Development of broadband cavity ring-down spectroscopy for biomedical diagnostics of liquid analytes

We present a spectrometer for sensitive absorption measurements in liquids across broad spectral bandwidths. The spectrometer combines the unique spectral properties of incoherent supercontinuum light sources with the advantages of cavity ring-down spectroscopy, which is a self-calibrating technique. A custom-built avalanche photodiode array is used for detection, permitting the simultaneous measurement of ring-down times for up to 64 different spectral components at nanosecond temporal resolution. The minimum detectable absorption coefficient was measured to be 3.2 × 10^–6 cm^–1 Hz^–1/2 at 527 nm. We show that the spectrometer is capable of recording spectral differences in trace levels of blood before and after hemolysis.