Frequency-comb-referenced molecular spectroscopy in the mid-infrared region

Abstract

A simple method for absolute-frequency measurements of molecular transitions in the mid-IR region is reported. The method is based on a cw singly resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3:45 μm. The mid-IR frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute-frequency measurement of the Pð7Þ transition of the ν 3 band of CH 4 are demonstrated.

Frequency-comb-referenced mid-infrared source for high-precision spectroscopy

“…The design of the singly resonant continuous-wave OPO is similar to that reported in our previous publications [15,23]. As a pump laser we use a narrow-linewidth Yb-fiber-laser system (IPG YAR-15K-1064-LP-SF), which produces up to 15 W of output power at 1064 nm wavelength.…”

“…At the moment, however, the fully stabilized mid-infrared OFCs are rather complex and are not commercially available. A more common solution is to reference the MIR laser to an NIR OFC via nonlinear optical frequency conversion [11][12][13][14][15][16][17][18][19]. This is typically done by using continuous-wave (cw) DFG [12,14] or a cw OPO [11,[15][16][17], following the scheme of Fig.…”

Fully stabilized mid-infrared frequency comb for high-precision molecular spectroscopy

“…This is required particularly in optical frequency metrology [4] and Fourier synthesis [5], but also with the most sophisticated molecular spectroscopy methods, such as dual-comb spectroscopy [6] and highprecision frequency comb assisted spectroscopy. [7][8][9] Mid-infrared frequency combs are typically generated by nonlinear optics, such as difference frequency generation (DFG) or optical parametric oscillation. An efficient version of the DFG approach is to divide the spectrum of an amplified femtosecond near-infrared (NIR) frequency comb into two portions, which are used as the pump and signal beams for DFG.…”

Frequency comb assisted two-photon vibrational spectroscopy

“…Because of the availability of commercial near-infrared frequency combs, the stabilization of a mid-infrared CW-OPO is often done indirectly, for example by locking both the pump and signal wavelengths with the comb. This also produces a stable idler wavelength due to the conservation of energy [25,26]. A more direct method uses second harmonic generation to convert some of the mid-infrared idler power into a near-infrared beam, which is then referenced to the frequency comb [27].…”