Abstract: A remote sensing system includes a transmitter for generating multiple beams of light; a combiner for combining the multiple beams of light and directing the combined multiple beams toward a target of multiple gases; and a receiver for receiving the combined multiple beams of light from the target. The first and second transmitted beams of light include, respectively, first and second sets of multiple distinct wavelengths that are simultaneously transmitted toward the target. The receiver receives the multiple distinct wavelengths, and simultaneously detects an intensity of each received wavelength. The first set of multiple distinct wavelengths is selected based on absorption characteristics of a first species of gas, and the second set of multiple distinct wavelengths is selected based on absorption characteristics of a second species of gas. The transmitter includes first and second mode-locked based lasers for generating, respectively, the first and second sets of distinct multiple wavelengths.

Abstract: A cavity ring down gas sensor may include a radiation source emits an input beam of light having a wavelength corresponding to an absorption line of a gas to be detected. The input beam of light is coupled into an optical cavity to amplify an internal beam of light that is reflected about the optical cavity. An optical element is disposed in the optical cavity at an angle close to, but not at, the Brewster's angle to reflect a relatively small portion of the internal beam of light to a detector. When a specified light intensity is reached in the optical cavity, the input beam of light may be prevented from entering the optical cavity, and a cavity ring down time decay may be measured. The cavity ring down time decay may be related to the gas concentration of a gas to be detected in the optical cavity.

Abstract: A device and method for the detection of one or more gases is disclosed. A MEMS structure comprising a micro gas cell array is provided comprising one or more micro gas cells having a predetermined gas therein. The micro gas cells define an optical path therethrough and may comprise a micro lens. Electromagnetic energy from a scene is collected and passed through one or more micro gas cells whereby electromagnetic energy emitted or reflected from a gas of interest in a scene is absorbed by a substantially identical gas contained within a micro gas cell. In this manner, the micro gas cell acts as a spectral filter. The electromagnetic outputs of the micro gas cells, which may comprise one or more spectrally inert micro gas cells, are received by one or more detector elements such as a photon detector array. The ratio of the outputs of the related detector elements are computed by processing electronics, resulting in the identification of the gas of interest.

Abstract: An apparatus and method are used to enhance the sensitivity of a spectrometer (sensor) for trace gas species detection by employing an external cavity continuously tunable CW quantum cascade laser and integrating the absorption spectra across multiple lines of the species. With this method the absorption spectra of NO2 is continuously recorded across the R-branch from 1628.8 cm?1 to 1634.5 cm?1. By integrating the resulting spectra, the detection sensitivity for NO2 is improved by a factor of 15 compared to the sensitivity achieved using single line laser absorption spectroscopy with the same apparatus. This procedure offers much shorter data acquisition times for the real-time monitoring of trace gas species compared with adding repeated scans of the spectra to improve the signal-to-noise ratio.

Abstract: A method and apparatus for enhancing the accuracy of spectroscopic measurements using a cavity ringdown spectrometer (CRDS) is provided. A first aspect of the invention consists of a novel algorithm for the processing of ring-down data that significantly reduces the amplitude of an exponential fitting artifact, and thereby gives a better estimate of the actual loss. The primary cause of the artifact is the presence of an unwanted backwards-traveling wave that counter-propagates within the ringdown cavity. Scattering due to small imperfections at the cavity mirrors produces this wave and its intensity may be minimized by adjustment of the mirror positions during cavity construction. A second aspect of the invention consists of an apparatus for measuring the backscattered wave within a cavity to allow such cavity mirror adjustments to be made.

Abstract: Systems and methods for scanning and analyzing characteristics of a gas sample utilizing electromagnetic radiation are disclosed. More particularly, the systems and methods utilize an electromagnetic radiation source connected to a transmitter and an analyzer connected to a receiver. A sample gas volume to be analyzed is placed between the transmitter and receiver and a frequency sweep of electromagnetic radiation is transmitted through the sample to create a series of spectral data sets, which are developed into a composite spectrogram by the analyzer and processed to determine the one or more characteristics of the sample. A magnetic field can alternatively be applied around the transmitter, receiver and sample to enhance some characteristic analysis applications and to make other characteristic analysis applications possible.

Abstract: The invention relates to a method for determining a gas concentration in a flowing gas mixture, wherein the flowing gas mixture includes solids having a defined size distribution, wherein by way of an optical spectrometer the concentration of a gas is measured in the flowing gas mixture, which includes a measurement beam of the optical spectrometer being conducted during the measurement through a measurement channel having walls made of a gas-permeable material. The invention also relates to a device for carrying out such a method.

Abstract: A gas detector is provided. The gas detector includes a measurement source of optical radiation, a reference source of optical radiation, a measurement detector configured to provide an output signal indicative of a gas of interest, a reference detector configured to provide an output signal at least partially independent of the gas of interest, a measurement optical path extending from the measurement source to the reference and measurement detectors, and a sample region for receiving a gaseous sample. The sample region is located along the measurement optical path. A window is positioned in the measurement optical path downstream from the measurement source and upstream from the reference and measurement detectors. The window is partially transparent to optical radiation and partially reflective to optical radiation.

Abstract: The present invention provides a particle counter capable of sensitively determining the contamination level of a light transmission window. The particle counter according to the present invention includes: a light source 281 for emitting light through a light incident window 24 to a measurement area 40 in a vacuum state or in an approximately vacuum state; a scattered light detector 32 for detecting scattered light through a detection window 30, the scattered light being generated when a light is delivered to the measurement area 40; a vacuum gauge 12 for measuring the pressure of the measurement area 40; a signal processor 13 for converting a detection signal of the scattered light into an electrical signal; and a contamination level determiner 19 for determining the contamination level of the transmission window from the time average of the electrical signal and the pressure.

Abstract: A laser gas analyzer which can include a light source unit including a diode laser that irradiates a gas to be measured with laser light while varying a wavelength thereof; a detection unit including a light receiving element, a gain-variable amplifier into which an output signal of the light receiving element is input, an A/D converter into which the output signal of the amplifier is input, and an arithmetic processing unit that performs a concentration analysis of the gas to be measured; a peak-to-peak detector that detects a peak-to-peak value of the output data of the A/D converter each time the wavelength of the laser light irradiated from the diode laser changes; and a gain adjustment unit that, when the output signal of the peak-to-peak detector deviates from a preset threshold, adjusts the gain of the amplifier in a direction of bringing the output signal back to within the threshold.

Abstract: Provided are sensors and methods of measuring the oxygen concentration of a fluid. An excitation light source is in optical communication with a transducer for transmitting an excitation light that is at least partially absorbed by the transducer. The transducer has a property of photoluminescence, and enters a higher energy state by at least partially absorbing the excitation light and enters a lower energy state through radiation of emitted light, thus producing spectral indicia. A light detection system, which is also in optical communication with the transducer, processes the spectral indicia to determine the concentration of oxygen in the fluid.

Abstract: A calibration card and method of using the card to calibrate an analytical instrument capable of reading a photoluminescent oxygen probe. The card includes at least (a) a first mass of an oxygen sensitive photoluminescent dye retained within a hermetically sealed space so as to isolate the dye from environmental oxygen, and in fluid communication with an activated metal-air battery whereby any oxygen permeating into the hermetically sealed space is quickly consumed by the battery, and (b) a second mass of an oxygen sensitive photoluminescent dye in fluid communication with the environment whereby the second mass of photoluminescent dye is exposed to an environmental concentration of oxygen.

Abstract: The present subject matter relates to methods of high-speed analysis of product samples during production of the product. Light is directed to a portion of a product under analysis and reflected from or transmitted through the product toward optical detectors. Signals from the optical detectors are compared to determine characteristics of the product under analysis. Temperature within the monitoring system may be monitored in order to provide compensation for the signals produced by the optical detectors. The products under analysis may be stationary, moved by an inspection point by conveyor or other means, or may be contained within a container, the container including a window portion through which the product illuminating light may pass.

Abstract: Embodiments of the present invention relate to the analysis of the components of one or more gases, for example a gas mixture sampled from a semiconductor manufacturing process such as plasma etching or plasma enhanced chemical vapor deposition (PECVD). Particular embodiments provide sufficient power to a plasma of the sample, to dissociate a large number of the molecules and molecular fragments into individual atoms. With sufficient power (typically a power density of between 3-40 W/cm3) delivered into the plasma, most of the emission peaks result from emission of individual atoms, thereby creating spectra conducive to simplifying the identification of the chemical composition of the gases under investigation. Such accurate identification of components of the gas may allow for the precise determination of the stage of the process being performed, and in particular for detection of process endpoint.

Abstract: A multi-color cavity ringdown based spectrometer system is housed in a light tight enclosure to detect the presence of trace quantities of gas phase molecules emanating from a subject, explosives, drugs, or hazardous materials. A method is also disclosed for simultaneous real time detection of gas phase molecules emanating from explosives, drugs, hazardous materials, a subject's breath skin or bodily fluid.

Abstract: The invention relates to a gas analyzer for measuring the mercury content of a gas having an Hg light source which transmits transmitted light having wavelengths of at least one spectral line of the mercury, a measuring cell in which the gas to be measured is present, a light receiver, an evaluation unit and a test cuvette which can be introduced into the beam path for checking the operability. To provide an improved gas analyzer which can be calibrated in a simple manner as well as a corresponding improved calibration method, provision is made that the test cuvette contains benzol as a test gas.

Abstract: An optical nose for detecting the presence of molecular contaminants in gaseous samples utilizes a tunable seed laser output in conjunction with a pulsed reference laser output to generate a mid-range IR laser output in the 2 to 20 micrometer range for use as a discriminating light source in a photo-acoustic gas analyzer.

Abstract: In a gas concentration measurement device using a TDLAS measurement, the distortion of peak waves originating from absorption by target components is prevented by reducing a higher-frequency noise signal which occurs in an output of a digital phase-sensitive detection process at the moment of switching the wavelength in a saw-tooth-formed wavelength-sweep operation. A modulating current having a predetermined frequency for component detection and a drive current having a saw-tooth form for wavelength-sweep are superimposed and supplied to a first laser diode (LD) 1, while a drive current having an inverted saw-tooth form, which changes in synchronization with the saw-tooth drive current and in the opposite direction, is supplied to a second LD 5. Laser beams emitted from the LDs 1 and 5 are respectively attenuated by ND filters 3 and 7 (for light-amount adjustments), and mixed by a half mirror 4, to be thrown into a measurement cell 9 filled with a gas to be analyzed.

Abstract: A gas concentration measurement device which utilizes a TDLAS measurement method, and in which the phase-sensitive detection can be performed by digital processing using an integer-arithmetic device, is provided. In the gas concentration measurement device according to the present invention, AC components corresponding to integer multiples of a modulation frequency f contained in an input signal are removed by taking a moving average of data obtained from an output signal of a multiplier 62 for a period of time corresponding to one cycle of the modulation frequency f. As a result, a DC component in the output signal of a digital filter 63 relatively increases, making it easier to extract the DC component by a digital low-pass filter 64, so that a sufficiently accurate phase-sensitive detection can be made even if a digital processing based on integer arithmetic is used.

Abstract: A Gas Filter Correlation Radiometer (GFCR) system and methods of using same are provided. The system's GFCR instrument includes a gas cell. A gas in the gas cell has a chemical composition that is different than that of a target gas in an atmospheric region being examined by the GFCR instrument. The gas included in the gas cell also possesses light absorption features with a portion thereof being at least partially correlated with light absorption features of the target gas. Measurement viewing(s) made with the GFCR instrument provide for at least one positive correlation for the portion of the at least partially correlated features so that the GFCR instrument generates a signal indicative thereof used in a gas filter correlation radiometry application.

Abstract: A system assesses a column of gas in an atmosphere. The system includes an optical transmitter for transmitting (a) an online signal tuned to an online wavelength of gas, (b) an offline signal tuned to an offline wavelength of the gas, and (c) an optical signal for providing altimetry data. A modulator is included for modulating the online signal with a first stepped chirp waveform and modulating the offline signal with a second stepped chirp waveform. A processor assesses the column of gas, after receiving a returned online signal, a returned offline signal and a returned optical signal. A lock-in amplifier is included for (a) multiplying a returned signal with the first stepped chirp waveform to obtain a detected online signal, and (b) multiplying the returned signal with the second stepped chirp waveform to obtain a detected offline signal. The processor is configured to remove ground reflections from the optical signal to obtain scattered noise, and assess the column of gas based on the scattered noise.

Abstract: A gas detector includes a receiver configured to receive light from a light source through gas, the light source having a bandwidth on the order of an absorption linewidth of the gas, the receiver including at least a first etalon having a transmission bandwidth on the order of the absorption linewidth of the gas, the transmission bandwidth of the first etalon being substantially smaller than the bandwidth of the light source. The gas detector further includes a first detector for detecting light transmitted through the first etalon, a second detector for detecting light reflected from the first etalon, and a processor that determines the quantity of gas based on the detected transmitted and reflected light. The gas detector can further include a second etalon with a transmission bandwidth approximately equal and adjacent to the transmission bandwidth of the first etalon.

Abstract: The invention relates to a method for controlling flat glass forming by flowing a molten glass over a liquid tin layer contained in a forming vat wherein a forming characteristic quantity is measured above the glass surface during forming by means of beams generated by at least one absorption spectroscopy-based analyser, wherein the light beams generated by said analyser form a net above the glass surface. A device for carrying out the inventive method comprising an arm for supporting a vessel which comprises a retroreflecting means for receiving a light beam and transmitting it in an opposite direction parallel to an incident optical path is also disclosed.

Abstract: The construct of a specially designed air sampler and its function in order to carry out the Effortless Recalibration (ERB) procedure to an Absorption Biased (AB) designed NDIR gas sensor with the use of a Calibration Master is described.

Abstract: A method for performing a gas migration test in a test area surrounding a ground surface end of a wellbore, including providing an optical gas detector configured to selectively detect methane, establishing a pattern of test points including a plurality of test points at a ground surface in the test area, and using the optical gas detector at each of the test points to obtain an indication of methane concentration at each of the test points.

Abstract: Two detectors of the same kind, each having an identical neutral band-pass filter to the target gas, are installed next to Signal channel and Reference channel detectors as pairs in an AB designed NDIR gas sensor layout, which are called Standard Signal channel detector and Standard Reference channel detector. “Standard” GAMMA is the ratio of Standard signal channel detector output over that of Standard Reference channel detector. “Standard” GAMMA is independent of the measurement Physics of NDIR gas sensors, is dependent only upon the performance characteristics of the sensor component and is also independent of the presence of any amount of target gas in the sample chamber. Consequently, “Standard” GAMMA can be used to proportionally correct and update GAMMA of the sensor as its components age over time thereby rendering such an AB designed NDIR gas sensor self-commissioning or staying accurate over time after initial calibration.

Abstract: A sensor with high sensitivity and selectivity for the detection of NO2 uses a simple diode laser operating nominally at 405 nm in the visible region, a high finesse optical cavity and a low noise photon detector. The sensor employs the multimode broad output of the diode laser with the high finesse optical cavity in an essentially off-axis arrangement that can provide large path lengths of the order of a km in a small volume cell. The detected absorption signal corresponds to multiple line integrated absorption spectroscopy (MLIS). Because the sensor uses visible radiation it can employ optics in the visible region that are normally less expensive. Also, the sensor is free from interference from atmospheric water vapor which is often a severe problem for sensors based on mid-infrared quantum cascade lasers operating in the mid-infrared (for example 1650 cm?1) region.

Abstract: A gas concentration measuring apparatus for measuring a concentration of a measurement target substance contained in a sample gas includes a light source unit in which a light source is arranged, and a sensor unit that is arranged on an optical path of the light source. The sensor unit includes a concentration measuring sensor configured to receive light from the light source after the light has passed through a sample cell unit and measure a concentration of the measurement target substance. The apparatus further includes an introducing device configured to introduce the sample gas to a vicinity of concentration measuring sensor. Therefore, a vicinity of the concentration measuring sensor is filled with an atmosphere of the sample gas so that a concentration of a measurement target substance contained in the sample gas is measured stably and accurately regardless of fluctuations in an ambient atmosphere of a measuring environment.

Abstract: Devices, configurations and methods for improving absorbance detection are provided. For example, methods and devices are provided for determining the absorbance of a droplet, e.g., a droplet on a droplet actuator, by providing an elongated light path through the droplet.

Abstract: A real-time monitoring of an equivalence ratio of a gas-fuel mixture of a gas turbine engine is provided. The system includes multiple optical probes arranged on a plurality of fuel nozzles for transmitting laser beams directly through a gas-fuel mixture or indirectly by reflecting the laser beams from a surface of a centerbody or burner tube of the fuel nozzle. The system also includes one or more detectors to measure the transmitted laser beams from the multiple optical probes. Further, the system includes a data acquisition subsystem for acquiring and processing signals from the one or more detectors to determine the equivalence ratio of the gas-fuel mixture of the nozzle.

Abstract: A wavelength-variable interference filter includes first and second electrodes provided at first and second substrates, respectively, the second substrate including a movable section, first and second electrode wires that extend from the first and second electrodes toward outer circumferential edges of the first and second substrates, respectively, a first opposite electrode wire disposed so as to be isolated from the second electrode, and a first conductive section that connects the first electrode wire with the first opposite electrode wire. The second electrode wire and the first opposite electrode wire extend passing through a center point of an imaginary circle of the movable section in respective directions and dividing the imaginary circle at regular angular intervals.

Abstract: The provision of a dryness fraction measuring device includes a light-emitting body for irradiating moist steam with light of a plurality of wavelengths; a light-receiving element for receiving light of the plurality of wavelengths that has traversed the moist steam; and a dryness fraction calculating device for calculating the dryness fraction of the moist steam based on the received light intensity at each of the plurality of wavelengths.

Abstract: A gas concentration-measuring device makes it possible to measure gas components in a gas sample. An interferometer, based on a dual-band Fabry-Perot interferometer (1), is provided with a transmission spectrum that can be set by a control voltage (38). The control voltage (38) of the dual-band Fabry-Perot interferometer (1) is synchronized over the course of time with the activation and deactivation of the radiation sources (11, 12).

Abstract: A method and apparatus are disclosed for assessment of a sealed package. Light is emitted from a narrow-band laser source towards said package from outside of said package. An absorption signal of said light scattered in said package is measured, wherein said absorption is caused by said at least one gas when said light is scattered and travels in said sealed package. Measuring is made outside of said package, whereby said assessment is non-intrusive with regard to said package. It is determined if a deviation exists from a predetermined, expected gas composition and/or concentration of said at least one gas within said sealed package based on said measured absorption signal. Thus sealing of said package for said gas is detected.

Abstract: A system generates a photoacoustic spectrum in an open or closed environment with reduced noise. A source focuses a beam on a target substance disposed on a base. The base supports a cantilever that measures acoustic waves generated as light is absorbed by the target substance. By focusing a chopped/pulsed light beam on the target substance, a range of optical absorbance may be measured as the wavelength of light changes. An identifying spectrum of the target may detected by monitoring the vibration intensity variation of the cantilever as a function of illuminating wavelength or color.

Abstract: A gas analyzer is disclosed herein. The gas analyzer includes a light source for transmitting a radiation and a sampling chamber having a first opening for receiving a gas sample, a second opening for removing the gas sample, at least one optical window towards the radiation allowing the radiation to traverse the gas sample and also having a first wall and a second wall opposite to the first wall, the first wall and second wall edging the sampling chamber to guide the gas sample from the first opening to the second opening. The gas analyzer also includes at least one detector for receiving the radiation after traversing the gas sample. The first wall and the second wall of the sampling chamber is curved and at a predetermined distance from each other, an overall shape of the second wall being mostly similar to the first wall.

Abstract: The invention relates to a gas sampling device comprising a probe for sampling gas, an exploiting device for exploiting the gases sampled, a pipe for transmitting the gases sampled by the probe to the exploiting device, and means for lowering the pressure of the gases sampled in the pipe, to lower the dew point of the gases sampled, the means for lowering the pressure comprising an expansion nozzle arranged in the probe and communicating with the pipe, and a suction device for sucking the gases sampled in the pipe through the exploiting device. Application of the invention to the analysis of hot gases loaded with water vapor.

Abstract: A device and method for gas measurements in body cavities are provided. These may be any body cavity containing a free gas, where there is an interest in detecting and/or measuring the concentration of said free gas by non-invasive or minimally invasive method. According to an exemplary embodiment measurement of free oxygen in cranium cavities is performed by scattering media absorption spectroscopy, and in particular variations of such oxygen. This is particularly useful for diagnostic purposes based on the measurements, for instance for detecting sinusitis or the like.

Abstract: Some embodiments of the invention generally relate to an apparatus configured to monitor emissions. The apparatus includes a sampling chamber, a gas analyzer, and a particulate matter analyzer. The sampling chamber is configured to receive a portion of an exhaust flow from an exhaust stack. The portion of the exhaust flow comprises one or more gases and particulate matter. The gas analyzer is configured to receive the portion of the exhaust flow to measure at least one emission level of the one or more gases using a laser and output a signal indicative thereof. The particulate matter analyzer is operatively connected to the sampling chamber and is configured to measure the particulate matter using optics and output a signal indicative thereof.

Abstract: A system including at least one laser device extending a beam through an in-situ non-restrictive flow path of the gas mixture; and a measurer coupled to each laser device for obtaining a plurality of dynamic measurements over time of at least one species in the gas mixture.

Abstract: Gas analyzer systems and methods for measuring concentrations of gases and in particular dry mole fraction of components of a gas. The systems and methods allow for rapid measurement of the gas density and/or dry mole fraction of gases for a number of environmental monitoring applications, including high speed flux measurements. A novel coupling design allows for tool-free removal of a cell enclosing a flow path to enable infield cleaning of optical components and to enable re-configuration between open- and closed-path analyzer configurations. In closed path configurations, the sample flow path is thermally isolated from the remainder of the gas analyzer to provide more accurate temperature measurements. Composite plastic/metal sample cells are presented with achieve this thermal isolation without compromising analyzer performance.

Abstract: Micro-cavity gas or vapor sensors and gas or vapor detection methods. Optical energy is introduced into a resonant micro-cavity having a deformable coating such as a polymer. The coating swells or expands when it is exposed to or absorbs a gas or vapor, thereby changing the resonant wavelength of optical energy circulating within the micro-cavity/coating. Expansion or swelling of the coating may be reversible such that it contracts when gas or vapor diffuses from the coating.

Abstract: An apparatus and technique are invented that enhance the sensitivity of a spectrometer for trace gas detection by employing wavelength modulation spectroscopy (WMS) and integrating the absolute value of the recorded spectra across multiple absorption lines (features) of the species. The sensitivity is further enhanced by conducting WMS with large modulation depths. This technique is implemented using a continuously tunable external cavity CW quantum cascade laser to record the second harmonic wavelength modulated spectra of NO2 across the peak of the R-branch from 1629.5 cm?1 to 1633.9 cm?1. By integrating the absolute value of the resulting spectra, the detection sensitivity of NO2 is improved by a factor of 40 compared to the sensitivity achieved using single line WMS with the same apparatus. A sensitivity of approximately 6 ppb can be obtained using a short-path cell (a 1 m absorption cell with 2 passes) which can be significantly improved using multipass cells and cavity enhanced techniques.

Abstract: According to an apparatus for inspecting defects of a honeycomb structure that is provided with a current plate and an air current formation means (air source and a header tube), fine defects or defects taking place in the vicinity of an outer periphery of the honeycomb structure can be detected with high sensitivity.

Abstract: A reference harmonic absorption curve of a laser absorption spectrometer, which can include a tunable or scannable laser light source and a detector, can have a reference curve shape and can include a first, second, or higher order harmonic signal of a reference signal generated by the detector in response to light passing from the laser light source through a reference gas or gas mixture. The reference gas or gas mixture can include one or more of a target analyte and a background gas expected to be present during analysis of the target analyte. The reference harmonic absorption curve can have been determined for the laser absorption spectrometer in a known or calibrated state.

Abstract: According to one embodiment, a method comprises producing a first hyperspectral imaging (HSI) data cube of a location at a first time using data from a HSI sensor; producing a second HSI data cube of the same location at a second time using data from the HSI sensor; subtracting on a pixel-by-pixel basis the second HSI data cube from the first HSI data cube to produce a raw difference cube; calibrating the raw difference cube to produce a calibrated raw difference cube; selecting at least one desired spectral band based on a gas of interest; producing a detection image based on the at least one selected spectral band and the calibrated raw difference cube; examining the detection image to determine presence of the gas of interest; and outputting a result of the examination. Other methods, systems, and computer program products for detecting the presence of a gas are also described.

Abstract: Thermally controlled enclosures that can be used with gas analyzers are described. The enclosures incorporate one or more phase changing materials that buffer ambient and internal heat loads to reduce the power consumption demand of mechanical or electronic heating apparatus. Maintenance of gas analyzer equipment at a consistent temperature can be important to achieving stable and reproducible results. Related systems, apparatus, methods, and/or articles are also described.

Abstract: Laser light is confined in a hollow waveguide between two highly reflective mirrors. This waveguide cavity is used to conduct Cavity Ringdown Absorption Spectroscopy of loss mechanisms in the cavity including absorption or scattering by gases, liquid, solids, and/or optical elements.

Abstract: A sensor for NO2 with ultrahigh sensitivity of detection is created by combining off-axis integrated cavity output spectroscopy (OA-ICOS) (which can provide large path lengths of the order of several km in a small volume cell) with multiple line integrated absorption spectroscopy (MLIAS) (where the absorption spectra is integrated over a large number of rotational-vibrational transitions of the molecular species to further improve the sensitivity). Employing an external cavity tunable quantum cascade laser operating in the 1601-1670 cm?1 range and a high finesse optical cavity, the absorption spectra of NO2 over 100 transitions in the R-band have been recorded. Based on the observed linear relationship between the integrated absorption vs. concentration of NO2, the sensor has an effective sensitivity of detection of 28 ppt for NO2, which is among the most sensitive levels of detection of NO2 to date.

Abstract: The invention relates to an apparatus for the continuous measurement of SO3 and/or H2SO4 concentrations in gases using a photometer having a light source, a cuvette, a receiver, an optical filter unit having at least one optical filter which is selected such that it lets a measurement wavelength pass through which is selected such that it is absorbed as much as possible by SO3 and/or H2SO4 and is absorbed as little as possible by the other components of the gas and the photometer is calibrated with SO3 and H2SO4 gases of known concentrations and having an evaluation unit which includes a memory unit, in which already measured transverse sensitivities at the measurement wavelengths are stored and the evaluation unit can determine a concentration value for SO3 and/or H2SO4 continuously from the photo signals and the stored transverse sensitivities.