A Dynamic Regulation Method for Nonlinear Absorption Coefficient and Nonlinear Refractive Index of Gold Nanofilm

Abstract

The present invention discloses a method for dynamically regulating the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer thin film, belonging to the technical field of nonlinear optics. This method uses physical vapor deposition technology to deposit a layer of gold nanometer thin film on a quartz glass sheet, connects metal wire electrodes at both ends of the gold nanometer thin film, and connects to a DC power supply to form an electrical circuit. By changing the voltage of the DC power supply, due to the Joule heat effect, the temperature of the gold nanometer thin film increases with the increase of the voltage, increasing the electron-phonon scattering probability in the gold nanometer thin film, and further adjusting its optical damping coefficient, so as to realize the dynamic regulation of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film. The present invention combines the optical, electrical, and thermal properties of the gold nanometer thin film, proposes based on the electrothermal effect, uses DC voltage to modulate the electron-phonon scattering and optical damping coefficient of the gold nanometer thin film, and further realizes the purpose of modulating the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film.

Description

Technical Field

[0001] The present invention belongs to the technical field of nonlinear optics, and particularly relates to a method for dynamically regulating the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer thin film. Background Art

[0002] Gold nanometer thin films have unique surface plasmon resonance characteristics, making them have important application prospects in the fields of optics, sensing, optoelectronics, etc. Surface plasmon resonance is generated by the collective resonance of surface free electrons and incident optical electric fields in metal nanomaterials. Compared with semiconductor or transparent dielectric materials, in gold nanometer thin films, the coupling of light and free electrons produces more significant field enhancement and ultrafast time response, thus greatly enhancing the nonlinear optical response of gold nanometer thin films.

[0003] Nonlinear optics is a physical phenomenon that occurs when a strong optical field interacts with matter. Under the action of low-intensity light, the optical response of the material is linearly related to the electric field amplitude. However, under the action of high-intensity light, the interaction between light and matter becomes more complex, resulting in nonlinear effects such as self-focusing, solitons, and high-order harmonics. The strong light absorption characteristics of gold nanometer thin films effectively excite free electrons. This strong light absorption generates non-equilibrium electron populations in the conduction band, resulting in its relatively high third-order nonlinearity, also known as Kerr nonlinearity. This Kerr nonlinearity is manifested as the changes in the real and imaginary parts of the refractive index with light intensity, corresponding to nonlinear refraction and nonlinear absorption respectively. Nonlinear refraction corresponds to the dependence of the phase on the intensity when the light field propagates in the material, resulting in self-focusing or self-defocusing effects of the light field; nonlinear absorption corresponds to the dependence of the absorption of the material on the intensity, resulting in the occurrence of effects such as saturable absorption and reverse saturable absorption of the material. The Kerr nonlinear optical characteristics of gold nanometer thin films play an important role in the generation of ultrashort pulse lasers, all-optical signal processing, and ultrafast optical switches.

[0004] Introducing a function for dynamically regulating the nonlinear optical properties in gold nanometer thin films will greatly expand their application fields. However, the free electron density in metals is too high (n B is approximately 5.9×10 22 cm -3 ), and it is very difficult to regulate. An effective method is to prepare an ultrathin gold film (with a thickness of t), and its surface free electron density n S = n B t. When the thickness of the ultrathin gold film is only a few nanometers, its surface electron concentration can be reduced to approximately 10 16 cm -2The magnitude is even lower. In this way, the surface electron concentration can be effectively regulated by external regulation, and then the optical properties of the ultrathin gold film can be regulated. However, at present, it is still very difficult to prepare an ultrathin continuous gold film. Moreover, there is no report on dynamically modulating the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer film by electrical regulation.

[0005] Therefore, exploring a dynamic regulation method for the nonlinear optical properties of gold nanometer films has important theoretical significance and practical application value. Summary of the Invention

[0006] Aiming at the problem that the nonlinear optical properties of gold nanometer films are difficult to dynamically regulate in the prior art, the present invention provides a dynamic regulation method for the nonlinear absorption coefficient and nonlinear refractive index of gold nanometer films, which combines the optical, electrical, and thermal properties of gold nanometer films, proposes a method based on the electrothermal effect, and uses a DC voltage to modulate the electron-phonon scattering and its optical damping coefficient of the gold nanometer film, so as to achieve the purpose of modulating the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer film.

[0007] The present invention is realized through the following technical solutions:

[0008] A dynamic regulation method for the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer film specifically includes the following content: using physical vapor deposition technology to evaporate a gold nanometer film on a quartz glass sheet, connecting metal wire electrodes at both ends of the gold nanometer film, and connecting to a DC power supply to form an electrical circuit; by changing the voltage of the DC power supply, due to the Joule heat effect, the temperature of the gold nanometer film increases with the increase of the voltage, increasing the probability of electron-phonon scattering in the gold nanometer film, and then adjusting its optical damping coefficient to achieve the dynamic regulation of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer film.

[0009] Further, the physical vapor deposition technology includes vacuum thermal evaporation, magnetron sputtering, or vacuum ion plating.

[0010] Further, by changing the voltage of the DC power supply to achieve the dynamic regulation of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer film, it specifically includes the following content:

[0011] By gradually increasing the voltage of the DC power supply, the temperature of the gold nanometer film will increase with the increase of the voltage, and use a Z-scan device to test the Z-scan curve of the gold nanometer film at different voltages to obtain the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer film at different voltages.

[0012] Further, the range of changing the DC power supply voltage is 0-10V, and the corresponding range of adjusting the surface temperature of the gold nanometer film is 299-353K.

[0013] Furthermore, the range of the changed DC power supply voltage is 0 to 10 V, and the corresponding change range of the optical damping coefficient of the gold nanometer thin film is 85.5 to 98.3 meV.

[0014] Furthermore, when the voltage of the DC power supply increases from 0 V to 10 V, the corresponding non-linear absorption coefficient of the gold nanometer thin film changes from -10×10 -5 m / W to -5.98×10 -5 m / W, and the non-linear refractive index of the gold nanometer thin film changes from -10×10 -12 m 2 / W to -6.73×10 -12 m 2 / W.

[0015] Furthermore, the regulation method specifically includes the following steps:

[0016] Step 1: First, ultrasonically clean the quartz glass sheet successively with acetone, ethanol, and deionized water, and dry it in a vacuum drying oven; then, use a vacuum evaporation coating instrument to evaporate a layer of copper thin film on the quartz glass sheet as a seed layer; finally, use the vacuum evaporation coating instrument to evaporate a layer of gold thin film at the position of the copper thin film to obtain a gold nanometer thin film;

[0017] Step 2: Place two metal wires at both ends of the gold nanometer thin film prepared in Step 1 respectively, and drop conductive silver glue at the contact points, and wait for it to dry naturally in the air; then, connect the two metal wires integrated with the above gold nanometer thin film to a DC power supply to form a closed loop.

[0018] Furthermore, in Step 1, the size of the quartz glass sheet is 30 mm×30 mm×1 mm; the cleaning time is 10 to 30 minutes, the drying time is 2 to 4 hours, the size of the copper thin film is 17 mm×3.5 mm, and the evaporation speed of the copper thin film is The size of the gold thin film is 17 mm×3.5 mm, and the evaporation speed of the gold thin film is

[0019] Furthermore, in Step 1, the thickness of the evaporated copper thin film is 1 to 5 nm, and the thickness of the evaporated gold thin film is 10 to 50 nm.

[0020] Furthermore, in Step 1, the shape of the obtained gold nanometer thin film is rectangular, the short side length range is 2 to 8 mm, and the long side length range is 10 to 30 mm.

[0021] The advantages of the present invention are as follows:

[0022] 1. A method for dynamically regulating the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer thin film according to the present invention combines the optical, electrical, and thermal properties of the gold nanometer thin film. By adjusting the voltage applied to the gold nanometer thin film, changing the temperature of the gold nanometer thin film, and the electron-phonon scattering probability and optical damping coefficient in the gold nanometer thin film, the dynamic modulation of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film is realized. It has a compact structure, simple operation, low cost, and can be integrated into optoelectronic devices for electrically regulated dynamic optical modulation.

[0023] 2. The gold nanometer thin film prepared according to the present invention does not require complex technologies such as photolithography, has a simple technological process, and a wide range of applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. In all the drawings, similar elements or parts are generally identified by similar reference numerals. In the drawings, the elements or parts are not necessarily drawn to scale.

[0025] Figure 1 It is a schematic structural diagram of an electrically regulated device based on a gold nanometer thin film according to the present invention;

[0026] Figure 2 It is an atomic force microscope image of a gold nanometer thin film according to the present invention;

[0027] Figure 3 It is a curve of the relationship between the temperature of a gold nanometer thin film and the applied voltage and a temperature image taken by an infrared thermal imager according to the present invention;

[0028] Figure 4 It is a curve of the relationship between the optical damping coefficient of a gold nanometer thin film and the applied voltage according to the present invention;

[0029] Figure 5 It is the absorption spectrum of a gold nanometer thin film under different voltages according to the present invention;

[0030] Figure 6 It is a schematic structural diagram of a Z-scan device for testing the nonlinear optical properties of a gold nanometer thin film under different voltages according to the present invention;

[0031] Figure 7 It is a curve of the relationship between the normalized transmittance of a gold nanometer thin film and the position under different voltages measured by open-aperture Z-scan and the relationship between the nonlinear absorption coefficient of the gold nanometer thin film and the voltage according to the present invention;

[0032] Among them, (a) is a curve of the relationship between the normalized transmittance of a gold nanometer thin film and the position under different voltages measured by open-aperture Z-scan according to the present invention;

[0033] (b) is the relationship between the nonlinear absorption coefficient of a gold nanometer thin film and the voltage according to the present invention;

[0034] Figure 8 This is the curve of the normalized transmittance of the gold nanometer thin film versus position under different voltages in the closed-aperture Z-scan test of the present invention, and the relationship between the nonlinear refractive index of the gold nanometer thin film and the voltage.

[0035] Among them, (a) is the curve of the normalized transmittance of the gold nanometer thin film versus position under different voltages in the closed-aperture Z-scan test of the present invention;

[0036] (b) is the relationship between the nonlinear refractive index of the gold nanometer thin film of the present invention and the voltage;

[0037] In the figure: 1. Pump laser, 2. Tunable attenuator, 3. Collimator, 4. Beam splitter, 5. Power meter, 6. Focusing lens, 7. Electrically tunable device based on gold nanometer thin film, 8. Electric displacement platform, 9. Beam splitter, 10. Focusing lens, 11. Power meter, 12. Small aperture diaphragm, 13. Focusing lens, 14. Power meter, 71. Quartz glass, 72. Gold nanometer thin film, 73. Conductive silver paste, 74. Silver wire, 75. DC power supply. Specific embodiments

[0038] To clearly and completely describe the technical solution of the present invention and its specific working process, in combination with the accompanying drawings of the specification, the specific embodiments of the present invention are as follows:

[0039] Example 1

[0040] Preparation of an electrically tunable device based on a gold nanometer thin film:

[0041] Figure 1 is a schematic structural diagram of an electrically tunable device based on a gold nanometer thin film. The preparation method of the gold nanometer thin film is as follows: First, a quartz glass sheet with a size of 30 mm × 30 mm × 1 mm is ultrasonically cleaned with acetone, ethanol, and deionized water for 30 minutes in sequence, and dried in a vacuum drying oven for 2 hours; then, a copper thin film with a size of 17 mm × 3.5 mm and a thickness of 1 nm is evaporated on the quartz glass sheet 71 by a vacuum evaporation coater, and the evaporation rate is After that, a gold thin film 72 with a thickness of 15 nm is evaporated at the original copper film position by the vacuum evaporation coater, and the evaporation rate is To obtain the gold nanometer thin film.

[0042] As Figure 1 shown, two silver wires 74 are respectively placed at both ends of the above-prepared gold nanometer thin film, and conductive silver paste 73 is dropped to fix them, and they are allowed to dry naturally in the air. Finally, the two electrodes of the gold nanometer thin film are connected to a DC power supply 75 to form a closed loop.

[0043] Figure 2It is the atomic force microscope photograph of the gold nanometer thin film. Using a copper thin film as the seed layer is beneficial to increasing the adhesion of the gold nanometer thin film and reducing the surface roughness of the gold nanometer thin film. According to atomic force microscope analysis, the root mean square surface roughness of the prepared gold nanometer thin film is about 1.08 nm.

[0044] After connecting the silver wire electrodes to the above-mentioned gold nanometer thin film, the total resistance between the two wire electrodes is measured to be about 21 Ω. Then, the two silver wire electrodes of the gold nanometer thin film are connected to a DC power supply to form a closed loop. By increasing the voltage of the above power supply, due to the Joule heat effect, the temperature of the gold nanometer thin film will gradually increase. As Figure 3 shown, when the power supply voltage increases from 0 V to 10 V, the temperature of the gold nanometer thin film increases from 299 K to 353 K.

[0045] After the temperature of the gold nanometer thin film increases, the electron-phonon scattering in the gold nanometer thin film will be significantly enhanced, resulting in a gradual increase in the optical damping coefficient of the gold nanometer thin film. As Figure 4 shown, through theoretical calculation, when the power supply voltage increases from 0 V to 10 V, the optical damping coefficient of the gold nanometer thin film increases from 85.5 meV to 98.3 meV.

[0046] Figure 5 It is the absorption spectrum of the gold nanometer thin film under different voltages. As the voltage increases, the optical damping coefficient of the gold nanometer thin film increases, resulting in a change in the gold dielectric constant. Finally, the absorption of the gold nanometer thin film gradually decreases.

[0047] Example 2

[0048] Electrically controlling the nonlinear optical properties of the gold nanometer thin film:

[0049] Figure 6 It is the schematic structural diagram of the Z-scan device for testing the nonlinear optical properties of the gold nanometer thin film under different voltages in the embodiment of the present invention. Using this device, the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film can be measured simultaneously. The pump laser 1 is a femtosecond fiber laser with a working wavelength of 1990 nm, a repetition frequency of 48 MHz, and a pulse width of 150 fs. The adjustable attenuator 2 is used to adjust the power of the pump light. The pump light is collimated by a collimator 3 with a focal length of 18.4 mm. Then, the collimated pump light is split into two beams by a beam splitter 4 with a ratio of 1:9. One of the beams is used as the reference light, and the power is recorded by a power meter 5; the other beam of light is focused by a lens 6 with a focal length of 150 mm. The beam waist radius of this beam at the focus is 50.7 μm. After calculation, the peak power density of the pump light at the focus is 84 MW / cm 2Place the electro-optically tunable device 7 based on the gold nanofilms on the motorized translation stage 8, and move it along the beam direction Z near the focus. The beam passes through the gold nanofilm 72 and is split into two beams by a 5:5 beam splitter 9. One of the beams is focused by a lens 10, and the power is recorded by a power meter 11. This optical path is the open-aperture Z-scan arm. The other beam first passes through a small aperture stop 12, then is focused by a lens 13, and finally the power is recorded by a power meter 14. This optical path is the closed-aperture Z-scan arm.

[0050] Each time the voltage applied to the gold nanofilm is changed, a set of Z-scan data is recorded, and the corresponding relationship between the transmittance of different gold nanofilm and the voltage can be obtained. As Figure 7 shown in (a), the data points are the curves of the normalized transmittance of the gold nanofilm versus the position Z under different voltages in the open-aperture Z-scan test, and the solid lines are the theoretically fitted curves. It can be seen from the figure that as the gold nanofilm gradually approaches the focus (Z = 0), its transmittance gradually increases, indicating that the gold nanofilm exhibits saturable absorption characteristics. By curve fitting, the nonlinear absorption coefficients of the gold nanofilm under different voltages can be calculated. As Figure 7 shown in (b), when the voltage of the gold nanofilm increases from 0 V to 10 V, its nonlinear absorption coefficients are -10×10 -5 m / W, -9.97×10 - 5 m / W, -9.69×10 -5 m / W, -9.3×10 -5 m / W, -8.23×10 -5 m / W, and -5.98×10 -5 m / W. The results show that the modulation of the nonlinear absorption coefficient of the gold nanofilm can be achieved by electro-optic tuning.

[0051] As Figure 8 shown in (a), the data points are the curves of the normalized transmittance of the gold nanofilm versus the position under different voltages in the closed-aperture Z-scan test, and the solid lines are the theoretically fitted curves. The "peak-valley" structure of the curves indicates that the gold nanofilm exhibits self-defocusing characteristics. By curve fitting, the nonlinear refractive indices of the gold nanofilm under different voltages can be calculated. As Figure 8 shown in (b), when the voltage of the gold nanofilm increases from 0 V to 10 V, its nonlinear refractive indices are -10×10 -12 m 2 / W, -9.88×10 - 12 m 2 / W, -9.49×10 -12 m 2 / W, -8.79×10 -12 m 2 / W, -8.07×10-12 m 2 / W, and -6.73×10 -12 m 2 / W. The results show that the modulation of the nonlinear absorption coefficient of the gold nanometer thin film can be realized by electrical regulation.

[0052] Note that the 'negative sign' of the nonlinear absorption coefficient only represents the saturable absorption property, and the 'negative sign' of the nonlinear refractive index only represents the self-defocusing property. It can be seen from the test results that the absolute values of the nonlinear absorption coefficient and the nonlinear refractive index of the gold nanometer thin film decrease with the increase of the applied voltage. This is because, with the increase of the voltage, the temperature of the gold nanometer thin film rises, resulting in an increase in the electron-phonon scattering probability therein, an increase in its optical damping coefficient, and thus causing changes in its nonlinear refractive index and nonlinear absorption coefficient.

[0053] The preferred embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solutions of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0054] In addition, it should be noted that, in the case of no contradiction, the various specific technical features described in the above specific embodiments can be combined in any appropriate manner. To avoid unnecessary repetition, the present invention will not separately describe various possible combination methods.

[0055] In addition, any combination can be made between various different embodiments of the present invention, as long as it does not violate the idea of the present invention, and it should also be regarded as the content disclosed by the present invention.

Claims

1. A method for dynamically regulating the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer thin film, characterized in that Specifically, it includes the following: A gold nanometer thin film is evaporated on a quartz glass sheet by physical vapor deposition technology. Metal wire electrodes are connected to both ends of the gold nanometer thin film and connected to a DC power supply to form an electrical circuit. By changing the voltage of the DC power supply, due to the Joule heat effect, the temperature of the gold nanometer thin film increases with the increase of the voltage, which increases the electron-phonon scattering probability in the gold nanometer thin film, and then adjusts its optical damping coefficient to achieve dynamic regulation of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film. Among them, by changing the voltage of the DC power supply to achieve dynamic regulation of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film, specifically including the following: By gradually increasing the voltage of the DC power supply, the temperature of the gold nanometer thin film will increase with the increase of the voltage, and the Z-scan curve of the gold nanometer thin film is measured by a Z-scan device at different voltages to obtain the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film at different voltages. The range of changing the voltage of the DC power supply is 0 - 10V, and the corresponding range of the surface temperature adjustment of the gold nanometer thin film is 299 - 353K. The range of changing the voltage of the DC power supply is 0 - 10V, and the corresponding range of the change of the optical damping coefficient of the gold nanometer thin film is 85.5 - 98.3 meV. When the DC power supply voltage increases from 0V to 10V, the corresponding nonlinear absorption coefficient of the gold nanometer thin film changes from -10×10 - 5 m / W to -5.98×10 -5 m / W, and the nonlinear refractive index of the gold nanometer thin film changes from -10×10 -12 m 2 / W to -6.73×10 -12 m 2 / W.

2. The dynamic regulation method of the nonlinear absorption coefficient and nonlinear refractive index of the gold nanometer thin film according to claim 1, wherein, The physical vapor deposition technology includes vacuum thermal evaporation, magnetron sputtering or vacuum ion plating.

3. The dynamic regulation method for the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer thin film according to claim 1, characterized in that, The regulation method specifically includes the following steps: Step 1: First, the quartz glass sheet is ultrasonically cleaned with acetone, ethanol and deionized water in sequence and dried in a vacuum drying oven. Then, a copper thin film is evaporated on the quartz glass sheet by a vacuum evaporation coater as a seed layer. Finally, a gold thin film is evaporated at the position of the copper thin film by the vacuum evaporation coater to obtain a gold nanometer thin film. Step 2: Two metal wires are respectively placed at both ends of the gold nanometer thin film prepared in Step 1, and conductive silver paste is dropped at the contact points and left to dry naturally in the air. Then, the two metal wires integrated with the above gold nanometer thin film are connected to a DC power supply to form a closed loop.

4. The dynamic regulation method of the nonlinear absorption coefficient and the nonlinear refractive index of the gold nanometer thin film according to claim 3, characterized in that In Step 1, the size of the quartz glass sheet is 30 mm × 30 mm × 1 mm; the cleaning time is 10 to 30 minutes, the drying time is 2 to 4 hours, the size of the copper thin film is 17 mm × 3.5 mm, and the deposition rate of the copper thin film is 0.5 to The size of the gold thin film is 17 mm × 3.5 mm, and the deposition rate of the gold thin film is 0.3 to 5. The dynamic regulation method of the nonlinear absorption coefficient and nonlinear refractive index of a gold nanometer thin film according to claim 3, characterized in that In Step 1, the thickness of the evaporated copper thin film is 1 - 5nm, and the thickness of the evaporated gold thin film is 10 - 50nm.

6. The dynamic regulation method of the nonlinear absorption coefficient and the nonlinear refractive index of the gold nanometer thin film according to claim 3, characterized in that, In Step 1, the shape of the obtained gold nanometer thin film is rectangular, the short side length range is 2 - 8mm, and the long side length range is 10 - 30mm.

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