Gerhard K. Ackermann

Processing of holographic AgBr films studied by x-ray fluorescence analysis

The feasibility of using x-ray fluorescence techniques to determine the concentrations of silver, bromine, and iodine in silver halogenide holographic films is studied. A small apparatus employing a 30-mCi (57)Co radioactive source and a germanium photon detector is described. AgBr films were exposed to different amounts of light and subjected to several types of chemical processing, and their silver and halogen contents were investigated. In addition, the relationship between the concentration of absorbing silver in the emulsion and its optical density was determined.

Holographic DESA emulsions

The DESA material is an ultra-fine grained silver bromide emulsion referring to the name of its four inventors (D)uenkel, (E)ichler, (S)chneeweiss, (A)ckermann of the University of Applied Sciences in Berlin, Germany. The thickness of the dried layer is between 5 and 7.5 μm, and the mean grain size is by about 15 nm, as determined by TEM. During manufacturing, emulsion precipitation and coating are separated strictly from spectral and chemical sensitization. Thus, a high performance could be obtained. Resolution is estimated higher than 8000 lp/mm. Sensitivity amounts to 80 up to 120 μJoules/cm2 for maximum diffraction efficiency by recording Denisyuk white-light reflection holograms at 632,8 nm (HeNe laser). The paper provides an insight into fundamentals of the ultra-fine grained silver halide technology together with new challenges for further developments under theoretical and practical aspects.

Microdisplays in holographic mastering applications

We demonstrate implementation and performance of microdisplay systems based on liquid-crystal technology in a variety of applications in holographic mastering. These displays can encode 2D objects information in grey scale or address holographic patterns in amplitude or phase. The main advantage is here to address any content dynamically with typically 60 Hz. Furthermore they show a resolution up to 1920×1200 pixels with a pixel size as small as 6.4 microns. Therefore they are extremely suitable for a dynamic or multi-exposure mastering process, to incorporate image content, phase-encode objects or any holographic features. This technology is already being used in holographic security applications as well as in commercial and display holography. We report about a few applications/implementations and show experimental results and performance parameters.

Polarization experiments in holographic interferometry

Experiments of real time holographic interferometry were performed with circular and linear polarized laser radiation. An object with a metallic and dielectric part of the surface was studied. It was found that holographic interferometry on the metallic surface can easily be understood with different combinations of the polarization of the different waves. However, unexpected results were found for experiments with the dielectric. The experiments can be explained assuming that the object wave of a diffuse scattering dielectric is different for illumination with right and left circular polarized radiation. Thus, the interference structure of a hologram originating from these waves is also different, in spite of the fact that the image of the object seems to be the same. A theoretical analysis can be performed extending the well-known Jones matrices for radiation depolarized by dielectrics. Theoretical and practical consequences are discussed that refer to the polarization structure of light and to holographic interferometry.

Advances with holographic DESA emulsions

DESA emulsions represent layer systems based on ultra-fine grained silver halide (AgX) technology. The new layers have an excellent performance for holographic application. The technology has been presented repeatedly in recent years, including the emulsion characterization and topics of chemical and spectral sensitization. The paper gives a survey of actual results referring to panchromatic sensitization and other improvements like the application of silver halide sensitized gelatine (SHSG) procedure. These results are embedded into intensive collaborations with small and medium enterprises (SMEs) to commercialize DESA layers. Predominant goals are innovative products with holographic components and layers providing as well as cost effectiveness and high quality.

Self-made silver-bromide-based emulsions for users in holography: manufacturing, processing, and application

Holography is the most fascinating technology for three-dimensional imaging. But despite of many decades of research, the seek for an ideal recording material has never been given up. From all ultra-fine materials, silver bromide emulsions with very small grain sizes have the highest sensitivity. In recent years however, many traditional manufacturers discontinued their production. Meanwhile, newcomers succeeded in manufacturing emulsions which are very suitable for holography, concerning extremely high resolution, brigthness and sensitivity1. But two problems may still linger: First, the deficient market situation for production and application on this field. Second, the reputation of the system of being extremely complicated for laboratory preparation. In such a crucial situation, the authors have succeeded in presenting a laboratory procedure for making do-it-yourself materials available to any expert who is well versed in holography, and who disposes of normal darkroom equipment2. The methodology is based on precipitation using the traditional double-jet method according to Thiry and predecessors3. But sensitization is carried out by a diffusion process according to the procedure as proposed by Blyth et al.4 Thus, precipitation and coating on one side and sensitization on the other one are separated strictly from one another. Efficient desaltation is an important process too, warranting the high opto-mechanical quality of the layer. The material has been sensitzed for HeNe-Laser radiation (632,8 nm) only up to now. The mean diameter of the silver bromide grains is about 15 nm, as determined by transmission electron microscopy (TEM). Phillips-Bjelkhagen Ultimate (PBU) or Fe3+ rehalogenation bleach are applied successfully5-6. In final result, a new generation of holograms with ultra-high resolution, proper contrast, excellent sharpness and light brightness has been obtained. Holography belongs to an advancing technology where the search for an ideal recording material is still going on. Of these materials, the ultrafine grain silver bromide emulsions are unsurpassed in sensitivity. But in recent years many traditional manufacturers discontinued their production. In such a critical situation, the authors have succeeded in developing a new technology to make do-it-yourself materials of very high quality. The procedure involves elements of two different methods: The traditional double-jet method by pouring silver nitrate and potassium bromide into a vigorously stirred gelatin solution, and a diffusion process to sensitize the coated layer efficiently. The material has been sensitized for He/Ne-laser radiation by 632.8 nm. Denisyuk holograms of real 3D-objects were obtained in ultrahigh resolution, excellent brightness and clarity with CW-C2 developer and PBU rehalogenation bleach according to Bjelkhagen et al. The material is characterized by TEM, reflexion spectroscopy, and other methods. The new results have been involved in university education already with great success. The fundamental principles of the methodology as well as new results by application in intellectual and hybrid systems were reported.

Holography in Germany

The world market in holography is about 1 Billion U

Analysis of vibration of holographic setups using the theory of time average interferometry

. Most of this part is connected to embossed holograms, especially for security, authentication, packaging, giftware and promotion. Display holograms, holographic optical elements and technical holographic applications are economically less important. Germany has only a very small part of this global market. In general, the present status of holography in this country is not very good. Many laboratories and companies closed in the last years and only few are remaining. In contrast to this economic situation, scientific applications ofholography are continuing to give good results. Germany has a National Society for Holography (Deutsche Holographische Gesellschaft, DGH e.V., do N. Moller, Marienstr. 28, D-06108 Halle, http://www.dgholo.de) with about 100 members. The society notifies the people about holographic activities and functions and gives young holographers a first contact. A second holographic society is Arbeitskreis Holographische Technik (AHT). Last summer the president G. Deutschmann passed away. German Holography will miss him dearly. In the following some remarks about the holographic activities in Germany are made. However, the survey is not complete as companies here work very independently. Please, excuse us for having omitted projects or companies which are not known to us.

Investigation of holographic AgBr-films: optical density, Ag-concentration and index of refraction

In this paper it is demonstrated, that the vibration of holographic tables can be described using Time Average Interferometry. The vibration amplitudes of vibrating optical elements are summarized in an effective displacement vector at the holographic plate. The calculations show, that the visibility is given by the Besselfunction J0. For very small amplitudes of displacement amplitudes this result is in accordance with earlier findings, where the visibility was a square function of displacement amplitude.

Diffraction efficiency of transmission holograms

In this note, measurements are presented on optical density, silver concentration, and index of refraction within uniformly exposed and processed holographic film. These data are important because they determine the diffraction efficiency of holograms. The silver analysis was performed by X-ray diffraction. The index of refraction was measured by a Brewster-angle method. The data show that the refractive index variation is of the order of 0.06 at an optical density of 2. The influence of these results on the design of holographic experiments is discussed.