An approach for carrying out depth profile measurement of an object with the plenoptic camera is proposed. A single plenoptic image consists of multiple lenslet images. To begin with, these images are processed directly with a refocusing technique to obtain the depth map, which does not need to align and decode the plenoptic image. Then, a linear depth calibration is applied based on the optical structure of the plenoptic camera for depth profile reconstruction. One significant improvement of the proposed method concerns the resolution of the depth map. Unlike the traditional method, our resolution is not limited by the number of microlenses inside the camera, and the depth map can be globally optimized. We validated the method with experiments on depth map reconstruction, depth calibration, and depth profile measurement, with the results indicating that the proposed approach is both efficient and accurate.
A reflection TIE system consisting of a reflecting microscope and a 4f relay system is presented in this paper, with which the transport of intensity equation (TIE) is applied to reconstruct the three-dimensional (3D) profile of opaque micro objects like wafer structures for 3D inspection. As the shape of an object can affect the phases of waves, the 3D information of the object can be easily acquired with the multiple phases at different refocusing planes. By electronically controlled refocusing, multi-focal images can be captured and used in solving TIE to obtain the phase and depth of the object. In order to validate the accuracy and efficiency of the proposed system, the phase and depth values of several samples are calculated, and the experimental results is presented to demonstrate the performance of the system.
In high power diode pumped solid-state lasers, thermal effects in the laser medium are important factors limiting the power scaling and beam quality. Besides total pump power, pump structure, such as pump geometry, cooling scheme, laser crystal shape and dimension all affect the result of thermal effects. The theoretical modelling and calculations may only conclude approximate results with the consideration of parts of factors. This paper introduces a new technique of measuring Nd:YAG rod thermal lensing by digital holography (DH). Both dynamic and steady state can be measured by this method. The digitally recorded hologram can reveal each part of the thermal effects in the crystal, and detailed variations of thermal effects can be mapped out through digital reconstructions of the captured holograms. It can help to study the uniformity of the pump distribution in the gain medium, find "hot" spots which may result in potential crystal crack. Moreover, an integrated thermal lensing can be accurately determined. DH is an informative tool to understand thermal effects and provide a guidance for laser cavity design and simulations.
Digital holographic microscopy provides 3D quantitative phase imaging that is suitable for high resolving investigations
on reflective surfaces as well as for transmissive materials. An optical configuration for a digital holographic microscope
and a method for digital holographic microscopy are presented. A cube beam splitter in the optical path, with a small
angle between the optical axis and its central semi-reflecting layer, both split and combine a diverging spherical
wavefront emerging from a microscope objective to give off-axis digital holograms. Since the object wave and the
reference wave go the same way to the CCD camera, it is called common-path digital holographic microscopy. When a
plane numerical reference wavefront is used for the reconstruction of the recorded digital hologram, the phase curvature
introduced by the microscope objective together with the illuminating wave to the object wave can be physically
compensated. A compound digital holographic microscope (with reflection mode and transmission mode) has been build
up based on this unique feature. Results from surfaces structures on silicon wafer and micro-optics on fused silica
demonstrate applications of this compound digital holographic microscope for technical inspection in material science.