Fig. 1. Gain as a function of for (a), (c) and (b), (d); (a), (b) and (c), (d); for (black curves), (green curves), (red curves) and (blue curves). The solid curves show the results of numerical simulation, while the dashed curves are plotted by Equation (4), with replaced by .

Fig. 2. Experimental layout. NS – noise source (randomly scratched 0.5 mm thick glass plate), NLP – nonlinear plate (BK7 glass or KDP), PHM – mirror with a pinhole.

Fig. 3. Experimental noise spectra (a) and noise gain (b).