Abstract
To expand the applicability of noise-immune cavity-enhanced optical heterodyne molecular spectrometer (NICE-OHMS), a universal system incorporating a fiber-coupled single-sideband modulator (f-SSM) for control of the laser frequency has been developed. A homemade PID servo mainly composed of two integrators has been designed, resulting in a locking bandwidth of 170 kHz and a continuous tuning range of 2.2 GHz. The system exhibits a noise-equivalent Doppler-broadened absorption limit of 8.0×10−14 cm−1 for an integration time of 64 s. Since the f-SSM is the sole external frequency actuator, this opens up for NICE-OHMS based on a multitude of laser systems.
Highlights
Benefiting from its superior characteristics, including high sensitivity and resolution, good selectivity, fast response and non-invasive measurement, laser absorption spectroscopy (LAS) has been applied to various fields, e.g. air pollution monitoring [1], industrial process control [2], medical diagnostics [3], isotope measurement [4], national defense security [5], and Mars methane detection [6]
The frequency calibrations of the error signals originate from the odd-symmetry error signals when scanning the laser or the modulation frequency, respectively, whose peak-to-peak voltage amplitude corresponds to a frequency deviation equal to the FWHM of cavity mode (6.9 kHz in our case)
A NICE-OHMS spectrometer for Doppler broadened (Db) trace gas detection has been developed around a fiber-coupled singlesideband modulator (f-SSM), which acts as a sole actuator of the frequency of the laser light
Summary
Benefiting from its superior characteristics, including high sensitivity and resolution, good selectivity, fast response and non-invasive measurement, laser absorption spectroscopy (LAS) has been applied to various fields, e.g. air pollution monitoring [1], industrial process control [2], medical diagnostics [3], isotope measurement [4], national defense security [5], and Mars methane detection [6]. One way to improve on this is to utilize a fast scanning scheme [10] or a modulation/demodulation [11] technique since such can encode the absorption information into audio/radio frequency range where the amount of technical noise is low. This reduces the 1/f noise and can provide an MDA in the 10−5−10−6 range
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