Video-rate laser Doppler vibrometry by heterodyne holography

We report a demonstration video-rate heterodyne holography in off-axis configuration. Reconstruction and display of 1 Megapixel holograms is achieved at 24 frames per second, with a graphics processing unit. Our claims are validated with real-time screening of steady-state vibration amplitudes in a wide-field, non-contact vibrometry experiment.Comment: Optics Letters (2011) 00

Lensfree computational microscopy tools for cell and tissue imaging at the point-of-care and in low-resource settings.

The recent revolution in digital technologies and information processing methods present important opportunities to transform the way optical imaging is performed, particularly toward improving the throughput of microscopes while at the same time reducing their relative cost and complexity. Lensfree computational microscopy is rapidly emerging toward this end, and by discarding lenses and other bulky optical components of conventional imaging systems, and relying on digital computation instead, it can achieve both reflection and transmission mode microscopy over a large field-of-view within compact, cost-effective and mechanically robust architectures. Such high throughput and miniaturized imaging devices can provide a complementary toolset for telemedicine applications and point-of-care diagnostics by facilitating complex and critical tasks such as cytometry and microscopic analysis of e.g., blood smears, Pap tests and tissue samples. In this article, the basics of these lensfree microscopy modalities will be reviewed, and their clinically relevant applications will be discussed

Single-shot compressed ultrafast photography: a review

Compressed ultrafast photography (CUP) is a burgeoning single-shot computational imaging technique that provides an imaging speed as high as 10 trillion frames per second and a sequence depth of up to a few hundred frames. This technique synergizes compressed sensing and the streak camera technique to capture nonrepeatable ultrafast transient events with a single shot. With recent unprecedented technical developments and extensions of this methodology, it has been widely used in ultrafast optical imaging and metrology, ultrafast electron diffraction and microscopy, and information security protection. We review the basic principles of CUP, its recent advances in data acquisition and image reconstruction, its fusions with other modalities, and its unique applications in multiple research fields

Optical Techniques for Defect Evaluation in Vehicles

The optical techniques are a powerful tool on situations where either the physical contact or invasive techniques for evaluation are not suitable. Vehicle environments constitute an application field for the optical techniques and are the focus of this chapter. In order to reinforce this kind of techniques, it must be clarified that the idea to manipulate the light backs to the second century before our age, when Archimedes planned to destroy enemy ships using a solar heat ray with an array of actuators to change the shape of a mirror (Bifano T., 2011). Therefore, the field of photonics is the one that offers the possibility to achieve one of the greatest realizations and applications because the light is present in all aspects of the human life and our way of living is impossible without light (Carmo J. P. et al., 2012a). Optical measurement systems are also suitable for harsh monitorization because they are non-contact and full-field techniques. This is the case of Moiré Interferometry, which is used for many optoelectronic applications as displacement measurements (Wronkowski L., 1995), evaluation of microelectronics devices deformation (Xie H. et al., 2004), optical communications (Chen L. et al., 2000), strain measurements with Fiber Bragg Grattings, FBGs, (Silva A. F. et al., 2011) and spectrography (Kong S. H. et al., 2001). In this context, it must be noted that the recent nuclear disaster in Fukushima, Japan, confirms the need of tighter security measures be done within harsh environments (which includes the automobiles) in order to increase both the safety of people and the reliability of vehicles’ parts

A real-time digital holographic microscope with an optical tweezer

The most significant advantage of the holographic microscopy is being able to image transparent objects such as biological cells without staining. Therefore, the cell image can be captured while it is alive. Moreover, Manipulating a living cell without destructing it’s structure can be achieved by the use of an optical tweezer which apply a pulling force around a tightly focused laser beam without a physical contact. Therefore, an instrument that combines the holographic microscope and the optical tweezer is quite useful for biological studies. Another advantage of holographic imaging is that, one does not need to do mechanical focusing for the scene when recording the hologram. Focusing is achieved by reconstructing the hologram at a certain depth. If the object’s optical depth from the recording plane is not known a priori, auto-focusing algorithms must be used to estimate this distance. However, auto-focusing and reconstruction can be quite time consuming as the hologram sizes increase and the microscope can not operate in real-time with high resolution holograms using traditional central processing units (CPUs). Therefore, for real-time operation, additional hardware accelerators are required for reconstructing high resolution holograms. A holograms can be reconstructed tens of times faster with a graphics processing unit than with the state-of-the-art main CPUs. In this thesis, an auto-focusing megapixel-resolution digital holographic microscope (DHM) that uses a commodity graphics card as the calculation engine is presented. The computational power of the GPU allows the DHM to work in realtime such that the reconstruction distance is estimated unsupervised, and the postprocessing of the hologram is transparent to the user. Performances of the DHM under GPU and CPU settings are presented and a maximum of 70 focused reconstructions per second (frps) are achieved with 1024 ⇥ 1024 pixels holograms. Moreover, a setup for incorporating an optical tweezer to the holographic microscope is provided. With this setup, it is possible to trap small particles while performing holographic imaging

Improved resolution in fiber bundle inline holographic microscopy using multiple illumination sources

Recent work has shown that high-quality inline holographic microscopy images can be captured through fiber imaging bundles. Speckle patterns arising from modal interference within the bundle cores can be minimized by use of a partially-coherent optical source such as an LED delivered via a multimode fiber. This allows numerical refocusing of holograms from samples at working distances of up to approximately 1 mm from the fiber bundle before the finite coherence begins to degrade the lateral resolution. However, at short working distances the lateral resolution is limited not by coherence, but by sampling effects due to core-to-core spacing in the bundle. In this article we demonstrate that multiple shifted holograms can be combined to improve the resolution by a factor of two. The shifted holograms can be rapidly acquired by sequentially firing LEDs, which are each coupled to their own, mutually offset, illumination fiber. Following a one-time calibration, resolution-enhanced images are created in real-time at an equivalent net frame rate of up to 7.5 Hz. The resolution improvement is demonstrated quantitatively using a resolution target and qualitatively using mounted biological slides. At longer working distances, beyond 0.6 mm, the improvement is reduced as resolution becomes limited by the source spatial and temporal coherence

Design and implementation of a digital holographic microscope with fast autofocusing

Holography is a method for three-dimensional (3D) imaging of objects by applying interferometric analysis. A recorded hologram is required to be reconstructed in order to image an object. However one needs to know the appropriate reconstruction distance prior to the hologram reconstruction, otherwise the reconstruction is out-of-focus. If the focus distance of the object is not known priori, then it must be estimated using an autofocusing technique. Traditional autofocusing techniques used in image processing literature can also be applied to digital holography. In this thesis, eleven common sharpness functions developed for standard photography and microscopy are applied to digital holograms, and the estimation of the focus distances of holograms is investigated. The magnitude of a recorded hologram is quantitatively evaluated for its sharpness while it is reconstructed on an interval, and the reconstruction distance which yields the best quantitative result is chosen as the true focus distance of the hologram. However autofocusing of highresolution digital holograms is very demanding in means of computational power. In this thesis, a scaling technique is proposed for increasing the speed of autofocusing in digital holographic applications, where the speed of a reconstruction is improved on the order of square of the scale-ratio. Experimental results show that this technique offers a noticeable improvement in the speed of autofocusing while preserving accuracy greatly. However estimation of the true focus point with very high amounts of scaling becomes unreliable because the scaling method detriments the sharpness curves produced by the sharpness functions. In order to measure the reliability of autofocusing with the scaling technique, fifty computer generated holograms of gray-scale human portrait, landscape and micro-structure images are created. Afterwards, autofocusing is applied to the scaleddown versions of these holograms as the scale-ratio is increased, and the autofocusing performance is statistically measured as a function of the scale-ratio. The simulation results are in agreement with the experimental results, and they show that it is possible to apply the scaling technique without losing significant reliability in autofocusing

Fast Autofocusing using Tiny Transformer Networks for Digital Holographic Microscopy

The numerical wavefront backpropagation principle of digital holography confers unique extended focus capabilities, without mechanical displacements along z-axis. However, the determination of the correct focusing distance is a non-trivial and time consuming issue. A deep learning (DL) solution is proposed to cast the autofocusing as a regression problem and tested over both experimental and simulated holograms. Single wavelength digital holograms were recorded by a Digital Holographic Microscope (DHM) with a 10$\mathrm{x}$ microscope objective from a patterned target moving in 3D over an axial range of 92 $\mu$m. Tiny DL models are proposed and compared such as a tiny Vision Transformer (TViT), tiny VGG16 (TVGG) and a tiny Swin-Transfomer (TSwinT). The experiments show that the predicted focusing distance $Z_R^{\mathrm{Pred}}$ is accurately inferred with an accuracy of 1.2 $\mu$m in average in comparison with the DHM depth of field of 15 $\mu$m. Numerical simulations show that all tiny models give the $Z_R^{\mathrm{Pred}}$ with an error below 0.3 $\mu$m. Such a prospect would significantly improve the current capabilities of computer vision position sensing in applications such as 3D microscopy for life sciences or micro-robotics. Moreover, all models reach state of the art inference time on CPU, less than 25 ms per inference

Off-axis quantitative phase imaging processing using CUDA: toward real-time applications

We demonstrate real time off-axis Quantitative Phase Imaging (QPI) using a phase reconstruction algorithm based on NVIDIA’s CUDA programming model. The phase unwrapping component is based on Goldstein’s algorithm. By mapping the process of extracting phase information and unwrapping to GPU, we are able to speed up the whole procedure by more than 18.8× with respect to CPU processing and ultimately achieve video rate for mega-pixel images. Our CUDA implementation also supports processing of multiple images simultaneously. This enables our imaging system to support high speed, high throughput, and real-time image acquisition and visualization

Current research activities on holographic video displays

"True 3D" display technologies target replication of physical volume light distributions. Holography is a promising true 3D technique. Widespread utilization of holographic 3D video displays is hindered by current technological limits; research activities are targeted to overcome such difficulties. Rising interest in 3D video in general, and current developments in holographic 3D video and underlying technologies increase the momentum of research activities in this field. Prototypes and recent satisfactory laboratory results indicate that holographic displays are strong candidates for future 3D displays. © 2010 SPIE