O₂(¹Δ_g) detection using broadband CARS

Abstract

1 Δ g oxygen was the active medium of chemical oxygen iodine laser (COIL), the concentration and distribution of 1 Δ g 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 Δ g 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 Δ g 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 O 2 ( 1 Δ g ) 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 O 2 ( 1 Δ g ) and O 2 ( 3 Σ) ; 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 O 2 ( 1 Δ g )and O 2 ( 3 Σ ) have different wavelengths, and their intensity was proportional to the square of the concentration of O 2 ( 1 Δ g ) and O 2 ( 3 Σ). By changing the focus spot of pump and stokes laser, the concentration distribution of O 2 ( 1 Δ g ) and O 2 ( 3 Σ)at different position could be obtained.