A. Y. Zherdev

Correlation method for quality control of master matrix used for embossing security holograms

Security holograms (SH) are widely used for authenticity protection of document and product due to difficulties of such a protection mark falsification. Mass production of SH uses widespread technology of hot foil or lavsan paper stamping. The quality of holograms significantly depends on perfection of nickel master-matrix that is used in stamping equipment. We represent the method for automated quality inspection of nickel mastermatrix based on digital processing of its surface relief images. Proposed processing algorithm is based on combination of image spatial frequency analysis and image matching using distortion invariant correlation filters. The results of our method application for real master-matrix inspection are shown in this paper.

Distortion invariant correlation filters application for quality inspection of master-matrix for security holograms

Security holograms (SH) are perspective for document and product authenticity protection due to difficulties of such a protection mark falsification. Mass production of SH uses widespread technology of hot foil or lavsan paper stamping. The quality of holograms significantly depends on perfection of nickel master-matrix that is used in stamping equipment. We represent the method of automatic quality inspection of nickel master-matrix based on digital processing of its surface relief microphotographs. Proposed processing algorithm is based on combination of image spatial frequency analysis and image matching using distortion invariant correlation filters. The results of our method application for real SH master-matrices inspection are shown in this paper.

Optical position encoder based on structured head diffraction grating

Optical position encoders working according to the interference method consists of a measurement scale and a measuring head moving along each other. The scale has a reflection diffraction grating on its surface and the measuring head has a transmission diffraction grating with same period inside. Laser light passing and diffracting through these two gratings creates an interference signal on an optical detector. Decoding of the interference signal phase allows to determinate current position. Known optical position encoders use complex optical schemes and some phase optical elements to form several quadrature signals with different phase for higher encoder accuracy. Previously we researched such kind of schemes [1, 2]. In this paper we propose to use a common optical scheme without phase elements but with a complex structured measuring head grating for this purpose to simplify an optical scheme and alignment requirements. The optical scheme of position encoder based on measuring head grating with specific structure is research and described in this paper.

Lithographic diffraction grating with a period failure

That paper focuses on diffraction gratings consisting some period failures provided by the errors of the electronbeam lithography method. Samples of lithographic phase gratings were tentatively analyzed to describe that technological errors. A small linear modulation of the period or a joint of a frame edges can cause not only diffraction efficiency losses but also functional breakdown. A simulation of the diffraction of a monochromatic wave at the described diffraction phase structures is carried out. Described diffraction gratings have interest in field of linear displacement encoders.

The schemes and methods for producing of the visual security features used in the color hologram stereography

Visual security elements used in color holographic stereograms - three-dimensional colored security holograms - and methods their production is describes in this article. These visual security elements include color micro text, color-hidden image, the horizontal and vertical flip - flop effects by change color and image. The article also presents variants of optical systems that allow record the visual security elements as part of the holographic stereograms. The methods for solving of the optical problems arising in the recording visual security elements are presented. Also noted perception features of visual security elements for verification of security holograms by using these elements. The work was partially funded under the Agreement with the RF Ministry of Education and Science № 14.577.21.0197, grant RFMEFI57715X0197.

Optical position encoder based on four-section diffraction grating

Optical position encoder consists of movable coding grating and fixed analyzing grating. Light passing and diffracting through these two gratings creates interference signal on optical detector. Decoding of interference signal phase allows to determinate current position. Known optical position encoders use several accurate adjusted optical channels and detectors to gather several signals with different phase for higher encoder accuracy. We propose to use one optical channel with several-section analyzing diffraction grating for this purpose to simplify optical scheme and adjusting requirements. Optical scheme of position encoder based on four-section analyzing diffraction grating is developed and described in this paper.

The small-sized ultraprecision sensor for measuring linear displacements

The article describes a new optical scheme of noncontact sensor for measuring linear displacement - linear encoder. This sensor is an optical device in which the measurement of displacement is performed by analyzing the optical signal, which pass through two diffraction gratings, one of which is moved relative to the other. The optical signal is obtained by the diffraction of light in these diffraction gratings and subsequent interference of diffracted beams. Often this type of sensors are multi-channel devices with symmetrically positioned of detectors. This scheme is proposed to use a multisection phase mask that allows to make a small-sized sensor. Sections of this multi-section phase mask are the optical windows and they made the final interference signals to be shifted relative to each other in phase. The number of sections in the multi-section phase mask can be varied. Estimated sufficient number of sections is four or more.

Experimental study of the method of recording color volume security holograms on different photosensitive materials on the base of the diffuser with a narrow indicatrix of laser radiation

The paper presents the practical results of recording holographic stereograms. Advantages and disadvantages of methods for producing holographic stereograms using diffusers with different indicatrices scattering of the radiation in the object branch and without the use of a diffuser are presented. A new security element - multi-color microtext, is presented. Shows how to use multi-color microtext as a hidden security element. The method of multi-color microtext visualization is shown. The work was partially funded under the Agreement with the RF Ministry of Education and Science no. 14.577.21.0197, grant RFMEFI57715X0197.

High-aperture diffractive lens for holographic printer

The optical scheme of holographic printer for obtaining of holographic stereograms with an increasing field of view is proposed. Conventional holographic printers allow obtaining holographic stereograms with the field of view up to 90°. Proposed scheme allows increasing field of view up to 120°. The optical scheme is based on a diffuser and a diffraction optical element, the high-aperture diffractive lens. The experience of using the composite holographic lens and the amplitude diffractive lens based on a binary Fresnel zone plate as a high-aperture diffractive lens is described. Samples of high-aperture diffractive lens with f-number f/0.3 are obtained and investigated. Samples of holographic stereograms are obtained using samples of high-aperture diffractive lens.

Plasmonic spectral filters based on diffraction gratings

Method for the analysis of plasmonic gratings is developed. The mathematical research of the spectral-angular characteristics of plasmonic gratings is realized. The dependency of spectral-angular characteristics on geometric parameters of the plasmonic grating are disclosed. Samples of plasmonic gratings are obtained. The results of mathematical modeling and theoretical studies are confirmed by the experimental samples. Spectral-angular characteristics of the plasmonic gratings samples qualitatively repeat theoretically modeled characteristics.