A calibration method for broad-bandwidth cavity enhanced absorption spectroscopy performed with supercontinuum radiation

An efficient calibration method has been developed for broad-bandwidth cavity enhanced absorption spectroscopy. The calibration is performed using phase shift cavity ring-down spectroscopy, which is conveniently implemented through use of an acousto-optic tunable filter (AOTF). The AOTF permits a narrowband portion of the SC spectrum to be scanned over the full high-reflectivity bandwidth of the cavity mirrors. After calibration the AOTF is switched off and broad-bandwidth CEAS can be performed with the same light source without any loss of alignment to the set-up. We demonstrate the merits of the method by probing transitions of oxygen molecules O-2 and collisional pairs of oxygen molecules (O-2)(2) in the visible spectral range

Chemical microanalysis with cavity-enhanced optical waveguide devices

Three examples of cavity-enhanced measurements of refractive index and optical absorption are discussed. Using microphotonic silicon-on-insulator ring-resonators we determine the concentration of cyclohexane and m-xylene at detection levels of 300-3000 ppm. The gases are first absorbed into a siloxane polymer and its refractive index change is detected by a characteristic wavelength shift of the cavity resonance. In a second device phase-shift cavity ring-down spectroscopy is applied to simultaneously measure the optical absorption at two wavelengths of either a dye, nucleic acids or a pharmaceutical component. Multiplexing the ring-down measurement permits dual wavelength absorption spectroscopy without the use of a dispersion element. Finally, a combination of resonance wavelength measurements and cavity ring-down spectroscopy is used to simultaneously determine the change in refractive index and the absorption induced by adsorption of ethylene diamine on a 300 \u3bcm silica sphere. A whispering gallery mode of the microsphere resonator is excited with intensity modulated light and the intensity and AM modulation phase of the Rayleigh backscattered light is measured. \ua9 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).Peer reviewed: YesNRC publication: Ye