Abstract: Disclosed is a system for measuring a chemical in a subsurface formation comprising housing component traversable within the well, a guide extending down the well from a fixed location being operatively connected to the housing, a radiation source, and an optical pathway between a sample and detector wherein the detector is located at the ground surface. Also disclosed is a method for reducing long distance transmission of radiation comprising placing a radiation source in a housing, placing a housing down in a well bore, lowering a spectrometer down the well bore, and controlling movement of a spectrometer by a guide wire controller at the ground surface. Further disclosed is a method of radiating a sample comprising, transmitting the radiation through at least one optical pathway, interacting a sample with the radiation, producing characteristic radiation from the sample, and transmitting by an optical pathway to a detector located in a spectrometer.

Abstract: Aspects of the invention are directed to a device and method for detecting characteristics of a gas. The gas includes an exhausted plume from a vehicle or factory plant, leaked gas from an oil well or gas resource, or unidentified gas from an unknown source. The method includes sweepingly directing a beam of light through the gas to a target surface on which the beam of light is scattered, acquiring the scattered light scattered from the target surface, and processing the acquired scattered light to determine the characteristics of the gas, where the characteristics of the gas comprise at least one of a temperature of the gas and an amount of at least one ingredient of the gas.

Abstract: The invention relates to an improved optoelectronic apparatus for optical gas analysis by means of which the interfering influence of the particles contained in the gas is reduced with regard to the intended measurement. For this purpose the optoelectronic apparatus in accordance with the invention has a light transmitter and a light receiver which define an optical measurement path including a measurement volume between one another. The received signals of the light receiver can be evaluated in an evaluation unit, to ultimately obtain the desired information therefrom, for example, the concentration of a specific gas content. In accordance with the invention an ionizer is further provided which is arranged upstream of the optical measurement path. The ionizer causes an ionization of the undesirable particles, i.e. e.g. the dust particles, smoke particles or such like aerosols so that the ionized particles can be deflected by electric fields or also magnetic fields by means of an ion acceleration apparatus.

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: An inspection probe for directly measuring a transmission spectrum of a solvent oil in a transformer includes a tube having a plurality of apertures spaced along a side of the tube to allow oil to pass therethrough, and first and second optical collimators disposed at opposing ends of the tube. The first and second collimators are aligned by the tube such that incident light is transmitted through the first collimator, the tube, and the second collimator to a spectrometer.

Abstract: The invention relates to an actuation and evaluation circuit for a laser diode (1) and a photodiode (3) for determining the concentration of a gas. The laser diode can generate light in the range of an absorption line of the gas. The circuit comprises a driver (10, 11, 12, 13) for generating a driving signal (17) for the laser diode (1), an assembly (8, 9) for generating a reference signal (20), and a subtractor (5) for subtracting the reference signal (20) from the signal (21) supplied by the photodiode. The invention further relates to a measuring device for determining the concentration of a gas by means of such an actuation and evaluation circuit. Finally, the invention relates to a corresponding method.

Abstract: A timing generating circuit outputs, to a laser controller, a change pulse signal for changing an oscillation wavelength of the laser beam, and outputs, to a data acquisition circuit, a timing pulse signal for outputting data to a processor. An edge detection circuit detects an edge of a measurement signal outputted from a detector circuit. A delay measuring circuit receives a change pulse signal outputted from the timing generating circuit, receives an edge detection signal outputted from the edge detection circuit, and measures a delay of a time for which the laser beam with an oscillation wavelength changed based on the change pulse signal reaches the detector circuit after the change pulse signal is outputted from the timing generating circuit. The timing generating circuit delays a time for outputting data from the data acquisition circuit to the processor based on the delay of time outputted from the delay measuring circuit.

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: An OPO is disclosed capable of rapid frequency tuning by non-mechanical means. The OPO includes a resonant cavity including one or more non-linear crystals in an optical path thereof. A pump laser pulse is transmitted into the resonant cavity simultaneously with a seed beam having a desired wavelength. The output beam from the resonant cavity has the same center wavelength as the seed beam. The wavelength of the seed beam may be modulated at a frequency larger than the pulse rate of the pump laser or larger than the inverse of the pulse duration. The OPO disclosed may be used to perform DIAL analysis wherein intra-pulse modulation of an output beam is used to obtain measurements of absorption at multiple frequencies for each pulse of a pump beam.

Abstract: A device that detects smoke, both indoor and outdoor; especially applicable in areas prone to sustained water flooding. It can be used in underground locations susceptible to water ingress so it can be submersed in up to 6 feet of water for up to 24 hours. Usable in applications that requires NEMA 6P or IP68 level of water protection.

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. A test harmonic absorption curve having a test curve shape is compared with the reference harmonic absorption curve to detect a difference between the test curve shape and the reference curve shape.

Abstract: The present disclosure relates to a gas sensor including a first layer and a second layer superimposed on each other along an interface between the two layers. The first layer includes an array of nanoparticles along the interface, the nanoparticles provided so as to allow, upon illumination with electromagnetic radiation, long range diffractive coupling of surface plasmon resonances resulting in a surface lattice resonance condition. The second layer includes a material that, when exposed to at least one predetermined gas, detectably affects the surface lattice resonance condition. The material of the second layer preferably has a porosity of at least 10%.

Abstract: A flux monitor system includes a light source and a sensor.

Abstract: A method of absorption spectroscopy to determine a rapidly variable gas parameter. The method includes transmitting light from a synchronization light source to a synchronization detector. The transmitted light is periodically interrupted by a moving mechanical part between the synchronization light source and synchronization detector. The output from the synchronization detector is used to generate a repeating time signal having variable phase delay. This signal is used to control the timing of laser spectroscopy wavelength scans. Multiple spectroscopic scans may be repeated at multiple selected time signal phase delay and the results averaged for each phase. Apparatus for implementing the above methods are also disclosed.

Abstract: The instant invention provides apparatuses for measuring the level or concentration of chlorine dioxide gas in a sample and methods of using the same. One aspect of the invention provides an apparatus for measuring a concentration of a chlorine dioxide gas in a sample. The apparatus includes a light emitting diode (LED), a light sensor, and a flow path between the LED and the light sensor, and a filter configured to remove chlorine dioxide from a reference stream. The flow path is capable of containing a sample. The sensor is capable of measuring the level of chlorine dioxide in the sample and the reference stream.

Abstract: A method and apparatus for detecting trace gas concentrations in the atmosphere. An absorption signal is provided that includes collected sunlight that has undergone absorption by a trace gas. The absorption signal is mixed with laser light at a nearby frequency to the absorption signal. An amplitude of a resulting RF signal is proportional to the concentration of the trace gas.

Abstract: A gas or particulate sensor is provided for the detection of at least two target gases and/or particulates. The sensor comprises: a chamber for containing a gas sample under test; a first optical measurement channel configured for the detection of a first target gas or particulate within the gas sample, and a second optical measurement channel configured for the detection of a second target gas or particulate within the gas sample, each optical measurement channel comprising a respective optopair which comprises a radiation source adapted to emit radiation and a radiation detector adapted to output a signal in response to detected radiation; and focusing optics able to form an image of an object.

Abstract: A non-invasive method for determining a concentration of a gas component in a gas mixture contained in a spacing of a glass unit having at least two glass sheets spaced apart from each other and forming the spacing. One or more light beams is applied at an angle to the surface of the glass unit, wherein the wavelength of the emitted light beam is varied around or over the at least one absorption line of the interest gas component. The light beams transmitted through or reflected from at least one surface or interface locating at the opposite side of the spacing are collected by a detector and non-linear variations in the intensity of the transmitted or reflected light beams over an absorption line of the interest gas is then component determined. The concentration of the gas component to be measured is determined based on the non-linear variations in the intensity.

Abstract: A GFCR system includes gas cells disposed to receive light energy associated with a field-of-view of an atmospheric region. Each gas cell has contents selected from the group consisting of a vacuum and a gas of unique composition. For each of the gas cells, the light energy passed therethrough is spectrally affected by the contents thereof and then output therefrom as a spectrally-affected beam of light energy associated with the field-of-view. An optical system disposed between the gas cells and an optical detector images each spectrally-affected beam on a unique region of the optical detector. One or more processors generate matched portions of each spectrally-affected beam so-imaged on the optical detector where each such matched portion corresponds to an identical portion of the field-of-view. GFCR computations can then be performed using the matched portions.

Abstract: A method and system comprising measuring concentrations of first and second isotopologues of a gas of interest within a first cavity that is sealably in contact with a soil location through an inlet membrane, and the first cavity being defined by chamber walls having openings covered by outlet membranes. Reference concentrations of the first and second isotopologues are measured in a second cavity having a closed bottom, the second cavity being defined by chamber walls having openings covered by more outlet membranes. Relative flux of the isotopologues can be calculated using the measured concentrations.

Abstract: A gas detector including: an assembly of two coaxial parabolic reflective caps having opposite concavities, and a wafer arranged in the focal plane of the two caps, at the center of this focal plane, comprising, back-to-back: a diverging light emitter directed towards the first cap and a light receiver directed towards the second cap, wherein the two caps are distant substantially by the sum of their focal distances plus the thickness of the wafer.

Abstract: A gas detector including an assembly of two hemispherical caps having opposite concavities, and which are reflective on at least a portion of their opposite surfaces, and a wafer arranged in an equatorial plane of the assembly of the two caps, in the vicinity of but spaced apart from the center of the equatorial plane, including, back-to-back: a diverging light emitter directed towards the first cap and a light receiver directed towards the second cap.

Abstract: Systems and methods for measuring the isotope ratio of one or more trace gases and/or components of gas mixtures such as different gas species present in a gas mixture. The system includes a resonant optical cavity having two or more mirrors and containing a gas, the cavity having a free spectral range that equals the difference between frequencies of two measured absorption lines of different gas species in the gas, or of two different isotopes, divided onto an integer number. The system includes a continuous-wave tunable laser optically coupled with the resonant optical cavity and a detector system for measuring an absorption of laser light by the gas in the cavity. The detector system includes a photo-detector to measure an intensity of the intra-cavity light, or both a photo-acoustic sensor to measure photo-acoustic waves generated in the cavity and a photo-detector to measure an intensity of the intra-cavity light.

Abstract: In one embodiment, a block for a physics package of an atomic sensor is provided. The block comprises one or more sections of optically transparent material defining a vacuum sealed chamber, and including a plurality of transmissive and reflective surfaces to define a plurality of light paths intersecting the vacuum sealed chamber. The one or more sections of optically transparent material include a first monolithic section defining at least a portion of the vacuum sealed chamber. The first monolithic section includes a first portion disposed across a first light path of the plurality of light paths such that light in the first light path is incident on the first portion of the first monolithic section.

Abstract: Optical feedback assisted cavity enhanced absorption spectroscopy systems and methods for measuring trace gases with improved long-term stability and reproducibility include a laser coupled with a resonant optical cavity containing a gaseous medium and having at least two cavity mirrors and a plurality of optical resonance cavity modes. The laser emits continuous wave laser light with a mean optical frequency of the laser being adjustable over a range of frequencies, and the laser is responsive to optical feedback light emerging from the cavity. The transmissivity of at least one of the cavity mirrors is selected such that the intensity of the optical feedback light impinging on the laser is below a threshold intensity value so as to ensure that a frequency hold interval range of the optical frequency of the laser is smaller than a free spectral range of the cavity.

Abstract: Cavity enhanced absorption spectroscopy systems and methods for detecting trace gases. When the frequency of laser light approaches the frequency of a resonance cavity mode, the laser begins to fill the cavity to that mode. Optical intensity inside the cavity reflects total cavity loss when the laser light frequency coincides with the cavity mode transmission peak. The intra-cavity optical power also depends on the coupling efficiency of the laser beam to the particular cavity mode. Measurement of intensities of three optical signals, namely, intensity of the light incident on to the cavity, intensity of the light reflected from the cavity, and intensity of the intra-cavity optical power, with their appropriate normalization advantageously significantly reduce effects of baseline calibration and drift as the normalized signal only depends on total cavity loss, and not the coupling efficiency, as in traditional approaches.

Abstract: An incoherent cavity ringdown spectroscopy (iCRDS) gas analyzer is provided with a gas flow path to introduce a sample gas into an enclosed volume bounded by a pair of mirrors defining an optical cavity. A pulsed broadband incoherent light source with a wavelength band that coincides with an absorption band of a specified gas species to be detected (e.g., NO2 or SO3) directs pulses of light into the optical cavity, while a photodetector is positioned to detect light exiting the cavity. A scrubber in an alternate flow path into the enclosed volume periodically scrubs the sample gas of the specified gas species. A processor determines the concentration of the specified gas species from the ringdown decay time of the photodetector measurement signals, with the periodic scrubbing of the sample gas providing a calibration reference from its slower decay time.

Abstract: Techniques are generally described related to a method and system for monitoring gas concentrations. One example gas monitoring apparatus includes a light source, a MEMS micro-mirror arranged to be in an optical path of a light from the light source that has passed through a sample and configured to direct selected wavelengths of the light to a single detection point, a detector arranged at the single detection point and configured to convert incident light into electrical signals, and a processor programmed to determine a gas concentration of one or more gases in the sample based on the electrical signals.

Abstract: An optical gas sensor with a light-emitting diode (2), a photosensor (8), a measuring section between the light-emitting diode and the photosensor, and a control and analyzing unit (16), which is set up to determine the concentration of a gas in the measuring section from the light intensity measurement by the photosensor. The control and analyzing unit (16) is set up to measure the forward diode voltage over the light-emitting diode at a constant current, to determine the temperature of the light-emitting diode from the detected forward diode voltage over the light-emitting diode by means of a preset temperature dependence of the forward diode voltage, and to apply a correction function as a function of the light-emitting diode temperature determined, with which the measurement is converted to that of a preset temperature of the light-emitting diode.

Abstract: A flux monitor system includes a light source and a sensor.

Abstract: A light absorption examining device includes a laser light source that emits the pulse laser beam, a measuring unit that retains the measuring object and irradiates the measuring object with the pulse laser beam, a light receiving unit that receives the pulse laser beam transmitted through the measuring object and outputs a light receiving signal, a pulse generator that produces a single rectangular pulse at a time when a signal level of the light receiving signal output from the light receiving unit intersects a set threshold, a laser driver that supplies the produced rectangular pulse to the laser light source to emit the pulse laser beam, and a control/processing unit that determines an accumulated delay time and examines absorption of the pulse laser beam by the measuring object using the determined accumulated delay time, the accumulated delay time representing a delay in a production timing of the rectangular pulse.

Abstract: A laser emitting section 59A and a laser receiving section 59B for measuring an oxygen concentration are provided on two sides of an inspection area so as to be moved toward and away from a bag-shaped container 1. Gas-filled chambers 61 provided on the end faces of the laser emitting section 59A and the laser receiving section 59B are brought into contact with the gas phase portion of the container 1 to keep a constant thickness of the gas phase portion. A tilting device 81 is provided to press the container 1, which is held by a container holder 16, from both sides with a container pressing member 88 and tilts the container 1 in a vertical plane. When an oxygen concentration is measured, the tilting device 81 tilts the bag-shaped container 1 to measure the gas phase portion at the shoulders of the container 1.

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. These methods can be practiced individually or in any combination.

Abstract: The disclosure relates to a method of detecting a change in a chemical composition by contacting a doped oxide material with a monitored stream, illuminating the doped oxide material with incident light, collecting exiting light, monitoring an optical signal based on a comparison of the incident light and the exiting light, and detecting a shift in the optical signal. The doped metal oxide has a carrier concentration of at least 1018/cm3, a bandgap of at least 2 eV, and an electronic conductivity of at least 101 S/cm, where parameters are specified at a temperature of 25° C. The optical response of the doped oxide materials results from the high carrier concentration of the doped metal oxide, and the resulting impact of changing gas atmospheres on that relatively high carrier concentration. These changes in effective carrier densities of conducting metal oxide nanoparticles are postulated to be responsible for the change in measured optical absorption associated with free carriers.

Abstract: [Problem to be Solved] To provide a smoke sensing system, a smoke sensor and a receiver that can accurately determine the type of smoke.

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 method and apparatus for detecting trace gas concentrations in the atmosphere. An absorption signal is provided that includes collected sunlight that has undergone absorption by a trace gas. The absorption signal is mixed with laser light at a nearby frequency to the absorption signal. An amplitude of a resulting RF signal is proportional to the concentration of the trace gas.

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: Method of determining a total HF concentration metric in an environment including measuring an uncorrected HF concentration metric in the environment based on a first infrared absorption measurement at a wavelength corresponding to a vibrational frequency of a non-hydrogen bonded gas phase HF molecule; determining an ambient H2O concentration metric in the environment available for reaction with the non-hydrogen bonded gas phase HF molecules at or about the time of obtaining the first infrared absorption measurement; calculating a HF hydrate concentration metric in the environment based on the uncorrected HF concentration metric, the ambient H2O concentration metric and a reaction equilibrium relationship between the non-hydrogen bonded gas phase HF molecule and the HF hydrate; and determining the total HF concentration metric in the environment based on the uncorrected HF concentration metric and an amount of HF determined by the HF hydrate concentration metric.

Abstract: One or more embodiments of the present invention pertain to a system, method, and apparatus that accurately measures concentration of a greenhouse gas in narrow atmospheric columns above multiple sites utilizing a network of autonomous low-cost beacons that turn on for short unannounced time intervals and point to a receiving satellite. For example, each beacon can activate for short time intervals and transmit a laser beam at eye-safe low transmission power levels to a receiving satellite. The receiving satellite includes a sensor configured to receive the laser beam from one or more activated beacon and generate raw greenhouse gas concentration data based on measurement of the received laser beam intensity at selected wavelengths.

Abstract: Disclosed are a system and a method for monitoring unsaturated zone gas and near-surface atmosphere in real time by using an isotope analyzer. The system includes a near-surface atmosphere analyzer including a fixing member, a plurality of near-surface gas inlets, a plurality of gas transfer members communicating with the near-surface gas inlets, an analyzing member including an isotope analyzer, which analyzes an isotope of gas transferred through the gas transfer members, a channel connected to the gas transfer members and the analyzing member to select one gas transfer member and to supply gas transferred through the selected gas transfer member to the analyzing member, and a connection member connecting the channel to the analyzing member, a communication device transmitting components of the isotope output from the isotope analyzer, and a monitoring server outputting the components of the isotope transmitted from the communication device.

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: If the specific gas concentration is relatively high, controller sets 0 as the modulation amplitude in a modulation amplitude controlling voltage generator for frequency modulation of laser light, controls a switching unit to select the output of a second ADC, and causes a computation unit to compute according to the direct absorption detection method to calculate the water molecule volume concentration. If the specific gas concentration is relatively low, the modulation amplitude is set to A, not 0, controls switching unit to select the output of a first ADC, which digitizes a synchronized detection signal, and causes the computation unit to compute according to the harmonic synchronous detection method to calculate the water molecule volume concentration. The concentration calculated using either of the methods is compared against a threshold value, and if decided that an accurate result cannot be obtained, the method is switched as the measurements are continuously executed.

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 present invention is related to a method for characterising transparent objects (2, 3) in a transparent medium (1), said transparent objects (2, 3) presenting an optical focal area (5, 6) said method comprising the steps of: illuminating a sample comprising the objects (2, 3) to be characterised by means of a directional light (7) source, thereby inducing light intensity peaks (5, 6) at the focal area of said transparent objects; determining at least one characteristic of the light intensity peak (5, 6) induced by said object to be characterised, determining from said light intensity peak (5, 6) at least one property of said object.

Abstract: An optical waveguide is provided comprising a non-solid core layer surrounded by a solid-state material, wherein light can be transmitted with low loss through the non-solid core layer. A vapor reservoir is in communication with the optical waveguide. One implementation of the invention employs a monolithically integrated vapor cell, e.g., an alkali vapor cell, using anti-resonant reflecting optical waveguides, or ARROW waveguides, on a substrate.

Abstract: Some embodiments relate to a photoacoustic sensor that includes a gas cell having an opening and a detector to collect pressure fluctuations within the gas cell to determine a spectral content of the pressure fluctuations within the ambient environment. The photoacoustic sensor further includes a light source to generate radiation to radiate sample gas within the gas cell and a control that receives signals from the detector that represent the spectral content of the pressure fluctuations within the ambient environment. The control adjusts a frequency of the radiation produced by the light source to a frequency that conflicts less with the spectral content of the pressure fluctuations within the ambient environment. The detector generates output electrical signals in response to acoustic signals generated by pressure fluctuations of the radiated sample gas.

Abstract: An optical absorption gas sensor has an LED light source and a photodiode light detector, a temperature measuring device for measuring the LED temperature and a temperature measuring device for measuring the photodiode temperature. The sensor is calibrated by measuring the response of photodiode current at zero analyte gas concentration and at a reference analyte gas concentration. From these measurement, calibration data taking into account the effect of photodiode temperature on the sensitivity of the photodiode and, independently, the effect of changes in the spectrum of light output by the LED on the light detected by the photodiode with LED temperature can be obtained. Calibration data is written to memory in the gas sensor and in operation of the gas sensor, the output is compensated for both LED and photodiode temperature. The LED and photodiode can therefore be relatively far apart and operate at significantly different temperatures allowing greater freedom of optical pathway design.

Abstract: Disclosed are methods and apparatus for treating and analyzing a gas stream to determine the ammonia concentration. A gas stream is continuously monitored to determine the ammonia concentration by extracting gas samples from one or more locations and sending it to a tunable diode laser absorption spectroscopy instrument for analysis. By proper placement of sampling probes within a duct, depending on the particular flow patterns that have been determined by suitable modeling, e.g., computational fluid dynamics or cold flow modeling, the valves can be operated manually or by a controller to take samples at predetermined locations within the duct. This will enable taking samples from particular locations, samples representative of the entire cross section, or samples that are an average of a particular cross section. It will be possible by judicious placement of the probes and operation of the valves to map the concentrations of ammonia at a plurality of load settings and will permit continuous control.

Abstract: A method for detecting leaks during high temperature selenization of Cu—In—Ga metal precursor films comprises positioning a light source on one side of a transparent reaction chamber or aligned with a window in an opaque reaction chamber. The method further comprises positioning a detector opposite the light source and detecting an intensity of light from the light source. Leaks in the seals of the reaction chamber will result in the formation of an opaque film on the walls of the reaction chamber. A decrease in the intensity of light incident on the detector will indicate the presence of the leak. A second method comprises measuring the reflection of the light source off of the reaction chamber wall or a window in the reaction chamber. An change in the reflected light will indicate a leak in the seals of the reaction chamber.