Intracavity trace molecular detection with a broadband mid-IR frequency comb source

Abstract

Ultrasensitive detection of methane, isotopic carbon dioxide, carbon monoxide, formaldehyde, acetylene, and ethylene is performed in the spectral range 2.5-5 μm using intracavity spectroscopy in broadband optical parametric oscillators (OPOs). The OPOs were operated near degeneracy and synchronously pumped either by a mode-locked erbium (1560 nm) or thulium (2050 nm) fiber laser. A large instantaneous bandwidth of up to 800 cm −1 allows for simultaneous detection of several gases. We observe an effective path-length enhancement due to coherent interaction inside the OPO cavity and achieve part-per-billion sensitivity levels. The measured spectral shapes are in good agreement with a model that takes into account group delay dispersion across the broad OPO frequency band.

Developments of mid-infrared optical parametric oscillators for spectroscopic sensing: a review

“…Femtosecond OPO provides high-power frequency combs in the mid-IR spectral region and fits very well for these applications. 97,98 These OPOs can operate both for broad band width and widely tunable applications. 99,100 Cavity-enhanced direct frequency comb spectroscopy (CE-DFCS) emerged as a powerful new technique that provides high spectral coverage, high resolution, and high sensitivity by combining the frequency comb with several other important elements, including an external enhancement cavity and a broadband, yet highly resolving, detection system.…”

“…104 Using intracavity spectroscopy of broadband OPO, researchers achieved ultrasensitive detection of methane, isotopic carbon dioxide, carbon monoxide, formaldehyde, acetylene, and ethylene as well. 105 Thanks to the precision spectroscopy, spectral shifts of transition frequencies associated with different isotopes can be detected. The determination of isotope ratios has proved to be a powerful tool in medical analysis, geology, and climate research.…”

Recent advances in ultrafast optical parametric oscillator frequency combs

“…33 The absence of an intense broadband laser or OPO sources oscillating in the mid-IR meant that until recently, intracavity techniques for mid-IR gas sensing were restricted only to cavity ring-down methods. Intracavity techniques offer a potentially simpler yet highly sensitive route to mid-IR gas sensing.…”

Fourier transform and Vernier spectroscopy using an optical frequency comb at 3–54 μm

“…In particular, OPOs based on orientation-patterned gallium arsenide (OP-GaAs) crystals pumped by Cr:ZnSe or Tm:fiber femtosecond lasers have made it possible to reach wavelengths beyond ~4.8 µm, a barrier for the well-established oxidebased materials [7,8]. Both DFG and OPO sources have been used for MIR optical frequency comb spectroscopy with different detection methods, namely a Fourier transform spectrometer [9][10][11][12][13], a virtually imaged phased array (VIPA) [14,15], mode-resolved Vernier spectroscopy [16], and dual comb spectroscopy [17,18]. However, the spectral range of all previous demonstrations was limited to <4.8 µm.…”