Visualization of expanding laser-ablation plume by a proposed frequency up-converted infrared spectroscopic imaging

Observing temporal and spatial distribution of infrared (IR) radiation is restricted by the lack of a fast-gated IR detector. To overcome this problem, frequency up-conversion detection of IR radiation in a nonlinear crystal has been developed by several investigators. We have proposed the frequency up-conversion imaging of an IR degenerate four-wave mixing (DFWM) signal. DFWM produce a coherent signal, so that the frequency up-conversion process is easily applied, which permits the remote detection and easy elimination of background noise. Also the sensitivity of DFWM in the infrared region is greater than other laser spectroscopy techniques such as LIF. To exhibit the capability of this scheme, we observed the laser ablated Cs plume.