Rapid and sensitive trace gas detection with continuous wave Optical Parametric Oscillator-based Wavelength Modulation Spectroscopy

Abstract

A fiber-amplified Distributed Bragg Reflector diode laser is used to pump a continuous wave, singly resonant Optical Parametric Oscillator (OPO). The output radiation covers the 3-4 µm with ability of rapid (100 THz/s) and broad mode-hop-free tuning (5 cm −1 ). Wavelength Modulation Spectroscopy is combined with the OPO to take optimal advantage of the spectral scan speed. The sensitivity of the system was determined as 0.8 ppbv (parts-perbillion by volume) for ethane (C 2 H 6 ) for the absorption peak at 2996.9 cm −1 recorded in 1.3 seconds, corresponding to a noise equivalent absorption sensitivity (NEAS) of 1.2 × 10 −9 cm −1 /Hz 1/2 . A comparison between results using the 1 st , 2 nd and 4 th harmonic derivative signal from wavelength modulation was performed. The broad continuous tunability was demonstrated by covering 35 cm −1 while recording absorption features of ethane, methane and water.

Real-time, subsecond, multicomponent breath analysis by Optical Parametric Oscillator based Off-Axis Integrated Cavity Output Spectroscopy

“…This shows that for precise measurements during long-term experiments the wavelength has to be controlled. However, the wavemeter (Wavemeter WA-1000 has a speed of 1 Hz) cannot follow the high scanning speeds, up to 100 THz/s, of the OPO [31]. Therefore, we measured the relative wavelength by tracking an etalon fringe pattern (see insertion in Fig.…”

Mid-infrared optical parametric oscillators and frequency combs for molecular spectroscopy

“…The mode-hopfree tuning range of the DFB and DBR diode lasers is typically a few tens of GHz, but an ECDL can be scanned up to several THz, which has proven useful in molecular spectroscopy [77,88,89]. Mode-hop-free SRO scanning speeds of several THz/s have been reported with both DBR lasers [90,91,92] and ECDLs [88].…”

“…for formaldehyde (H 2 CO) has been achieved with a spectrometer that combines WMS with a multipass cell, and utilizes a 3.5-µm DFG source [163]. Demonstrations of WMS using CW mid-infrared OPOs have also been reported [164], including a measurement of ethane (C 2 H 6 ) with a detection limit of ~1ppb in ~1 second at 3.3 µm (NNEA = 1.2×10 -9 cm -1 Hz -1/2 ) [91]. The theory and general aspects of WMS are well summarized in a paper by Silver [161], and discussed in more detail in papers of Axner's group [165,166].…”

Gas exchange in fruits related to skin condition and fruit ripening studied with diode laser spectroscopy

“…Laser spectroscopy of gases emitted from fruits is a powerful and accurate method. 15 For the internal gas contents and gas exchange measurements, techniques based on intrusive electrode probes or extraction of gas from the fruit interior by syringes are commonly used. 16,17 The techniques described can be used to measure gas contents and gas dynamics but are frequently complicated or intrusive, thus influencing the fruit tissue which might affect the physiological processes.…”