Novel Optical Element – Holographic Prism Based on Fluorite Crystal with Quasi-Colloidal Color Сenters
Tech Area / Field
- INS-MEA/Measuring Instruments/Instrumentation
- PHY-SSP/Solid State Physics/Physics
3 Approved without Funding
Vavilov State Optical Institute (GOI), Russia, St Petersburg
- St Petersburg State University of Aerospace Instrument Engineering, Russia, St Petersburg\nRussian Academy of Sciences / Physical Technical Institute, Russia, St Petersburg
- Friedrich-Schiller-Universitat / Institut fur Angewandte Optik, Germany, Jena\nWaseda University, Japan, Tokyo
Project summaryIntroduction and Overview.
An angle is the only physical unit that has the natural etalon, the total angle, 360o. However, the high-precision measurement of angles is a sufficiently complicated technical problem. The traditional element-carrier, which realizes the piding of angle, is a multivalued angle measure, the regular fused quartz prism. Optical normals to prism facets determine shares of the total angle. Such prism may be considered as a carrier of standard angles used for calibration of angle-assigning devices. A goal of this Project is development of the principally novel optical source of standard angles, the holographic prism. Such prism represents a crystal with a written system of planar holographic gratings. This system splits the incident reference laser beam into an array of beams in the plane normal to the reference beam, every beam being formed by a separate grating. One beam of the holographic prism response is equivalent to reflection of the crosshair in the autocollimator focus at the facet of the optical prism and the angle between two beams is an analog of the angle between two normals to the facets of this prism. In both cases the standard angle is determined by a prism turn about the axis of rotation that results in matching of positions of either reflected at two facets of autocollimator crosshair (reflecting prism) or two rays of the beam (holographic prism).
The holographic prism demonstrates substantial advantages compared to the reflection prism: (i) it allows rendering automatic the registration of measurement results and keeping these results on the external information carrier; (ii) it allows realization of the non-uniform array of directions that can ensure a very small calibration step; (iii) a device using this prism can be rather compact that can provide a new quality; (iv) smaller dimensions of the device make it less sensitive to vibrations that lower precision of the angle measurements; (v) the fused quartz prism endures very slow but aging accompanying modification of its configuration whereas many crystals are stable in geological time scale; (vi) elaboration of optical prisms is a piece-work and very time- and money-consuming whereas fabrication of holographic prisms is more economical (though, with relatively high initial expenses for deriving a new technology).
To elaborate the holographic prism the collaboration of three Institutions is established:
- S.I. Vavilov State Optical Institute, where the photochromic medium on the base of fluorite crystals with quasi-colloidal centers has been developed. The holographic prism will be created on the basis of this medium that demonstrates an exclusive stability: the holograms written in these crystals 15 years ago remain absolutely unchanged. Researchers of this Institution have large experience in growth, studies, and application of fluorides, in particular, the fluorite crystals.
- Saint-Petersburg State University of Aerospace Instrumentation. Researchers of this University have vast experience in planning and execution of high-accuracy linear-angular measurements including development complicated-manner organized techniques of measuring.
- A.F. Ioffe Physico-Technical Institute. Here, effective techniques for studies of color centers in crystals have been derived; these techniques are supposed to be widely used in the Project.
The above-mentioned photochromic medium represents fluorite crystals containing a set of simple color centers that consist of small number of impurity atoms and anion vacancies. Upon illumination and temperature they aggregate in quasi-colloidal centers; this process underlines the hologram writing. One should note that photo-thermal transformations leading to quasi-colloidal center formation are studied insufficiently and it is little known of the nature of these centers. During the Project execution studies of these problems will be carried out aimed at development of a laboratory technology of formation of quasi-colloidal centers in fluorite crystals. The process of hologram writing in these crystals is sufficiently complicated, since the writing is carried out at the elevated temperature of (70 150)оС under the ultra-violet laser radiation, here the crystal should be immersed into an immersion liquid for formation of the necessary response configuration. The writing process takes hours and during this time the laser, optical scheme of writing, and the crystal should be immobile relative each other. An optical stand fitting these demands will be created and a procedure of the hologram writing will be elaborated. The writing of the hologram system (the holographic prism) undermines that it ensures the optimal set of saved and reproduced by it basic (standard) angles. The choice of these angles directly determines the calibration step and the excessiveness of gained data. In perspective the holographic prism is supposed to be installed into set-ups equipped with angle sensors to ensure the self-calibration of the holographic prism and calibrated set-up. Technique for measurement execution at mutual calibration of circular scales will be developed as well as the system of readout of the holographic prism indications. This system includes the direction sub-system ensuring the prism turn by angles determined with the measuring procedure, executive mechanism of the turn, and sub-system of registration based on CCD-matrixes, which record the signal and transmit it to an external information carrier. Determining of the holographic prism characteristics will be carried out with a special stand for determining reproduced angles, the angle response selectivity, and thermal stability of the response.
Expected Results and their Applications.
The Project proposed is an applied study in the fields of optics and metrology. Below are given the main expected results.
- nature of simple color centers and mechanism of their conversion into quasi-colloidal centers will be studied;
- stand for hologram writing will be built up;
- technology of hologram writing that ensures an optimization of the hologram characteristics will be developed;
- technique for the choice of the optimal array of base (standard) angles kept and reproduced by holograms written in the crystal will be elaborated;
- measuring procedures of calibrating and mutual calibrating of circle scales based on this array will be derived as well as the procedure of self-calibrating of high-accuracy goniometric and angle-assigning devices with incorporated holographic prisms;
- multivalued angle measure based on holographic prism and incorporated in the device for self-calibrating regular angle sensor will be developed;
- system of reading-out by the CCD-matrix of the beam of rays split by the holographic prism will be elaborated;
- stand for determining the optical and metrological characteristics of holographic prism will be built up.
Further, the Project participants along with interested firms will be able to participate in development of technology of fabrication of holographic prism which prototypes will be elaborated in the course of the Project execution. Realization of the Project will enable formation of a new metrological element, the holographic prism, which using should simplify and reduce the price of calibrating the angle-assigning devices.
Meeting ISTC goals and objectives.
The Project will allow the scientists and engineers with the knowledge in the field of systems and devices for the nuclear and laser armaments to convert their activity toward the civil technological problems that will result in elaboration of the basic element of an instrument for testing and calibrating the industrial angle-assigning devices that will simplify and reduce the price of the above-mentioned procedures. The Project will support basic and applied research aimed at peaceful goals, promote integration of Russian scientists into the international scientific community, contribute to the solution of domestic and international problems related to high optical technologies, facilitate the transition to the market economy meeting the demands of the present-day civil society.
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