Continuous-wave (CW) laser-based spectroscopic techniques provide much higher signal-to-noise, accuracy, and resolution than traditional spectroscopic tools such as Fourier-Transform Spectrometers (FTS’s) at the expense of measurement bandwidth. Optical frequency comb (OFC) based techniques aim to combine the advantages of CW lasers with broadband output allowing for measurements not possible with other light sources. OFC advances in the mid-infrared bring these advantages to the molecular fingerprint region where more sensitive spectroscopy is possible.<br/><br/>To date, demonstrations of MIR OFC’s have suffered from low power, poor wavelength coverage, or low sensitivity. Systems that do excel in these areas have high cost and complexity. The technique and measurements reported here demonstrate that singly resonant, single frequency optical parametric oscillators (OPO’s) are a powerful platform for generating MIR OFC’s.<br/><br/>An EOM frequency comb is first generated via phase modulation of CW light near 1064 nm. An inexpensive direct digital synthesizer (DDS)-based scheme is used to generate a chirped pulse modulation resulting in a ~1 GHz-wide frequency comb with uniform mode heights and repetition rates between 1 MHz and 10 MHz. This comb pumps the OPO, resulting in an “idler” output that is a MIR OFC tunable between 2200 - 4000 nm with &gt;1 W output power. This technique is utilized to perform frequency comb spectroscopy on select rovibrational features near 3000 nm in methane and acetylene.

Technique for mid-infrared spectroscopy using a continuous-wave OPO pumped by an optical frequency comb

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