Technique of detecting optical components based on coherent modulation imaging

Abstract

As one of the coherent diffractive imaging (CDI) techniques, coherent modulation imaging (CMI) is a lensless phase imaging technology with diffraction limited resolution in theory. Unlike multiple measurement phase retrieval algorithms, the CMI can achieve fast convergence speed with single-shot measurement by introducing a pre-characterized random phase modulator. Besides, it has simple structure without reference wave based on iterative engine. Despite the fact that the matured phase imaging can be used to implement the on-line wave diagnostics of laser pulse, in this work we accurately measure the face-type of optical component with peak-to-valley value below 0.5<i>λ</i> (<i>λ</i> = 632.8 nm) by using the CMI for the first time. In order to verify its measurement capability, 10 quartz windows with a diameter of 80 mm and PV value between 0.1<i>λ</i> and 0.5<i>λ</i> are repeatedly measured. Compared with the results of commercial interferometer, the root mean square error (Root MSE) of the peak-to-valley (PV) ratio of the results of the CMI is 0.0305<i>λ</i>, and the Root MSE of the root mean square (RMS) is 0.00522<i>λ.</i> The measurement accuracy of PV ratio and RMS can reach 0.1<i>λ</i> and 0.01<i>λ</i> respectively. In addition, the parallel flat with PV ratio = <i>λ</i>/20 is measured and analyzed with CMI, and its noise level is also analyzed. Considering that the potential improvement of CMI is available in the future, the CMI is expected to become a new technique for optical metrology with high precision, which is different from interferometry.