molecular precision spectroscopy [4], chemical catalysis [5], biological analysis [6], environmental monitoring [7], and clinical pathology [8]
No post processing (except for fast Fourier transform (FFT)) of the raw data was performed in our experiments
High mutual coherence of the dual comb generated by the optical parametric amplification (OPA) process makes it possible to resolve comb lines of a Fourier-limited width of approximately 10 mHz without active carrier envelop phase stabilization at high signal-to-noise ratio (SNR)
Summary
Laser frequency comb spectroscopy with enhanced measurement speed, sensitivity, and precision has been used in various applications [1, 2], including distance metrology [3], molecular precision spectroscopy [4], chemical catalysis [5], biological analysis [6], environmental monitoring [7], and clinical pathology [8]. Among different laser comb technologies, dual-comb spectroscopy offers the prospect of surpassing the widely used Fourier transform spectroscopy (FTS) techniques. Dual-comb spectroscopy (DCS), which measures the time-domain interference between two combs with slightly different line spacing, is capable of very fast spectral measurements with high precision and sensitivity [9, 10]. The technique can be understood as a multi-heterodyne detection of pairs of neighboring comb lines, by which the optical frequency combs are down-converted to a single radio-frequency comb [11]. The technique of dual-comb spectroscopy has not yet realized its full potential, mostly because of the difficulty of synchronizing the pulse trains of two comb lasers to achieve (2020) 1:7 a narrow relative linewidth between the pairs of teeth of the two combs. The timing and phase between the two pulses must be accurate to within a fraction of an optical cycle [12, 13]
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