Low speckle contrast and high reflectivity aerogel optical material, preparation method and application thereof

Abstract

This invention discloses a low speckle contrast, high reflectivity aerogel optical material, its preparation method, and its applications. The low speckle contrast, high reflectivity aerogel optical material comprises a transparent aerogel matrix serving as an optical framework; and light-scattering nanoparticles dispersed therein. The aerogel optical material has a first surface and a second surface arranged opposite to each other in the thickness direction. From the first surface to the second surface, the light-scattering nanoparticles exhibit a graded distribution in particle size, with the particle size gradually increasing. This invention utilizes the ultra-low refractive index of the aerogel to suppress Fresnel interface reflection, improve luminous efficiency, and provide a high refractive index difference. Through a "sedimentation-gel synergy" process, a gradient structure with a continuous particle size distribution in the thickness direction is constructed in situ within a single matrix, simultaneously achieving extremely low speckle contrast (<4%) and high light utilization (average visible light reflectivity >90%), while also possessing advantages such as ultra-light weight and good environmental stability.

Description

Technical Field

[0001] This invention belongs to the field of display and optical materials technology, specifically relating to a low speckle contrast, high reflectivity aerogel optical material and its preparation method, as well as its application in the field of laser projection display. Background Technology

[0002] Laser display technology, with its advantages of high brightness, wide color gamut, and long lifespan, has become the mainstream display technology of the new generation. However, the high coherence of lasers causes coherent interference on the projection screen surface, producing randomly distributed speckles, or "speckle" noise. Speckle significantly reduces image clarity and uniformity, and is a core challenge hindering the widespread adoption of laser projection. Speckle suppression technologies are mainly divided into three categories: using different optical materials at the light source, along the optical path, and at the screen end to suppress speckle.

[0003] Light source suppression technology is mainly achieved by constructing random lasers based on scattering materials: Unlike traditional coherent light sources with fixed resonant cavities, random lasers utilize the multiple scattering of photons by the scattering medium to effectively reduce the coherence of the laser. Patent CN102684063B uses titanium dioxide (TiO2) nanoparticles as random scatterers to obtain white light output with narrow linewidth, high intensity, and low coherence; CN104716553B discloses an optically pumped SiO2... The Rh6G gel random laser and its fabrication method achieve low coherence laser output by utilizing the multiple scattering and gain effect of pump light inside the gel, thereby suppressing speckle at the source.

[0004] At the optical transmission end, the core of speckle suppression lies in modulating the phase and angle of the laser beam by introducing scattering optical materials, diffraction optical materials, or optical beam splitting materials, thereby destroying the coherence of the laser: CN103869475B employs a wedge-shaped disk scattering optical material driven by a motor to generate a dynamic and continuously changing angular distribution. By introducing a transiently changing random phase, it disrupts the temporal coherence of the laser within the integration time, thereby achieving speckle suppression. CN107678171B develops a one-dimensional binary diffraction optical material with different tilt angles. Driven by a motor, the phase distribution of the laser beam is dynamically modulated in time during transmission, achieving decoherence and suppressing speckle. CN207976655U uses an optical beam splitter to divide a laser beam into multiple beams. These sub-beams pass through multiple optical transmission paths with different optical path lengths, ensuring that the optical path difference between any two paths is greater than the coherence length of the laser. Since these sub-beams become incoherent, their individual speckle patterns are also uncorrelated. Finally, after being superimposed by a beam combiner, the speckle contrast is significantly reduced. CN109557680A first uses diffraction elements to decompose the collimated laser into sub-beams of different diffraction orders to reduce spatial coherence; then, the sub-beams are coupled into a multimode optical waveguide, and the transmission delay difference between different modes (greater than the coherence time) is used to further eliminate temporal coherence. By dually controlling spatial and temporal coherence, a better speckle suppression gain is obtained.

[0005] Currently, existing technical solutions for suppressing speckle on screens mainly include: Mechanical vibration / motion screens: Patents CN109917558A and CN107257939A invented a system for vibrating a screen to reduce speckle. Based on a highly reflective optical material (screen), a motor or transducer drives the screen substrate to perform high-frequency micro-vibrations, utilizing the persistence of vision effect to achieve time-averaging of speckle. Patent CN105453545A proposed a projection screen fixing system that uses a mechanical device to move the screen to eliminate image interference.

[0006] Multi-layer composite scattering optical material (screen): Patent CN214795559 U invented a scattering optical material that can be used as a laser projection screen. It adopts a layered superimposed structure, in which the adhesive layer is colored and contains diffusing particles. This structure uses diffusing particles to disperse the light beam, which can improve the overall viewing angle of the product. The scratch-resistant and stain-resistant layer has a small amount of diffusing particles, which has a certain fogging effect. The fog level in this range is not too high to affect the display brightness, and it is not too low to cause reflection. Patent CN214670068 U invented an optical material that can be used as a speckle-reducing projection screen. Its structure includes a functional layer, a substrate layer, a Fresnel lens layer, and a reflective layer arranged sequentially along a first direction. The functional layer is provided with diffusing particles to suppress speckle. Patent CN219831616 U invented an optical material that can be used as a uniform light projection screen. Its structure includes a speckle suppression layer, a filter layer, an air gap layer, a reflective layer, and a backlight protection layer. The speckle suppression layer contains scattering particles, which can reduce the coherence of the projected light and weaken the speckle effect. The air gap layer is used to extend the optical path and weaken the speckle effect.

[0007] Fluid-based optical materials (screens): Patent CN 102402113 A provides an optical material based on transparent bubbles or liquid bubbles, which can be used as an anticoherence screen for laser projection, and the light path can be changed by controlling the expansion or contraction of the bubble.

[0008] However, the aforementioned optical materials still have the following prominent problems in practical applications: 1. System Reliability and Noise: While screens (high-reflectivity optical materials) that apply mechanical vibration, such as those in CN103869475B, CN107678171B, and CN109917558A, are highly effective and have high reflectivity, they rely on moving mechanical components like motors. This not only increases system size and power consumption but also leads to problems like mechanical wear, operating noise, and limited lifespan, hindering miniaturization and quiet operation. Fluid-based optical materials, such as those in CN102402113A, have poor internal phase stability and are easily affected by temperature and gravity, leading to uneven distribution or leakage risks, making their engineering implementation extremely difficult.

[0009] 2. Insufficient speckle suppression rate: (1) For speckle suppression at the light source: Due to the accumulation of the optical material (titanium dioxide nanoparticles) in CN102684063B, only the surface nanoparticles scatter, which cannot make each nanoparticle fully exert its scattering effect. The scattering matrix of CN104716553B is a gel, and the refractive index difference between the matrix and the scattering material is small, resulting in weak scattering ability. These two types of optical materials are difficult to reduce speckle to below 4%; (2) For speckle suppression on the optical path: Due to the limitations of the equipment rotation speed and the sample scattering ability, the rotating scattering sheet of CN103869475B has limited reduction in temporal coherence, which is difficult to reduce speckle. To reduce the speckle contrast to below 4%, the flexible diffraction material of CN107678171B, the diffraction optical device of CN207976655U and CN109557680A have a limited number of beam splits. The limited number of phases of light leads to a limited speckle suppression effect after superposition, and it is also difficult to reduce the speckle contrast to below 4%. (3) For suppressing speckle at the screen end: The high refractive index of the matrix weakens the scattering ability of diffused particles: The matrix material used in the existing screen (such as TPU, with a refractive index of 1.5-1.6) has a refractive index close to that of the scattering particles (such as PMMA, with a refractive index of 1.49), resulting in weak scattering ability. The ability of scattering particles to scatter light is related to the difference in refractive index between the particles and the matrix. The larger the refractive index difference, the stronger the scattering ability. When the particle scattering ability is weak, it is impossible to effectively suppress speckle through scattering.

[0010] 3. Suppressing speckle and reducing light efficiency: (1) Suppressing speckle at the light source: The random lasers of CN102684063B and CN104716553B rely on light scattering, and the directionality of emitted light deteriorates, resulting in a decrease in the proportion of light that can be effectively utilized, causing light loss; (2) Suppressing speckle on the optical path: The diffraction materials of CN107678171B and CN109557680A require the design of complex optical paths to meet the control of the light direction. During use, small changes such as vibration and structural deformation will cause the light to deviate from the original direction, resulting in light loss; In addition, during multiple focusing and reflection, light absorption and interface reflection will occur, reducing the light utilization rate; (3) Suppressing speckle at the screen end: The high refractive index of the matrix causes specular reflection of the screen, affecting light efficiency: Currently, the screen uses conventional high refractive materials such as acrylic resin and PET, with a refractive index of 1.5-1.6. Due to the high refractive index, the surface produces strong Fresnel interface reflection, forming specular reflection that cannot be used for projection imaging. Even with CN214795559U, the addition of diffusing particles to the anti-fouling layer to create a certain degree of fogging still reduces imaging brightness. Interface reflection and structural discontinuities also reduce light efficiency. Layered composite structures like CN214795559U, CN214670068U, and CN219831616U exhibit significant refractive index differences between different material layers, easily leading to severe interface reflection and energy loss. CN219831616U, considering insufficient laser penetration depth, introduces an air gap layer (1000-1500 μm) to extend the light path and increase scattering. While this ensures penetration depth and speckle suppression, the increased screen thickness causes light to scatter laterally due to the excessively long diffusion distance, resulting in image blurring and additional interface energy loss. Summary of the Invention

[0011] The main objective of this invention is to provide a low speckle contrast, high reflectivity aerogel optical material and its preparation method, thereby overcoming the shortcomings of the prior art.

[0012] Another object of the present invention is to provide the application of the aforementioned low speckle contrast and high reflectivity aerogel optical material in the field of laser projection display.

[0013] To achieve the aforementioned objectives, the technical solution adopted by this invention includes: A first aspect of the present invention provides a low speckle contrast, high reflectivity aerogel optical material, comprising: a transparent aerogel matrix serving as an optical framework; and light-scattering nanoparticles dispersed in the transparent aerogel matrix; wherein the low speckle contrast, high reflectivity aerogel optical material has a first surface and a second surface disposed opposite to each other in the thickness direction, and the light-scattering nanoparticles exhibit a size-gradient distribution from the first surface to the second surface, with the particle size of the light-scattering nanoparticles gradually increasing.

[0014] A second aspect of this invention provides a method for preparing a low speckle contrast, high reflectivity aerogel optical material, comprising: Provide aerogel precursor solution; Light-scattering nanoparticles with a graded particle size distribution are added to the aerogel precursor solution and dispersed evenly. A catalyst is added to initiate the sol-gel reaction, and then the mixture is allowed to stand, allowing the light-scattering nanoparticles to settle under gravity. At the same time, the sol gels, forming a gel structure with continuously graded particle sizes in the thickness direction. The obtained gel structure was aged, solvent replaced, and dried to prepare aerogel optical material with low speckle contrast and high reflectivity.

[0015] A third aspect of the present invention provides the application of the aforementioned low speckle contrast, high reflectivity aerogel optical material in the field of laser projection display.

[0016] Furthermore, a fourth aspect of the present invention provides a laser projection display system, characterized in that it includes: the aforementioned low speckle contrast high reflectivity aerogel optical material as a projection display terminal, wherein the first surface of the low speckle contrast high reflectivity aerogel optical material is close to the observation side, and the second surface is away from the observation side.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes the ultra-low refractive index of aerogel to suppress Fresnel interface reflection, increase the proportion of light coupling into the material, improve light efficiency, and provide a high refractive index difference (0.4~0.85) with scattering nanoparticles, thereby enhancing the scattering ability of the scattering nanoparticles. At the same time, through the combination of gravity-driven sedimentation of light-scattering nanoparticles and sol-gel transformation, a gradient structure with continuous particle size variation in the thickness direction is constructed in situ (the size gradually increases from top to bottom). This eliminates the need for multi-layer structures and avoids the addition of extra interfaces that would lead to light efficiency loss. It effectively suppresses speckle and achieves extremely low speckle contrast (<4%) and high light utilization (average visible light reflectance >90%) without any mechanical moving parts. It also has advantages such as being ultra-lightweight and having good environmental stability. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram illustrating the structure and effect of a low speckle contrast, high reflectivity aerogel optical material in a typical embodiment of the present invention. Figure 2 This is a schematic diagram of the preparation process of the low speckle contrast high reflectivity aerogel optical material in Embodiment 2 of the present invention; Figure 3 This is a comparison between the low speckle contrast and high reflectivity aerogel optical material obtained in Embodiment 1 of the present invention and the speckle pattern of a laser projection taken at a distance of about 100 cm using an area array camera on an ordinary screen. Figure 4 The reflectance curve of the low speckle contrast high reflectance aerogel optical material obtained in Example 2 of this invention was tested using an ultraviolet-visible-near-infrared spectrophotometer with an integrating sphere accessory. Figure 5 This is a comparison chart of the color gamut of the low speckle contrast and high reflectivity aerogel optical material obtained in Example 3 of the present invention and that of a conventional screen spectral radiance meter. Figure 6 The visible light average reflectance and speckle contrast of the optical composite materials prepared by different types of nanoparticles in Examples 1, 7, and 8 of this invention are shown. Detailed Implementation

[0020] Addressing the challenges of existing laser display technologies, such as the inability to simultaneously achieve high laser reflectivity (luminous efficiency) and strong speckle suppression, as well as the large size and limited lifespan of mechanical vibration solutions, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The invention primarily provides a low speckle contrast, high reflectivity aerogel optical material and its preparation method, applicable to the screen end of a laser projection system. It utilizes the ultra-low refractive index of the aerogel to suppress Fresnel interface reflection, improving luminous efficiency, and providing a high refractive index difference. Through a "sedimentation-gel synergy" process, a gradient structure with continuous particle size distribution in the thickness direction is constructed in situ within a single matrix, achieving extremely low speckle contrast (<4%) and high light utilization (average visible light reflectivity >90%).

[0021] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The following are explanations of the terms that need to be provided: Speckle: A random, granular intensity distribution formed by the interference of multiple coherent beams when a coherent laser propagates on a rough surface or in a scattering medium.

[0023] Laser modes include longitudinal modes (standing wave modes along the optical axis) and transverse modes (field distribution modes of the beam cross-section), which determine the laser frequency, spot shape, and coherence.

[0024] Speckle contrast C: A parameter used to quantitatively characterize the intensity of speckle, typically the ratio of the intensity standard deviation σ to the average intensity. The ratio (C=σ / ).

[0025] Anti-speckle screen: A display screen material used in laser projection displays to reduce speckle contrast.

[0026] Light-scattering nanoparticles (LSNs) are nanoparticles that do not absorb visible light and can effectively scatter laser light.

[0027] Aerogels are porous solid materials with high porosity and multiple solid-gas interfaces. They have low refractive index, no absorption, and adjustable transparency, making them suitable as optical substrates.

[0028] Solid-gas interface: The interface formed between the aerogel nanoframework and the air inside the pores provides a high refractive index difference, which significantly enhances the scattering efficiency.

[0029] Fresnel reflection: The phenomenon of light being reflected at the interface of media with different refractive indices, which manifests as specular reflection on the surface.

[0030] Sedimentation-gel synergy (synchronous sedimentation-gelation): The sol-gel transition occurs simultaneously with particle sedimentation, fixing the particle size distribution in the solidified network.

[0031] Gradual backscattering structure: In the thickness direction, the forward scattering region dominated by small particles gradually transitions to a strong backscattering region enriched by large particles, achieving low speckle and high luminous efficiency.

[0032] D 50 It is the median particle size of powder or particulate matter, indicating that 50% of the particles in the sample have a particle size smaller than this value, and 50% of the particles have a particle size larger than this value.

[0033] Specifically, as one aspect of the technical solution of the present invention, a low speckle contrast high reflectivity aerogel optical material includes: a transparent aerogel matrix as an optical framework; and light scattering nanoparticles dispersed in the transparent aerogel matrix; wherein the low speckle contrast high reflectivity aerogel optical material has a first surface and a second surface arranged opposite to each other in the thickness direction, and the light scattering nanoparticles are distributed in a size gradient from the first surface to the second surface, and the particle size of the light scattering nanoparticles gradually increases.

[0034] In some embodiments, the transparent aerogel matrix has a porosity of over 90%, a refractive index of 1.02 to 1.10, and a transmittance of >95% at a thickness of 1.2 mm.

[0035] In some embodiments, the material of the transparent aerogel matrix may include one or more combinations of silica aerogel, organosilicon aerogel, etc., but is not limited to these, as long as it satisfies the requirements of low absorption, high permeability, and the ability to form a highly porous structure. Specifically, the organosilicon aerogel may include, but is not limited to, one or more combinations of polymethylsilsesquioxane (PMSQ) aerogel, polyvinyltrimethoxysilane (PVTMS) aerogel, etc.

[0036] In some embodiments, the light-scattering nanoparticles may include one or more combinations of silica nanoparticles, zinc oxide nanoparticles, titanium oxide nanoparticles, etc., but are not limited thereto.

[0037] In some embodiments, the particle size distribution of the light-scattering nanoparticles can cover the effective region of visible light scattering, for example, the particle size D can be... 50 The nm value is 50~400 nm, preferably 50~300 nm.

[0038] In some preferred embodiments, the light-scattering nanoparticles are dispersed in a three-dimensional porous network contained in the transparent aerogel matrix.

[0039] In some preferred embodiments, the low speckle contrast high reflectivity aerogel optical material includes a transmission layer near a first surface and a reflection layer near a second surface. The transmission layer is formed by enriching light-scattering nanoparticles with a particle size of 10-50 nm, and the number of light-scattering nanoparticles contained in the transmission layer accounts for 10-20% of the total number of light-scattering nanoparticles. The reflection layer is formed by enriching light-scattering nanoparticles with a particle size of 300-600 nm, and the number of light-scattering nanoparticles contained in the reflection layer accounts for 10-30% of the total number of light-scattering nanoparticles.

[0040] In some embodiments, the volume fraction of light-scattering nanoparticles in the low speckle contrast high reflectivity aerogel optical material is 0.1~2.0 vol.

[0041] In some embodiments, the low speckle contrast, high reflectivity aerogel optical material has a thickness of 0.8–2.5 mm and a density of 0.1–0.3 g / cm³. 3 If the material is too thin, it will limit the formation of hierarchical structures; if it is too thick, it may increase light leakage at the edges, requiring structural and encapsulation optimization. Furthermore, the large refractive index difference between the light-scattering nanoparticles and the matrix enhances the scattering ability of the light-scattering nanoparticles, reducing the required concentration. Excellent speckle suppression and overall light reflectivity can be obtained at low filler concentrations. The enhanced scattering ability of the light-scattering nanoparticles requires a smaller laser penetration depth / diffusion distance, thus resulting in a smaller overall thickness (minimum 0.8 mm).

[0042] In some embodiments, the low speckle contrast, high reflectivity aerogel optical material exhibits low speckle contrast and high reflectivity, reducing speckle contrast from approximately 30% to below the human eye's perceptible threshold (<4%) under RGB laser conditions; after hydrophobication and damp heat treatment, it maintains a low speckle level of approximately 2.4% to 3.1%, and an average reflectivity >90% in the visible light band. The speckle contrast is measured using a speckle contrast testing system, and the average visible light reflectivity is measured using a spectrophotometer with an integrating sphere.

[0043] In some implementations, the low speckle contrast high reflectivity aerogel optical material maintains resolution, color gamut, and viewing angle uniformity, thus preserving the spatial resolution of the projected image; its color gamut is almost indistinguishable from that of ordinary screen imaging; and the scattering properties of the light-scattering nanoparticles enable the low speckle contrast high reflectivity aerogel optical material to possess brightness uniformity over a wide viewing angle range.

[0044] In some embodiments, the low speckle contrast, high reflectivity aerogel optical material possesses ultralight properties and a low density (0.1~0.3 g / cm³). 3 Suitable for portable / suspended / airborne applications.

[0045] In some embodiments, the low speckle contrast high reflectivity aerogel optical material is environmentally resistant, can be modified to obtain a superhydrophobic surface and maintain long-term humid heat stability, and the modification does not significantly damage the internal porous structure and optical properties.

[0046] In some more specific implementation schemes, such as Figure 1 As shown, a low speckle contrast, high reflectivity aerogel optical material is used at the screen end of a laser projection system. The optical material (i.e., the screen) is a monolithic aerogel composite material, specifically comprising: (1) Transparent aerogel matrix: as an optical framework, it provides a matrix with high porosity and ultra-low refractive index; (2) Gradual scattering region: Light scattering nanoparticles with a continuous size distribution along the thickness direction of the optical material, the size of which gradually increases from the first surface to the second surface. The size distribution is as follows: the size of the light scattering nanoparticles gradually increases from the viewing side to the back side of the screen. Taking the size gradually increasing from top to bottom as an example, the upper part is dominated by small particles, and the light is mainly transmitted. As the size gradually increases, the light gradually becomes backscattered, achieving a deeper penetration depth and sufficient scattering, significantly reducing speckle contrast. (3) High reflectivity layer: Located at the bottommost part (i.e., the second surface) away from the observation side, it is formed by the enrichment of large particles and is used to improve the overall laser reflectivity of light energy.

[0047] As another aspect of the technical solution of the present invention, it also relates to a method for preparing the aforementioned low speckle contrast, high reflectivity aerogel optical material, comprising: Provide aerogel precursor solution; Light-scattering nanoparticles with a graded particle size distribution are added to the aerogel precursor solution and dispersed evenly. A catalyst is added to initiate the sol-gel reaction, and then the mixture is allowed to stand, allowing the light-scattering nanoparticles to settle under gravity. At the same time, the sol gels, forming a gel structure with continuously graded particle sizes in the thickness direction. The obtained gel structure was aged, solvent replaced, and dried to prepare aerogel optical material with low speckle contrast and high reflectivity.

[0048] In some embodiments, the preparation method specifically includes: mixing a silicon source with a solvent to obtain an aerogel precursor solution with a concentration of 25-50 wt%.

[0049] In some embodiments, the preparation method of the low speckle contrast high reflectivity aerogel optical material specifically includes: (1) Mix the silicon source with the solvent to obtain an aerogel precursor solution; (2) Add light-scattering nanoparticles with a wide particle size distribution to the aerogel precursor solution according to the set volume fraction and disperse them evenly; (3) Add a catalyst to start the sol-gel reaction. After the system is injected into the mold, it is left to stand without disturbance. During the standing stage, the light scattering nanoparticles undergo particle size-related sedimentation under gravity. At the same time, the sol gradually gels. By controlling the gelation time (settling window), the "settling-gelation" is synchronized, thereby locking the continuous particle size distribution in the thickness direction, forming a gel structure with continuous particle size distribution in the thickness direction, and forming a backscattering / reflection layer at the bottom. (4) The obtained gel is aged to enhance the network strength, and solvent replacement and drying are performed to obtain an integral low speckle contrast high reflectivity aerogel optical material.

[0050] In some preferred embodiments, in step (1), the silicon source may include one or more of tetramethoxysilane (TMOS), tetraethoxysilane (TEOS), methyltrimethoxysilane (MTMS), etc., but is not limited to these.

[0051] In some preferred embodiments, in step (1), the solvent may include one or a combination of two of dimethyl sulfoxide (DMSO) and alcohol, wherein the alcohol may be one or a combination of methanol, ethanol, benzyl alcohol, etc., but is not limited thereto.

[0052] In some preferred embodiments, step (2) includes: adding light-scattering nanoparticles to the aerogel precursor solution according to a set volume fraction, and dispersing them uniformly by ultrasonication or high-speed shearing; the volume fraction of the added light-scattering nanoparticles is 0.1~2.0 vol%, and the particle size D of the light-scattering nanoparticles is... 50 The wavelength range is 50–400 nm. If the volume fraction of light-scattering nanoparticles added is too low, it will lead to insufficient reflection; if it is too high, it will cause excessive scattering and increase speckle.

[0053] In some preferred embodiments, in step (3), the catalyst includes one or a combination of two alkaline catalysts such as ammonia and tetramethylammonium hydroxide, used to regulate the gelation time window.

[0054] Furthermore, the amount of catalyst used is as follows: the dilution ratio of ammonia water is 6 μL of ammonia water diluted in 360 μL of water, and the volume used is 15~200 μL.

[0055] In some preferred embodiments, in step (3), the temperature of the sol-gel reaction is 20~25°C, and the gelation time is controlled by adjusting the amount of catalyst used to be 0.5~7h.

[0056] In some preferred embodiments, in step (4), the aging temperature is 50~90 ℃ and the time is 24~96h. In some preferred embodiments, in step (4), the solvent used for solvent replacement includes one or a combination of two of anhydrous ethanol or acetone, and the number of solvent replacements is 4 to 6.

[0057] In some preferred embodiments, in step (4), the drying can be supercritical CO2 drying. Under the premise of sufficient surface modification and suppression of capillary collapse, atmospheric pressure drying or other drying methods can also be used as alternatives.

[0058] In some preferred embodiments, the preparation method may further include a hydrophobication treatment step after the aging and solvent replacement steps and before drying. The hydrophobication agent used in this treatment is a silanizing agent, specifically one or a combination of two of hexamethyldisilazane (HMDS), trimethylchlorosilane (TMCS), or other silanizing agents. Further, it may involve moisture- and heat-resistant surface modification and encapsulation to obtain a directly applicable aerogel optical material with low speckle contrast and high reflectivity.

[0059] In summary, the principle of the preparation method of the present invention is explained as follows: Light-scattering nanoparticles (preferably SiO2 nanoparticles) with a wide particle size distribution are dispersed in an aerogel sol system. During the settling process, particle size-dependent sedimentation occurs: larger particles settle faster and are more easily enriched at the bottom, while smaller particles are retained in the upper and middle parts. Simultaneously, the sol gels and gradually solidifies, forming a "sedimentation-gel synergy." This fixes the formed silica aerogel with a particle size hierarchy in a three-dimensional porous network, creating a size-gradient distribution (gradually increasing in size from top to bottom). This eliminates the need for multilayer structures and avoids the addition of extra interfaces that would lead to light efficiency loss.

[0060] The preparation method of the present invention does not require mechanical moving parts such as vibration, rotation or MEMS, and has higher reliability, longer life, and is easy to miniaturize and operate with low noise.

[0061] This structure achieves two types of synergistic scattering: (i) the upper part is dominated by small particles, where light is mainly transmitted. As the size gradually increases, the light gradually becomes backscattered, resulting in a deep transmission depth while being fully scattered, significantly reducing speckle contrast; (ii) the lower part is enriched with large particles to form a backscattering / reflection layer, reflecting more energy to the observation side, improving light utilization efficiency and brightness. At the same time, the high porosity of the aerogel provides a large number of solid-gas interfaces, offering a high refractive index difference, further improving scattering efficiency, and enabling effective speckle reduction even with a low filler content.

[0062] As another aspect of the technical solution of the present invention, it also relates to the application of the low speckle contrast and high reflectivity aerogel optical material in the field of laser projection display.

[0063] Correspondingly, another aspect of the technical solution of the present invention provides a laser projection display system, which includes: the aforementioned low speckle contrast high reflectivity aerogel optical material as a projection display terminal, wherein the first surface of the low speckle contrast high reflectivity aerogel optical material is close to the observation side, and the second surface is away from the observation side.

[0064] By employing the above technical solution, this invention utilizes the ultra-low refractive index of aerogel to suppress Fresnel interface reflection, improve light efficiency, and provide a high refractive index difference. Through a "sedimentation-gel synergy" process, a gradient structure with a continuous particle size distribution in the thickness direction is constructed in situ within a single matrix, effectively suppressing speckle without requiring a multi-layer structure. Without any mechanical moving parts, it simultaneously achieves extremely low speckle contrast (<4%) and high light utilization (average visible light reflectance >90%), and possesses advantages such as ultra-light weight and good environmental stability.

[0065] The technical solution of the present invention will be further described in detail below through several embodiments and in conjunction with the accompanying drawings. However, the selected embodiments are only for illustrating the present invention and do not limit the scope of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or according to the conditions recommended by the manufacturer. Unless otherwise specified, the experimental materials used in the embodiments below can be purchased from conventional biochemical reagent companies.

[0066] Example 1 Dilute ammonia solution by first diluting 6 μL of ammonia solution in 360 μL of water. Mix 375 μL of TMOS with 650 μL of DMSO until homogeneous, then add 0.7 vol% of polydisperse silica light-scattering nanoparticles (with graded particle size distribution, Dsize). 50 =150 nm), after thorough stirring, ultrasonic dispersion was performed for about 10 min, then 50 μL of diluted ammonia was added to the precursor, stirred for about 20 s, poured into a mold, and allowed to gel at 20 °C for 7 h, with the thickness controlled at 1.2 mm. After gelation, it was aged at 60 °C for about 72 h. Subsequently, solvent replacement was performed with anhydrous ethanol (4 times), followed by supercritical CO2 drying (40 °C, 10 MPa, about 24 h), resulting in a low speckle contrast, high reflectivity aerogel optical material.

[0067] Example 2 like Figure 2 As shown, a dilute ammonia solution was prepared by first diluting 6 μL of ammonia solution in 360 μL of water. 375 μL of TMOS and 650 μL of DMSO were mixed thoroughly, and then 0.1 vol% of polydisperse silica light-scattering nanoparticles (with a graded particle size distribution, D0.05) were added. 50 = 400 nm), after thorough stirring, ultrasonic dispersion was performed for about 10 min, then 200 μL of diluted ammonia was added to the precursor, stirred for about 20 s, poured into a mold, and allowed to gel at 25 °C for 0.5 h, with the thickness controlled at 0.8 mm. After gelation, it was aged at 90 °C for about 24 h. Subsequently, solvent replacement was performed with anhydrous ethanol (5 times), followed by supercritical CO2 drying (40 °C, 10 MPa, about 24 h), resulting in a low speckle contrast, high reflectivity aerogel optical material.

[0068] Example 3 Dilute ammonia solution by first diluting 6 μL of ammonia solution in 360 μL of water. Mix 375 μL of TMOS with 650 μL of DMSO until homogeneous, then add 2.0 vol% of polydisperse silica light-scattering nanoparticles (with graded particle size distribution, Dsize). 50 = 50 nm), after thorough stirring, ultrasonic dispersion was performed for about 10 min, then 15 μL of diluted ammonia was added to the precursor, stirred for about 20 s, poured into a mold, and allowed to gel at 22℃ for 5 h, with the thickness controlled at 2.5 mm. After gelation, it was aged at 50℃ for about 96 h. Subsequently, solvent replacement was performed with acetone (5 times), followed by supercritical CO2 drying (40℃, 10 MPa, about 24 h), resulting in a low speckle contrast, high reflectivity aerogel optical material.

[0069] Example 4 (Hydrophobication) Prepare a dilute ammonia solution by diluting 6 μL of ammonia solution in 360 μL of water. Mix 375 μL of TMOS with 650 μL of DMSO until homogeneous, then add 0.7 vol% of polydisperse silica light-scattering nanoparticles (with a graded particle size distribution, Dsize). 50 = 150 nm), after thorough stirring, ultrasonic dispersion was performed for about 10 min, then 50 μL of diluted ammonia was added to the precursor, stirred for about 20 s, poured into a mold, and allowed to gel at 23 ℃ for 4 h, with the thickness controlled at 1.2 mm. After gelation, it was aged at 60 ℃ for about 72 h. Subsequently, solvent replacement was performed with anhydrous ethanol (6 times), followed by treatment with a hydrophobic treatment solution of HMDS: EtOH = 1:4 for 24 h, followed by solvent replacement with anhydrous ethanol (5 times), and then supercritical CO2 drying (40 ℃, 10 MPa, about 24 h). After drying, a low speckle contrast and high reflectivity aerogel optical material was obtained.

[0070] Example 5 14 μL of tetramethylammonium hydroxide was pre-diluted in 54 μL of water. 250 μL of PVTMS (polyvinyltrimethoxysilane) was mixed thoroughly with 650 μL of benzyl alcohol (BzOH), and then 0.7 vol% of polydisperse silica light-scattering nanoparticles (with a graded particle size distribution, D0) were added. 50 = 150 nm) were mixed evenly. Diluted tetramethylammonium hydroxide was added to the precursor, and after stirring for about 20 s, the mixture was poured into a mold and allowed to gel at 25 °C for 3 h. After gelation, it was aged at 80 °C for about 72 h. Subsequently, solvent replacement was performed with anhydrous ethanol (e.g., 5 times), and finally supercritical CO2 drying was carried out at 40 °C and 10 MPa to obtain aerogel optical material with low speckle contrast and high reflectivity.

[0071] Example 6 Mix 0.5 ml of MTMS (methyltrimethoxysilane) with 1.5 ml of 0.01 M hydrochloric acid aqueous solution until homogeneous. Then add 0.5 g of urea and 80 mg of CTAB and mix well. Finally, add 0.7 vol% of polydisperse silica light-scattering nanoparticles (with a graded particle size distribution, particle size distribution D) 50 = 150 nm) were mixed evenly. Diluted tetramethylammonium hydroxide was added to the precursor, and after stirring for about 20 s, the mixture was poured into a mold and allowed to gel at 25 °C for 6 h. After gelation, it was aged at 80 °C for about 72 h. Subsequently, it was replaced with deionized water 5 times, and then with anhydrous ethanol for solvent replacement (e.g., 5 times). Finally, it was dried with supercritical CO2 at 40 °C and 10 MPa to obtain aerogel optical material with low speckle contrast and high reflectivity.

[0072] Example 7 Dilute ammonia solution by first diluting 6 μL of ammonia solution in 360 μL of water. Mix 375 μL of TMOS with 650 μL of DMSO until homogeneous, then add 0.7 vol% of polydisperse titanium dioxide light scattering nanoparticles (with a graded particle size distribution, Dsize). 50 =150 nm), after thorough stirring, ultrasonic dispersion was performed for about 10 min, then 50 μL of diluted ammonia was added to the precursor, stirred for about 20 s, poured into a mold, and allowed to gel at 25 °C for 7 h, with the thickness controlled at 1.2 mm. After gelation, it was aged at 60 °C for about 72 h. Subsequently, solvent replacement was performed with anhydrous ethanol (5 times), followed by supercritical CO2 drying (40 °C, 10 MPa, about 24 h), resulting in a low speckle contrast, high reflectivity aerogel optical material.

[0073] Example 8 Dilute ammonia solution by first diluting 6 μL of ammonia solution in 360 μL of water. Mix 375 μL of TMOS with 650 μL of DMSO until homogeneous, then add 0.7 vol% of polydisperse zinc oxide light-scattering nanoparticles (with a graded particle size distribution, Dsize). 50 =150 nm), after thorough stirring, ultrasonic dispersion was performed for about 10 min, then 50 μL of diluted ammonia was added to the precursor, stirred for about 20 s, poured into a mold, and allowed to gel at 25 °C for 7 h, with the thickness controlled at 1.2 mm. After gelation, it was aged at 60 °C for about 72 h. Subsequently, solvent replacement was performed with anhydrous ethanol (5 times), followed by supercritical CO2 drying (40 °C, 10 MPa, about 24 h), resulting in a low speckle contrast, high reflectivity aerogel optical material.

[0074] Please see Figure 3The comparison between the low speckle contrast and high reflectivity aerogel optical material obtained in Example 1 and the speckle pattern of laser projection taken at a distance of about 100 cm using an area array camera on an ordinary screen shows that the laser spots (speckle) on the aerogel optical material are significantly reduced, the image is more uniform, and the speckle contrast is reduced to below 4%.

[0075] Figure 4 The reflectance curve of the low speckle contrast high reflectance aerogel optical material obtained in Example 2 was tested using an ultraviolet-visible-near-infrared spectrophotometer with an integrating sphere. This shows that the aerogel optical material has high visible light reflectance, with an average visible light reflectance of over 90%.

[0076] Figure 5 The image shows a comparison of the color gamut of the low speckle contrast, high reflectivity aerogel optical material obtained in Example 3 with that of a regular screen measured by a spectral radiance meter. This demonstrates that, compared to a regular screen, the aerogel optical material suppresses speckle contrast without affecting the presented color (color gamut).

[0077] Figure 6 The average visible light reflectance and speckle contrast of optical composite materials prepared from different types of nanoparticles in Examples 1, 7, and 8 are shown.

[0078] Comparative Example 1 The difference between this comparative example and Example 1 is that the added silica light scattering nanoparticles have the same particle size, are not hierarchically distributed, and all have a diameter of 400 nm.

[0079] The resulting aerogel optical material has a higher reflectivity, with an average visible light reflectivity of 98%, but its speckle suppression ability is limited, only reducing the speckle contrast from 30% to 10%.

[0080] Comparative Example 2 The difference between this comparative example and Example 1 is that the added silica light scattering nanoparticles have the same particle size, are not hierarchically distributed, and all have a diameter of 20 nm.

[0081] The resulting aerogel optical material has even lower reflectivity, with an average visible light reflectivity of 40%.

[0082] Comparative Example 3 The difference between this comparative example and Example 1 is that silica light scattering nanoparticles are added to the PDMS matrix.

[0083] The obtained PDMS matrix has high transmittance but also high refractive index. The resulting composite optical material is superior to the matrix PDMS, which has a higher refractive index and a smaller difference in refractive index with nanoparticles. The nanoparticles have a weaker ability to scatter light, so the composite material has a lower reflectance, with an average visible light reflectance of 20%.

[0084] Comparative Example 4 The difference between this comparative example and Example 1 is that the silicon source is a mixture of DMDMS and MTMS in a volume ratio of 1:1.

[0085] The resulting aerogel matrix, although still having a low refractive index, is opaque. The resulting composite aerogel optical material has high reflectivity, with an average visible light reflectivity of 95%.

[0086] In addition, the inventors of this case also conducted experiments with other raw materials and conditions listed in this specification, referring to Examples 1 to 8, and similarly obtained aerogel optical materials with low speckle contrast and high reflectivity for use in laser projection system screens.

[0087] It should be understood that the above descriptions are only some embodiments of the present invention. It should be pointed out that for those skilled in the art, other modifications and improvements can be made without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A low speckle contrast, high reflectivity aerogel optical material, characterized in that, include: Transparent aerogel matrix as an optical framework; And light-scattering nanoparticles dispersed in the transparent aerogel matrix; wherein the low speckle contrast high reflectivity aerogel optical material has a first surface and a second surface arranged opposite to each other in the thickness direction, and the light-scattering nanoparticles are distributed in a size gradient from the first surface to the second surface, and the size of the light-scattering nanoparticles gradually increases.

2. The low speckle contrast, high reflectivity aerogel optical material according to claim 1, characterized in that: The transparent aerogel matrix has a porosity of over 90%, a refractive index of 1.02~1.10, and a transmittance of >95% at a thickness of 1.2 mm. And / or, the material of the transparent aerogel matrix includes one or a combination of two of silica aerogel and organosilicon aerogel, preferably, the organosilicon aerogel includes one or a combination of two of polymethylsilsesquioxane aerogel and polyvinyltrimethoxysilane aerogel.

3. The low speckle contrast, high reflectivity aerogel optical material according to claim 1, characterized in that: The light-scattering nanoparticles include one or more combinations of silicon dioxide nanoparticles, zinc oxide nanoparticles, and titanium oxide nanoparticles. And / or, the particle size D of the light-scattering nanoparticles 50 The nm range is 50~400 nm, preferably 50~300 nm; And / or, the light-scattering nanoparticles are dispersed in a three-dimensional porous network contained in the transparent aerogel matrix.

4. The low speckle contrast, high reflectivity aerogel optical material according to claim 1, characterized in that: The low speckle contrast, high reflectivity aerogel optical material comprises a transmission layer near a first surface and a reflection layer near a second surface. The transmission layer is formed by enriching light-scattering nanoparticles with a particle size of 10-50 nm, and the number of light-scattering nanoparticles in the transmission layer accounts for 10-20% of the total number of light-scattering nanoparticles. The reflection layer is formed by enriching light-scattering nanoparticles with a particle size of 300-600 nm, and the number of light-scattering nanoparticles in the reflection layer accounts for 10-30% of the total number of light-scattering nanoparticles. And / or, the volume fraction of light-scattering nanoparticles in the low speckle contrast, high reflectivity aerogel optical material is 0.1~2.0 vol% And / or, the thickness of the low speckle contrast, high reflectivity aerogel optical material is 0.8~2.5 mm, and the density is 0.1~0.3 g / cm³. 3 ; And / or, the speckle contrast of the low speckle contrast high reflectivity aerogel optical material is less than 4%, and the average reflectivity of visible light is greater than 90%.

5. The method for preparing the low speckle contrast, high reflectivity aerogel optical material according to any one of claims 1 to 4, characterized in that, include: Provide aerogel precursor solution; Light-scattering nanoparticles with a particle size distribution were added to the aerogel precursor solution and dispersed evenly. A catalyst is added to initiate the sol-gel reaction, and then the mixture is allowed to stand, allowing the light-scattering nanoparticles to settle under gravity. At the same time, the sol gels, forming a gel structure with continuously graded particle sizes in the thickness direction. The obtained gel structure was aged, solvent replaced, and dried to prepare aerogel optical material with low speckle contrast and high reflectivity.

6. The preparation method according to claim 5, characterized in that, include: The silicon source was mixed with a solvent to obtain an aerogel precursor solution with a concentration of 25-50 wt%. Preferably, the silicon source includes one or more combinations of tetramethoxysilane, tetraethoxysilane, and methyltrimethoxysilane; Preferably, the solvent includes one or a combination of two of dimethyl sulfoxide and alcohols, and more preferably, the alcohol includes one or a combination of methanol, ethanol, and benzyl alcohol.

7. The preparation method according to claim 5, characterized in that, include: Light-scattering nanoparticles were added to the aerogel precursor solution according to a predetermined volume fraction and dispersed uniformly by ultrasonication or high-speed shearing; the volume fraction of the added light-scattering nanoparticles was 0.1~2.0 vol%. And / or, the catalyst comprises one or a combination of two of ammonia, tetramethylammonium hydroxide; And / or, the sol-gel reaction is carried out at a temperature of 20~25℃ for a time of 0.5~7h.

8. The preparation method according to claim 5, characterized in that: The aging temperature is 50~90 ℃, and the time is 24~96 h; And / or, the solvent used for solvent replacement includes one or a combination of two of anhydrous ethanol and acetone, and the number of solvent replacements is 4 to 6. And / or, the drying includes one or a combination of two of supercritical CO2 drying and atmospheric pressure drying; And / or, the preparation method further includes a hydrophobic treatment step, wherein the hydrophobic agent used in the hydrophobic treatment is a silanizing agent, preferably including one or a combination of two of hexamethyldisilazane and trimethylchlorosilane.

9. The application of the low speckle contrast, high reflectivity aerogel optical material according to any one of claims 1 to 4 in the field of laser projection display.

10. A laser projection display system, characterized in that, include: The low speckle contrast high reflectivity aerogel optical material according to any one of claims 1 to 4 is used as a projection display terminal, wherein the first surface of the low speckle contrast high reflectivity aerogel optical material is close to the observation side, and the second surface is away from the observation side.

Images