An improvement on the 4f coherent imaging system for measuring the nonlinear refraction

We present a new experiment system to improve the original 4f coherent imaging system developed by Georges Boudebs et al. In the new experiment system we take off the monitor branch, add another 4f system before the main 4f system and place one more CCD camera after the first 4f system. Our new experiment system has five advantages: firstly, the old system needs three steps to measure the nonlinear refraction index of the nonlinear sample, however the new system only needs two steps. Secondly, in the developed system the CCD camera after the first 4f system can monitor the energy fluctuation as well as the intensity distribution of the input laser pulse, while the original system can only monitor the energy fluctuation. Thirdly, the new system realizes the real single-pulse measurement, and can avoid the energy instability completely. Fourthly, in the new system we can detach the diaphragm and the phase object, so they can adjust separately. Lastly, the added 4f system can be used as a spatial filter. The shortcomings of our improved system are that the experiment system becomes a little more complex and the additional CCD camera adds the experiment expenditure.