Absorption spectroscopic determination of specific gas components in mixtures, using frequency modulated laser, particularly in medical applications, e.g. monitoring of patient's oxygen levels during anaesthesia

摘要

The method involves irradiating a gas sample from a stable, single mode laser diode, whose output wavelength is continuously modulated by varying the control current. The intensity of the laser beam after transmission through the gas sample is measured by a detector for the components corresponding to the direct current component and the doubled sinusoidal frequency of the second harmonic. The laser control current is varied by imposing a predetermined sinusoidal alternating current on a direct current energy supply, so that a laser wavelength is produced which is in the same region as the absorption line for the selected gas species. The concentration of the selected gas species is calculated from the absorption line width of the minimum and maximum of the second harmonic. Preferably, the laser diode is a vertical cavity surface emitting laser diode. The second harmonic for the detector signal is determined using a lock in amplifier. An Independent claim is included for a device for implementing the method.