Mixed ferroelectric nematic phase liquid crystal material and method for enhancing second harmonic by removing ferroelectric nematic phase liquid crystal dimer

Abstract

The invention discloses a mixed ferroelectric nematic phase liquid crystal material and a method for enhancing second harmonics by removing ferroelectric nematic phase liquid crystal dimers. The mixed ferroelectric nematic liquid crystal with the second harmonic enhancement effect is obtained by doping polar or non-polar small molecules containing large dipole moment in the ferroelectric nematic liquid crystal, the second harmonic enhancement multiple is linearly related to the dipole moment of a dopant, and the larger the dipole moment of the doped small molecules is, the higher the second harmonic enhancement multiple is. On the basis of deep understanding and understanding of a ferroelectric nematic phase liquid crystal'head-tail 'reverse polarization arrangement micro-domain, secondary harmonic enhancement of a large dipole small molecule dispolarity nematic phase liquid crystal dimer is realized for the first time.

Description

Technical Field

[0001] The invention belongs to the field of performance improvement and application of nonlinear optical materials, and relates to a method for enhancing second harmonic by releasing ferroelectric nematic liquid crystal dimers. Background Art

[0002] Nematic (N) liquid crystal is a highly fluid, long-range ordered fluid with only orientation order but no position order. Generally speaking, their molecular long axes tend to be arranged along the orientation direction, but in the entire medium system, the local orientation direction of the molecules will be slightly different. Traditional nematic (N) liquid crystals are composed of rod-shaped molecules with a dipole moment lower than 6D. Since the dipole moment of the molecules themselves in this system is small, the dipole-dipole interaction between molecules is usually difficult to overcome the thermal perturbation energy of the material system. Therefore, the macroscopic polarity of the material is basically close to zero, that is, the polarization director n of the liquid crystal molecules is arbitrarily arranged up and down in the orientation direction, that is, n = -n, such as Fig.11 (b) as shown.

[0003] In 2017, two nematic liquid crystals with ferroelectricity were introduced. They were synthesized by Mandle of York University in the UK and Nishikawa et al. of Kyushu University in Japan. They are wedge-shaped molecules with large dipole moment (μ>6D) and are named RM734 and DIO. The chemical structure of the molecules is as follows: Fig.11 (a) As shown. This type of molecule will show the Schlieren texture of traditional non-polar nematic liquid crystal at high temperature, and will show the typical hysteresis loop and strong second harmonic response of ferroelectric materials at low temperature (<130℃), which shows that the material system has macroscopic polarity at low temperature, and the polar order of its molecules will spontaneously polarize along the direction of the director at the microscopic level, so the head and tail of the polar liquid crystal molecule are no longer equivalent, that is, n≠-n, such as Fig.11 (c) As shown. In 2018, Mertelj et al. proposed that the new phase formed by RM734 molecules at low temperatures is a nematic phase with local polarity, in which the "heads" and "tails" of the polarized molecules are arranged in parallel and in opposite directions, with a certain periodicity. In 2020, Clark et al. observed through a microscope that RM734 molecules spontaneously form reverse polarity domains unique to ferroelectrics at low temperatures. By applying an in-plane alternating electric field, it was found that the reverse domains would reverse as the direction of the electric field changed, which provided the most direct evidence that RM734 liquid crystal molecules have ferroelectricity. So far, this new nematic phase liquid crystal with a large dipole moment has been confirmed to be a liquid crystal with ferroelectricity. It can not only be used to prepare flexible optoelectronic devices, but also is a fluid nonlinear photonic material. The emergence of this new state of matter brings possibilities for the future development of soft matter nonlinear photonic devices.

[0004] Nonlinear optics (NLO) is an emerging discipline born in the 1960s and 1970s. It is the phenomenon that after the interaction of high-energy monochromatic strong light with the medium, the atoms and electrons in the medium generate an induced electric polarization field under the action of the photoelectric field, and radiate new photons with this polarization field as the excitation source. In the field of nonlinear optics, different light waves can exchange energy, change frequency, and transmit phase information through interaction with the medium. In 1961, PA Franken and others first used the principle of nonlinear optics to prepare a frequency-converting laser, which opened the door to the application research of strong field nonlinear optics. Generally speaking, when light propagates in a medium, it often has various interactions and responses with matter, such as thermal response, electron orbit distortion response, light polarization response, photostriction response, light folding response, etc. Among them, when the intensity of the incident light electric field (E) is small, the interaction is linear response, and the typical linear optical phenomena are mainly refraction, interference or diffraction phenomena that mainly change the propagation direction and spatial distribution of light; when the intensity of the incident light electric field (E) is large, the interaction is nonlinear response. At this time, the light wave can change the frequency through the interaction with the medium, the phase information can be transmitted between the light beams, and the physical parameters of the material will change with the intensity of the incident light beam. Common nonlinear optical effects include: frequency doubling, frequency combination, stimulated Raman scattering, optical phase conjugation, Kerr effect, nonlinear absorption and dispersion, self-focusing and other phenomena.

[0005] According to the description of polarization theory: when a beam of light shines on a material, it causes the charge in the atoms to oscillate. Usually, the frequency of the charge oscillation induced by the linear photoresponse is the same as the frequency of the incident light electric field (E), which makes the induced polarization intensity (P) of the medium different from the instantaneous intensity of the applied light electric field (E j ), which can be described as:

[0006]

[0007] When the incident light is a strong field, the above linear process is not valid. The polarization of the material charge is not proportional to the applied photoelectric field (E). In addition to the linear part, there is also a nonlinear component. The relationship describing this process is expanded according to the Taylor series, and the expression is as follows:

[0008]

[0009] Where P is the induced polarization intensity of the material under the action of the photoelectric field, P 0 is the static polarization intensity of the material, χ (n) is the n-order nonlinear optical polarization tensor, ε 0 is the dielectric constant of vacuum.

[0010] From a microscopic perspective, the nonlinear optical process can be considered as the nonlinear component of the dipole moment generated by chemical molecules after the interaction between matter and light. This process can be described as:

[0011] μ=μ 0 +ε 0 α ij E j +ε 0 β ijk E j E k +ε 0 γ ijkl E j E k E l

[0012] Where μ is the dipole moment of the molecule under the action of the photoelectric field, μ 0 is the static dipole moment, α ij , β ijk , γ ijkl are the first-order polarizability, first-order hyperpolarizability and second-order hyperpolarizability of the molecule respectively.

[0013] Polarization tensor χ (n) In all directions with the molecule's α ij , β ijk , γ ijkl It can be described by the following relationship:

[0014]

[0015]

[0016]

[0017] Where N is the number of molecules per unit volume, F(ω n ) is the frequency ω n The local field factor under the condition of ij , β ijk , γ ijkl ) or the local polarization degree (F(ω n )) is a key method to improve the overall nonlinear optical tensor of a material.

[0018] Among the numerous nonlinear optical (NLO) effects, the most widely studied is the second-order nonlinear optical effect, which is the most typical, important and basic technology in nonlinear optical mixing technology, and is also the cornerstone of lightwave wavelength conversion technology. The second-order nonlinear optical effect is also called the frequency doubling effect or second harmonic generation (SHG), which is specifically manifested as follows: a fundamental frequency laser with a frequency of ω is incident on a non-centrosymmetric medium. In addition to the fundamental frequency laser, a new photon with a frequency of 2ω is generated at the output end. This new photon is called frequency-doubled light. The discovery of second harmonics can be traced back to 1961, when Franken et al. observed the phenomenon of second harmonic generation in quartz. They used a wavelength of λ 1 = 694.3nm ruby ​​laser penetrates quartz crystal and uses prism to split the light, irradiates on the exposure film, and finds that at wavelength λ 2 = There is an exposure ink spot at 347.15nm. However, under the theoretical and experimental conditions at that time, the conversion efficiency of SHG was very low, only 10 -8 At present, the SHG effect has become an important means of frequency conversion in laser technology, greatly expanding the wavelength range of lasers; in the field of life sciences, the SHG effect is used to detect nonlinear signals in biological tissues, allowing tissues to be observed more clearly; in the field of materials science, the SHG effect can be used to detect the symmetry-breaking structure of materials, thereby inferring the structural characteristics or information of materials, and is also widely used in the study of the properties of material surfaces or interfaces; in the field of communication technology, SHG technology is the cornerstone of wavelength conversion and is widely used in technologies such as optical signal modulation, optical storage, and optical frequency combs.

[0019] In summary, the second-order nonlinear optical (NLO) effect has broad application prospects. At present, most common nonlinear photonic device materials are solid-state photonic crystals. Since the advent of ferroelectric nematic liquid crystals with symmetry-breaking structures, fluid nonlinear photonic devices have been developed. However, due to the high-order nonlinear optical effect, the polarizability tensor χ (n) Therefore, by removing the polarization micro-regions of the "head-tail" reversely arranged dimers of the ferroelectric nematic phase liquid crystal, the local polarization degree of the NF liquid crystal molecules can be improved, which has a new era of prospect and significance for the enhancement and application of the second harmonic. Summary of the invention

[0020] The present invention discloses a type of ultra-high polarity fluid material with a reverse polarized dimer disassembly structure. The mixed system compensates for the polarity loss of the "head-to-tail" reversely arranged polarization cancellation microdomains in the ferroelectric nematic phase liquid crystal molecule body, maximizes the net polarization intensity of the ferroelectric nematic phase liquid crystal body, and realizes the modulation of the second harmonic enhancement of the ferroelectric nematic phase liquid crystal by selecting the size of the dopant dipole moment.

[0021] At present, the main method to achieve second harmonic enhancement by increasing the second-order nonlinear coefficient is to synthesize molecules with higher nonlinear coefficients. However, most of the preparation processes of this method are cumbersome and complicated, not only time-consuming and labor-intensive, but also the synthesized products do not exist in liquid crystal phase most of the time. The present invention uses a simple method of doping and mixing to achieve second harmonic enhancement of liquid crystal phase by dissolving the "head-tail" reverse arrangement of dimer microdomains of ferroelectric nematic liquid crystal. The de-dimerized mixed ferroelectric nematic liquid crystal material has a very strong second harmonic response characteristic, which can excite photons by itself. At the same time, the second harmonic enhancement multiple of this ferroelectric nematic liquid crystal can be flexibly tuned by changing the dipole moment of the doped small molecule, and can be tuned to 2 to 20 times the second harmonic intensity of the undoped ferroelectric nematic liquid crystal. This fast and convenient way to enhance the second harmonic enhancement is very necessary for the development of flexible ferroelectric liquid crystal photonic devices that meet the actual application power. Moreover, compared with many traditional methods of second harmonic enhancement, this technology has the characteristics of simple preparation method, convenient tuning of SHG enhancement multiple and no need for synthesis, which can effectively increase the application prospect of the medium in the field of soft material optical frequency doubling.

[0022] The purpose of the present invention is to achieve the following measures:

[0023] A ferroelectric nematic liquid crystal material with higher net polarization intensity is obtained by uniformly mixing and doping polar or non-polar small molecules with large dipoles into ferroelectric nematic liquid crystals at a certain mass fraction, wherein the mass fraction of the large dipole small molecules in the mixture (the mixture is two substances, small molecules with large dipole moments and ferroelectric nematic liquid crystals) is 2% to 50%. The ferroelectric nematic liquid crystal material has a spontaneous polarization order with higher macroscopic polarity on the basis of the "head-tail" equivalent molecular director order structure of traditional nematic liquid crystals, and the high macroscopic polarity is provided by doping with large dipole small molecules; the disassembly technology of the reverse polarization dimer structure is caused by the coupling of high polarity small molecules and ferroelectric nematic liquid crystals.

[0024] Furthermore, the high polarity ferroelectric nematic liquid crystal has a molecular polarizability (β ijk ) or the local polarization degree F(ω n ), the stronger the polarity of the above-mentioned large dipole small molecule materials, the smaller the doping concentration for improving the SHG performance.

[0025] Furthermore, the tuning of the second harmonic enhancement characteristics of the high-polarity ferroelectric nematic liquid crystal material can be achieved by changing the mass ratio of the doping molecules to the ferroelectric nematic liquid crystal (2 to 50% by mass fraction of chiral molecules).

[0026] Furthermore, the high-polarity ferroelectric nematic liquid crystal material is ferroelectric and non-crystalline within a temperature range of 128 to 25° C., and has extremely strong second harmonic response characteristics.

[0027] Furthermore, the second harmonic response characteristic of the high polarity ferroelectric nematic liquid crystal material is 60-450 times that of a quartz crystal, that is, X (2) It can be increased to 4.2~31.5pm / V.

[0028] Furthermore, the high-polarity ferroelectric nematic liquid crystal material has a dimer disassembly phenomenon with adjustable ratio as the doping concentration changes, and the net polarization intensity of the liquid crystal system can be tuned.

[0029] Furthermore, the high polarity ferroelectric nematic liquid crystal material can evenly distribute the polarization strength of a certain number of dedimerized small molecules in a parallel oriented liquid crystal cell, as shown in the attached Figure 3 Schematic diagram of wavelength conversion in ferroelectric nematic liquid crystals showing polar arrangement of small molecules doped with large dipoles.

[0030] Furthermore, after the high polarity ferroelectric nematic liquid crystal material is mixed with large even-order crystalline molecules, the maximum value of the dielectric constant ε of the mixed sample can be as high as 28152, and the maximum value of its spontaneous polarization intensity Ps is about 5.32μC / cm 2 In addition, the second harmonic intensity of the mixed system material will continue to increase with the increase of the dipole moment of the crystalline small molecule, see Figure 6a to Figure 6c Change of SHG intensity of 10% R1 / RM734, 5% R2 / RM734, and 5% R3 / RM734 samples with temperature.

[0031] Furthermore, after the high polarity ferroelectric nematic liquid crystal material is mixed with large even-order conventional nematic liquid crystal molecules, the second harmonic intensity will increase rapidly at a very low doping ratio, see Figure 6a to Figure 6c The SHG signal value changes with temperature. The SHG test was carried out in a parallel-oriented liquid crystal cell with a thickness of less than 5μm.

[0032] Furthermore, the second harmonic intensity of the blend of the high polarity ferroelectric nematic liquid crystal material (RM734) and the low polarity ferroelectric nematic liquid crystal small molecules (DIO) will be greatly reduced as the doping ratio increases.

[0033] The present invention obtains a mixed ferroelectric nematic liquid crystal with a second harmonic enhancement effect by doping a polar or non-polar small molecule containing a large dipole moment in a ferroelectric nematic liquid crystal. The second harmonic enhancement factor is linearly related to the dipole moment of the dopant. The larger the dipole moment of the doped small molecule, the higher the second harmonic enhancement factor. The method is to remove the dimer microdomains of the "head-to-tail" reverse polarization arrangement in the ferroelectric nematic liquid crystal molecule body by introducing a strong dipole small molecule, thereby eliminating the loss of the macroscopic polarity of the material caused by the "head-to-tail" reverse polarization arrangement, effectively improving the nonlinear optical effect of the ferroelectric nematic liquid crystal, and exciting it to produce a higher intensity second harmonic. Based on the in-depth understanding and recognition of the "head-to-tail" reverse polarization arrangement microdomain of the ferroelectric nematic liquid crystal, the present invention realizes for the first time the second harmonic enhancement of the polar nematic liquid crystal dimer by the large dipole small molecule.

[0034] A method for preparing liquid crystal with second harmonic enhancement by disassembling the liquid crystal dimer structure:

[0035] Two glass substrates made of polyimide parallel friction alignment were made into a 5μm thick liquid crystal box with the same direction and parallel orientation. Ferroelectric nematic liquid crystal was poured into the liquid crystal box by capillary force. The liquid crystal texture was observed by cooling in the temperature range of 250-25℃, and the change range of the NF phase window temperature range after mixing was measured.

[0036] Furthermore, the second harmonic performance of the high-polarity ferroelectric nematic phase liquid crystal can be jointly adjusted by the dipole moment of the small molecule doping substance and its mixed mass fraction. When the dipole moment is greater than the blended base liquid crystal, the SHG of the mixture is enhanced; when the dipole moment is less than the blended base liquid crystal, the SHG of the mixture is reduced; the greater the dipole moment of the doped small molecule, the lower the concentration of the required doping ratio.

[0037] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0038] The high polarity ferroelectric nematic liquid crystal material of the present invention has a very strong second harmonic response, and its nonlinear optical properties are comparable to those of quartz in crystals, which is very rare in fluid soft materials. By changing the dipole moment and doping concentration of the small molecule dopant, the intensity of the second harmonic signal can be adjusted, thereby realizing the actual commercial application after the second harmonic enhancement. Compared with the polar nematic liquid crystal without small molecules, the second harmonic intensity is increased by more than 2 to 20 times. Compared with the existing nonlinear optical crystals, the macroscopic polarity of the material can be flexibly adjusted, the sample preparation method is convenient and simple, the steps are simple, and no equipment operation is required. At the same time, the temperature range of the ferroelectric nematic state can be adjusted, which is convenient for finding high polarity fluid ferroelectric liquid crystal materials that can be applied to room temperature. Compared with general nonlinear optical crystals, ferroelectric nematic liquid crystals have the characteristics of softness, easy processing and external field drive, which can realize many working scenes that crystals cannot be applied to, and have more cost advantages, and can be better applied to nonlinear photonic devices and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 This is a diagram of the principle path of second harmonic enhancement;

[0040] Figure 2 This is the second diagram of the principle path of second harmonic enhancement;

[0041] Figure 3 It is a schematic diagram of wavelength conversion of ferroelectric nematic liquid crystal after second harmonic enhancement. The nonlinear optical effect of ferroelectric nematic liquid crystal converts the incident light with a wavelength of 2λ into the outgoing light with a wavelength of λ.

[0042] Figure 4 It is the molecular structure parameters and second harmonic enhancement multiple statistics of small molecule materials doped in mixed ferroelectric nematic liquid crystal materials;

[0043] Figure 5 This is a graph showing the change of phase transition characteristics with concentration and temperature after doping crystalline small molecules with different dipole moments with ferroelectric nematic liquid crystals;

[0044] Figure 6a to Figure 6c This is a graph showing the variation of the second harmonic signal intensity with concentration and temperature after doping crystalline small molecules with different dipole moments with ferroelectric nematic liquid crystals;

[0045] Figure 7 This is a graph showing the change of phase transition characteristics with concentration and temperature after doping large dipole conventional nematic small molecules with ferroelectric nematic liquid crystals;

[0046] Figure 8 This is a graph showing the variation of the second harmonic signal intensity with concentration and temperature after doping large dipole conventional nematic small molecules with ferroelectric nematic liquid crystals;

[0047] Fig. 9This is a graph showing the change of phase transition characteristics of low dipole ferroelectric nematic liquid crystal (DIO) and high dipole ferroelectric nematic liquid crystal (RM734) with concentration and temperature after doping;

[0048] Figure 10a to Figure 10b This is a graph showing the variation of the second harmonic signal intensity with concentration and temperature after doping with low dipole ferroelectric nematic liquid crystal (DIO) and high dipole ferroelectric nematic liquid crystal (RM734).

[0049] Fig.11 Figure 1 shows the dipole moment and polarization order structure of nematic liquid crystal molecules. Figure a shows the chemical structures of two typical ferroelectric nematic liquid crystal molecules; Figure b shows the orientation order of traditional nematic liquid crystal molecules; and Figure c shows the orientation order of new ferroelectric nematic liquid crystal molecules.

[0050] DETAILED DESCRIPTION OF THE EMBODIMENTS The present invention will be further described in detail below in conjunction with the embodiments, but the scope of the present invention is not limited thereto.

[0051] Example 1

[0052] The preparation method of the mixed ferroelectric nematic liquid crystal with a large dipole crystalline small molecule R3 doping concentration of 5.0% is as follows:

[0053] Using chloroform as solvent, the matrix liquid crystal molecules (RM734) and the crystalline small molecules (R3) were weighed to prepare a solution with a mass fraction of 2%. A 5.0% mixture solution was prepared according to the doping concentration of the mixed ferroelectric nematic phase liquid crystal. After ultrasonic oscillation, it was dried in a vacuum drying oven at 55°C. After 6 to 8 hours, a uniform white solid mixture molecule was obtained, which was marked as 5.0% R3 / RM734.

[0054]

[0055] The above is the chemical molecular structure formula of the matrix ferroelectric nematic liquid crystal in the blend system.

[0056]

[0057] The above is the chemical molecular structure formula of the crystalline small molecules doped in the blend system.

[0058] Example 2

[0059] The implementation of the second harmonic enhancement method is as follows:

[0060] Prepare two glass substrates (1 cm 2 ), and then rubbed with velvet cloth to prepare a liquid crystal box, the thickness of which is 5μm. The prepared ferroelectric nematic liquid crystal is heated to liquid phase, and the liquid crystal enters the liquid crystal box under the action of capillary force. Its molecular orientation order structure is as follows Figure 3As shown. After cooling to the NF phase, the sample is irradiated with a pulsed pump light of 1064nm. Due to the nonlinear optical properties of the polar nematic phase liquid crystal, a second harmonic of 532nm is generated during emission. The emission intensity of SHG is adjusted by changing the doping concentration of the crystalline small molecules to achieve the best effect of second harmonic enhancement. The emitted second harmonic is detected using a photomultiplier detector and compared with the second harmonic response light intensity of quartz under the same conditions. Figure 4 The dipole moments and molecular morphologies of small molecules doped with different polarization intensities and matrix ferroelectric nematic phase liquid crystal molecules are compared, and the maximum enhancement factor of the second harmonic generation (SHG) of the mixed liquid crystal after blending is listed. It can be seen that when the dipole moment of the doped molecule is larger, the SHG signal value of the mixed sample increases more. The highest effective second-order nonlinear coefficient is as high as 31.5pm / V; Figure 5 After the large dipole moment non-polar crystals (R1, R2, R3) with different polarization strengths are mixed with the matrix ferroelectric nematic liquid crystal (RM734), the phase transition temperature of the mixed liquid crystal changes with the doping ratio of large dipole moment small molecules; Figure 6a , Figure 6b , Figure 6c It is the variation of the second harmonic generation (SHG) intensity of the mixed liquid crystal with different polarization strengths, after large dipole moment non-polar crystals (R1, R2, R3) are mixed with the matrix ferroelectric nematic liquid crystal (RM734). Figure 7 After the large dipole moment non-polar liquid crystal (2d) is mixed with the matrix ferroelectric nematic liquid crystal (RM734), the phase transition temperature of the mixed liquid crystal changes with the doping ratio of the large dipole moment small molecule; Figure 8 It is the variation of the second harmonic generation (SHG) intensity of the mixed liquid crystal with large dipole moment non-polar liquid crystal (2d) and matrix ferroelectric nematic liquid crystal (RM734) with temperature; Fig. 9 After the small dipole moment polar liquid crystal (DIO) and the small dipole moment non-polar liquid crystal (E7) are mixed with the matrix large dipole moment polar liquid crystal (RM734), the phase transition temperature of the mixed liquid crystal changes with the concentration of doped small molecules; Fig.10a It is the variation of the second harmonic generation (SHG) intensity of the mixed liquid crystal with small dipole moment (DIO) and the matrix polar liquid crystal with large dipole moment (RM734) with temperature; Fig.10b It is the variation of the second harmonic generation (SHG) intensity of the mixed liquid crystal with small dipole moment (E7) and the matrix large dipole moment polar liquid crystal (RM734) with temperature.

[0061] The above embodiments are preferred implementations of the present invention, but the implementations of the present invention are not limited to the above embodiments. For those skilled in the art of the present invention, without departing from the concept of the present invention, several simple deductions or substitutions can be made, which should all fall within the protection scope of the present invention.

Claims

1. A second harmonic enhanced hybrid ferroelectric nematic liquid crystal material, characterized in that: The mixed ferroelectric nematic liquid crystal material is obtained by uniformly mixing small molecules with large dipole moments and ferroelectric nematic liquid crystals. After releasing the "head-to-tail" reverse polarization arrangement dimers, the mixed ferroelectric nematic liquid crystal material will cause the dimers in the system to be broken, so that the ferroelectric nematic liquid crystal obtains a higher net polarization strength; the dimer release is formed by the interaction between the large dipole molecules and the ferroelectric nematic liquid crystals.

2. The second harmonic enhanced hybrid ferroelectric nematic liquid crystal material according to claim 1, characterized in that: The mass fraction of the small molecules with large dipole moment in the mixture is 2% to 50%.

3. The second harmonic enhanced hybrid ferroelectric nematic liquid crystal material according to claim 1, characterized in that: After the "head-to-tail" reverse polarization dimer is released, the frequency-doubled light intensity of the mixed ferroelectric nematic liquid crystal material increases by 0.5 to 5 times. The macroscopic polarity of the ferroelectric nematic liquid crystal material is enhanced because the net polarization intensity of the material system increases after the "head-to-tail" reverse polarization is cancelled, making the macroscopic polarity of the entire mixed system stronger.

4. The second harmonic enhanced hybrid ferroelectric nematic liquid crystal material according to claim 1, characterized in that: The multiple of the second harmonic enhancement of the ferroelectric nematic liquid crystal is related to the dipole moment of the doped small molecules and the doping concentration.

5. The second harmonic enhanced hybrid ferroelectric nematic liquid crystal material according to claim 1, characterized in that: The doped large dipole molecules are non-polar crystal materials, non-polar liquid crystal materials or polar liquid crystal materials. The ferroelectric nematic liquid crystal material can improve the second harmonic intensity of the mixed liquid crystal as long as it is mixed with molecules containing large dipole moments.

6. The second harmonic enhanced hybrid ferroelectric nematic liquid crystal material according to claim 1, characterized in that: The temperature range of the mixed ferroelectric nematic liquid crystal material is between 25°C and 128°C.

7. The second harmonic enhanced hybrid ferroelectric nematic liquid crystal material according to claim 5, characterized in that: The second harmonic response characteristic of the mixed ferroelectric nematic liquid crystal material is 60-450 times that of a quartz crystal.

8. The method for realizing second harmonic enhancement using the mixed ferroelectric nematic liquid crystal material according to any one of claims 1 to 7, characterized in that: The enhancement of the second harmonic can only be achieved by eliminating the dimers with reverse polarization arrangement in the ferroelectric nematic phase liquid crystal material and increasing the spontaneous polarization alignment of the material system.

9. The method according to claim 8, characterized in that: The mixed ferroelectric nematic liquid crystal material can adjust the degree of disassembly of reverse polarization aligned dimers as the doping concentration of different large dipole molecules changes. The greater the degree of dimer disassembly, the stronger the macroscopic polarity of the mixed ferroelectric nematic liquid crystal material.

10. The method according to claim 8, characterized in that: After the material system is doped with small molecules with different dipole moments, the second-order nonlinear coefficient of the mixture increases with the increase of the dipole moment. (2) The value range is 4~35pm / V.

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