In-situ Quantitative Phase Imaging during Multi-photon Laser Printing

Shape optimization of microstructures such as microlenses and diffractive optical elements fabricated by multi-photon laser printing is routinely performed by optical characterization after completing printing and development (ex situ). It is, however, highly desirable, instead of or in addition, to optically characterize the samples during the printing process before development (in situ). Here, we successfully demonstrate the integration of in-situ quantitative phase imaging into a commercial multi-photon laser printer. In terms of hardware, this integration merely requires adding illumination by a collimated LED and a small aperture to the existing beam path. In terms of software, we use well-established reconstruction algorithms based on a stack of through-focus, wide-field optical images acquired within a few seconds. We verify this approach by inspecting the topography of various microoptical elements printed with different photoresists and comparing the results with ex-situ measurements obtained by using a spinning-disk confocal optical microscope.