O2 (1Δg) detection using broadband CARS

Abstract

1 Δg oxygen was the active medium of chemical oxygen iodine laser (COIL), the concentration and distribution of 1 Δg oxygen was important for the output power and beam quality. However, the current test technique, such as fluorescence detection method, absorption spectrum method could not get accurate 1 Δg oxygen information, due to the interference from the iodine fluorescence or the rigorous request of the laser source and optics and detection elements. The anti-stokes Raman spectrum of 1 Δg oxygen was regarded as a potential technique to obtain desirable signal, and the coherent anti-stokes Raman scatter (CARS) was the most feasible technique to get better signal to noise ratio (SNR). In this paper, we reported a broadband nanosecond coherent anti-stokes Raman scatter (CARS) detecting system built up for the detection of the concentration and distribution of O2( 1 Δg) in COIL：The second harmonic of a Nd: YAG pulse laser was separated into two parts, one part was used to pump a broadband nanosecond dye laser to generate light of 578-580 nm, which covered both stokes lines of O2 ( 1 Δg）and O2 (3 ∑）; The other part was combined with dye laser output by a dichroic mirror, and then introduced into the detection region of COIL through a focus lens. CARS signals for O2（1 Δg）and O2 （3 ∑）have different wavelengths, and their intensity was proportional to the square of the concentration of O2（1 Δg） and O2( 3 ∑). By changing the focus spot of pump and stokes laser, the concentration distribution of O2（1 Δg） and O2（3 ∑）at different position could be obtained.