Abstract: For cavity enhanced optical spectroscopy, the cavity modes are used as a frequency reference. Data analysis methods are employed that assume the data points are at equally spaced frequencies. Parameters of interest such as line width, integrated absorption etc. can be determined from such data without knowledge of the frequencies of any of the data points. Methods for determining the FSR index of each ring-down event are also provided.

Abstract: This work provides event selection in the context of gas leak pinpointing using mobile gas concentration and atmospheric measurements. The main idea of the present approach is to use a moving minimum to estimate background gas concentration, as opposed to the conventional use of a moving average for this background estimation.

Abstract: In cavity ring-down spectroscopy (CRDS), scattering into the backward mode of a traveling wave ring-down cavity can degrade conventional CRDS performance. We have found that this performance degradation can be alleviated by measuring the backward mode signal emitted from the ring-down cavity, and using this signal to improve the processing for extracting ring-down times from the measured data. For example, fitting an exponential to the sum of the intensities of the forward and backward signals often provides substantially better results for the ring-down time than fitting an exponential to the forward signal alone. Other possibilities include extracting cavity eigenmode signals from the forward and backward signals and performing separate exponential fits to the eigenmode signals. An optical circulator can be used to facilitate measurement of the backward mode signal.

Abstract: For cavity enhanced optical spectroscopy, the cavity modes are used as a frequency reference. Data analysis methods are employed that assume the data points are at equally spaced frequencies. Parameters of interest such as line width, integrated absorption etc. can be determined from such data without knowledge of the frequencies of any of the data points.

Abstract: Improved gas leak detection from moving platforms is provided. Automatic horizontal spatial scale analysis can be performed in order to distinguish a leak from background levels of the measured gas. Source identification can be provided by using isotopic ratios and/or chemical tracers to distinguish gas leaks from other sources of the measured gas. Multi-point measurements combined with spatial analysis of the multi-point measurement results can provide leak source distance estimates. Qualitative source identification is provided. These methods can be practiced individually or in any combination.

Abstract: In cavity ring-down spectroscopy (CRDS), scattering into the backward mode of a traveling wave ring-down cavity can degrade conventional CRDS performance. We have found that this performance degradation can be alleviated by measuring the backward mode signal emitted from the ring-down cavity, and using this signal to improve the processing for extracting ring-down times from the measured data. For example, fitting an exponential to the sum of the intensities of the forward and backward signals often provides substantially better results for the ring-down time than fitting an exponential to the forward signal alone. Other possibilities include extracting cavity eigenmode signals from the forward and backward signals and performing separate exponential fits to the eigenmode signals.

Abstract: In cavity ring-down spectroscopy (CRDS), scattering into the backward mode of a traveling wave ring-down cavity can degrade conventional CRDS performance. We have found that this performance degradation can be alleviated by measuring the backward mode signal emitted from the ring-down cavity, and using this signal to improve the processing for extracting ring-down times from the measured data. For example, fitting an exponential to the sum of the intensities of the forward and backward signals often provides substantially better results for the ring-down time than fitting an exponential to the forward signal alone. Other possibilities include extracting cavity eigenmode signals from the forward and backward signals and performing separate exponential fits to the eigenmode signals.

Abstract: Improved calibration of a dual-etalon frequency monitor having x-y outputs is provided. An ellipse is fit to the (x,y) points from a set of calibration data. For each (x,y) point, an angle ? is determined. A linear fit of frequency to ? is provided. Differences between this linear fit and the determined values of ? are accounted for by including a spline fit to this difference in the calibration.

Abstract: In a dual etalon wavelength monitor, improved performance is obtained by identifying first and second dead zones where the first and second etalon signals respectively have significantly reduced sensitivity. When a measurement is in the first dead zone, only the second etalon signal is employed to determine wavelength. When a measurement is in the second dead zone, only the first etalon signal is employed to determine wavelength. When a measurement is in neither zone, both first and second etalon signals are employed to determine the wavelength.

Abstract: Improved calibration of a dual-etalon frequency monitor having x-y outputs is provided. An ellipse is fit to the (x,y) points from a set of calibration data. For each (x,y) point, an angle ? is determined. A linear fit of frequency to ? is provided. Differences between this linear fit and the determined values of ? are accounted for by including a spline fit to this difference in the calibration.

Abstract: In a dual etalon wavelength monitor, improved performance is obtained by identifying first and second dead zones where the first and second etalon signals respectively have significantly reduced sensitivity. When a measurement is in the first dead zone, only the second etalon signal is employed to determine wavelength. When a measurement is in the second dead zone, only the first etalon signal is employed to determine wavelength. When a measurement is in neither zone, both first and second etalon signals are employed to determine the wavelength.