Abstract: An optical diagnostic system based on line imaging of spontaneous Raman-scattering(SRS) light has been developed. Designed a nanosecond-long laser pulse external face lifting optics by means of two series multiple optical ring-cavities converts a 400 mJ energy, 0.4 GW peak power, 6.5 ns-long input laser pulse into an approximately 120 mJ, 0.02 GW, 35 ns-long (FWHM) output laser pulse. In laser spontaneous Raman scattering excitation gas experiments, it could avoid effectively strong laser induced plasma spark and optical components/window damage in the focused beam path and laser igniting flammable gas, so that it improved substantially the signal to noise ratio of the weak signal levels generated by the Raman effect. Designed a beam expanding device and a beam shrinking device converts 8mm diameter original laser into 1mm diameter parallel laser. Designed composite achromatic lens converts 66 mm long scattering light into 6.6 mm high real image to match with the ICCD vertical height at maximum limit. Using the DDG^TM in ICCD carries out the timing synchronization between laser and ICCD. The experiment of gas Raman spectrum with multiple channel tests and verifies the system practicability. Furthermore, the system can be applied to quantitative measurement of density and temperature of residual and fresh charge mixing in an optical engine using spontaneous Raman scattering method.

Key words: optical diagnostic, spontaneous Raman scattering, line imaging, laser pulse face lifting, gas