Abstract: The disclosure relates to an infrared spectrometer comprising first and second opposing reflectors spaced apart by a spacing length, and a plurality of discrete concave reflecting facets, the reflecting facets being facets of at least one of the opposing reflectors. An infrared laser source is arranged to form a laser beam. The opposing reflectors are arranged such that the laser beam is reflected alternately from each of the opposing reflectors, including being reflected at least once by each of the reflecting facets. A detector is arranged to detect spectral properties of the laser beam after reflection from each of the plurality of reflecting facets, and an analyser then determines properties of a sample disposed between the first and second opposing reflectors from the detected spectral properties.

Abstract: The invention provides a chirped laser dispersion spectrometer having two tunable lasers each with a bias current supply, a chirp signal source to provide a matching chirp pattern, a beam splitter to produce a single beam from the two first and second tunable lasers and active-phase locking means to render the two beams phase coherent and to produce a radio frequency carrier signal capable of programmable phase modulation by means of an optical beat signal. The invention also provides a method for generating at least two optical frequency signals for use in a frequency modulation spectroscopy (FMS) process for the detection and/or measurement of molecular species in a gas mixture and a method for generating at least two optical frequency signals for use in a chirped laser dispersion spectroscopy (CLaDS) process for the detection and/or measurement of molecular species in a gas mixture.

Abstract: Methods and apparatus are disclosed for detecting one or more species in a sample, wherein laser probe light is frequency swept across at least one infra red absorption spectrum feature of each of the species. A path from the probe light source to a single detector element may be switched between at least one sample absorption cell or volume and one or more reference cells or volumes.

Abstract: There is described an infrared spectrometer having an optical circuit which comprises one or more hollow waveguides provided by elongate channels formed in a substrate. The optical circuit is arranged such that infrared light in the optical circuit acquires one or more spectral properties for detection by the spectrometer. A laser source couples laser light into an input hollow waveguide portion of the optical circuit, and an optical detector receives the light from an output hollow waveguide portion of the optical circuit, so that an analyser can determine said one or more spectral properties from the detected light.

Abstract: The disclosure relates to an infrared spectrometer comprising first and second opposing reflectors spaced apart by a spacing length, and a plurality of discrete concave reflecting facets, the reflecting facets being facets of at least one of the opposing reflectors. An infrared laser source is arranged to form a laser beam. The opposing reflectors are arranged such that the laser beam is reflected alternately from each of the opposing reflectors, including being reflected at least once by each of the reflecting facets. A detector is arranged to detect spectral properties of the laser beam after reflection from each of the plurality of reflecting facets, and an analyser then determines properties of a sample disposed between the first and second opposing reflectors from the detected spectral properties.

Abstract: The invention relates to a method and apparatus for reducing speckle noise in a system comprising a sensor for detecting electro-magnetic radiation backscattered from a target, comprising: illuminating the target with a first illuminating beam having a first optical path; illuminating the target with a second illuminating beam having a second optical path different to the first optical path; capturing at the sensor first and second backscattered radiation components associated with respectively the first and second illuminating beams, each of the backscattered radiation components comprising a speckle pattern; and taking a time-averaged measurement of the intensities of the first and second backscattered radiation components; wherein the capturing step is carried out within an integration time ? of the sensor, such that the time-averaged intensity measurement results in a decrease in speckle noise present in a signal representing the backscattered radiation.

Abstract: A method is provided of obtaining a vapor phase spectrum of a compound. The method comprises providing an isolated condensed phase sample of the compound, vaporizing the sample and supplying the vapor to an absorption cell of a spectrometer. A rate at which vapor enters the absorption cell is determined and a steady state concentration of vapor in the absorption cell is established. The spectrum of the vapor is then measured.

Abstract: An active heterodyne detection system comprises a continuously tuneable laser source (1) emitting infra-red radiation, means (8) to split the infra-red radiation into a first part and a second part, means (4) to provide a frequency shift between the first part and the second part, means (8, 9) to direct the first part of the infra-red radiation to a target (2), means (4) to provide the second part of the infra-red radiation as a local oscillator, means (8, 9) to collect a scattered component of the first part of the infra-red light from the target (2), and means (5) to mix the scattered component and the local oscillator and route them to a detector (3) for heterodyne detection over a continuous spectral range. A method of active heterodyne detection over a continuous spectral range is also disclosed.

Abstract: Method and apparatus for external cavity laser absorption spectroscopy There is disclosed an apparatus, and corresponding methods, for determining one or more characteristics of a sample in an absorption cell using laser absorption spectroscopy. For example, the characteristic may be concentration of a species in the sample. The apparatus comprises an external cavity semiconductor laser comprising a semiconductor gain medium within an optical resonator. The absorption cell is located within the optical resonator of the external cavity semiconductor laser so as to be optically coupled with the gain medium. A controller is arranged to provide a varied injection current to the semiconductor gain medium. A photodetector is arranged to detect laser light output by the external cavity semiconductor laser. An analyzer is arranged to determine one or more characteristics of the sample from behavior of the detected laser light output as a function of the varied injection current.

Abstract: Method and apparatus for detecting a species in a dilute medium, the species having a spectral feature, the apparatus comprising: a beam source arranged to generate a first laser beam and a second laser beam coherent with each other, and having a matching chirp pattern. Beam guide arranged to pass at least the first laser beam through the dilute medium; a beam mixer arranged to mix the first and the second laser beams to form a mixed beam. Detector arranged to detect, during the chirp pattern, the mixed beam and to measure changes in the mixed beam caused by refractive index variations in the dilute medium across a spectral feature. Output providing a signal that changes in response to the measured changes.

Abstract: The invention relates to a method and apparatus for reducing speckle noise in a system comprising a sensor for detecting electro-magnetic radiation backscattered from a target, comprising: illuminating the target with a first illuminating beam having a first optical path; illuminating the target with a second illuminating beam having a second optical path different to the first optical path; capturing at the sensor first and second backscattered radiation components associated with respectively the first and second illuminating beams, each of the backscattered radiation components comprising a speckle pattern; and taking a time-averaged measurement of the intensities of the first and second backscattered radiation components; wherein the capturing step is carried out within an integration time t of the sensor, such that the time-averaged intensity measurement results in a decrease in speckle noise present in a signal representing the backscattered radiation.

Abstract: A method is provided of obtaining a vapour phase spectrum of a compound. The method comprises providing an isolated condensed phase sample of the compound, vaporising the sample and supplying the vapour to an absorption cell of a spectrometer. A rate at which vapour enters the absorption cell is determined and a steady state concentration of vapour in the absorption cell is established. The spectrum of the vapour is then measured.

Abstract: Method and apparatus for external cavity laser absorption spectroscopy There is disclosed an apparatus, and corresponding methods, for determining one or more characteristics of a sample in an absorption cell using laser absorption spectroscopy. For example, the characteristic may be concentration of a species in the sample. The apparatus comprises an external cavity semiconductor laser comprising a semiconductor gain medium within an optical resonator. The absorption cell is located within the optical resonator of the external cavity semiconductor laser so as to be optically coupled with the gain medium. A controller is arranged to provide a varied injection current to the semiconductor gain medium. A photodetector is arranged to detect laser light output by the external cavity semiconductor laser. An analyser is arranged to determine one or more characteristics of the sample from behaviour of the detected laser light output as a function of the varied injection current.

Abstract: An active heterodyne detection system comprises a continuously tuneable laser source (1) emitting infra-red radiation, means (8) to split the infra-red radiation into a first part and a second part, means (4) to provide a frequency shift between the first part and the second part, means (8, 9) to direct the first part of the infra-red radiation to a target (2), means (4) to provide the second part of the infra-red radiation as a local oscillator, means (8, 9) to collect a scattered component of the first part of the infra-red light from the target (2), and means (5) to mix the scattered component and the local oscillator and route them to a detector (3) for heterodyne detection over a continuous spectral range. A method of active heterodyne detection over a continuous spectral range is also disclosed.

Abstract: Method and apparatus for detecting a species in a dilute medium, the species having a spectral feature, the apparatus comprising: a beam source arranged to generate a first laser beam and a second laser beam coherent with each other, and having a matching chirp pattern. Beam guide arranged to pass at least the first laser beam through the dilute medium; a beam mixer arranged to mix the first and the second laser beams to form a mixed beam. Detector arranged to detect, during the chirp pattern, the mixed beam and to measure changes in the mixed beam caused by refractive index variations in the dilute medium across a spectral feature. Output providing a signal that changes in response to the measured changes.

Abstract: Method and apparatus for detecting, by absorption spectroscopy, an isotopic ratio of a sample, by passing first and second laser beams of different frequencies through the sample. Two IR absorption cells are used, a first containing a reference gas of known isotopic ratio and the second containing a sample of unknown isotopic ratio. An interlacer or reflective chopper may be used so that as the laser frequencies are scanned the absorption of the sample cell and the reference cell are detected alternately. This ensures that the apparatus is continuously calibrated and rejects the baseline noise when phase sensitive detection is used.

Abstract: Method and apparatus for detecting, by absorption spectroscopy, an isotopic ratio of a sample, by passing first and second laser beams of different frequencies through the sample. Two IR absorption cells are used, a first containing a reference gas of known isotopic ratio and the second containing a sample of unknown isotopic ratio. An interlacer or reflective chopper may be used so that as the laser frequencies are scanned the absorption of the sample cell and the reference cell are detected alternately. This ensures that the apparatus is continuously calibrated and rejects the baseline noise when phase sensitive detection is used.

Abstract: Method and apparatus for detecting, by absorption spectroscopy, an isotopic ratio of a sample, by passing first and second laser beams of different frequencies through the sample. Two IR absorption cells are used, a first containing a reference gas of known isotopic ratio and the second containing a sample of unknown isotopic ratio. An interlacer or reflective chopper may be used so that as the laser frequencies are scanned the absorption of the sample cell and the reference cell are detected alternately. This ensures that the apparatus is continuously calibrated and rejects the baseline noise when phase sensitive detection is used.

Abstract: Method and apparatus for detecting, by absorption spectroscopy, an isotopic ratio of a sample, by passing first and second laser beams of different frequencies through the sample. Two IR absorption cells are used, a first containing a reference gas of known isotopic ratio and the second containing a sample of unknown isotopic ratio. An interlacer or reflective chopper may be used so that as the laser frequencies are scanned the absorption of the sample cell and the reference cell are detected alternately. This ensures that the apparatus is continuously calibrated and rejects the baseline noise when phase sensitive detection is used.