No abstract

Just as photolithography technology brought about the miniaturization of integrated circuits and drove multiple market opportunities in the electronics sector, a similar inflection point has arrived for ultrafast lasers. While these femtosecond class lasers have long enabled the precise manipulation of matter without heat affects, only recently, with the advent of commercial grade systems, has the potential of the technology been realized. Fiber optic architecture, embedded software control and robust telecom components have been leveraged to ensure the reliability, ease of use, and performance standards required in manufacturing settings. With femtosecond laser microfabrication tools now accessible to industry, the relevance of femtosecond lasers to modern manufacturing has become clear based on compelling economics, unparalleled precision, and new flexibility with respect to materials. These new capabilities are opening up enormous opportunities in automotive components, consumer electronics, medical devices, aerospace and bioscience applications.

Wide field, lensless microscopes have been developed for telemedicine and for resource limited setting [1]. They are based on in-line digital holography which is capable to provide amplitude and phase information resulting from numerical reconstruction. The phase information enables achieving axial resolution in the nanometer range. Hence, such microscopes provide a powerful tool to determine three-dimensional topologies of microstructures.In this contribution, a compact, low-cost, wide field, lensless microscope is presented, which is capable of providing topological profiles of microstructures in transparent material. Our setup consist only of two main components: a CMOSsensor chip and a laser diode without any need of a pinhole. We use this very simple setup to record holograms of microobjects. A wide field of view of ~24 mm², and a lateral resolution of ~2 µm are achieved. Moreover, amplitude and phase information are obtained from the numerical reconstruction of the holograms using a phase retrieval algorithm together with the angular spectrum propagation method. Topographic information of highly transparent micro-objects is obtained from the phase data. We evaluate our system by recording holograms of lines with different depths written by a focused laser beam. A reliable characterization of laser written microstructures is crucial for their functionality. Our results show that this system is valuable for determination of topological profiles of microstructures in transparent material.