Dual-comb spectroscopy in the spectral fingerprint region using OPGaP optical parametric oscillators

Mid-infrared dual-comb spectroscopy with absolute frequency calibration using a passive optical reference

“…Compared to fully stabilized dual-comb spectrometers based on femtosecond OPOs [13], our developed system is less complicated and demanding; but it provides coarser spectral resolution and frequency precision. On the other hand, compared to similar OPObased DCS systems using cross-correlation of the measured spectrum for offset correction [18,19], our method provides an absolute-frequency-calibrated spectrum, with a consistent and good frequency precision, long term stability and spectral resolution; fully independent from the SNR of the sample spectrum. Finally, compared to conventional Fourier transform spectrometers, our method provides similar spectral resolution and precision, but the measurement time is a few orders of magnitude shorter than a typical mechanical FTS.…”

“…One can also use two singly-resonance OPOs (SROPOs), which eliminates the need for active stabilization of the length of the OPO cavities. DCS is demonstrated by using two freerunning mode-locked lasers pumping two singly-resonance OPOs [18,19]. In the first demonstration, the repetition rate difference (Δf rep ) as well as the f ceo of the two pump lasers were recorded along with the time domain interferogram.…”

“…Each single interferogram was recorded in a time much faster than the de-coherence time of the two idler combs (specially the fluctuations in f ceo values of the two idler combs), thus the spectral information remains intact in each spectrum obtained after Fourier transform, and is only shifted to a different center frequency. The same cross-correlation algorithm is used to correct for the shifts, achieving a spectral resolution of ~0.3 cm −1 after averaging [19]. In both cases the averaged spectrum needs to be shifted manually (by comparison to the simulated spectrum) to achieve absolute frequency calibration.…”

“…The general idea is to monitor an absorption line of a known gas sample, as well as the broadband spectrum of the sample under test. Similar to [19], as long as the measurement time for each individual interferogram is shorter than the de-coherence time of the two idler combs, we can assume that the f ceo of the idler combs are constant for each individual measurement. Therefore, a simple frequency shift after Fourier transform would correct for the f ceo changes in consecutive measurements.…”

Introduction: Nonlinear Optics (NLO) 2017 feature issue

“…The 21 papers in this issue (17 Optics Express and 4 Optical Materials Express) cover a broad range of nonlinear optical effects. Following a trend in recent NLO conferences as well as in the photonics community, ultrafast NLO plays an prominent role, including frequency comb generation [1][2][3], mode-locking of lasers [4], pulse compression [5] and ultrafast spectroscopy [6]. Another central theme of NLO with significant application impact as well as representation in this issue is the generation of new wavelengths, via second order nonlinearities [7][8][9][10] or Raman processes [2,11,12].…”