The essential requirements for any digital holography-based system to get employed as an inspection device in electronic industry are portability and ability to automatically focus on the reconstruction plane. Any deviation from the exact propagation distance between the hologram plane and the reconstruction plane may result in erroneous measurement of the surface features under inspection. We report for the first time, to the best of our knowledge, the autofocus capability in a digital holography-based portable camera for full-field quantitative inspection of solder joint defects in a printed circuit board. An intensity gradient-based algorithm is developed and applied to the digital hologram to automatically locate the reconstruction plane and determine the propagation distance. For a given range of distance, the algorithm calculates the maximum value of high frequency components in the reconstructed image and the corresponding propagation distance is used in the reconstruction. The autofocus algorithm along with the double exposure digital holographic interferometry is applied on the printed circuit board under thermal loading. 2D and 3D deformation maps are analyzed to detect different kinds of solder joint defects such as holes, irregular shapes, excess soldering and bridging. The work presented in this manuscript may further stimulate development of digital holographic techniques for several applications in metrology and inspection in the electronics manufacturing industry.

The coupling efficiency of light beams is a crucial factor for waveguide displays. Generally, the light beam is not coupled with maximum efficiency in the holographic waveguide without employing a prism in the recording geometry. Use of prisms in recording geometry leads to restricting the propagation angle of the waveguide to a specific value only. The issue of efficient coupling of a light beam without using prisms could be overcome via Bragg degenerate configuration. In this work, the simplified expressions of the Bragg degenerate case are obtained for the realization of normally illuminated waveguide-based displays. Using this model, by tuning the parameters of recording geometry, a range of propagation angles can be produced for a fixed normal incidence of a playback beam. Numerical simulations and experimental investigations of the Bragg degenerate waveguides of different geometries are performed to validate the model. A Bragg degenerate playback beam is successfully coupled in four waveguides recorded with different geometries and yields good diffraction efficiency at normal incidence. The quality of transmitted images is characterized using the structural similarity index measure. The augmentation of a transmitted image in the real world is experimentally demonstrated through the fabricated holographic waveguide for near-eye display applications. Bragg degenerate configuration can provide flexibility in the angle of propagation while maintaining the same coupling efficiency achievable with a prism for holographic waveguide displays.

This paper describes detection of cracks in ceramic tableware using a portable digital holographic camera working on the principle of double-exposure digital holographic interferometry. Digital image processing techniques are applied on amplitude and phase information obtained from the numerically reconstructed wavefronts of the test object to locate position of the defect. Speckles generated due to illumination of the rough surface of the ceramic cup with the coherent light source deteriorate quality of the interferometric phase. Several iterations of the averaging filter with optimized kernel size are applied on sine and cosine components of the interferometric phase to minimize the speckle noise. The effect of kernel size of the matrix used in the averaging filter on quality of the interferometric phase is analyzed by evaluating the signal-to-noise ratio. The experimentally obtained size of crack on a ceramic cup (0.08 mm) is validated by a mechanical profiler with an error of 6.6%. This study may help in improving the quality criteria of tableware items.

In this work, quality evaluation of a reconstructed amplitude image in digital holography is presented. The digital holograms are recorded using three different digital holographic experimental configurations, namely, conventional off-axis digital holography, concave-lens-based digital holography, and the digital holographic camera developed for non-destructive testing applications [ Opt. Lasers Eng. 137, 106359 (2021)OLENDN 0143-8166 10.1016/j.optlaseng.2020.106359 ]. The quality of reconstructed images is measured by calculating the quality evaluation parameters such as speckle index, peak signal-to-noise ratio, and structural similarity index measure for these experimental configurations. Optimization of the power of the light source and exposure time of the recording sensor is performed for the three configurations based on the quality evaluation of reconstructed images. A comparison of the quality of reconstructed images is made for the three experimental configurations to analyze their performance for different source power and exposure time of the recording image sensor.

Digital holography (DH) is an important method for three-dimensional (3D) imaging since it allows for the recording and reconstruction of an object’s amplitude and phase information. However, the field of view (FOV) of a DH system is typically restricted by the finite size of the pixel pitch of the digital image sensor. We proposed a new configuration of the DH system based on Fresnel’s bi-mirror to achieve doubling the camera FOV of the existing off-axis DH system which leveraged single-shot acquisition and a common-path optical framework. The dual FOV was obtained by spatial frequency multiplexing corresponding to two different information-carrying beams from an object. Experimental evidence of the proposed dual FOV-DH system’s viability was provided by imaging two different areas of the test object and an application to surface profilometry by measuring the step height of the resolution chart which showed excellent agreement with an optical profiler. Due to the simple configuration, the proposed system could find a wide range of applications, including in microscopy and optical metrology.

Optical properties of lenses play significant role in digital holographic setups to increase their applications in several fields of imaging and non-destructive testing. In present work, we investigate the effect of introduction of lenses on quality of reconstructed images when they are placed between the object and the image sensor in digital holography. We define a range of propagation distance suitable for recording digital holograms using different off-axis digital holographic setups. The reconstruction results of conventional off-axis digital holographic setup are taken as reference to compare them with lens-based digital holographic setups. Three different digital holographic setups are realised using lenses i.e. concave lens-based setup, convex lens-based setup, and combined concave and convex lenses-based setup. The quality of the reconstructed image is measured by calculating their structural similarity index measure (SSIM) values. These values compare the reconstructed image obtained in the experiment with a reference image of the object obtained through its computer generated hologram (CGH). Performance of these digital holographic setups is compared on the basis of SSIM values of reconstructed images calculated for different separation between object to sensor. On the basis of SSIM values, a range of distances suitable for recording digital holograms for each setup is obtained as 220 mm to 400 mm for the concave lens-based setup, 560 mm to 800 mm for convex lens-based setup, and 220 mm to 600 mm for the concave-convex lens-based setup using concave lens of 50 mm focal length and a convex lens of 80 mm focal length in the experiments.