Imagine techniques for aligning in the degenerate four -wave mixing experiment

Phase-match in degenerate four-wave mixing (DFWM) is not automatically achieved in the forward folded boxcars geometry. In this paper, we first design a simple image aligning system composed of an optical system, CCD camera and the related software. We can feasibly obtain well overlapped spot in the sample cell without moving the sample cell under this system. Also, we have proven the three pumping light beams are well overlapped in the sample cell when the three pumping light beams are on the same spot on CCD camera. This method minimizes the deviation by our eyes aligning. We can easily and timely know the effect of the pointing stability on the optical path by monitoring facula changing with the laser beam pointing and disturbs of the environment. So, this is a good choice for fast adjusting the light path and finding the overlapped spot. Finally, Steady DFWM signals have been obtained in the iodine vapor. This system makes it feasible that the potential application of FG-DFWM is used as a diagnostic tool in combustion research and environment monitoring.