A method for processing a microcavity array by femtosecond laser

Abstract

The application discloses a method for processing a microcavity array by using a femtosecond laser, and relates to the field of optical microcavities, and comprises the following steps: focusing a laser on the surface of a rhodamine-doped polymer film and controlling the laser to process a plurality of microcavities, and the plurality of microcavities form a microcavity array on the surface of the rhodamine-doped polymer film. The application uses rhodamine and a polymer as a carrier of the microcavities, forms a microcavity array on the film by using a femtosecond laser, controls the excitation path of rhodamine 6G excitons, improves the fluorescence efficiency and quantum yield of a substrate film which is processed to have the microcavity array, and uses the processing mode of the femtosecond laser, thereby improving the processing precision, reducing a heat-affected zone and having good repeatability.

Description

Technical Field

[0001] This application relates to the field of optical microcavities, and in particular to a method for fabricating microcavity arrays using femtosecond lasers. Background Technology

[0002] Optical microcavities can confine and manipulate light with high quality within a small volume, and their research has become a trend in advanced sensors and laser applications, improving light-matter interactions. Microcavities can manipulate spontaneous recombination rates, polaron generation, mode splitting, and Rabi oscillations. Changes in the local optical field within a microcavity are also caused by laser irradiation, leading to structural changes in self-assembled molecules interacting with the microcavity.

[0003] Microcavities have been extensively studied for their confinement mechanisms. They can confine light through total internal reflection, thereby achieving high-quality resonance and producing phenomena that are difficult to observe in conventional optical microcavities. This has made significant contributions to the development of cavity quantum electrodynamics, nonlinear optics, quantum optics, and non-Hermitian photonics. Advances in manufacturing processes have provided favorable conditions for producing high-quality microcavities. Photolithography, self-assembly, electrospinning, and other methods have been used to produce microcavities. However, direct-contact fabrication techniques are easily affected by materials and the processing environment, leading to poor repeatability.

[0004] Rhodamine is a cationic xanthracene dye that, compared to other dye molecules, exhibits advantages in fluorescence quantum yield, fluorescence lifetime, and fluorescence stability, leading to its widespread use in biolabeling and fluorescence imaging. It is also used as a photonic medium in the fabrication of hybrid organic photonic devices. However, the self-assembly and aggregation of rhodamine molecules occur in solution or solids. According to exciton theory, the dipole interactions of aggregated monomolecules can split the absorption bands of the two monomers. The formation of new absorption bands can alter the spectral characteristics of the dimer, significantly reducing the fluorescence efficiency and quantum yield of the dye molecule. Summary of the Invention

[0005] In view of the shortcomings of the aforementioned related technologies, this application provides a method for femtosecond laser processing of microcavity arrays. This application uses rhodamine and a polymer as carriers for the microcavities, and forms a microcavity array on a thin film using a femtosecond laser. This allows for the modulation of the 6G exciton transition path of rhodamine, improving the fluorescence efficiency and quantum yield of the substrate thin film with the microcavity array. Furthermore, the use of femtosecond laser processing improves processing accuracy, reduces the heat-affected zone, and ensures good repeatability.

[0006] Firstly, the method for processing microcavity arrays using femtosecond lasers provided in this application adopts the following technical solution: A method for processing a microcavity array using a femtosecond laser includes the following steps: focusing a laser onto the surface of a rhodamine-doped polymer film and controlling the laser to process multiple microcavities, wherein the multiple microcavities form a microcavity array on the surface of the rhodamine-doped polymer film.

[0007] Preferably, the spacing between adjacent microcavities in the microcavity array is 2-10 μm, and the microcavities are disk-shaped.

[0008] Preferably, the spacing between adjacent microcavities in the microcavity array is 5 μm, and the microcavities are disk-shaped.

[0009] Preferably, the diameter of the microcavity is 5-35 μm and the depth is 500-1000 nm.

[0010] Preferably, the diameter of the microcavity is 10-20 μm and the depth is 800 nm.

[0011] Preferably, the polymer used in the rhodamine-doped polymer film is one or more of polymethyl methacrylate, polystyrene, and polyvinyl alcohol.

[0012] Preferably, the polymer used in the rhodamine-doped polymer film is polymethyl methacrylate.

[0013] Preferably, the rhodamine used in the rhodamine-doped polymer film is one or more of rhodamine 6G, rhodamine B, and rhodamine 123.

[0014] Preferably, the rhodamine used in the rhodamine-doped polymer film shown is rhodamine 6G.

[0015] Preferably, the rhodamine-doped polymer film is prepared by the following steps: dissolving rhodamine and polymer in a solvent to obtain a mixed solution, preparing the mixed solution into a thin film, and annealing it to obtain the rhodamine-doped polymer film.

[0016] Preferably, the weight ratio of rhodamine to the polymer is 1:8-15.

[0017] Preferably, the weight ratio of rhodamine to the polymer is 1:10.

[0018] Preferably, the film is prepared by drop coating, specifically as follows: the mixed solution is dropped onto the substrate of the spin coater while the rotation speed is increased from 800-1200 rpm to 4000 rpm with an acceleration of 2000 rpm, and then the rotation speed is maintained at 4000 rpm for 20-40 seconds.

[0019] Preferably, the film is prepared by drop coating, specifically as follows: the mixed solution is dropped onto the substrate of the spin coater while the rotation speed is increased from 1000 rpm to 4000 rpm with an acceleration of 2000 rpm, and then the rotation speed is maintained at 4000 rpm for 30 seconds.

[0020] Preferably, the annealing temperature is 90-110℃ and the time is 3-8 minutes.

[0021] Preferably, the annealing temperature is 100°C and the time is 5 minutes.

[0022] Secondly, the microcavity array provided in this application adopts the following technical solution: A microcavity array is fabricated using a femtosecond laser microcavity array fabrication method.

[0023] Thirdly, the femtosecond laser processing system for microcavity arrays provided in this application adopts the following technical solution: A system for processing microcavity arrays using femtosecond lasers includes a femtosecond laser for generating laser light, a harmonic regenerator for adjusting the laser wavelength, a two-dimensional energy attenuator for controlling the laser energy density, and an electric stage for placing a rhodamine-doped polymer film, arranged sequentially. The femtosecond laser, the harmonic regenerator, and the two-dimensional energy attenuator are optically connected, and a focusing objective lens for focusing the laser light onto the rhodamine-doped polymer film is disposed between the two-dimensional energy attenuator and the electric stage.

[0024] Preferably, the femtosecond laser generates laser light with a wavelength of 1026 nm, a repetition frequency of 200 kHz, an output power of 200 mW, and a pulse width of 190 fs.

[0025] In summary, this application includes at least one of the following beneficial technical effects: 1. This application uses rhodamine and polymers as a substrate film, and fabricates a microcavity array on it to regulate the exciton transition path of rhodamine 6G, effectively reducing the exciton transfer from the monomer molecules of rhodamine 6G to the dimer molecules, thereby improving the fluorescence efficiency and quantum yield of the substrate film with microcavity array.

[0026] 2. This application utilizes femtosecond lasers to fabricate microcavity arrays on thin films, resulting in high fabrication precision, a small heat-affected zone, and good repeatability; 3. The femtosecond laser processing system for microcavity arrays in this application controls the wavelength and energy density of the laser, and processes microcavities on a thin film to form a microcavity array using an electric stage, thereby improving the accuracy and efficiency of microcavity array processing. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the overall structure of the femtosecond laser processing microcavity array system of this application.

[0028] Figure 2 This is a diagram illustrating the fabrication process of the femtosecond laser-processed microcavity array in this application; Figure 3 These are comparative optical mirror images of disk microcavity arrays on the surface of rhodamine-doped PMMA thin films processed using the femtosecond laser processing method of Examples 2-7 in this application. Figure 4 These are spectral images of a disk-shaped microcavity array fabricated on the surface of a rhodamine-doped PMMA film using the femtosecond laser microcavity array fabrication method described in Examples 2-7, and a rhodamine-doped PMMA film (film) without fabricated disk-shaped microcavity arrays. Figure 4 (a) is the ultraviolet absorption spectrum. Figure 4 (b) is the fluorescence spectrum. Figure 4 (c) is the white light spectrum; Figure 5 The transient absorption spectra of Rhodamine-doped PMMA films without fabrication of disk microcavity arrays and disk microcavity arrays on the surface of Rhodamine-doped PMMA films fabricated using the femtosecond laser fabrication method of Examples 2-4 are shown. Figure 6 This is a global analysis diagram of the transient absorption spectra of a rhodamine-doped PMMA thin film without a fabricated disk microcavity array and a disk microcavity array on the surface of a rhodamine-doped PMMA thin film fabricated using the femtosecond laser fabrication method of Example 2.

[0029] Reference numerals: 1. Femtosecond laser; 2. Harmonic generator; 3. Two-dimensional energy attenuator; 4. Polarization rotating mirror; 5. First reflecting mirror; 6. First beam splitter; 7. Laser galvanometer scanning system; 8. Spatial light modulator; 9. First dichroic mirror; 10. Second dichroic mirror; 11. Second beam splitter; 12. CCD camera; 13. LED light source; 14. Focusing lens; 15. Motorized stage; 16. Marble substrate. Detailed Implementation

[0030] The present application will be further described in detail below with reference to the embodiments. The following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified, specific conditions in the following embodiments were performed under conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, the methods used are conventional methods known in the art, and the consumables and reagents used are commercially available. Unless otherwise stated, the technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be applied to the present invention.

[0031] The raw materials used in the examples and comparative examples are all commercially available.

[0032] Example 1 Embodiment 1 of this application provides a system for processing microcavity arrays using femtosecond lasers.

[0033] Reference Figure 1 A system for processing microcavity arrays using femtosecond lasers includes a femtosecond laser, a harmonic generator, a two-dimensional energy attenuator, a polarization rotating mirror, a first reflecting mirror, a first beam splitter, a laser galvanometer scanning system, a spatial light modulator, a first dichroic mirror, a second dichroic mirror, a second beam splitter, a CCD camera, an LED light source, a focusing objective lens, a motorized stage, and a marble substrate, all arranged sequentially. The components are optically interconnected. A pre-set femtosecond laser is output from the femtosecond laser. The harmonic generator doubles the 1026nm wavelength light to 513nm. The two-dimensional energy attenuator attenuates the laser energy to 10% of its original value. After passing through the first reflecting mirror and the first beam splitter, the laser enters the laser galvanometer scanning system and the spatial light modulator. The laser then passes through the second dichroic mirror and is focused onto the motorized stage by a 50x objective lens. Simultaneously, the CCD camera 12 and the CCD's LED light 13 operate for auxiliary adjustment and real-time monitoring, but are not used for sample processing.

[0034] Among them, the femtosecond laser source uses potassium gadolinium ytterbium tungstate (Yb:KGW) as the gain medium, the laser output wavelength is 1026nm, the pulse width is 190fs, the maximum power can reach 10W, and the repetition frequency is 200kHz.

[0035] Harmonic generator: This system can convert 1026nm femtosecond laser into second and third harmonics to generate a second harmonic with a wavelength of 515nm, with a conversion efficiency of 50%.

[0036] Two-dimensional energy attenuator: It consists of tunable filters and adjusts the laser energy by adjusting the transmission path of the beam.

[0037] A polarization rotating mirror, also known as a half-wave plate, is used to adjust the polarization state of a femtosecond laser beam.

[0038] The first reflecting mirror, the first beam splitter, the first dichroic mirror, the second dichroic mirror, and the second beam splitter are all used to adjust the direction of the laser beam path.

[0039] Laser galvanometer scanning system: The laser beam path is adjusted through the interaction of two mirrors.

[0040] Spatial light modulator: Used for laser beam shaping.

[0041] A CCD camera is a charge-coupled device used to collect image information.

[0042] LED light sources emit white light through LEDs, which is used for field of view observation.

[0043] The focusing objective lens is used for focusing, employing a 50x magnification lens with a numerical aperture of 0.42 to focus a 513nm wavelength laser to 1μm.

[0044] The marble substrate is used to support the above-mentioned components, improving the safety and stability of laser processing.

[0045] Example 2 Embodiment 2 of this application provides a method for femtosecond laser processing of microcavity arrays, referring to... Figure 2 The preparation process is illustrated in the following steps: Quartz sheets were ultrasonically cleaned for 15 minutes each in deionized water, ethanol, isopropanol, and acetone, respectively, and then dried with a nitrogen gun. 5 mg of Rhodamine 6G powder and 50 mg of PMMA were dissolved in 1 mL of dichloromethane and stirred at room temperature for 2 hours. The mixture was then filtered through a 0.45 µm oil filter to obtain a mixed solution. A thin film was prepared using the drop-coating method with the mixed solution. The spin coater was used to add the mixed solution dropwise onto the substrate, increasing the spin coater speed from 1000 rpm to 4000 rpm with an acceleration of 2000 rpm. The speed was then maintained at 4000 rpm for 30 seconds. Finally, the spin-coated sample was heated on a hot plate at 100 °C for 5 minutes to remove residual solvent, yielding a Rhodamine-doped PMMA thin film. Rhodamine-doped PMMA films are fixed on an electric stage in a femtosecond laser-processed microcavity array system. Disk microcavities are fabricated on the Rhodamine-doped PMMA films using the femtosecond laser processing system to form a disk microcavity array. The diameter of the disk microcavities is 10 μm, the depth is 800 nm, and the spacing between two adjacent disk microcavities is 5 μm.

[0046] In this embodiment, the femtosecond laser generates a laser wavelength of 1026nm, a repetition frequency of 200kHz, an output power of 200mW, and a pulse width of 190fs. The wavelength of the laser is converted to 513nm by a harmonic generator, and the laser energy is attenuated to 10% of the original energy by a two-dimensional energy attenuator. After passing through the first reflecting mirror and the first beam splitter, the laser enters the laser galvanometer scanning system and the spatial light modulator. Then, the laser passes through the second dichroic mirror and is focused onto the thin film surface by a 50x objective lens, with a spot diameter of 1μm. The moving speed is controlled to be 0.03mm / s by controlling the movement of the electric stage.

[0047] Example 3 Embodiment 3 of this application provides a method for processing microcavity arrays using femtosecond lasers. The difference between Embodiment 3 and Embodiment 2 is that the diameter of the disk microcavity processed in Embodiment 3 is 15 μm.

[0048] Example 4 Embodiment 4 of this application provides a method for processing microcavity arrays using femtosecond lasers. The difference between Embodiment 4 and Embodiment 2 is that the diameter of the disk microcavity processed in Embodiment 4 is 20 μm.

[0049] Example 5 Embodiment 5 of this application provides a method for processing microcavity arrays using femtosecond lasers. The difference between Embodiment 5 and Embodiment 2 is that the diameter of the disk microcavity processed in Embodiment 5 is 25 μm.

[0050] Example 6 Embodiment 6 of this application provides a method for processing microcavity arrays using femtosecond lasers. The difference between Embodiment 6 and Embodiment 2 is that the diameter of the disk microcavity processed in Embodiment 6 is 30 μm.

[0051] Example 7 Embodiment 7 of this application provides a method for processing microcavity arrays using femtosecond lasers. The difference between Embodiment 7 and Embodiment 2 is that the diameter of the disk microcavity processed in Embodiment 7 is 35 μm.

[0052] Testing and Inspection The surface of the rhodamine-doped PMMA thin film, fabricated using the femtosecond laser microcavity array method described in Examples 2-7, was imaged using an optical microscope. Comparison images of the optical microscope images of the disk microcavity array are shown below. Figure 3 As shown. Spectroscopic measurements were performed on the surface of a rhodamine-doped PMMA film fabricated using the femtosecond laser microcavity array method described in Examples 2-7, as well as on a rhodamine-doped PMMA film without fabricated disk microcavity arrays. The test results are as follows. Figure 4 As shown, where Figure 4 (a) is the ultraviolet absorption spectrum. Figure 4(b) is the fluorescence spectrum. Figure 4 (c) shows the white light spectrum. Transient absorption spectra were performed on rhodamine-doped PMMA films without fabricated disk microcavity arrays and on disk microcavity arrays on the surface of rhodamine-doped PMMA films fabricated using the femtosecond laser fabrication method described in Examples 2-4. The results are as follows: Figure 5 As shown, proceed in sequence Figure 5 (a)-(d) arrangement. A global analysis of the transient absorption spectra of rhodamine-doped PMMA films without fabricated disk microcavity arrays and disk microcavity arrays on the surface of rhodamine-doped PMMA films fabricated using the femtosecond laser fabrication method of Example 2 was conducted, and an evolution-related differential spectrum (EADS) was obtained using a sequential model. Figure 6 As shown, proceed in sequence Figure 6 (a)-(b) arrangement. Results analysis The following combination Figure 3-6 The experimental results provided provide a detailed explanation of this application.

[0053] Reference Figure 3 The disk microcavity array on the surface of the rhodamine-doped PMMA thin film was fabricated using the femtosecond laser microcavity array method described in Examples 2-7. The disk microcavity array was neatly arranged, with a surface roughness of less than 0.4 μm, regular disk edge morphology, and no cracks or molten residue. The disk microcavity array on the surface of the rhodamine-doped PMMA thin film fabricated by the femtosecond laser had high completion rate and good repeatability.

[0054] Reference Figure 4 ,like Figure 4 As shown in the UV absorption spectrum of (a), the shoulder peak at 500 nm exhibits a blue shift as the microdisk diameter decreases. This blue shift may be attributed to the characteristics of the H-type rhodamine 6G dimer, where some rhodamine 6G molecules aggregate in PMMA. The disk-shaped microcavity array on the surface of the rhodamine-doped PMMA film, fabricated using the femtosecond laser processing method described in Examples 2-7, shows enhanced absorption in the 570 nm to 700 nm range compared to the rhodamine-doped PMMA film sample, and the absorption intensity further increases with decreasing microdisk diameter. Figure 4 As shown in the fluorescence spectrum of (b), the fluorescence spectrum exhibits a blue shift trend as the diameter of the disk microcavity decreases, as... Figure 4 The white light spectrum in (c) shows that the blue shift in the absorption spectrum is not caused by the interference effect of the disk microcavity array.

[0055] Reference Figure 5The negative absorption band observed at 530 nm corresponds to the bleaching of the monomer absorption band and the associated stimulated emission phenomenon, consistent with the initial fluorescence spectrum. This negative absorption band leads to the initial transient absorption of the thin film and the disk microcavity array. As the diameter of the disk microcavity decreases, the shoulder peak undergoes a blue shift. In a disk microcavity array with a diameter of 10 µm, the shoulder peak is located at 480 nm, which is consistent with... Figure 4 The blue shift of the shoulder peak in the UV absorption spectrum of (a) is consistent with this, indicating that the decrease in microcavity diameter leads to the blue shift of the shoulder peak. Furthermore, a change in the excited-state absorption (ESA) signal was observed in the transient absorption spectrum of the disk microcavity array. Specifically, the wavelength of the excited-state absorption signal blue-shifted from 614 nm for the 20 µm diameter microcavity array to 569 nm for the 10 µm diameter microcavity array, showing a trend of blue shift with decreasing disk microcavity diameter.

[0056] Reference Figure 6 , Figure 6 In (a), the peak at 498 nm shows almost no decay within 75.7 ps. However, the peak at 530 nm decreases significantly, likely due to electron transfer from the monomer to the dimer molecule. (See reference...) Figure 6 (b) In the global analysis of the 10 μm disk microcavity array, the peak centers at 480 nm and 530 nm showed the same decreasing trend with increasing delay time. This suggests that the presence of the microcavities enhances the internal electric field, leading to changes in the excited states of the molecules and raising the energy levels of the rhodamine 6G dimer. This may increase the potential barrier between the rhodamine 6G monomer and dimer energy levels, thus hindering electron transfer. This also explains the variation in the relative intensity of the main peak and the shoulder peak. Furthermore, compared to the transient absorption spectra of rhodamine-doped PMMA thin film samples without the fabricated disk microcavity array, Figure 6 (b) Positive intensity excited-state absorption signals were observed in the 560-700 nm wavelength range. As mentioned above, this is attributed to the resonance of light emitted by the Rhodamine 6G molecule in interaction with the microcavity, thereby enhancing the exciton density of states. Therefore, the Rhodamine 6G-doped PMMA microcavity array fabricated by femtosecond laser processing enables the modulation of the exciton transition path of Rhodamine 6G, effectively reducing the exciton transfer from monomeric to dimer molecules. Since the exciton transfer from monomeric to dimer molecules significantly reduces the fluorescence efficiency and quantum yield of Rhodamine 6G, the disk microcavity array on the surface of the Rhodamine-doped PMMA film fabricated using the femtosecond laser processing method described in Example 2 is beneficial for improving the fluorescence efficiency and quantum yield of optical devices.

[0057] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for processing microcavity arrays using femtosecond lasers, characterized in that: The process includes the following steps: focusing a laser onto the surface of a rhodamine-doped polymer film and controlling the laser to process multiple microcavities, forming a microcavity array on the surface of the rhodamine-doped polymer film; the spacing between adjacent microcavities in the microcavity array is 2-10 μm, and the microcavities are disk-shaped; the diameter of the microcavities is 5-35 μm, and the depth is 500-1000 nm; The rhodamine-doped polymer film is prepared by the following steps: dissolving rhodamine and polymer in a solvent to obtain a mixed solution, preparing the mixed solution into a thin film, and annealing it to obtain the rhodamine-doped polymer film. The weight ratio of rhodamine to the polymer is 1:8-15; The parameters for femtosecond laser processing are: the initial laser wavelength is 1026nm, the repetition frequency is 200kHz, the output power is 200mW, the pulse width is 190fs, the laser wavelength is converted from 1026nm to 513nm, and the laser energy is attenuated to 10% of the initial laser energy.

2. The method for processing microcavity arrays using femtosecond lasers according to claim 1, characterized in that: The polymer used in the rhodamine-doped polymer film is one or more of polymethyl methacrylate, polystyrene, and polyvinyl alcohol.

3. The method for processing microcavity arrays using femtosecond lasers according to claim 1, characterized in that: The film is prepared by drop coating. The specific process is as follows: the mixed solution is dropped onto the substrate of the spin coater while the rotation speed is increased from 800-1200 rpm to 4000 rpm with an acceleration of 2000 rpm. Then, the rotation speed is maintained at 4000 rpm for 20-40 seconds.

4. The method for processing microcavity arrays using femtosecond lasers according to claim 1, characterized in that: The annealing temperature is 90-110℃ and the time is 3-8 minutes.

5. A microcavity array, characterized in that: It is fabricated by any one of the femtosecond laser processing microcavity arrays according to any one of claims 1-4.

6. A system for processing microcavity arrays using femtosecond lasers as described in any one of claims 1-4, characterized in that: The device includes a femtosecond laser for generating laser light, a harmonic regenerator for adjusting the laser wavelength, a two-dimensional energy attenuator for controlling the laser energy density, and an electric stage for placing a rhodamine-doped polymer film, arranged sequentially. The femtosecond laser, the harmonic regenerator, and the two-dimensional energy attenuator are optically connected. A focusing objective lens for focusing the laser light onto the rhodamine-doped polymer film is disposed between the two-dimensional energy attenuator and the electric stage.

Images