| 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 mum supercontinuum excitation source. The design of a high finesse optical cavity made from two prism retroreflectors is fully described. Optical beam propagation calculations to determine the specification of prism angles and relative dimensions, the size of the astigmatic TEM00 beam as it propagates in the cavity, and the sensitivity of the optic axis to changes in prism alignment and fabrication errors are presented. The effects of material dispersion are also quantified for three different materials: fused silica, calcium fluoride, and barium fluoride. Using prisms made from fused silica an effective cavity reflectivity of >99.99% at 1.064 mum 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 A rms noise equivalent absorption (alphamin) 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-1were achieved for the molecular oxygen band and the acetylene overtone, respectively. |
