Gabor Hologram Research Articles

Single-shot wavelength-multiplexed phase microscopy under Gabor regime in a regular microscope embodiment

Phase imaging microscopy under Gabor regime has been recently reported as an extremely simple, low cost and compact way to update a standard bright-field microscope with coherent sensing capabilities. By inserting coherent illumination in the microscope embodiment and producing a small defocus distance of the sample at the input plane, the digital sensor records an in-line Gabor hologram of the target sample, which is then numerically post-processed to finally achieve the sample’s quantitative phase information. However, the retrieved phase distribution is affected by the two well-known drawbacks when dealing with Gabor’s regime, that is, coherent noise and twin image disturbances. Here, we present a single-shot technique based on wavelength multiplexing for mitigating these two effects. A multi-illumination laser source (including 3 diode lasers) illuminates the sample and a color digital sensor (conventional RGB color camera) is used to record the wavelength-multiplexed Gabor hologram in a single exposure. The technique is completed by presenting a novel algorithm based on a modified Gerchberg–Saxton kernel to finally retrieve an enhanced quantitative phase image of the sample, enhanced in terms of coherent noise removal and twin image minimization. Experimental validations are performed in a regular Olympus BX-60 upright microscope using a 20X 0.46NA objective lens and considering static (resolution test targets) and dynamic (living spermatozoa) phase samples.

Omnidirectional 3D shape measurement using image outlines reconstructed from Gabor digital holography

We propose an omnidirectional 3D shape measurement method using the contour information of an object from Gabor holograms captured in omnidirectional measurements. To obtain the correct contour information from Gabor holograms, an edge-enhanced image reconstruction method is developed. The 3D shape can be restored by the rigid-body transformation of the contour information acquired from all directions. Omnidirectional 3D shape measurements are conducted using an aspheric lens and a spiral-shaped wire. The proposed method can successfully restore the complex 3D shapes of objects.

Inline holography of miniaturized objects with an intrinsic reference angle determined by the sagitta

The twin image problem, well known in Gabor holography, greatly obstructs the output of high-quality holograms. Previous solutions include numerical and instrumental means to eliminate or mitigate the issue. The proposed method demonstrates the feasibility of using the sagitta angle in a spherical reference beam as an intrinsic reference angle within in-line holography. Along with a miniaturized version of the object, to allow for a wide range of object sizes, from millimeters to meters, with a small variation within the original optical system. The inherent reference angle allows for a separation of the twin images in the reconstruction of a Gabor hologram, while maintaining the system on axis. Under lens-less Fourier criteria, the peripheral information of the visual field interferes with a spherical wave to generate an interference pattern that results in a hologram with separated images.

Phase imaging microscopy under the Gabor regime in a minimally modified regular bright-field microscope

Quantitative phase imaging (QPI) is nowadays a powerful tool for visualization and analysis of biological processes. QPI is usually attained from specifically designed optical microscopes retrieving phase information in a quantitative way. In this paper we report on an extremely simple, low cost and compact way to update a standard bright-field microscope with coherent sensing capabilities. It is based on the in-line Gabor holography concept and only needs to replace the illumination broadband source of the regular microscope with a coherent one. The proposed methodology is completed by the recording of a digital in-line Gabor hologram instead of regular imaging conditions and by the numerical processing of the recorded hologram to finally achieve QPI. The selection of the defocus distance is critical to finally achieve high quality phase imaging, so calibration considering phase and amplitude test targets is presented for the proper definition of such defocus distance. In addition, the selected configuration is experimentally validated using different samples (microbeads, cheek cells and alive spermatozoa). All the experiments are implemented in a regular Olympus BX-60 upright microscope using a 20X 0.46NA objective lens. The proposed method shows how to convert a regular microscope into a holographic one with probably the minimum needed modifications and with the main limitation coming from the Gabor imaging conditions (weak diffractive samples and twin image presence).

Holographic optical field recovery using a regularized untrained deep decoder network

Image reconstruction using minimal measured information has been a long-standing open problem in many computational imaging approaches, in particular in-line holography. Many solutions are devised based on compressive sensing (CS) techniques with handcrafted image priors or supervised deep neural networks (DNN). However, the limited performance of CS methods due to lack of information about the image priors and the requirement of an enormous amount of per-sample-type training resources for DNNs has posed new challenges over the primary problem. In this study, we propose a single-shot lensless in-line holographic reconstruction method using an untrained deep neural network which is incorporated with a physical image formation algorithm. We demonstrate that by modifying a deep decoder network with simple regularizers, a Gabor hologram can be inversely reconstructed via a minimization process that is constrained by a deep image prior. The outcoming model allows to accurately recover the phase and amplitude images without any training dataset, excess measurements, or specific assumptions about the object’s or the measurement’s characteristics.

Noise-free quantitative phase imaging in Gabor holography with conditional generative adversarial network.

This paper shows that deep learning can eliminate the superimposed twin-image noise in phase images of Gabor holographic setup. This is achieved by the conditional generative adversarial model (C-GAN), trained by input-output pairs of noisy phase images obtained from synthetic Gabor holography and the corresponding quantitative noise-free contrast-phase image obtained by the off-axis digital holography. To train the model, Gabor holograms are generated from digital off-axis holograms with spatial shifting of the real image and twin image in the frequency domain and then adding them with the DC term in the spatial domain. Finally, the digital propagation of the Gabor hologram with Fresnel approximation generates a super-imposed phase image for the C-GAN model input. Two models were trained: a human red blood cell model and an elliptical cancer cell model. Following the training, several quantitative analyses were conducted on the bio-chemical properties and similarity between actual noise-free phase images and the model output. Surprisingly, it is discovered that our model can recover other elliptical cell lines that were not observed during the training. Additionally, some misalignments can also be compensated with the trained model. Particularly, if the reconstruction distance is somewhat incorrect, this model can still retrieve in-focus images.

Wavelet processing and digital interferometric contrast to improve reconstructions from X-ray Gabor holograms.

In this work, the application of an undecimated wavelet transformation together with digital interferometric contrast to improve the resulting reconstructions in a digital hard X-ray Gabor holographic microscope is shown. Specifically, the starlet transform is used together with digital Zernike contrast. With this contrast, the results show that only a small set of scales from the hologram are, in effect, useful, and it is possible to enhance the details of the reconstruction.

Imaging on the surfaces of an uneven thickness medium based on hybrid phase retrieval with the assistance of off-axis digital holography

A hybrid phase retrieval method with the assistance of off-axis digital holography is proposed for imaging objects on the surfaces of a transparent medium with uneven thickness. The approximate phase distribution is obtained by a constrained optimization approach from the off-axis hologram, and it is used in an iterative procedure for retrieving the complex field of the object from the Gabor hologram. Furthermore, principal component analysis is introduced for compensating for phase aberrations caused by the medium. Numerical simulations and optical experiments were carried out to validate the proposed method. The quality of the reconstructed image is improved remarkably compared to only off-axis digital holography.

Optical proximity correction using holographic imaging technique

In this work, the preliminary results of the holographic imaging technique (HIT) as a resolution enhancement technique (RET) hybrid inverse lithography technique (ILT) optical proximity correction mask correction is presented. The proposed technique is based on the illumination system and free space propagation of the mask. First, an in-line hologram (Gabor hologram) is generated by computing the target pattern diffraction pattern. Second, the computed hologram is synthesized as pattern contours to form a mask for a conventional optical system. In this study, a simple HIT corrected mask is validated with compact lithographic exposure system mathematical model for demonstrating the preliminary validity of the proposed method. Future plans to validate HIT for the most aggressive process nodes are proposed. The proposed technique has not been exercised against conventional ILT or other RET techniques, and does not contain analysis of resolution improvement achievable with those techniques.

English

This paper investigates the application of Fresnel based numerical algorithms for the reconstruction of Gabor in-line holograms. A simple in-line digital holographic system was used to record blood cell. The Fresnel transformation (FS) method was used for reconstruction of the hologram. High contrast blood cell images were used to demonstrate numerical reconstruction process by Matlab. Sine, cosin, and amplitude holograms were reconstructed. This method provides new insights into the dynamics of the red blood cells and will be further used to investigate the effect of physiological and pharmacological effectors on RBCs. The spontaneous cell membrane fluctuations (CMF) of the red blood cell (RBC) was investigated, by calculating both thickness and refraction index of the cell blood.   Key words: Digital holography, blood cell, refractive index.

Optimization of electromagnetic fields in holographic lithography using the method of local variations

The problem of optimization of the Gabor hologram for creating light images with required intensity distribution is considered. The amplitude of the image intensity variation is decreased to technologically acceptable values as a result of optimization of a computer synthesized hologram, which essentially reduced the "Gibbs effect", the distortions occurring at the edges of the created object in the case of physical hologram recording. The results of optimization of electromagnetic fields using the method of local variations are demonstrated.

Millimeter-wave compressive holography

We describe an active millimeter-wave holographic imaging system that uses compressive measurements for three-dimensional (3D) tomographic object estimation. Our system records a two-dimensional (2D) digitized Gabor hologram by translating a single pixel incoherent receiver. Two approaches for compressive measurement are undertaken: nonlinear inversion of a 2D Gabor hologram for 3D object estimation and nonlinear inversion of a randomly subsampled Gabor hologram for 3D object estimation. The object estimation algorithm minimizes a convex quadratic problem using total variation (TV) regularization for 3D object estimation. We compare object reconstructions using linear backpropagation and TV minimization, and we present simulated and experimental reconstructions from both compressive measurement strategies. In contrast with backpropagation, which estimates the 3D electromagnetic field, TV minimization estimates the 3D object that produces the field. Despite undersampling, range resolution is consistent with the extent of the 3D object band volume.

Recording and reconstruction of digital Gabor hologram

This paper looks at some as yet undisclosed observations in the recording and reconstruction of digital Gabor hologram. Small particles on the specimen plane diffract the illuminating spherical wave to form the object wave which interferes with the un-diffracted reference to form the in-line hologram. The interference is similar to that between two spherical wavefronts. It is shown that resolution enhancement can be achieved in the recording process through the use of wavefronts with different curvature. Numerical reconstruction of this hologram with a conjugate of the illuminating (reference) wave provides the in-focus real image at the object plane. It is exemplified that the proper choice of the reconstruction wavefront can optically magnify the reconstructed image enabling one to better visualize the resolution enhancement. Both theoretical analysis and experimental confirmation are provided for these observations.

Reconstruction algorithms applied to in-line Gabor digital holographic microscopy

This paper investigates the application of Fresnel based numerical algorithms for the reconstruction of Gabor in-line holograms. We focus on the two most widely used Fresnel approximation algorithms, the direct method and the angular spectrum method. Both algorithms involve calculating a Fresnel integral, but they accomplish it in fundamentally different ways. The algorithms perform differently for different physical parameters such as distance, CCD pixel size, and so on. We investigate the constraints for the algorithms when applied to in-line Gabor digital holographic microscopy. We show why the algorithms fail in some instances and how to alter them in order to obtain useful images of the microscopic specimen. We verify the altered algorithms using an optically captured digital hologram.

Numerical Optical Sectioning for 3D Holographic Images with EUV Lasers

Through a careful analysis of numerically reconstructed holographic images, it is possible to obtain 3D information from a single high-aperture EUV Gabor hologram.

Volume extreme ultraviolet nano-holographic imaging with numerical optical sectioning

Three dimensional images were obtained using a single high numerical aperture hologram recorded in a high resolution photoresist with a table top lambda = 46.9 nm laser. Gabor holograms were numerically reconstructed over a range of image planes by sweeping the propagation distance in the numerical reconstruction algorithm, allowing numerical optical sectioning. A robust three dimension image of a test object was obtained with numerical optical sectioning, providing a longitudinal resolution of approximately 2 mum and a lateral resolution of 164 nm.

Holographic and speckle screens for projecting images

This paper presents versions of screens for projecting images. In the first case, a holographic screen for the projection of horizontal aspects of a three-dimensional scene is considered. The screen transforms a luminous point into a vertical luminous diffuse line. When aspects of a three-dimensional scene are projected onto such a screen, the observer sees a two-dimensional image localized on the screen whose configuration varies, depending on the observation point, in the same way as when he observes an actual three-dimensional object. In the second case, various versions of axial diffuse screens recorded on the basis of a Gabor hologram are investigated. © 2005 Optical Society of America

On-axis diffuse screen based on a reference-free volume hologram

A new type of hologram that elaborates upon the simplest (Gabor) on-axis hologram is suggested. The new approach makes it possible to eliminate the projected image distortions typical of the Gabor hologram. Specifically, based on a reference-free thick hologram, an on-axis holographic screen that does not transmit the zeroth order is prepared. In addition, this screen does not produce a halo and the conjugate image. It allows for recording in one spectral range and reconstruction in another, thereby greatly simplifying the choice of a light-sensitive record medium. With this screen, a color image can be projected.

Reconstruction of a complex object from two in-line holograms

A novel numerical algorithm is proposed to reconstruct a complex object from two Gabor in-line holograms. With this algorithm, both the real and imaginary parts of the complex amplitude of the wave front in the object field can be retrieved, and the "twin-image" noise is eliminated at the same time. Therefore, the complex refractive index of the object can be obtained without disturbance. Digital simulations are given to prove the effectiveness of this algorithm. Some practical experimental conditions are investigated by use of error estimation.

Resolution of the interference patterns of doubly exposed Gabor hologram

In this paper, the resolution of the four interference patterns of the doubly exposed Gabor hologram was investigated. For a small axial shift, the resultant pattern was found to be outside the field of diffraction of an Airy's disk of the speckles. As for the other three interference gaps, the patterns for each order of interference were not resolved. The phase shift between these patterns was found to be less than the minimum phase change for the Rayleigh criterion of resolution. Moreover, the difference in the radii for the patterns at each order of interference was found to be much less than the experimental error.