Fast measurement of the laser beam quality factor based on phase retrieval with a liquid lens

In this paper, a new method for measuring the beam quality (M2) of lasers based on phase retrieval with a liquid lens is proposed. With intensity profiles obtained under different focal lengths in a certain position, a variable-focus iterative retrieval algorithm is established for the reconstruction of the complex amplitude. Then M2 can be calculated with the angular spectrum theory. Feasibility of the proposed method is demonstrated with single- and multimode lasers through both simulations and experiments. Compared with the traditional liquid lens method, the M2 of lasers can be measured faster with the proposed method.