Laser limiting method based on light-controlled particle polarity-reversed suspension, materials and applications

Abstract

The application provides a laser limiting method, material and application based on light-controlled particle polarity inversion suspension, and relates to the fields of nonlinear optics and laser protection. The method comprises the following steps: constructing a target suspension theoretical model meeting a polarity inversion condition; preparing the target suspension based on the target suspension theoretical model; shooting laser into the target suspension to realize laser limiting; verifying the transmittance of the output laser; if the weak light transmittance and the strong light transmittance meet expected values, it is determined that the current target suspension meets the requirements; if any one of the weak light transmittance or the strong light transmittance does not meet the expected values, the target suspension is prepared again until the current target suspension meets the requirements. The method experimentally verifies the stable transmission and high transmittance of 1064 nm weak signal light based on the light-controlled particle polarity inversion suspension. For stronger laser, the method realizes the inversion of the suspension polarization rate, and then realizes the high attenuation of 1064 nm strong laser, and achieves the purpose of nonlinear optical limiting.

Description

Technical Field

[0001] This invention relates to the fields of nonlinear optics and laser protection, and in particular to a laser limiting method, material, and application based on a light-controlled particle polarity reversal suspension. Background Technology

[0002] With the continuous development of high-power lasers, protection for personnel and sensitive optoelectronic equipment under high-power laser irradiation is needed in fields such as laser processing, laser medicine, and laser detection. Laser protection technology has increasingly become a research hotspot in the field of laser application technology. The essence of laser protection technology is laser limiting technology, which limits the energy density and power density of the incident laser to protect personnel and equipment under laser irradiation. Simultaneously, due to the advantages of strong monochromaticity, good directionality, and high brightness, lasers are often used as a signal transmission medium. Therefore, limiting protection is necessary for high-power lasers, while low-power signal lasers do not require limiting.

[0003] Currently, commonly used laser limiting technologies can be divided into three main categories based on their principles: optical limiting technology based on phase transition principles, optical limiting technology based on linear optics principles, and optical limiting technology based on nonlinear optics principles. Among these, optical limiting technology based on phase transition principles requires a certain recovery time during the process of the material transitioning from a metallic to a semiconductor state. During this time, the phase transition material exhibits low transmittance, and the photoelectric sensor cannot receive signals normally. Laser limiting technology based on linear optics principles also has several drawbacks. It is difficult to protect against multi-wavelength lasers, and its transmittance cannot be dynamically adjusted according to the intensity of the incident laser, making it difficult to meet the requirements of high transmittance for weak signal light and high attenuation for strong harmful light within the same wavelength band. Existing YAG laser protective glasses designs based on the bandgap reflection of one-dimensional photonic crystals operate on linear optics principles, and therefore suffer from the drawback of not being able to dynamically control the laser transmittance according to the laser intensity.

[0004] Optical limiting technology based on nonlinear optics principles can achieve high transmittance for weak light and high attenuation for strong light, thus serving as an effective means of nonlinear laser protection. Currently, most reported nonlinear laser limiting materials can be divided into two categories: solid materials and suspension materials. Compared to suspension materials, solid nonlinear optical limiting materials have a lower damage threshold and are easily damaged under strong light irradiation. Suspended nonlinear optical limiting materials are mainly based on two mechanisms: nonlinear absorption and nonlinear scattering. Nonlinear absorption can effectively reduce the light intensity of relatively strong incident lasers, but it loses its limiting effect when the incident laser power density is too high. On the other hand, nonlinear scattering originates from bubbles generated by the boiling of the solvent in the suspension, resulting in significant solvent consumption due to heating. Therefore, researching a novel nonlinear optical limiting method based on suspension materials to address these challenges is of great significance. Summary of the Invention

[0005] Purpose of the invention: To propose a laser limiting method, material and application based on a light-controlled particle polarity reversal suspension, which achieves high transmittance for weak light while achieving high attenuation for strong light, so as to solve the above-mentioned problems proposed by the prior art.

[0006] Firstly, a laser limiting method based on optically controlled particle polarity reversal suspension is proposed, with the following steps:

[0007] S1. Construct a theoretical model for the target suspension that satisfies the polarity reversal condition;

[0008] S2. Based on the theoretical model of the target suspension, the target suspension is prepared;

[0009] S3. Inject the laser into the target suspension to achieve laser amplitude limiting;

[0010] S4. Verify the transmittance of the laser light incident on the target suspension in step S3:

[0011] If the weak light transmittance is greater than the first expected value and the strong light transmittance is less than the second expected value, then the current target suspension is considered to meet the requirements.

[0012] If either the transmittance under weak or strong light does not meet the expected value, then repeat steps S1 to S3 until the current target suspension meets the requirements.

[0013] In a further embodiment of the first aspect, step S1 further includes:

[0014] S1-1, Determine the polarizability α of the target suspension:

[0015]

[0016] In the formula, V p The volume of solute particles in the target suspension is represented by ε0; the vacuum dielectric constant is represented by m; and the refractive index of solute P is represented by m.

[0017] S1-2, Determine the optical gradient force F that drives the movement of solute P. grad :

[0018]

[0019] In the formula, y is the Laplace operator; I(y) represents the transverse intensity distribution of the power of the Gaussian beam at the beam waist.

[0020] S1-3. Establish the relationship between the transmittance of the target suspension and the incident laser power density:

[0021]

[0022] In the formula, k is the absorption coefficient; N eff Q is the effective particle number; L is the thickness of the suspension; Q is the effective particle number. scat I is the scattering cross section of solute P; ave denoted as average optical power; r as laser spot radius; S0 as the area of ​​the suspension irradiated by the laser; S as the cross-sectional area of ​​the solute particles; R as the ideal gas constant; T as the absolute temperature; c0 as the initial concentration of the suspension; I N This refers to the power density required for the optical gradient force to overcome resistance and propel solute particles.

[0023] In a further embodiment of the first aspect, step S2 further includes:

[0024] S2-1, Screening the solute P and background solvent B for preparing the target suspension;

[0025] S2-2. Using mechanical oscillation and / or ultrasonic oscillation, m groups of solute P of different masses are uniformly dispersed in background solvent B to form m groups of target suspensions; the transmittance of each group of target suspensions under weak light is measured using a spectrometer, and the stability of the target suspensions is compared through a static test.

[0026] S2-3. Judge the performance of the prepared target suspension: If the transmittance and stability of the target suspension under weak light meet the requirements, proceed to step S3; if the requirements are not met, return to step S2-1 to reselect solute P and background solvent B that meet the polarity reversal condition.

[0027] In a further embodiment of the first aspect, the solute P and the background solvent B need to simultaneously satisfy the following conditions:

[0028] Condition 1: The linear refractive index of solute P is less than the linear refractive index of background solvent B, and the deviation value is less than the first predetermined value;

[0029] Condition 2: The nonlinear refractive index of solute P is greater than the nonlinear refractive index of background solvent B, and the deviation value is greater than the second predetermined value.

[0030] Condition 3: Solute P does not react chemically with background solvent B, and P is merely dispersed in B without dissolving.

[0031] In a further embodiment of the first aspect, step S3, which involves directing a laser beam into the target suspension, includes the following stages:

[0032] S3-1, Low light high transmittance stage: When the target suspension is obtained under low incident light power, the refractive index of solute P is less than that of background solvent B. At this time, the suspension is a negative polarization suspension.

[0033] S3-2, High light attenuation stage: As the incident light power increases, according to the optical Kerr effect, when the incident light power exceeds a certain threshold, the refractive index of solute P is greater than that of the background solvent B. At this time, the suspension is transformed into a positive polarization suspension.

[0034] In a further embodiment of the first aspect, the low-light high transmittance stage further includes:

[0035] After the incident laser sub-beams a and b are refracted by solute P, their propagation directions change, and the momentum of the photons also changes accordingly. According to the law of conservation of momentum, the solute P is also subjected to two forces F at this time. a and F b Since the incident laser is a Gaussian beam, its optical power distribution is high at the center of the optical axis and low around the edges. Therefore, the optical power of sub-beam a is greater than that of sub-beam b, which in turn makes F... a Greater than F b ;

[0036] Through orthogonal decomposition, it is determined that solute P is subjected to an optical scattering force F in the same direction as the laser propagation direction. scat And an optical gradient force F that is perpendicular to the optical axis and points outward from the optical axis. grad ;

[0037] In the optical gradient force F grad Under the influence of this, solute P is pushed out of the optical path, reducing scattering during laser transmission and thus increasing the transmittance of the suspension under weak light.

[0038] In a further embodiment of the first aspect, in step S3-1, when the incident light power is less than a preset limit value, the optical gradient force F grad It is also less than the preset limit value, and cannot overcome the resistance of the background solvent B to the solute P; therefore, before step S3-1 occurs, the permeability of the suspension is a constant value.

[0039] In a further embodiment of the first aspect, the high light attenuation stage further includes:

[0040] Optical gradient force F grad The change in direction pushes solute P into the optical path; the concentration of solute P in the optical path increases, which increases scattering during laser transmission and thus reduces the transmittance of the suspension under strong light.

[0041] In a second aspect, the present invention provides a laser limiting material comprising solute P and background solvent B; wherein a stable suspension is formed by mixing solute P into solvent B in a predetermined ratio and then ultrasonically oscillating.

[0042] The solute P is an organic polymer material, and the solvent B is an organic solvent.

[0043] In a further embodiment of the second aspect, in a nonlinear laser limiting structure suitable for a laser wavelength of 1064 nm, the solute P is made of polystyrene microspheres with a particle size of 1.5 μm; and the solvent B is made of carbon disulfide.

[0044] A third aspect of the present invention proposes the application of the aforementioned laser limiting material in the field of laser protection, wherein the laser limiting material is used to make laser protective lenses to protect personnel under laser irradiation; or the laser limiting material is used to make protective panels to protect equipment under laser irradiation.

[0045] In addition, the application of the laser limiting method based on optically controlled particle polarity reversal suspension in the field of laser protection is also proposed.

[0046] Beneficial Effects: This invention provides a laser limiting method based on a light-controlled particle polarity-reversed suspension using solute PS microspheres and background solvent CS2. This method simultaneously achieves stable transmission of weak signal light and high attenuation of strong damaging light. The polarity-reversed suspension is a limiting method utilizing the optical Kerr effect and photomechanical interaction. Compared to traditional suspension-type limiting materials, the polarity-reversed suspension effectively increases the transmittance of weak light, better protecting photosensitive devices while ensuring their normal operation. Since the photomechanical interaction of laser light on the particles in the suspension is wavelength-independent, the limiting method based on the light-controlled particle polarity-reversed suspension is insensitive to the wavelength of the protected laser, achieving wide-band protection. Furthermore, the suspension-type laser limiting material has a high damage threshold. Compared to solid materials, this laser limiting method can effectively protect against higher-power lasers, significantly improving the laser damage threshold of the nonlinear limiter. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the limiting principle of the optically controlled particle polarity reversal suspension of the present invention.

[0048] Figure 2 This is a schematic diagram of the photocontrolled particle technology in polarity reversal suspension of the present invention.

[0049] Figure 3 This is a schematic diagram showing how the transmittance of the polarity-reversed suspension of the present invention changes with the increase of incident light power.

[0050] Figure 4 This is a schematic diagram of the optical path for the optical limiting experiment of the sample suspension.

[0051] Figure 5 The results are from a limiting experiment on the suspension at four different concentrations with incident light wavelengths of 1064 nm.

[0052] Figure 6This is a schematic diagram comparing the experimental results and calculated results of the sample suspension. Detailed Implementation

[0053] In the following description, numerous specific details are set forth in order to provide a more thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can be practiced without one or more of these details. In other instances, certain technical features well-known in the art have not been described in order to avoid obscuring the invention.

[0054] Example 1:

[0055] This embodiment presents a laser limiting method based on a light-controlled particle polarity reversal suspension, specifically including the following steps:

[0056] Step S1: Construct a theoretical model of the target suspension that satisfies the polarity reversal condition. This step is used to analyze the feasibility of the optical limiting method based on the polarity reversal suspension.

[0057] Theoretical model construction. The polarizability of the suspension can be expressed by formula (1):

[0058]

[0059] In the formula, α is the polarizability of the suspension, and V p =4πr 3 / 3 is the volume of the solute particles, ε0 is the vacuum permittivity, and m = n p / n b Let P be the ratio of the refractive indices of solute P to those of the background solvent B. According to formula (1), if the refractive index of the solute is smaller than that of the background solvent, the polarizability of the suspension is negative, and the suspension is a negative polarizability suspension. If the refractive index of the solute is larger than that of the background solvent, the polarizability of the suspension is positive, and the suspension is a positive polarizability suspension.

[0060] The optical gradient force F that drives the movement of solute P grad It can be expressed using formula (2):

[0061]

[0062] In the formula, Let I(y) be the Laplace operator. I(y) represents the transverse intensity distribution of the power of the Gaussian beam at the beam waist.

[0063] Based on Beer Lambert's law, the relationship between the transmittance of the suspension and the incident laser power density can be established, as shown in formula (3):

[0064]

[0065] In the formula, k is the absorption coefficient, and N eff Where L is the effective particle number, Q is the thickness of the suspension, and L is the effective particle number. scat I is the scattering cross section of solute P. ave R is the average optical power, r is the laser spot radius, S0 is the area of ​​the suspension irradiated by the laser, S is the cross-sectional area of ​​the solute particles, and R = 8.314 J·K. -1 ·mol -1 Here, T is the ideal gas constant, T is the absolute temperature, c0 is the initial concentration of the suspension, and I is the initial concentration of the suspension. N For the optical gradient force F grad The power density required to overcome resistance and propel solute particles.

[0066] Figure 3 The curves showing the transmittance versus incident laser power density in a polarity-reversed suspension, plotted according to Formula 3. Figure 3 As shown, with the increase of incident light power density, the transmittance of the suspension went through three stages: constant transmittance, increased transmittance, and decreased transmittance. Figure 3 In the diagram, points parallel to the horizontal direction represent the stage where transmittance remains constant, when the incident light power density is less than the self-focusing threshold I. N At this point, the suspension exhibits linear optical properties with a constant transmittance. Subsequently, when the incident light power density exceeds the self-focusing threshold I... N Afterwards, the optical gradient force F grad Overcoming solvent resistance and propelling particle movement alters the concentration distribution of particles in the suspension. Following this, the suspension exhibits a self-focusing nonlinear refraction phenomenon (points in the rising and falling segments of Figure (3)). Figure 3 In the diagram, the points in the rising segment represent the increasing stage of the suspension's transmittance, at which point the incident light power density is between the self-focusing threshold I. N and inversion threshold I inv During this period, because the suspension is originally NP-type, the optical gradient force pushes the solute particles out of the light path, reducing the scattering effect on the light path. Simultaneously, the change in particle concentration alters the refractive index distribution within the suspension, resulting in self-focusing. Therefore, during this stage, the transmittance of the suspension increases with increasing incident light power density. Figure 3 In the diagram, the points in the falling segment represent the decreasing phase of the suspension transmittance. This is because the incident light power density further increases and exceeds the inversion threshold I. inv Subsequently, due to the optical Kerr effect, the suspension undergoes a polarity reversal, transforming into a PP suspension. The solute particles are then subjected to an optical gradient force F. grad Under the influence of the incident light power density, the light beam is focused onto the optical path, increasing scattering and absorption during laser transmission. Simultaneously, as the incident light power density increases, the self-focusing effect intensifies, causing beam instability and collapse. Therefore, during this stage, the transmittance of the suspension decreases with increasing incident light power density.

[0067] Step S2: Based on the theoretical model of the target suspension, the target suspension is prepared.

[0068] Polarity reversal refers to the change in polarizability of a suspension from negative to positive (or from positive to negative) as the incident light power increases from weak to strong, thereby causing the suspension to exhibit opposite nonlinear optical properties under different incident light powers.

[0069] The target suspension has a high transmittance to low-power incident lasers, generally greater than 90%, and a low transmittance to high-power incident lasers, generally less than 30%. Furthermore, considering practical applications, the target suspension also needs to possess a certain degree of stability to prevent sedimentation or aggregation that could cause the suspension to lose its function.

[0070] The preparation process is as follows:

[0071] Step S2-1: Screening the solute P and background solvent B for preparing the suspension. According to the optical Kerr effect, the actual refractive index of a substance changes with the incident light power, i.e., n = n0 + γI (n is the actual refractive index of the substance, n0 is the linear refractive index, γ is the nonlinear refractive index, and I is the incident light power). By selecting a solute P with a linear refractive index close to that of the background solvent B (n0 is the linear refractive index of the substance, γ is the nonlinear refractive index, and I is the incident light power), the suspension can be prepared. 0p <n 0b At the same time, it ensures that the nonlinear refractive index of solute P is much greater than that of the background solvent B (γ). P >>γ B This allows the prepared suspension to meet the polarity reversal condition;

[0072] Step S2-2: Solute P of different masses and background solvent B are thoroughly mixed to form multiple suspensions. Since the concentration of solute P affects the transmittance of the suspension under weak light, and the stability of the suspension is also affected by the solute concentration, multiple suspensions of different concentrations need to be prepared to obtain suspensions with excellent amplitude limiting effect, and their transmittance and stability under weak light need to be compared. Mechanical oscillation and ultrasonic oscillation methods can be used to uniformly disperse solute P in the background solvent B to form a suspension. Then, the transmittance of each suspension under weak light is measured using a spectrometer, and the stability of the suspensions is compared through a static test.

[0073] Step S2-3: Judge the results of the prepared suspension. If the transmittance and stability of the suspension under weak light meet the requirements, proceed to step S3; if not, return to step S2-1 and reselect solute P and background solvent B that meet the polarity reversal condition.

[0074] In the above process, the following should also be noted regarding the selection of solute P and background solvent B:

[0075] Solute P does not react chemically with the background solvent B, and P is merely dispersed in B without dissolving.

[0076] The relevant parameters of solute P and background solvent B can be obtained from z-scan experiments or by directly consulting literature.

[0077] Background solvent B can be a mixture of two solvents, thereby controlling its linear transmittance to make it sufficiently close to the refractive index of solute P.

[0078] Step S3: Use the target suspension to achieve laser limiting with high transmittance for weak light and high attenuation for strong light.

[0079] The nonlinear optical effects of the target suspension mainly originate from the changes in the direction of optical force under different polarizabilities and the resulting weakening or enhancement of nonlinear scattering. The specific process is as follows:

[0080] Step S3-1: High transmittance of the suspension under low incident light power. Based on the obtained target suspension, under low incident light power, the refractive index of solute P is less than that of the background solvent B (n... p <n b At this point, the suspension is a negative polarizability suspension (NP). For example... Figure 2 As shown in (a), after sub-beams a and b are refracted by solute P, their propagation directions change, and the momentum of the photons also changes accordingly. According to the law of conservation of momentum, solute P is also subjected to two forces F at this time. a and F b Since the incident laser is a Gaussian beam, its power distribution is high at the center of the optical axis and low around the edges. Therefore, the power of sub-beam a is greater than that of sub-beam b, which in turn makes F... a Greater than F b Through orthogonal decomposition, it can be determined that the solute P is subjected to an optical scattering force F in the same direction as the laser propagation direction. scat And an optical gradient force F that is perpendicular to the optical axis and points outward from the optical axis. grad In the optical gradient force F grad Under the influence of [the light source], solute P is pushed out of the optical path, reducing scattering during laser transmission and thus increasing the transmittance of the suspension under weak light, such as [the light source]. Figure 1 As shown in (a).

[0081] Step S3-2: High attenuation of strong light in the suspension. As the incident light power increases, according to the optical Kerr effect, when the incident light power exceeds a certain threshold, the refractive index of solute P becomes greater than that of the background solvent B (n). p >n b At this point, the suspension transforms into a positively polarizable suspension (PP). For example... Figure 2 As shown in (b), the optical gradient force F gradThe change in direction pushes solute P into the optical path. The increased concentration of solute P in the optical path increases scattering during laser transmission, thereby reducing the transmittance of the suspension under strong light, such as... Figure 1 As shown in (b).

[0082] In step S2-1, when the incident light power is extremely small, the optical gradient force F grad If the value is too small, it cannot overcome the resistance of the background solvent B to the solute P. Therefore, before step S2-1 occurs, the permeability of the suspension is a constant value.

[0083] Step S4: Verify the transmittance of the laser beam that was injected into the target suspension in step S3.

[0084] Experimental results of multi-concentration polarity reversal suspensions: Figure 4 The optical path and sample suspension used in the optical limiting experiment are shown. The laser source used in the experiment is a 1064nm Nd:YAG laser with a repetition rate of 1Hz and a pulse width of 10ns. The laser beam output from the laser is split into two beams by a 1:1 beam splitter after passing through an adjustable attenuator. Energy meter 1 is used to record the energy of the laser pulse reflected by the beam splitter, and the attenuator in front of it is used to protect the energy meter. The suspension is placed at the focal point of the lens, and the transmission image of the laser in the suspension is captured by a side camera. After the laser beam passing through the beam splitter is focused and illuminates the sample, its pulse energy is measured by energy meter 2. A photograph of the sample suspension placed in a cuvette is shown. Figure 4 The illustration shows that the permeability of the suspension can be obtained by comparing the energy densities measured in energy meters 1 and 2.

[0085] For 1064nm lasers, in the limiting method based on optically controlled particle polarity reversal suspension of this invention, the solute P is made of polystyrene microspheres with a linear refractive index of n. p =1.59, nonlinear refractive index coefficient is γ p =10 -14 ~10 -13 m 2 / W; Solvent B is made of carbon disulfide with a linear refractive index of n. b =1.62, nonlinear refractive index coefficient is γ b =10 -18 ~10 - 17 m 2 / W. When the optical power density is less than 160MW / cm² 2 At that time, the laser transmittance was greater than 80%; the optical power density was 260 MW / cm². 2 At that time, the transmittance was 92%; the optical power density was greater than 400 MW / cm². 2At that time, the permeability was less than 30%.

[0086] Figure 5 The figures show the experimental results. As can be seen from the graph, the transmittance trends of each suspension group are consistent with the theoretical model. The suspension with a concentration of 4.72 g / L showed a maximum transmittance of 92% under weak light and a minimum transmittance of 29.9% under strong light, meeting the amplitude limiting requirements of this method.

[0087] Comparison of experimental and calculated results for the sample suspension: Figure 6 This figure compares the experimental and calculated results for the sample suspensions at various concentrations. The points in the figure represent the transmittance of the suspensions measured experimentally at different incident light power densities, while the lines represent the theoretical calculations. Shaded areas represent measurement errors in the experimental results. The trend of the fitted curves in the figure agrees well with the experimental results, and the differences between each group of data and the fitted results are within 5%. Considering the attenuation of the incident laser by the cuvette and lens, as well as the fluctuations in laser output energy, these errors are tolerable. Furthermore, comparing the four sub-figures reveals that the trend of transmittance variation is consistent with our theoretical analysis. Therefore… Figure 6 The results show that our proposed novel laser limiting method has good feasibility.

[0088] Example 2:

[0089] This embodiment discloses a laser limiting material, which consists of solute P and background solvent B. Solute P is mixed into solvent B in a certain proportion, and then ultrasonically vibrated to form a stable suspension. Solute P is an organic polymer material, and solvent B is an organic solvent.

[0090] Solute P and solvent B are stable and do not react chemically when mixed. When fully mixed, they form a stable polarity-reversed suspension. Because the refractive index of solute P is lower than that of solvent B, the initial polarizability of the suspension is negative. Under the influence of optical force, the solute particles P in the suspension move away from the central optical path, reducing scattering and absorption during laser transmission, thus allowing for higher transmittance of weaker signal light at specific wavelengths. As the incident light power density increases, due to the optical Kerr effect, the refractive index of solute P in the suspension increases and surpasses that of solvent B, causing the suspension to switch to positive polarizability. Under the influence of optical force, solute P accumulates along the optical path, enhancing scattering and absorption during laser transmission, thereby reducing transmittance and achieving high attenuation of highly damaging light.

[0091] Furthermore, in the nonlinear laser limiting structure suitable for a laser wavelength of 1064 nm, the solute P is made of polystyrene microspheres (PS), and the solvent B is made of carbon disulfide (CS2).

[0092] Furthermore, in a nonlinear laser constriction structure suitable for a laser wavelength of 1064 nm, the linear refractive index of solute P is n p =1.59, nonlinear refractive index coefficient is γ p =10 -14 ~10 -13 m 2 / W; the linear refractive index of solvent B is n b =1.62, nonlinear refractive index coefficient is γ b =10 -18 ~10 -17 m 2 / W.

[0093] Furthermore, it is suitable for nonlinear laser limiting structures with a laser wavelength of 1064 nm, where the optical power density is less than 160 MW / cm². 2 At that time, the laser transmittance was greater than 80%; the optical power density was 260 MW / cm². 2 At that time, the transmittance was 92%; the optical power density was greater than 400 MW / cm². 2 At that time, the transmittance was less than 30%.

[0094] Example 3:

[0095] Laser protective lenses can be made using the laser limiting method based on optically controlled particle polarity reversal suspension disclosed in Example 1 and the laser limiting material disclosed in Example 2 to protect personnel under laser irradiation; or the laser limiting material can be used to make protective panels to protect equipment under laser irradiation.

[0096] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A laser limiting method based on a light-controlled particle polarity reversal suspension, characterized in that, Includes the following steps: S1. Construct a theoretical model for the target suspension that satisfies the polarity reversal condition; S2. Based on the theoretical model of the target suspension, the target suspension is prepared; S2-1. Screening the solute P and background solvent B for preparing the target suspension; the material of solute P is polystyrene microspheres, and the material of solvent B is carbon disulfide; S2-2. Using mechanical oscillation and / or ultrasonic oscillation, m groups of solute P of different masses are uniformly dispersed in background solvent B to form m groups of target suspensions; the transmittance of each group of target suspensions under weak light is measured using a spectrometer, and the stability of the target suspensions is compared through a static test. S2-3. Judge the performance of the prepared target suspension: If the transmittance and stability of the target suspension under weak light meet the requirements, proceed to step S3; if they do not meet the requirements, return to step S2-1 to reselect solute P and background solvent B that meet the polarity reversal condition. Wherein, the solute P and the background solvent B must simultaneously satisfy the following conditions: Condition 1: The linear refractive index of solute P is less than the linear refractive index of background solvent B, and the deviation value is less than the first predetermined value; Condition 2: The nonlinear refractive index of solute P is greater than the nonlinear refractive index of background solvent B, and the deviation value is greater than the second predetermined value. Condition 3: Solute P does not react chemically with the background solvent B, and P is merely dispersed in B without dissolving; S3. The laser is injected into the target suspension to achieve laser amplitude limiting; the laser wavelength is 1064 nm. S4. Verify the transmittance of the laser light incident on the target suspension in step S3: If the weak light transmittance is greater than the first expected value and the strong light transmittance is less than the second expected value, then the current target suspension is considered to meet the requirements. If either the transmittance under weak or strong light does not meet the expected value, then repeat steps S1 to S3 until the current target suspension meets the requirements.

2. The laser limiting method based on optically controlled particle polarity reversal suspension according to claim 1, characterized in that, Step S1 further includes: S1-1. Determine the polarizability of the target suspension. : In the formula, This indicates the volume of solute particles in the target suspension; ρ is the vacuum dielectric constant; m is the ratio of the refractive index of solute P to that of background solvent B; S1-2, Determine the optical gradient force that drives the movement of solute P. : In the formula, For the Laplace operator; This represents the transverse intensity distribution of the power of a Gaussian beam at the beam waist. S1-3. Establish the relationship between the transmittance of the target suspension and the incident laser power density: In the formula, k is the absorption coefficient; N eff Q is the effective particle number; L is the thickness of the suspension; Q is the effective particle number. scat I is the scattering cross section of solute P; ave denoted as average optical power; r as laser spot radius; S0 as the area of ​​the suspension irradiated by the laser; S as the cross-sectional area of ​​the solute particles; R as the ideal gas constant; T as the absolute temperature; c0 as the initial concentration of the suspension; I N This refers to the power density required for the optical gradient force to overcome resistance and propel solute particles.

3. The laser limiting method based on optically controlled particle polarity reversal suspension according to claim 2, characterized in that, Step S3 involves directing the laser into the target suspension, which includes the following stages: S3-1, Low light high transmittance stage: When the target suspension is obtained under low incident light power, the refractive index of solute P is less than that of background solvent B. At this time, the suspension is a negative polarization suspension. S3-2, High light attenuation stage: As the incident light power increases, according to the optical Kerr effect, when the incident light power exceeds a certain threshold, the refractive index of solute P is greater than that of the background solvent B. At this time, the suspension is transformed into a positive polarization suspension.

4. The laser limiting method based on optically controlled particle polarity reversal suspension according to claim 3, characterized in that, The low-light high transmittance stage further includes: After the incident laser sub-beams a and b are refracted by solute P, their propagation directions change, and the momentum of the photons also changes accordingly. According to the law of conservation of momentum, the solute P is also subjected to two forces F at this time. a and F b Since the incident laser is a Gaussian beam, its optical power distribution is high at the center of the optical axis and low around the edges. Therefore, the optical power of sub-beam a is greater than that of sub-beam b, which in turn makes F... a Greater than F b ; Through orthogonal decomposition, it is determined that solute P is subjected to an optical scattering force F in the same direction as the laser propagation direction. scat And an optical gradient force F that is perpendicular to the optical axis and points outward from the optical axis. grad ; In the optical gradient force F grad Under the influence of this, solute P is pushed out of the optical path, reducing scattering during laser transmission and thus increasing the transmittance of the suspension under weak light.

5. The laser limiting method based on optically controlled particle polarity reversal suspension according to claim 4, characterized in that, In step S3-1, when the incident light power is less than a preset limit value, the optical gradient force F grad It is also less than the preset limit value, and cannot overcome the resistance of the background solvent B to the solute P; therefore, before step S3-1 occurs, the permeability of the suspension is a constant value.

6. The laser limiting method based on optically controlled particle polarity reversal suspension according to claim 3, characterized in that, The high-attenuation phase of intense light further includes: Optical gradient force F grad The change in direction pushes solute P into the optical path; the concentration of solute P in the optical path increases, which increases scattering during laser transmission and thus reduces the transmittance of the suspension under strong light.

7. A laser limiting material, characterized in that, The laser limiting material is composed of solute P and background solvent B; by mixing solute P into solvent B in a predetermined ratio, a stable suspension is formed by ultrasonic oscillation. The solute P is an organic polymer material, and the solvent B is an organic solvent; In a nonlinear laser limiting structure suitable for a laser wavelength of 1064 nm, the solute P is made of polystyrene microspheres with a particle size of 1.5 μm; the solvent B is made of carbon disulfide. Wherein, the solute P and the background solvent B must simultaneously satisfy the following conditions: Condition 1: The linear refractive index of solute P is less than the linear refractive index of background solvent B, and the deviation value is less than the first predetermined value; Condition 2: The nonlinear refractive index of solute P is greater than the nonlinear refractive index of background solvent B, and the deviation value is greater than the second predetermined value. Condition 3: Solute P does not react chemically with background solvent B, and P is merely dispersed in B without dissolving.

8. The application of the laser limiting material as described in claim 7 in the field of laser protection, characterized in that: Laser protective lenses can be made using the aforementioned laser limiting material to protect personnel exposed to laser radiation. Alternatively, the laser limiting material can be used to make a protective panel to protect equipment exposed to laser irradiation.

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