BigPatents India

A method of monitoring pressure of a gas species up to at most a predetermined maximum pressure value is disclosed. The method includes exposing the gas species to transmission of laser light, periodically modulating the wavelength a the laser light over a wavelength band including at least one absorption line of the gas species, optoelectrically, converting the transmitted laser light, thereby generating an electric output signal, performing at least one of first filtering the electric output signal with a filter characteristic having a lower cut-off frequency not lower than a transition frequency and of second filtering the electric output signal with a band pass filter characteristic having an upper cut-off frequency not higher than the transition frequency and a lower cut-off frequency above the modulation frequency of tie periodic wavelength modulation. The output of at least one of the filtering is evaluated as a pressure indicative signal. (FIG. - 1)