Trace gas detection with cavity ring down spectroscopy

Abstract

Depth-resolved cathodoluminescence spectroscopy of silicon supersaturated with sulfur Appl. Phys. Lett. 102, 031909 (2013) Effect of plasma N2 and thermal NH3 nitridation in HfO2 for ultrathin equivalent oxide thickness J. Appl. Phys. 113, 044103 (2013) Atomic-scale characterization of germanium isotopic multilayers by atom probe tomography J. Appl. Phys. 113, 026101 (2013) Monitoring metal contamination of silicon by multiwavelength room temperature photoluminescence spectroscopy AIP Advances 2, 042164 (2012) Annealing studies of heteroepitaxial InSbN on GaAs grown by molecular beam epitaxy for long-wavelength infrared detectors J. Appl. Phys. 112, 083107 (2012) Additional information on Rev. Sci. Instrum. Trace gas detection of small molecules has been performed with cavity ring down (CRD) absorption spectroscopy in the near UV part of the spectrum. The absolute concentration of the OH radical present in trace amounts in heated plain air due to thermal dissociation of H 2 0 has been calibrated as a function of temperature in the 720-1125 0 C range. Detection of NH 3 at the 10 ppb level is demonstrated in calibrated NH 3 /air flows. Detection of the background Hg concentration in plain air is performed with a current detection limit below 1 ppt. The effect of the laser linewidth in relation to the width of the absorption line is discussed in detail. Basic considerations regarding the use of CRD for trace gas detection are given and it is concluded that CRD spectroscopy holds great promise for sensitive L(sub)-ppbl and fast (kHz) detection of many small molecules.

Toward real-time measurement of atmospheric mercury concentrations using cavity ring-down spectroscopy

“…Jongma et al (1995) pioneered ultraviolet CRDS detection of trace gases including Hg 0 with a frequency-doubled, pulsed dye laser (linewidth of 0.1 cm −1 ) pumped by a frequency-tripled Nd:YAG laser at 355 nm and a 0.45 m length open-path CRDS cavity using mirrors with 99.6% reflectivity. This setup was used to measure Hg 0 background concentrations (i.e., 63 ng m −3 ) in their laboratory with a noise-equivalent (1σ detection limit of 9 ng m −3 for 3 s averaging time.…”

Measurement of the beam intensity in a laser desorption jet-cooling mass spectrometer

“…9,14,15 With the cavity designed as described above, the cavity mode spectrum is quasicontinuous 16 due to the lifting of the degeneracy of the longitudinal and transverse modes. As long as the laser linewidth is spectrally narrower than the absorption feature of the species under study, the time dependence of the light intensity inside the cavity is correctly described with a single exponentially decaying curve.…”

“…As long as the laser linewidth is spectrally narrower than the absorption feature of the species under study, the time dependence of the light intensity inside the cavity is correctly described with a single exponentially decaying curve. 15,17 It is noted once more, that in a CRD experiment the rate of absorption of a light pulse confined in a closed optical cavity is measured and the measurement is therefore independent of light source intensity fluctuations, as long as the spectral intensity distribution of the light stays constant from pulse to pulse. The ring down transient is displayed on the same digital oscilloscope, and averaged over typically 25 laser pulses.…”

Polarization dependent cavity ring down spectroscopy

“…5 As long as mirrors with a sufficiently high reflectivity, detectors with a sufficiently fast time response, and tunable ͑pulsed͒ light sources are available there is no intrinsic limitation to the spectral region in which CRD can be applied. By now, successful application of CRD spectroscopy has been demonstrated from the uv part of the spectrum 6 to the ir spectral region. 7,8 The application of CRD is most straightforward if it can be assumed that the linewidth of the light source can be neglected relative to the width of the molecular absorption.…”

“…It has been shown, however, that if this assumption is no longer valid, one can still extract the correct absorption coefficient from the measured transients, provided the spectral intensity distribution of the light source is known. 6,9 As a consequence, it has been experimentally demonstrated that one does not necessarily need a narrow-band pulsed laser to perform a CRD experiment. One might just as well use a polychromatic light source and extract the spectral information after spectrally dispersing the light exiting the cavity, either in a monochromator or by using a Fourier transform spectrometer.…”