Near-infrared broad-band cavity enhanced absorption spectroscopy using a superluminescent light emitting diode

Abstract

A fibre coupled near-infrared superluminescent light emitting diode that emits ∼10 mW of radiation between 1.62 and 1.7 µm is employed in combination with a broad-band cavity enhanced spectrometer consisting of a linear optical cavity with mirrors of reflectivity ∼99.98% and either a dispersive near-infrared spectrometer or a Fourier transform interferometer. Results are presented on the absorption of 1,3-butadiene, and sensitivities are achieved of 6.1 × 10⁻⁸ cm⁻¹ using the dispersive spectrometer in combination with phase-sensitive detection, and 1.5 × 10⁻⁸ cm⁻¹ using the Fourier transform interferometer (expressed as a minimum detectable absorption coefficient) over several minutes of acquisition time.