Reflection Holographic Optical Elements Research Articles

Time-scheduled exposure method for full-color high diffraction efficiency and uniformity of a photopolymer

A full-color reflection holographic optical element (HOE) with uniform diffraction efficiency, achieved via time-scheduled exposure, is proposed in which 660, 532, and 473 nm wavelengths are used for recording. To enhance the diffraction efficiency, the exposure energy of three wavelengths should be controlled to react uniformly in the photopolymer. The photopolymer’s optical characteristics present that the absorptance of the three wavelengths differs, moreover, the reactivity of the photopolymer to exposures is variant at the three wavelengths. The high-efficiency full-color HOE is implemented by determining the pre-exposure times of the three lasers for a set beam intensity. In order to verify the proposed method, we conduct repetitive optical experiments and analyze the results. Finally, a full-color reflection hologram is manufactured with an average efficiency of 61.6 % (standard deviation, 0.5) when the beam intensity of the three lasers is 0.4 mW/cm2. The reconstructed images of the full-color hologram show good uniformity and color reproduction.

CHIMERA, a new holoprinter technology combining low-power continuous lasers and fast printing.

This paper presents CHIMERA, a third-generation digital holographic printing system that solves the known problems of the two previous generations. This holoprinter is based on the use of low-power RGB continuous lasers combined with the ultrafine-grain silver-halide material Ultimate U04 and is capable of printing at a frequency equal to or greater than 25 hogels per second, full-color, 120° full-parallax digital reflection holograms or holographic optical elements with a size of up to 60×80cm and a hogel size ranging from 250 to 500 µm. A 3D scanner using a 4K video camera has been specially designed for scanning real objects printable on CHIMERA, which offers new achievements in terms of color rendition, palette, and accuracy and opens new perspectives for digital holography applications and holography in general.

Investigation of the Properties of a Beam Reconstructed from Volume Holographic Optical Elements Used in Optical Observation Devices

The process of recording and reading of a holographic optical element for a holographic collimator sight is investigated. Theoretical calculations show that the possibilities of using reflection holographic optical elements in systems allowing significant tuning of the working wavelength of the employed light source are significantly limited.

Paper No P4: The Development of the Integrated Holographic Recording Head for Synthesized 3D Hologram Recording

AbstractAn integration of several total internal reflection (TIR) holographic optical elements (HOEs) for the design of compact holographic recording system is discussed. Methods of waveguide holography (WGH) permits to realize the concept of pure HOE recording setup for synthesizing three‐dimensional (3D) holograms. So the idea of homogeneous technology for “HOLOGRAMS BREEDING” was approved. The several schemes for light guiding HOE recording was proposed to obtain integrated TIR illumination and reference beam forming units. In this paper, it is shown that the specific light transformation waveguide holograms permit to construct efficient recording setup for 3D synthesized micro‐hogel recording. It is also shown several experimental schemes of reflection/transmition variants of 3D synthesized hologram recording. The schemes of HOE operation improvement are discussed and some experimental results are shown.

Study of reflection gratings recorded in polyvinyl alcohol/acrylamide-based photopolymer

High-spatial-frequency fringes associated with reflection holographic optical elements are difficult to obtain with currently available recording materials. In this work, holographic reflection gratings were stored in a polyvinyl alcohol/acrylamide photopolymer. This material is formed of acrylamide photopolymer, which is considered interesting material for optical storage applications such as holographic memories. The experimental procedure for examining the high-spatial-frequency response of this material is explained, and the experimental results obtained are presented. With the aim of obtaining the best results, the performance of different material compositions is compared.

Compact electronic speckle pattern interferometer using a near infrared diode laser and a reflection holographic optical element

The complicated experimental set-ups required for existing electronic speckle pattern interferometers limit their application potential. To overcome the limitations we present a simple and very compact electronic speckle pattern interferometer. Our system does not use expensive and complicated optical elements. We used a near infrared reflection holographic optical element for the first time in an out-of-plane sensitive electronic speckle pattern interferometer operating with a near infrared diode laser. The use of a holographic optical element drastically reduces the number of optical elements; the final system only consists of a CCD camera, a HOE and a test object, with significant reductions in system costs and time spent aligning the system. Reflection holographic optical elements were recorded in HP-650 emulsions using a He?Ne laser. The hologram was reconstructed using a laser diode operating at 784?nm by swelling the emulsion. Current modulation of the laser diode was utilized to introduce the desired phase shifts for fringe analysis.

Holographic optical elements as scanning lidar telescopes

We have developed and investigated the use of holographic optical elements (HOEs) and holographic transmission gratings for scanning lidar telescopes. Rotating a flat HOE in its own plane with the focal spot on the rotation axis makes a very simple and compact conical scanning telescope. We developed transmission and reflection HOEs for use at the first three harmonic wavelengths of Nd:YAG lasers. The diffraction efficiency, diffraction angle, focal length, focal spot size and optical losses were measured for several HOEs and holographic gratings, and found to be suitable for use as lidar receiver telescopes, and in many cases could also serve as the final collimating and beam steering optic for the laser transmitter. Two lidar systems based on this technology have been designed, built, and successfully tested in atmospheric science applications. This technology will enable future spaceborne lidar missions by significantly lowering the size, weight, power requirement and cost of a large aperture, narrow field of view scanning telescope.

Holographic optical elements recorded in silver halide sensitized gelatin emulsions. Part 2. Reflection holographic optical elements.

Silver halide sensitized gelatin (SHSG) holograms are similar to holograms recorded in dichromated gelatin (DCG), the main recording material for holographic optical elements (HOEs). The drawback of DCG is its low energetic sensitivity and limited spectral response. Silver halide materials can be processed in such away that the final hologram will have properties like a DCG hologram. Recently this technique has become more interesting since the introduction of new ultra-fine-grain silver halide (AgHal) emulsions. In particular, high spatial-frequency fringes associated with HOEs of the reflection type are difficult to construct when SHSG processing methods are employed. Therefore an optimized processing technique for reflection HOEs recorded in the new AgHal materials is introduced. Diffraction efficiencies over 90% can be obtained repeatably for reflection diffraction gratings. Understanding the importance of a selective hardening process has made it possible to obtain results similar to conventional DCG processing. The main advantage of the SHSG process is that high-sensitivity recording can be performed with laser wavelengths anywhere within the visible spectrum. This simplifies the manufacturing of high-quality, large-format HOEs, also including high-quality display holograms of the reflection type in both monochrome and full color.

Prototype holographic atmospheric scanner for environmental remote sensing

A ground‐based atmospheric lidar system that utilizes a holographic optical telescope and scanner has been developed and successfully operated to obtain atmospheric backscatter profiles. The Prototype Holographic Atmospheric Scanner for Environmental Remote Sensing is built around a volume phase reflection holographic optical element (HOE). This single optical element both directs and collimates the outgoing laser beam as well as collects, focuses, and filters the atmospheric laser backscatter while offering significant weight savings over existing telescope mirror technology. Conical scanning is accomplished as the HOE rotates on a turntable sweeping the 1.2 mrad field of view around a 42° cone. During this technology demonstration, atmospheric aerosol and cloud return signals have been received in both stationary and scanning modes. The success of this program has led to the further development of this technology for integration into airborne and eventually satellite Earth‐observing scanning lidar telescopes.

Optimal composition of an acrylamide and N,N′-methylenebisacrylamide holographic recording material

We study the effect of the addition of a cross-linking agent (N,N′-methylenebisacrylamide) to a photopolymerizable matrix for real-time holography. Optimization of the concentration of this component has been achieved, paying attention to holographic parameters such as energy sensitivity and diffraction efficiency. Diffraction efficiencies of around 88% have been obtained with energy exposures of 12 mJ cm−2. At the same time considering a nonlinear response of the material we have carried out a theoretical study of the experimental results. We observed a nonlinear response of the material with regard to the storage intensity. This is a very interesting point in reflection holographic optical elements.

Dichromated gelatin reflection holographic optical element derived from Kodak 649F plates

The characteristics of diffraction efficiency and spectral bandwidth of dichromated gelatin reflection holograms formed by a modified processing method are presented.

Color control in reflection holograms by humidity

A method is presented which permits control of the reconstruction wavelength of reflection holograms and holographic optical elements. This approach makes use of developer and bleach which minimize emulsion shrinkage combined with control of ambient humidity to control the emulsion shrinkage during formation and reconstruction. A simple index matching approach to the elimination of the wood grain effect in reflection holograms is also presented.