Thermal Fringe Formation During a Hologram Recording Using a Dry Photopolymer

In this study we investigated the undesired but possible fringe formation during the recording of large size holographic optical elements (HOE) using a dry photopolymer. We identified the deformation of the recording element during hologram exposure as the main source for this fringe formation. This deformation is caused mainly by the one-sided heating of the recording element, namely, the dry photopolymer–recording plate stack. It turned out that the main source for this heating was the heat of polymerization in the dry photopolymer released during the exposure interval. These insights were translated into a physical model with which quantitative predictions about thermal fringe formation can be made depending on the actual HOE recording geometry, recording conditions and characteristics of the dry photopolymer. Using this model, different types of large size HOEs, used as components to generate a steerable confined view box for a 23” diagonal size display demonstrator, could be recorded successfully without thermal fringe formation. Key strategies to avoid thermal fringe formation deduced from this model include balancing the ratio of lateral recording plate dimension R to its thickness h, recording the power density P or equivalently the exposure time texp at a fixed recording dosage E, and most importantly recording the the linear coefficient of thermal expansion (CTE) of the recording plate material. Suitable glass plates with extremely low CTE were identified and used for recording of the above-mentioned HOEs.

Fast Image Reconstruction Technique for Parallel Phase-Shifting Digital Holography

For incoherent and coherent digital holography, the parallel phase-shifting technique has been used to reduce the number of exposures required for the phase-shifting technique which eliminates zero-order diffraction and conjugates image components. Although the parallel phase-shifting technique can decrease the hologram recording time, the image interpolations require additional calculation time. In this study, we propose a technique that reduces the calculation time for image interpolations; this technique is based on the convolution theorem. We experimentally verified the proposed technique and compared it with the conventional technique. The proposed technique is more effective for more precise interpolation algorithms because the calculation time does not depend on the size of interpolation kernels.

Bitmap and vectorial hologram recording by using femtosecond laser pulses

In this paper, we present two approaches for recording a quasi-hologram on the steel surface by femtosecond laser pulses. The recording process is done by rotating the polarization of the laser beam by a half-wave plate or a spatial light modulator (SLM), so we can control the spatial orientation of the formed laser-induced periodic surface structures (LIPSS). Two different approaches are shown, which use vector and bitmap images to record the hologram. For the first time to our knowledge, we managed to record a hologram of a bitmap image by continuously adjusting the laser beam polarization by SLM during scanning. The developed method can substantially improve hologram recording technology by eliminating complex processing procedures, which can lead to increasing the fabrication speed and reducing the cost.

Bitmap and Vectorial Hologram Recording by Using Femtosecond Laser Pulses

In this paper, we present two approaches for recording a quasi-hologram on the steel surface by femtosecond laser pulses. The recording process is done by rotating the polarization of the laser beam by a half-wave plate or a spatial light modulator (SLM), so we can control the spatial orientation of the formed laser-induced periodic surface structures (LIPSS). Two different approaches are shown, which use vector and bitmap images to record the hologram. For the first time to our knowledge, we managed to record a hologram of a bitmap image by continuously adjusting the laser beam polarization by SLM during scanning. The developed method can sabstantially improve hologram recording technology by increasing its speed, reducing the price, and eliminating complex processing procedures.

Особенности получения изображений протяженных объектов, восстанавливаемых импульсными голограммами

The features of the dimensional transformation of images of depth-extended objects reconstructed by transmission pulse holograms are considered, when the spectral and geometric parameters of hologram recording and image reproduction are different. A method for improving the characteristics of images is proposed, which makes it possible to reduce the requirements for the output characteristics of pulsed lasers.

Пространственный фотоотклик, формфактор и требования к голографическим материалам

Reviewed the problems arising during the recording of holograms in bulk media, which manifest themselves in the first queue as the spatial resonance of the hologram recording field with refractive index inhomogeneities due to the already recorded part of the holographic lattice. And secondly, as a cross-interaction of two nonlinearities at recording holograms - nonlinearity of diffraction efficiency and nonlinearity of field distribution holograms of exposure and visibility of a registered holographic lattice. It is noted that the appearance one more nonlinearity - the nonlinear photoresponse of the holographic material - for certain conditions leads not to a decrease in diffraction efficiency, but to its increase. The main classes of volume holographic media — dynamic media that form a photoresponse during the exposure without chemical treatment and with chemical treatment — are determined. The maximum achievable diffraction efficiencies for both types materials are shown. Recommendations are made to eliminate the undesirable consequences of the detected effects, based on the analysis of the basic laws of photoresponse formation taking into account spatial resonance and the presence of a formfactor.