A novel spectrometer for the rapid and sensitive detection of liquid phase analytes at trace concentrations is presented. Broad bandwidth supercontinuum radiation was coupled into a linear optical cavity incorporating an intracavity liquid-sample cuvette. Cavity enhanced absorption spectra of trace species covering more than 300 nm were acquired on time scales of milliseconds. Single shot acquisition times of 10-50 ms are demonstrated here. The effective absorption path length exceeds 2 m in sample volumes measuring 2.7 mL. A key feature of the instrument is that it can be calibrated using cavity ring-down spectroscopy without the requirement of changing the optical alignment. The sensitivity of the instrument is exemplified by measurements of trace concentrations of dye molecules and nickel sulfate dissolved in water. A minimum detectable absorption coefficient of 9.1 x 10(-7) cm(-1) Hz(-1/2) at 550 nm was obtained. The capability to capture broad bandwidth absorption spectra on short time scales permits kinetic studies of liquid phase reactions. We demonstrate this by recording the oscillatory behavior of a Belousov-Zhabotinsky reaction.
We report use of a dispersed supercontinuum generated in an all-normal-dispersion fibre to record low-noise spectra from atmospheric molecules at least an order of magnitude faster than has been previously reported. Supercontinuum generation in standard, anomalous dispersion photonic-crystal fibres is inherently connected with large pulse-to-pulse fluctuations resulting in detrimental consequences for high resolution spectroscopy if temporal averaging is not permitted. Replacing the standard PCF with a specially designed all-normal dispersion PCF we find that a substantially superior noise performance is achieved and present its use for high repetition rate absorption spectroscopy where spectra covering 100s of nm in spectral bandwidth can be captured of gases at 100s of kHz repetition rates.
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.
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