RU2751147C1 - Optical method for magnetic field measurement - Google Patents

Abstract

FIELD: constant magnetic field measurement.

SUBSTANCE: invention relates to methods for measuring a constant magnetic field and can be used in the creation and operation of magnetic sensors and magnetometers. The optical method for measuring the magnetic field includes the effect of a magnetic field on the active element of the detector and registration of its magneto-optical characteristics, while the absorption spectrum of nanoparticles in the measured magnetic field is recorded and the magnitude of the magnetic field induction is determined from the frequency interval between the split components of the spectrum, and the active element of the detector is made of spherical silver nanoparticles.

EFFECT: expansion of methods and simplification of the processes of non-contact measurement of a constant magnetic field.

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Description

The invention relates to methods for measuring a constant magnetic field and can be used in the creation and operation of magnetic sensors and magnetometers. An important role in magnetometry is played by the optical method of measuring the magnetic field, which makes it possible to carry out measurements without contact.

Today, various methods are used to measure the magnitude (induction) of the magnetic field using the Hall effect, the Faraday effect in a magnetometer with a fiber-optic sensor, using the properties of nitrogen-vacancy centers (NV centers) in diamond, which make it possible to optically register magnetic resonance, etc.

Known technical solution for RF patent RU2725650 (IPC G01R 33/032, publ. 10.02.2020). The technical result is achieved in a device (magnetoplasmonic crystal - MPlK), consisting of a one-dimensional diffraction grating with a subwavelength period and deposited on it a thin layer of a noble metal with a negative real part of the dielectric constant, a thin layer of ferromagnetic metal, and a dielectric passivating layer. This type of MPLC is characterized by the possibility of excitation of surface plasmon-polaritons by the diffraction method, which makes it possible to enhance magneto-optical effects in a narrow spectral range of excitation of surface plasmon-polaritons.

Known technical solution for RF patent RU2694798 (IPC G01R 33/02, publ. 04.24.2018). The method for measuring the characteristics of the magnetic field in this method is that a diamond crystal with NV centers is placed in the region of the measured magnetic field, to which electromagnetic radiation in the optical range is directed, leading to spin polarization of the NV centers. To the specified crystal is applied at least once an alternating magnetic field oriented in some predetermined direction. Measure the dependence of the fluorescence signal on the magnitude of the alternating magnetic field. As a diamond sample, polycrystalline diamond with NV centers with a random orientation of the axes is used. The position of the only cross-relaxation resonance in the fluorescence signal is used to determine the projection of the measured magnetic field. The technical result is to simplify the method for measuring the characteristics of the magnetic field.

Known technical solution for the RF patent RU 2 695 593 (IPC G01R 33/24, B82Y 35/00, publ. 06/28/2018). The method includes exposure to a silicon carbide crystal containing spin centers with a ground quadruplet spin state, focused laser radiation, a frequency-tunable radio-frequency electromagnetic field and a constant radio-frequency electromagnetic field. One of the RF fields is low frequency modulated. In this case, the intensity of the luminescence of the spin centers is measured at different frequencies of the tunable radio-frequency field at different values of the external magnetic field. From the values of the frequencies of the inflection point of the curves of the change in the luminescence intensity corresponding to various values of the external constant magnetic field, a calibration dependence of the magnetic field value on the frequency of the inflection point is constructed. Then, measurements are made for the test sample and the frequency of the inflection point of the curve for changing the luminescence intensity near the frequency of the constant radio frequency field is determined. The magnitude of the magnetic field created by the test sample is determined from the frequency of the inflection point on the calibration curve. The technical result consists in increasing the sensitivity and accuracy of determining the magnetic fields.

In the article (Zong-Wei Ma, Jun-Pei Zhang, Xia Wang, Ying Yu, Jun-Bo Han, Gui-Huan Du, and Liang Li Magnetic field induced great photoluminescence enhancement in an Er 3+: YVO 4 single crystal used for high magnetic field calibration // Optics Letters. 2013, Vol. 38, No. 19, pp. 3754-3757) presents the results of the developed simple method for accurate pulse calibration and remote detection of large magnetic fields using the dependence of the photoluminescence of an Er3: YVO4 single crystal on the magnetic field ... Photoluminescence is excited by a laser with a wavelength of 487.5 nm and can be significantly enhanced by a magnetic field at certain values of the field.

The closest in terms of the measurement method is the method for determining a constant magnetic field, described in the patent application of the Russian Federation RU2071077 (IPC G01R 33/34, publ. 09.07.1991), taken as a prototype.

The method consists in measuring the parameters of the magnetic field, including the action of the magnetic field on the active element of the sensor and the registration of its magneto-optical characteristics. An exciton photoluminescence signal is excited in the active element of the sensor and the spectrum of its resonances in the measured magnetic field is recorded. Determine the magnetic field by the width of the spectrum resonances. In a magnetic field sensor, an active element in the form of a TlGaS single crystal₂, can be replaced by FlGaS single crystal₂...

One of the disadvantages of the prototype is that during measurements, the direction of the magnetic field must always be directed parallel to the normal to the layers of the TlGaS ₂ single crystal. The temperature of the medium in which the single crystal is placed should be only 2 K, which is a relatively difficult value. Since the magnitude of the magnetic field is determined by the half-width of the resonance line, a change in temperature by a small value can lead to a broadening of the spectrum, hence, to a measurement error.

The technical result, to which the invention is directed, is to expand the methods and simplify the processes of contactless measurement of a constant magnetic field.

FIG. 1 shows the absorption cross section of a spherical silver nanoparticle in a magnetic field with an induction of 0-10 T.

FIG. 2 shows the dependence of the relative frequency of the resonant band on the magnetic field strength, where ω _{0 is the} resonance frequency in zero magnetic field.

The problem to be solved by the claimed invention is achieved by the fact that the optical method for measuring the magnetic field, including the effect of a magnetic field on the active element of the detector and registration of its magneto-optical characteristics, which removes the absorption spectrum of nanoparticles in the measured magnetic field and determines the magnitude of the magnetic field induction from the frequency the interval between the split spectral components, and the active element of the detector is made of spherical silver nanoparticles.

The invention is based on its own theoretical studies, which are partially described in publications: Kucherenko M.G., Nalbandyan V.M .: Modification of the spectrum of the electric dipole polarizability of a cluster of two conducting spherical nanoparticles in an external magnetic / Vestnik OSU. 2014. No. 1. Issue. 162 s. 118-126; Kucherenko M., Nalbandyan V. Absorption and spontaneous emission of light by molecules near metal nanoparticles in external magnetic field / Physics Procedia. 2015. V.73. p. 136-142 .; Kucherenko M.G., Nalbandyan V.M. Formation of the spectral contour width of nanoparticles plasmon resonance by electron scattering on phonons and a boundary surface / Eurasian Physical Technical Journal. 2018. V.15. No. 2 (30). p. 49-57.

The invention can be implemented as follows. The active element of the detector with spherical silver nanoparticles is placed in a cryogenic optical chamber to reach a temperature of 20-40 K - only in this case it is possible to observe the splitting of absorption spectra lines under the action of a magnetic field. Using a spectrophotometer, the absorption spectrum of spherical silver nanoparticles is measured. The source of the magnetic field is a superconducting electromagnet, which makes it possible to create a field with an induction of up to 10 T.

In the developed optical method for measuring the magnetic field, spherical silver nanoparticles are used as an active element of the magnetic field detector. By measuring the absorption spectrum of spherical silver nanoparticles, the graph will show one spectral absorption band at the resonant frequency (at the plasmon resonance frequency). When a constant magnetic field with induction B is switched on, in the absorption spectrum, instead of one plasmon resonance band, two components will be observed, into which the main line is split. The amount of splitting depends on the induction B of the magnetic field . By measuring the frequency spacing between the split components (stripes), you can determine the magnitude of the magnetic induction.

To observe the splitting of absorption spectra by spherical silver nanoparticles in the optical frequency range, the following conditions must be met:

- The frequency of collisions of γ electrons in a metal with phonons should take on values of the order of 10 ¹¹ -10 ¹² s ^-1 , while at room temperatures it is much higher: γ ~ 10 ¹³ -10 ¹⁴ s ^-1 . A significant change in the collision frequency γ towards its decrease can be achieved, for example, by reducing the metal temperature to 20-40 K.

- In addition to the need to take into account the temperature dependence of the frequency of electron-phonon collisions, it is also important to take into account the dependence on the radius of spherical silver nanoparticles. This radius should be about 50 nm in order to reduce the contribution to the γ value of electron scattering on the surface of spherical silver nanoparticles.

рассеиваемой световой волны. В случае когда векторы Е и В коллинеарны, спектральная линия становится немагниточувствительной. - The induction vector of the external magnetic field B must be directed perpendicular to the vector of the electric field strength

scattered light wave. In the case when the vectors E and B are collinear, the spectral line becomes non-magnetosensitive.

One of the main characteristics that determine the optical properties of a metal is its complex dielectric constant. In a constant magnetic field, the metal acquires anisotropic properties, while the scalar dielectric constant becomes a tensor quantity [Ginzburg V.L., Rukhadze A.A. Waves in Magnetoactive Plasma. 1975. M .: Nauka .. 256 pp.] As well as the electric polarizability of a metal particle with a magnetized electron plasma.

, где

- плазменная частота металла. В магнитном поле спектральная полоса изменяется, а именно, полоса расщепляется на две одинаковые по амплитуде и форме компоненты, которые постепенно расходятся друг от друга по частотной шкале с увеличением индукции магнитного поля (фиг. 1). Такое расщепление связано с влиянием магнитного поля на траекторию движения свободных электронов в металлической плазме. Математически, это можно объяснить, проведя анализ отдельных компонент тензорного выражения электрической поляризуемости α(ω) металлической наночастицы [Кучеренко М.Г., Налбандян В.М. Вестник ОГУ. 2014. № 1. Вып. 162. с. 118-126.].The absorption spectrum of homogeneous metal nanoparticles has a single spectral band at the resonant frequency, called the Mie frequency

where

is the plasma frequency of the metal. In a magnetic field, the spectral band changes, namely, the band splits into two components of the same amplitude and shape, which gradually diverge from each other along the frequency scale with increasing magnetic field induction (Fig. 1). This splitting is associated with the influence of a magnetic field on the trajectory of free electrons in a metal plasma. Mathematically, this can be explained by analyzing the individual components of the tensor expression for the electric polarizability α (ω) of a metal nanoparticle [MG Kucherenko, VM Nalbandyan. OSU Bulletin. 2014. No. 1. Issue. 162 s. 118-126.].

и

матричных элементов α(ω) формируются плазмонные резонансы. В случае вакуума

из первого резонанса получаем частоту

Ми:

. Из условия

получаем две резонансные частоты

: From the conditions of minimization (and for γ = 0 - vanishing) the denominators

and

of matrix elements α (ω), plasmon resonances are formed. In the case of a vacuum

from the first resonance we get the frequency

Mi:

... From the condition

we get two resonant frequencies

:

или

,

or

,

,

,

;Where

,

,

;

– циклотронная (ларморовская) частота электронов в магнитном поле;

- cyclotron (Larmor) frequency of electrons in a magnetic field;

– плазменная частота электронов;

- plasma frequency of electrons;

ω- frequency of the monochromatic electromagnetic field;

– диэлектрическая проницаемость среды, окружающая металлическую частицу.

- dielectric constant of the medium surrounding the metal particle.

, то есть основная частота плазмонного резонанса расщепляется на две компоненты, расстояние между которыми равно ларморовской частоте

(фиг. 2). С ростом индукции магнитного поля интервал разбегания компонент растет пропорционально полю.From these equations it immediately follows

, that is, the fundamental frequency of the plasmon resonance is split into two components, the distance between which is equal to the Larmor frequency

(Fig. 2). With an increase in the magnetic field induction, the interval of divergence of the components increases in proportion to the field.

Claims (1)

An optical method for measuring a magnetic field, including the effect of a magnetic field on the active element of the detector and registration of its magneto-optical characteristics, characterized in that the absorption spectrum of nanoparticles in the measured magnetic field is taken and the magnitude of the magnetic field induction is determined from the frequency interval between the split components of the spectrum, and the active element of the detector is made of spherical silver nanoparticles.

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