A process for measuring the absorption spectrum of a target
analyte using a cavity
ring down spectrometer, comprising the steps of: i) tuning the
spectrometer laser so that the light transmitted from the
laser into the
spectrometer optical cavity is varied over a
wavelength interval which encompasses both the absorption
wavelength of a spectral feature of the target
analyte and a plurality of the free spectral ranges of the
optical cavity; ii) triggering a plurality of ringdown events; iii) for each ringdown event, recording the
decay time constant and the trigger time at which the light into the cavity is shut off; iv) organizing the
decay time constants, light wavelengths and trigger times as a function of trigger time; v) ordering said light wavelengths by increasing value and placing groups of wavelengths into individual bins; vi) computing the average
wavelength of each bin group; vii) grouping the
decay time constants and trigger times into bins that parallel said wavelength bins, with the decay time constants in each of said parallel bin being arranged by increasing trigger time; viii) computing the average decay time for each decay time bin and using this decay
time average, together with the average wavelength from the parallel wavelength bin, to compute the optical loss for the target
analyte at said average wavelength.