Laser dispersion spectrometer

Abstract

A laser dispersion spectrometer 10 comprises a laser source 100 forming a laser beam 25; an electro-optic phase modulator 110 which adds a plurality of sidebands 35 to the laser beam responsive to an RF modulation signal 115; and optics 40 to transmit the laser beam including the sidebands through a sample 20. A photodetector 130 receives the laser beam from the optics 40 following transmission through the sample and generates a corresponding electrical photodetector output 135. A DC / RF splitter 140 splits the photodetector output 135 into a DC component and an RF modulated component 145. An IQ demodulator 150 demodulates the RF modulated component to form demodulated quadrature components, and a calculation element calculates a phase parameter which is related to optical phase of the laser beam following transmission of the laser beam through the sample using the DC and demodulated quadrature components. An analyser 180 may determine the concentration of the component species of the sample, such as methane, using the phase parameter as a function of scanned laser beam frequency.

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