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 .