RU2780732C1 - Method for producing terahertz nanocrystalline optical fibers of the agbr-agi system - Google Patents

Abstract

FIELD: terahertz radiation registration.

SUBSTANCE: invention can be used in the manufacture of channels for the delivery and registration of terahertz radiation in thermal imaging systems, military equipment, space technology, analytics, medicine, biotechnology, pharmaceuticals, terahertz optoelectronics and photonics. The extrusion parameters are preliminarily determined by computer simulation using the finite element method - temperature, plunger pressure on the workpiece and its speed. Single-crystal blanks are prepared based on solid solutions of bromide - silver iodide in the following ratio of ingredients, wt.%: silver bromide - 70-96; silver iodide - 30-4 and heat them at 175-185°C and a pressure of 700 - 900 MPa to move through the spinneret at a speed of 0.2-0.3 mm/min. Terahertz nanocrystalline fibers of the AgBr–AgI system obtained by extrusion have a nanocrystalline structure, are photo- and radiation-resistant, non-toxic, non-hygroscopic, and highly transparent in the terahertz range from 11 to 30 THz, and are also characterized by low losses.

EFFECT: invention provides high reproducibility and manufacturability of their production.

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Description

SUBSTANCE: invention relates to terahertz (THz) element base, namely to THz flexible light guides, which are intended for use as a channel for delivery and registration of terahertz radiation to a given point in space with the least losses. THz radiation occupies the frequency range from 0.1 to 30.0 THz, which corresponds to the spectral range from 3000 to 10 μm [G. Z. Gareev, V.V. Luchinin, The use of THz radiation to ensure human life, Interdisciplinary platform "Biotechnosphere", 2014, No. 6, (36), p. 71-79].

Known are the most promising polymer fibers based on polyethylene, polypropylene, Teflon, capable of transmitting broadband terahertz pulses over a distance of several meters [A.S. Akhmanov, A.A. Angeluts, A.V. Balakin et al. Terahertz optoelectronics and its application. Polymer devices for delivery of terahertz radiation, Modern laser information technologies, Moscow, Interkontakt Nauka, 2014, p. 758-785]. The disadvantage of polymer terahertz flexible waveguides is a high absorption coefficient and a limited range of transparency.

The closest technical solution is polycrystalline single-layer IR light guides, transparent from 2 to 18 microns, made by extrusion from crystals of solid solutions of the AgCl - AgBr system [Artyushenko V., Wojciechowski C., Ingram J., Kononenko V., Lobachev V., Sakharova T., Ludczak J., Grzebieniak A., Wojciechowski Z. Specialty fibers for broad spectra of wavelength and power, Proceedings of SPIE - The International Society for Optical Engineering, 2005, Vol. 5951, P. 1 - 8]. These fibers, like single crystals, are also transparent in the high-frequency terahertz region of 30 THz [L. V. Zhukova, D. D. Salimgareev, A. S. Korsakov, A. E. Lvov, Promising terahertz materials: crystals and ceramics: textbook. Yekaterinburg: UMC UPI Publishing House, 2020. - 308 p.], but non-toxic optical fibers based on single crystals of the AgCl - AgBr system used in medicine are photosensitive, which significantly limits their use.

There is a problem in developing a reproducible and economical extrusion method when creating new photo- and radiation-resistant, nanocrystalline, non-toxic, non-hygroscopic and highly transparent in the terahertz range from 11 to 30 THz (27 ÷ 10 μm) flexible fibers of the AgBr - AgI system with low losses for medicine, biotechnology, pharmaceuticals, terahertz optoelectronics and photonics.

The solution to the problem is achieved due to the fact that a method has been developed for obtaining terahertz nanocrystalline fibers of the AgBr - AgI system, including the production of fibers by extrusion from single-crystal silver halide blanks, characterized in that the extrusion parameters are preliminarily determined by computer simulation using the finite element method - temperature, plunger pressure on the workpiece and the speed of its movement, then a terahertz single-crystal blank based on solid solutions of silver bromide-iodide in the following ratio of ingredients, wt. %:

silver bromide - 70 ÷ 96;

silver iodide - 30 ÷ 4

heated at 175 - 185 ° C and a pressure of 700 - 900 MPa, which ensures its movement through the spinneret at a speed of 0.2 - 0.3 mm per minute in order to obtain a nanocrystalline structure of terahertz fibers.

The new THz fibers of the AgBr - AgI system have the following advantages over the known fibers of the AgCl - AgBr system:

- the use of computer simulation using the finite element method made it possible to optimize the parameters of the extrusion process and ensure high reproducibility, efficiency and manufacturability of THz fibers of a nanocrystalline structure;

- resistance to photo- and radiation radiation of new THz optical fibers in comparison with the photosensitive prototype significantly expands the fields of application, including terahertz medicine, THz optics and photonics;

- extended transmission range in the far IR region (THz region) up to 27 μm compared to the prototype - 18 μm, with high transparency - up to 75% (Fig. 1. Transmission spectra of THz fibers based on the AgBr-AgI system).

The essence of the invention lies in the fact that a reproducible and technological method has been developed for obtaining a new class of silver halide terahertz fibers of the AgBr-AgI system using computer simulation, which at the initial stage determines the parameters of the extrusion process - temperature from 175 to 185 ° C, pressure on a single-crystal workpiece from 700 up to 900 MPa and its movement through the spinneret at a speed of 0.2-0.3 mm per minute. The simulated extrusion modes refer to the production of a nanocrystalline structure of light guides from a single-crystal preform based on solid solutions of silver bromide-iodide with a composition in wt. %:

silver bromide - 70 ÷ 96;

silver iodide - 30 ÷ 4.

The nanocrystalline structure (Fig. 2. Nanostructure of a terahertz fiber according to the results of scanning electron microscopy) of terahertz fibers provides high flexibility up to a radius of 10 mm with a fiber diameter of 500 μm without deteriorating optical properties.

The transparency of optical fibers up to 75% is a theoretical value, which indicates a high degree of purity and perfection of the structure of not only terahertz fibers, but also single crystals with a purity of 99.9999 wt. % and more from which they are derived, see examples.

The light guides transmit without absorption windows from 3 to 27 μm (Fig. 1), which corresponds to the high-frequency spectrum from 11 to 30 THz - the optical range from 27 to 10 μm. In this case, the optical fibers have optical losses that are optimal for practical use - 0.46 dB/m at the wavelength of the CO ₂ laser.

The replacement of the bromine anion in the AgBr crystal lattice by the iodine anion, which is heavier in molecular weight, provides high photoresistance to ultraviolet and visible radiation, as well as radiation resistance to β-radiation with a dose of up to 400 kGy and more in new terahertz fibers.

Example 1

A terahertz single crystal with a purity of 99.9999 wt % was grown by the vertical Bridgman method. % based on a solid solution composition in wt. %: silver bromide - 70;

silver iodide - 30.

A billet for extrusion was made from it, it was placed in a container with a die at one end, and a fluoroplastic plug at the other end, which has similar viscosity values \u200b\u200bwith silver halides at a temperature of 170 - 200 ° C. The plug ensures uniform heating and the inaccessibility of air to the crystal, which is pressed by the plunger. Then the crystal was heated to 185°C and, at a plunger pressure of 700 MPa, the workpiece was moved through the spinneret at a rate of 0.2 mm/min. These regimes make it possible to stably obtain flexible nanocrystalline terahertz fibers with a bending radius of 10 mm and a diameter of 500 μm from single crystals.

The transmission spectra of the light guides were taken on an IR Fourier spectrometer IR Prestige-21, Shimadzu (1.28 - 41.7 μm) with test fibers (Fig. 1). Light guides transmit without absorption windows in the optical range from 3 to 27 µm with high transparency up to 75%, that is, in the THz range from 11 to 30 THz (27-10 µm).

The optical loss was 0.46 dB/m at a wavelength of 10.6 μm in terahertz fibres. They are determined by the method of segments when taking transmission spectra in the background mode at different lengths of the fibers [S. Israeli, A. Katzir, Attenuation, absorption, and scattering in silver halide crystals and fibers in the mid infrared, J. App. Phys. 115 (2014) 023104]. The study of the resistance of optical fibers to beta radiation with a gradual increase in dose from 50 to 400 kGy and more was carried out on a linear accelerator of the electronic model UELR-10-10S. The light guides are also resistant to ultraviolet and visible radiation at wavelengths of 260-500 nm.

Example 2

Experiments and studies of functional properties were carried out as in example 1. A single-crystal blank was made from a terahertz single crystal of composition in wt. %: silver bromide - 96;

silver iodide - 4,

from which, by extrusion at a temperature of 175 °C, a pressure of 900 MPa, and at a speed of 0.3 mm per minute, a flexible THz fiber of a nanocrystalline structure was pulled out. The bending radius of a light guide with a diameter of 500 μm was 10 mm. The light guide is transparent up to 73% without absorption windows from 3 to 25 µm, optical losses were 0.46 dB/m at a wavelength of 10.6 µm. The terahertz fiber is resistant to ultraviolet, visible radiation and beta radiation with doses up to 400 kGy or more.

Example 3

Made from a terahertz single crystal by extrusion a flexible terahertz fiber composition in wt. %: silver bromide - 85;

silver iodide - 15

at a temperature of 180 °C, a pressure of 800 MPa and a drawing speed of 0.25 mm/min. A THz fiber with a nanocrystalline structure has the same functional properties as in example 1.

Thus, the use of computer simulation by the finite element method to determine the extrusion regimes for obtaining THz fibers of optimal chemical composition is confirmed by experimental data (see examples). This made it possible to significantly reduce, reduce the cost and stably obtain high-quality flexible nanocrystalline structure terahertz fibers by extrusion. In case of deviation from the chemical composition and the developed extrusion parameters, it is not possible to obtain flexible THz fibers with the unique properties given in the examples.

Technical result . A new class of terahertz nanocrystalline fibers based on the AgBr - AgI system and a method for their production have been developed. THz fibers are intended for use as delivery channels for terahertz radiation in thermal imaging systems, military equipment, space technologies, as well as for applications in biotechnology, analytics, and medicine. The introduction of silver iodide into silver bromide provided high photo- and radiation resistance of optical fibers, which allows them to be used without a thick protective shell and retains high flexibility, which is necessary for many areas of science and technology, including nuclear power.

Claims (3)

A method for producing terahertz nanocrystalline fibers of the AgBr - AgI system, including the production of fibers by extrusion from single-crystal silver halide blanks, characterized in that the extrusion parameters are preliminarily determined by computer simulation using the finite element method - temperature, plunger pressure on the blank and its speed, then a terahertz single-crystal blank based on solid solutions of bromide - silver iodide in the following ratio of ingredients, wt. %: silver bromide 70-96 silver iodide 30-4, heated at 175 - 185 ° C and a pressure of 700 - 900 MPa, which ensures its movement through the spinneret at a speed of 0.2-0.3 mm per minute in order to obtain a nanocrystalline structure of terahertz fibers.

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