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PODLIPNOV, Vladimir; KHONINA, Svetlana; SKIDANOV, R.. Design, technology of fabrication of diffractive optical elements and they investigation in the IPSI RAS. In: Materials Science and Condensed Matter Physics. Ediția a 9-a, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, p. 289.
|Materials Science and Condensed Matter Physics
Ediția a 9-a, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
Chișinău, Moldova, 25-28 septembrie 2018
Diffraction optical elements (DOE) are used in laser technology, optical communication, optical instrumentation. Designing and manufacturing of DOE is a long-time, multi-stage process. Modeling using computer diffraction optics allows to significantly shorten the duration of creation of new elements and their optimization. The basic idea of computer optics is to solve the inverse problem of diffraction relative to the boundaries and profile of DOE zones and to fabricate the diffractive microrelief on a planar substrate. With the spread of electronic technologies and the increase in the spatial resolution of microrelief recording devices, the mathematical methods describing the process of light diffraction on DOEs have also changed. The modern methods of diffractive optics and nanophotonics are based on solving Maxwell‘s equations. The most common of them are the finite difference time domain (FDTD) method for solving Maxwell‘s equations; the finite element (FEM) method to calculate the diffraction of a monochromatic field based on the piecewise linear approximation of amplitude for triangle mesh regions; and the Fourier mode method, effective for studying monochromatic radiation diffraction by periodical binary structures (or rigorous coupled wave analysis (RCWA) method). An example of a phase Fresnel zone plates (ZP) of the focal distance of 0.532 μm, radius of 7.7 μm, and relief depth of 510 nm fabricated and studied in IPSI RAS is demonstrated in Fig. 1. Using a scanning near-field optical microscope, we studied the passage of a linearly polarized Gaussian beam with wavelength λ = 532 nm through such a ZP. The experimental study was performed using the scanning near field optical microscope NTEGRA Spectra (NT MDT).The diameter of a focal spot at the half maximum of the intensity FWHM = 0.44 λ. This diameter is 18% smaller than the diffraction limit (FWHM = 0.51 λ), which is a record breaking result for ZPs. High-quality binary microlenses  are fabricated in quartz substrates as follows. A thin Cr film is deposited on a quartz substrate, followed by deposition of thin film of ZEP520A resist. A subwavelength mask was fabricated in the resist layer by electron beam lithography. The mask in resist was then transferred into the chromium oxide (Cr2O3) layer by resist etching. A quartz substrate is then etched by plasma in a gas environment (SF6) through the Cr2O3 mask . PSI RAS also investigated a generation of inhomogeneously polarized beams . In this case, the study of methods for visualizing the polarization inhomogeneities of laser beams is urgent .