Cavity enhanced absorption spectroscopy using a broadband prism cavity and a supercontinuum source

We report the design and construction of a cavity enhanced absorption spectrometer using broadband Brewster's angle prism retroreflectors and a spatially coherent 500 nm to >1.75 microm supercontinuum excitation source. Using prisms made from fused silica an effective cavity reflectivity of >99.99% at 1.064 microm was achieved. A proof of principle experiment was performed by recording the cavity enhanced absorption spectrum of the weak b-X (1?0) transition of molecular oxygen at 14529 cm-1 and the fifth overtone of the acetylene C-H stretch at 18430 cm(-1). CCD frames were integrated for 150 sec and 30 sec, with 3 frames (each 100 cm(-1) wide) and 1 frame (266 cm(-1) wide) required to observe the O(2) and C(2)H(2) spectra, respectively. A rms noise equivalent absorption (alpha(min)) of 7.21x10(-8) cm(-1) Hz(-1/2) and 1.28x10(-7) cm(-1) Hz(-1/2) with full width half maximum line widths of 0.18 cm(-1) and 0.44 cm(-1) were achieved for the molecular oxygen band and the acetylene overtone, respectively.