A frequency-measurement method uses a dual frequency-comb spectrometer as an optical wavemeter to measure the frequency of a reference laser that is used to frequency-stabilize the spectrometer. The method includes measuring a walking rate of center bursts in a sequence of interferograms recorded by the spectrometer, determining a number of teeth in each of a plurality of Nyquist windows formed by the dual frequency-comb spectrometer, and determining a Nyquist number of the one Nyquist window covering the laser frequency. The reference laser frequency can then be determined from the number of teeth in each Nyquist window, the Nyquist number, and the comb spacing of either one of the two frequency combs of the dual frequency-comb spectrometer. The reference laser frequency does not need to be measured with a separate wavemeter, or calibrated with respect to a known atomic or molecular transition.

A short-pulse, narrowband, line-selectable and tunable solid-state laser is described. The device requires a pump source, an active solid-state laser medium, an enclosing cavity, mirrors to contain the light, a method of removing the pulse from the cavity, a wavelength selection system, and a laser linewidth narrowing system. One implementation of this is an Er:YAG laser, side pumped by semiconductor lasers in the erbium absorption band near 1475 nm, with an intracavity etalon and a switchable spectral filter. To remove the pulse from the cavity, cavity dumping issues, which assures constant pulse energy and pulse length over a range of repetition rates, in this case from 100 Hz to 20 kHz. Line selection is obtained by use of wavelength filters and fine tuning with an etalon, which also acts as the linewidth narrowing system.

The invention relates to a system for monitoring an airspace for an extensive area, with at least two optical sensors with a passive Fourier transform infrared spectrometer, wherein each optical sensor has an adjustable monitoring range and wherein the monitoring ranges of the at least two optical sensors overlap at least in sections, having a server for evaluating the measurement data and for controlling the at least two optical sensors, the server being set up to monitor the optical sensors for automatic scanning of the monitored areas, wherein the server assigns a respective solid angle to the measurement data on the basis of the position data of the optical sensor, evaluates the measurement data of the optical sensors to derive the spectral intensity distribution of the received IR radiation for each solid angle and, by means of correlation of the intensity distribution with known gas spectra, to identify at least one target substance, in the event of an incident, if a first optical sensor identifies a target substance in a first solid angle, to control at least one further optical sensor, to scan the overlap region with the monitoring region of the first optical sensor, to identify the target substance from the measurement data of the at least one further optical sensor and, in the event of an incident, to control at least one further optical sensor, to scan the overlap region with the monitoring region of the first optical sensor, to identify the target substance from the measurement data of the at least one further optical sensor, identifying at least one further solid angle with an infrared signal of the target substance, and determining the coordinates of the overlap region with increased concentration of the target substance from the solid angle information of the first solid angle and of the at least one further solid angle, wherein the measurement signals of the at least one further optical sensor in spatial directions with too small a measurement radius are not included in the evaluation.

Measurement apparatuses and methods are disclosed for generating high-precision and—accuracy gas concentration maps that can be overlaid with 3D topographic images by rapidly scanning one or several modulated laser beams with a spatially-encoded transmitter over a scene to build-up imagery. Independent measurements of the topographic target distance and path-integrated gas concentration are combined to yield a map of the path-averaged concentration between the sensor and each point in the image. This type of image is particularly useful for finding localized regions of elevated (or anomalous) gas concentration making it ideal for large-area leak detection and quantification applications including: oil and gas pipeline monitoring, chemical processing facility monitoring, and environmental monitoring.

A filter for a micropulse differential absorption LIDAR is provided. The filter comprises an etalon including a free spectral range substantially the same as a difference between a first laser wavelength and a second laser wavelength, the etalon further including a finesse providing substantial background noise suppression and substantially constant transmission of the first laser wavelength and the second laser wavelength over a predetermined range of wavelengths, and a first filter having a first filter bandpass selected to include the first laser wavelength and the second laser wavelength.

A system and method to accurately estimate the strength and changes of the monitoring signal for sensing applications, this invention involves the monitoring of signal strength and changes through the use of a pseudorandom binary sequence bit stream to modulate the transmitter of a data link, when beating the transmitter signal with absorption structure signal from the sensor at the receiver, the changes in the received signal strength are proportional to the sensing signal being monitored. The received signal bit pattern is monitored by an error detector scheme to report a Bit Error Rate level based on the changes in the sensing signal level as compared to the bit stream from the transmitter. This results in a very accurate robust monitoring technique with high consistency and repeatability.

Apparatus and associated methods relate to determining metrics of water particles in clouds by directing light pulses at a cloud and measuring a peak, a post-peak value and a high-frequency fluctuation of light signals reflected from the cloud. The light pulses include: a first pulse having circularly polarized light of a first wavelength; and a second pulse of a second wavelength. The reflected light signals include: a first reflected light signal having left-hand circular polarization of the first wavelength; a second reflected light signal having right-hand circular polarization of the first wavelength; and a third reflected light signal of the second wavelength. An extinction coefficient and a backscatter coefficient are determined based on the measured peak and post-peak slopes of the first and second reflected light signals. The measured high-frequency fluctuations of the three reflected light signals can be used to calculate cloud particle sizes.

Systems, methods and devices to detect target substances in confined or open spaces, and from the ground or remote locations are disclosed. A system includes a radiation emission source and one or more transducers configured to detect target substances. The transducer to detect target substances includes a filter that allows various wavelengths of light to pass through while attenuates or reflects others; and one or more chambers disposed within the optical path of the filter. The transducer may also include electromagnetic radiation detectors to detect electromagnetic radiation at wavelengths different from the wavelengths transmitted by the filter. The systems, methods, and devices disclosed allow shifting the detection range of phenomena in which the detection/observation technology is not efficient to other detection ranges where detection can be optimized.

A freeform imaging system with a spectrometer and telescope components optically connected and optimized to increase the spectral and spatial resolution capabilities. Many embodiments of the system are capable of producing a spectral resolution of approximately 1 nm and a spatial resolution less than 30 m such that the imaging system can be used to accurately capture and measure point source plumes of various atmospheric gases including CH.sub.4, CO.sub.2, CO, N.sub.2O, and H.sub.2O.

Interferometric speckle visibility spectroscopy methods, systems, and non-transitory computer readable media for recovering sample speckle field data or a speckle field pattern from an off-axis interferogram recorded by one or more sensors over an exposure time and determining sample dynamics of a sample being analyzed from speckle statistics of the speckle field data or the speckle field pattern.