Abstract: A method for reducing fringe interference of light created in a passive cavity defined by partially reflecting optical surfaces in a laser spectroscopy system, wherein the optical path length of the cavity is varied with a triangular back-and-forth movement (x). In accordance with the invention, the spectroscopic measurement is performed in successive measurement cycles with a time interval between each two successive measurement cycles, the triangular movement is performed such that the turning points of the triangular movement (x) are positioned in successive ones of the time intervals, and after each or at each n-th measurement cycle, the time position of the turning points is moved relative to the measurement cycle.

Abstract: An apparatus for reducing fringe interference of light created in the optical system of a laser spectroscopy system comprising an electromagnetic actuator for generating, along a laser path, physical translational vibration of an optical element of the optical system and a control device for controlling the amplitude and frequency of said vibration. The optical element is arranged on a cantilever body which is, at one end, attached to a base by a flexural pivot and, at the other free end, coupled to the electromagnetic actuator, and the control device includes a controller that controls the amplitude of the vibration and a vibration sensor attached to the cantilever body and providing the actual vibration value to the controller to improve fringe interference reduction, especially with longer wavelengths.

Abstract: An optical measuring head for a duct gas monitoring system is provided, the measuring head being mounted to an outer wall of a gas duct through which the duct gas flows. The measuring head has a longitudinal chamber which at one end opens into the gas duct and at the other end contains an active optical component. The chamber is flushed with a purge gas which, after flushing the chamber, is discharged into the gas duct. A gas line is installed between the chamber and interior of the gas duct at a point upstream of a discharge point and the purge gas is a branch-off of the duct gas.

Abstract: An apparatus for reducing fringe interference of light created in the optical system of a laser spectroscopy system comprising an electromagnetic actuator for generating, along a laser path, physical translational vibration of an optical element of the optical system and a control device for controlling the amplitude and frequency of said vibration. The optical element is arranged on a cantilever body which is, at one end, attached to a base by a flexural pivot and, at the other free end, coupled to the electromagnetic actuator, and the control device includes a controller that controls the amplitude of the vibration and a vibration sensor attached to the cantilever body and providing the actual vibration value to the controller to improve fringe interference reduction, especially with longer wavelengths.

Abstract: A method for reducing fringe interference of light created in a passive cavity defined by partially reflecting optical surfaces in a laser spectroscopy system, wherein the optical path length of the cavity is varied with a triangular back-and-forth movement (x). In accordance with the invention, the spectroscopic measurement is performed in successive measurement cycles with a time interval between each two successive measurement cycles, the triangular movement is performed such that the turning points of the triangular movement (x) are positioned in successive ones of the time intervals, and after each or at each n-th measurement cycle, the time position of the turning points is moved relative to the measurement cycle.

Abstract: An optical measuring head for a duct gas monitoring system is provided, the measuring head being mounted to an outer wall of a gas duct through which the duct gas flows. The measuring head has a longitudinal chamber which at one end opens into the gas duct and at the other end contains an active optical component. The chamber is flushed with a purge gas which, after flushing the chamber, is discharged into the gas duct. A gas line is installed between the chamber and interior of the gas duct at a point upstream of a discharge point and the purge gas is a branch-off of the duct gas.

Abstract: In a wavelength modulation spectroscopy method and system the light of a tunable light source is modulated with a frequency f0, while the wavelength is swept over an interaction feature of a sample to be measured. The light of the light source is passed to a sample for interacting and thereafter detected and demodulated at a higher harmonic Nf0. To suppress effects of fluctuations of the optical transmission of the system on the measurement, originating from varying dust loads, high temperature, gas turbulence etc. in the measurement path (3), a burst signal in form of an envelope modulated pilot tone is added to the modulation of the light (1) of the light source (2) synchronously with the wavelength sweeps at a wavelength outside the interaction feature of the sample. The injected burst signal is at the detection frequency Nf0, where N?2, and is detected together with the measured spectrum from the sample and act as absorption normal, which the spectrum can be calibrated against.

Abstract: In a wavelength modulation spectroscopy method and system the light of a tunable light source is modulated with a frequency f0, while the wavelength is swept over an interaction feature of a sample to be measured. The light of the light source is passed to a sample for interacting and thereafter detected and demodulated at a higher harmonic Nf0. To suppress effects of fluctuations of the optical transmission of the system on the measurement, originating from varying dust loads, high temperature, gas turbulence etc. in the measurement path (3), a burst signal in form of an envelope modulated pilot tone is added to the modulation of the light (1) of the light source (2) synchronously with the wavelength sweeps at a wavelength outside the interaction feature of the sample. The injected burst signal is at the detection frequency Nf0, where N?2, and is detected together with the measured spectrum from the sample and act as absorption normal, which the spectrum can be calibrated against.