Spectroscopic apparatus and method

摘要

There is described a spectroscopic apparatus 2 for measuring an amount of an analyte in a mixture. The apparatus 2 has a laser source 6 for generating a frequency-modulated laser beam 22. A cavity 36 receives the frequency-modulated laser beam 22 and a photodetector 46 obtains an intensity signal indicative of an interaction between the frequency-modulated laser beam 22 and the mixture. The apparatus 2 has a first demodulator 76 for producing a first demodulation signal. A frequency locking arrangement uses the first demodulation signal to lock a carrier frequency of the frequency-modulated laser beam 22 and a mode of the cavity 36 to each other. The apparatus has a second demodulator 50 for producing a second demodulation signal and for generating, on the basis of the second demodulation signal, an output indicative of the amount of the analyte in the mixture. The cavity 36 may be provided by a micro-resonator or Fabry-Perot etalon.