LT4625B - A device for measuring of a temperature dependence of two kinds break of ferroelectric crystal and a hysteresis of it - Google Patents

Abstract

The device for the measurement of the temperature dependency of the double rupture of Ferro-electric crystals belongs to the field of optics and may be used for the research in the field of optical characteristics of Ferro-electric crystals and phasic transformations.The equipment consists of the source of light (1), mono-chromator (2), polariser (3), cryostat (4) with a built-in specimen holder and temperature measurer (5), λ4 phasic disc (6), analyser (7), photo-receivers (8,9), accumulators (11,12), voltage-division blocks (13,14) analogical-numerical block (12), quadruple signal blocks (15,16), triangular-shaped-signal formation block (17), special phasic difference measurer and a two-co-ordinate registering device (19).

Description

The invention relates to the field of optics and can be applied to the investigation of optical properties and phase transitions of ferroelectric crystals.

Known crystal dual-refractive temperature dependence device consisting of a light source, a monochromator, a light polarizer, a cryostat with a sample holder, a temperature meter, an analyzer, a photo receiver, a recorder (former USSR al. 807079). By changing the sample temperature T in this device, the recorder records the luminous intensity / temperature dependence of the passage through the analyzers 7 (7). Knowing the temperature dependence I (T) of the passing beam through the analyzers and the peak intensity of passing the analyzers 7 ₀ , we find the linearly polarized waves generated by two mutually perpendicular double refraction Δη, followed by the temperature dependence Δφ (Γ).

From Equation ₄ ΊπΔηΙ

-Τ'where Δφ is the phase difference, Δη is the double fracture, l is the thickness of the sample, the temperature dependence of the double fracture Δη (T) is found.

Also known is a dual-refractive temperature dependence device of ferroelectric crystals consisting of a light source, a monochromator, a polarizer, a crystal with a sample holder, a temperature meter, a compensator, an analyzer, a photodetector and a double recorder (former USSR a.l. In this device, two mutually perpendicular linearly polarized waves of phase refraction J // having a phase difference Δφ are emitted from the sample. Compensator restores dual fracture zl /? generated phase difference Δφ, the magnitude of which is visible on the compensator scale.

In the above-mentioned dual-fracture temperature dependence measuring devices Δφ {Τ) and Δη (Τ) measurement errors are caused by the following reasons';

1. The luminous intensity [(T) passed through the analyzers is slightly dependent on the temperature in the region close to Δφ «n y (/ 7 = 0,1,2,3 ...).

2. The intensity of light passing through the sample and analyzers 7 ^ (7) depends on the temperature of the sample since the absorption coefficient of the sample depends on the temperature.

3. The oscillations of light intensities I and I 'are caused by instabilities of the light source producing Δφ instabilities.

The object of the invention is to increase the accuracy of the temperature dependence of the phase difference Δφ (Τ) and the double refraction / 1 // (7).

This object is achieved by a dual-refractive temperature dependence / 1 // (7) measuring device for ferroelectric crystals consisting of a light source (1), a monochromator (2), a light polarizer (3), a cryostat (4) with a sample holder and a temperature meter. (5), compensator and analyzer (7), photodetector (8), and bi-coordinate recorder (19). Optionally, a second photo opener (9) optically connected by a second light beam and λ / 4 in place of the compensator

J phase plate (6). The outputs of the photographic receivers (8, 9) are connected to the first inputs of the summing device (10, 11) and their second inputs are connected to the first outputs of the analogue digital unit (12). The outputs of the summing units (10, 11) are connected to the first inputs of the voltage division blocks (13, 14) and the analog-to-digital unit (12). The second outputs of the analog-to-digital unit (12) are connected to the second inputs of the voltage division blocks (13, 14). the outputs of the voltage division blocks (13, 14) are connected to the inputs of the quadrature signal blocks (15, 16) whose outputs are connected to the first inputs of a special phase difference Δφ meter 18, the second inputs of which are connected to the inputs of the quadrature signal blocks (15, 16). The outputs of the phase difference Δφ meter (18) and the temperature meter (5) are connected to the two inputs of the dual coordinate recorder (19).

Proposed ferroelectric crystal double refraction temperature dependence of the measuring arrangement has a larger phase difference evil? (7) and the double refraction / 1/7 (7) The measurement accuracy for registration used triangular, composed of linear parts of the _U-T signal having an amplitude independent of the sample This triangular U _T signal is fed to a special phase difference meter (x7) which produces a signal proportional to Δφ (Γ) or / 1/7 (7) and evaluates the Δφ and / 1/7 sign. The dynamic, continuous change of the sample temperature, using a special phase difference detector (T) meter, highlights the fine structure of Δφ (Τ) and / 1/7 (7) and increases the measurement accuracy of the hysteresis loop in the phase transition region.

The invention is explained in the drawings, wherein Fig. 1 is a block diagram of the proposed device, Fig. 2 - signal dependence on Δφ (from photo receivers (8, 9) to voltage divider blocks (13, 14)), Fig. 3 - signal dependence on Δφ (voltage divider). blocks (13, 14) to the registrar (19)).

The proposed device for measuring the dual-refractive temperature dependence of ferroelectric crystals Δη (Τ) consists of an optically coupled light source (1), a monochromator (2), a polarizer (3), a cryostat (4), and a sample holder (5) embedded therein. a phase plate (6), an analyzer (7), two photo receivers (8, 9), the outputs of which are connected to the first inputs of the two summing units (10, 11) and their second outputs to the inputs and voltage divisions of the analogue digital unit (12) (13, 14) of the first entrances. The first outputs of the analog-to-digital unit (12) are connected to the second inputs of the summing units (10, 11) and the second outputs of the analog-to-digital unit (12) are connected to the second inputs of the voltage division units (13, 14). The outputs of the voltage divider blocks (13, 14) are connected to the inputs of the quadrature signal blocks (15, 16) and the first inputs of the Δφ meter (18). The outputs of the square signals (15, 16) are connected to the inputs of the triangular signal Ur forming unit (17), the outputs of which are connected to the second inputs of the Δφ meter (18). The output of the Δφ meter (18) is connected to the first input of the dual coordinate recorder (19). The second input of the bi-coordinate recorder (19) is connected to the output of the temperature gauge (5). Place the sample in the sample holder provided in the cryostat (4).

The unit operates as follows. From the source (1), white light enters the monochromator (2), where it emits a wavelength λ of a certain wavelength, polarized by the polarizer (3). The first ray of light reaches the anisotropic crystal in the cryostat (4). In the crystal, due to the dual refraction, Δη produces perpendicular linearly polarized waves with phase difference

Δφ. As the second ray of light passes through the λ / 4 phase plate (6) (λ monochromatic light wavelength), an additional phase difference of 90 ° = π / 2 occurs between the two perpendicular linearly polarized waves. The analyzer (7) converts two orthogonal waves into two coherent interfering waves (polarized light interference occurs). The photo receivers (8, 9) generate two electrical signals J] and U ₂ . The photo receiver (9) produces a signal U? = 24cos ² Δφ / 2, and the photo receiver (8) produces a signal f / 2 = 24cos ² (zlr /? / 2-π / 4), where 24 is the amplitude of signals U \ and lh, Δφ - difference of two mutually perpendicular linearly polarized wave phases. The signals (Fig. 2 - 1 (a, b)) acting on the output of the photographic receivers (8, 9) are fed to the first inputs of the summing device (10, 11). The signals U \ and U2 consist of the constant dcosle of A and the variable components ?, 4cos (zł> - π / 2):

where 24 is the amplitude of the signals U \ and U ₂ , Δφ is the phase difference.

In order to eliminate the constant component 4 having a value equal to the amplitude in the signals U \ and U _2, a negative signal having a value equal to the amplitude (-4) is output from the first outputs of the analog-digital unit (12) to the second inputs of the summing units (10, 11). . After performing the signal L'i and U ₂ and (-4), the outputs of the summing units (10, 11) output the signals (ill. 2 - 2 (a, b)):

U, = 4 cosAę ?,

U, - A cos

A sin Δφ, where / 1 is the amplitude of signals U \ and U ₂ , Δφ- phase difference.

As the sample temperature changes, the amplitude T varies. The voltage divider units (13, 14) and the analogue-digital unit (12) perform the division operation U [! A and U ₂ / A.

In this way, the first and second outputs of the voltage division blocks (13, 14) operate on the signals (Figures 3 - 1 (a, b)): in the first output U \ i = cosle ?, in the second output i / v2 ⁼ sinzly7, where Δφ- phase difference .

The signals i and Č (v2 are fed to the inputs of the quadrature signal blocks (15, 16). These blocks (15, 16) perform two-way comparison (f g. 3 - 2 (a, b)). Signals from the blocks (15, 16) fed into the shape of a triangle signal U _T-forming unit (17) inputs. blocks (17) carried out an operation and deprivation trigger triangular signal

Ur ⁼ | s inzl ζή-i coszl (Ą, where Δφ is the phase difference. As a result of this operation, the linearity of the triangle signal Uf (fg. 3 - 3) resulting in the phase difference interval Δφ = ± 45 ° is about 2%. the first inputs of the Δφ meter (18), and the second inputs of the Δφ meter (18) from the outputs of the voltage divider blocks (13, 14), U _t \ - to and U, \ 2- Δφ of the triangular background signal U _T receives a signal υ _Δφ directly proportional to Δφ (fg. 3 4) The signal υ _Δφ from the _output of the Δφ meter (18) is fed to the pin input of the dual coordinate recorder (19) and the signal from the temperature meter to the second input of the double coordinate recorder (19). (5) Output The two-coordinate registrar (19) plots the graph Δφ {T) or Δη ('Γ).

Because the dual-refractive temperature dependence of ferroelectric crystals can measure Δη (Τ) as the temperature increases and decreases, it can be used to study zl /? (7) hysteresis. The nature of the stroke and the size of the hysteresis loop determine Διι {Γ) the type and type of phase transition (first or second phase, critical phase).

The proposed device has a higher measurement accuracy of Δφ (Γ) or Δη (Τ) than other similar devices of the type described above, for the following reasons:

1. The amplitudes of the signals (7, v, = cos / l <to>, U, \ - ₂ = sin / l? And U _T = | sin / l <p) - Osc / l ^ are independent of the sample temperature. The signal G) ·, which is fed to the Δφ meter, consists of linear Δφ {Τ) dependencies. In this way, the measurement accuracy of Δφ ^ Γ) is independent of the size of the temperature range ΔΤ.

2. A special Δφ (Τ) meter is used, which produces a signal directly proportional to Δφ (Γ). By measuring the Δφ mark, the meter increases the measurement accuracy of the hysteresis loop in the phase transition region.

3. The device measures Δφ ^ Γ) or / 1 // (73 when the temperature of the ferroelectric crystal under study changes very slowly (0.1 ° C for 1 min.) And continuously. This dynamic temperature mode gives rise to the zl \ 7) or / 1 // (7) fine structure and increases measurement accuracy.

4. An automated electro-optic device, which has no moving mechanical assemblies, is more sensitive and accurate to changes in Δφ (7), facilitates assembly of the device and its alignment with the least measurement error.

5. The electro-optical scheme of the device is chosen so that the light source instabilities do not affect the measurement accuracy of Zkz (7j.) This allows to reduce the device dimensions using a white light source and monochromator semiconductor variable wavelength laser.

Claims (1)

DEFINITION OF INVENTION Dual refraction temperature dependence device for ferroelectric crystals, consisting of an optically coupled light source (1), a monochromator (2), a light polarizer (3), a cryostat (4) with an integrated sample holder and a temperature meter (5), an analyzer (7) , a photodetector (8) and a dual-coordinate recorder (19), characterized in that a second photodetector (9) optically coupled to the second light beam and an Λ / 4 phase plate (6) placed in front of the analyzer are additionally connected, the outputs of the photodetectors (8, 9) the first inputs of the sumers (10, 11) and their second inputs connected to the first outputs of the analog-to-digital unit (12), the outputs of the summing units (10, 11) to the voltage division blocks (13, 14) and the analog-to-digital unit (12) ) with the first inputs, the second outputs of the analog-to-digital unit (12) connected to the second to the voltage divider units (13, 14) The outputs of the voltage divider blocks (13, 14) are connected to the inputs of the quadrature signal blocks (15, 16), the outputs of which are connected to the first inputs of a special phase difference Δφ meter (18). , the second inputs of which are connected to the inputs of the quadrature signal blocks (15, 16), the outputs of the phase difference Δφ meter (18) and the temperature meter (5) are connected to the two inputs of the double coordinate recorder (19).