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

Long-wave infrared generation from femtosecond and picosecond optical parametric oscillators based on orientation-patterned gallium phosphide

“…It was noted by Morz et al that OPOs require significant stabilisation for sensitive applications [2], and this is certainly true for application such as microspectroscopy and DCS (as we have demonstrated separately [34]). The passive stability of our fs OPO described here is still suitable for many applications.…”

“…The first OPGaP optical parametric oscillator (OPO) pumped with a 1-µm laser-generated nanosecond mid-IR pulses at 4.6 µm [14]. We previously demonstrated the first 1-µm-pumped OPGaP OPO producing mid-IR beyond the transparency range of PPLN, using a modelocked fiber laser producing 200-fs pulses at 1040 nm, achieving tuning to 12-µm using a range of different OPGaP grating periods [33], and also demonstrated mid-IR DCS with dual OPGaP OPOs [34].…”

High-power frequency comb at 2 μm wavelength emitted by a Tm-doped fiber laser system

“…Frequency combs at around 2 μm wavelength are currently of tremendous interest for next-generation spectroscopy targeting sensitive detection of certain gases (e.g., CO 2 , NH 3 ) [14,15] and/or to further extend the wavelength coverage of frequency combs to the molecular fingerprint region (3-20 μm) via parametric downconversion in nonlinear crystals [16,17]. With only very few exceptions [18,19], nonlinear crystals with high transmission in the mid-IR (>5 μm) are opaque at around 1 μm wavelength or high-power operation is severely limited by multiphoton absorption, exactly where the most powerful driving lasers operate [20]. It is for that reason that the development of powerful laser sources at wavelengths >1.5 μm are in urgent demand by a large community, which targets next-generation metrology and spectroscopy and relies on powerful frequency combs in the mid-IR.…”

Computational coherent averaging for free-running dual-comb spectroscopy

“…If implemented successfully, the time-dependent distribution of the spectral power will be aligned in the frequency domain enabling averaging without dispersing the power over a large rf bandwidth, so called coherent averaging, also known in radar systems as coherent integration. It is important to note that for some applications a straightforward alignment of multiple short-time DCS magnitude spectra [4][5][6] or time-domain interferogram bursts [7] may be sufficient. Nevertheless, there are some inherent disadvantages of this approach: the linewidths of the beat notes are limited by the acquisition time of a single frame and the lack of repetition rate correction does not account for the cumulative broadening of the beat notes at the edges of the spectrum.…”