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Zhao Y Y, Jin F, Dong X Z, et al. Femtosecond laser two-photon polymerization three-dimensional micro-nanofabrication technology[J]. Opto-Electron Eng, 2023, 50(3): 220048. doi: 10.12086/oee.2023.220048
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Femtosecond laser two-photon polymerization three-dimensional micro-nanofabrication technology
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Abstract
Femtosecond laser two-photon polymerization (TPP) micro-nano fabrication technology, as an important method for the preparation of three-dimensional (3D) micro-nanostructures, has become a hot spot of international frontier research. Using the two-photon absorption effect and the threshold effect of the interaction between laser and matter, this technology can break through the diffraction limit of classical optical theory and achieve nanoscale laser fabrication resolution. It is expected to play an important role in the field of 3D functional micro-nano device fabrication. In this paper, the basic principles of photophysical and photochemical processes in femtosecond pulsed laser TPP fabrication technology will be described, and the research progress and development of this technology in improving line width and fabrication resolution, and improving fabrication efficiency will be reviewed. Then, using the high spatial resolution and true 3D fabrication characteristics of femtosecond laser TPP micro-nano fabrication technology, the researchers prepared various micro-optical devices, integrated optical devices, micro-electromechanical systems, and biomedical devices, fully demonstrating the application prospect of this technology. Finally, how to achieve high-precision, high-efficiency, low-cost, large-area, multi-functional materials and microstructure fabrication, as well as existing challenges and future development directions are discussed and prospected.-
Keywords:
- femtosecond laser /
- two-photon polymerization /
- optical diffraction limit /
- resolution /
- efficiency
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References
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Overview
Femtosecond laser two-photon polymerization (TPP) micro-nanofabrication technology is a new type of three-dimensional lithography technology that integrates nonlinear optics, ultra-fast pulsed laser, microscopic imaging, ultra-high-precision positioning, three-dimensional (3D) graphics CAD modeling, and photochemical materials. It has the characteristics of simplicity, low cost, high resolution, true 3D, and so on. Different from the technical route of shortening the wavelength of the traditional lithography, this TPP technology breaks through the optical diffraction limit using the ultrafast laser in the near-infrared and the nonlinear optical effect of the interaction between the laser and the material. TPP can achieve true 3D fabrication of complex 3D structures. After the femtosecond pulse laser is tightly focused in space, photopolymerization is initiated by the two-photon absorption(TPA), which can limit the fabrication area in the center of the focus. The interaction time of the ultrashort pulse with the material is much lower than the thermal relaxation of the material, avoiding the photothermal effect. The lateral linewidth can be reduced to about 100 nm due to the strong threshold characteristics of the two-photon absorption process. Thus, TPP is an ideal fabrication method in the field of 3D micro-nanostructure. Since 2001, Kawata’s team has used a near-infrared femtosecond laser with a wavelength of 780 nm to fabricate a "nanobull" with the size of red blood cells. It fully demonstrated the advantages of TPP in the preparation of three-dimensional micro-nano structures. At the same time, a polymer nanodot with a size of 120 nm was fabricated, which was only 1/7 of the laser wavelength, breaking the optical diffraction limit in this study. Since then, scientists from various countries have improved the line width, resolution, and other parameters of 3D structure by continuously improving the materials, structure, processing technology and light field control, and other aspects. At the same time, with the continuous development and improvement of the 3D nanostructure fabrication technology, the advantages of TPP technology are also reflected in some application fields, such as micro-optical devices, integrated optical devices, micro-electromechanical systems, and biomedical devices. This paper will systematically introduce the femtosecond laser TPP micro-nanofabrication technology, including the fabricating principle, the development of fabricating methods, and its research overview in many application fields. Finally, its existing problems and future development and application prospects are discussed.
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Zhao Y Y, Jin F, Dong X Z, et al. Femtosecond laser two-photon polymerization three-dimensional micro-nanofabrication technology[J]. Opto-Electron Eng, 2023, 50(3): 220048. doi: 10.12086/oee.2023.220048
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Figure 1.
Schematic diagram of one-photon absorption, two (multi-) photon absorption, multi-photon ionization, and photopolymerization process[45-47]
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Figure 2.
Cross-linking process and degree of conversion. (a) Schematic diagram of the polymerization and cross-linking process of monomer molecules[64]; (b) Degree of conversion calculated from the Raman spectra for TPP with different scanning velocities in the commercial (acrylate-based) photoresist IP-L 780[67]
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Figure 3.
Distribution of the photopolymerization threshold and the damage threshold. (a) Laser exposure threshold intensity as a function of exposure time[71]; (b) Laser power threshold at different scan speeds measured by darkfield microscopy[47]; (c) Threshold laser intensities at single and multiple exposures measured by darkfield and in situ microscopy[47]
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Figure 4.
Sub-diffractive feature-scale structures by TPP and topography models of Voxel. (a) Schematic diagram of the TPP[15]; (b) The prepared "nano bull"[19]; (c) The nonlinear relationship between line width and exposure time[19]; (d) Light intensity distribution of the focus, where the dotted line is the square of light intensity[47]; (e) The relationship between voxel length and exposure power[78]; (f) The relationship between voxel linewidth and exposure power[78]
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Figure 5.
Schematic diagram of the TPP system. (a) Optical path diagram of a typical TPP based on the piezoelectric stage scanning[49]; (b) Schematic diagram of different scanning strategies on different substrates[17]; (c) Galvanometer scanning, (d) immersion scanning, (e) STED assised and (f) SLM based TPP system[17]
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Figure 6.
The nanodots/wires structures fabricated by TPP.(a) 120 nm[19], (b) 100 nm[98], (c) 80 nm[100], (d) 90 nm[101], (e) 50 nm[103], (f) 35 nm[74], (g) 30 nm[104], (h) 23 nm[105], (i) 7 nm, 8 nm and 9 nm[106] feature size in the nanodots/wires structures
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Figure 7.
The nanowires structures fabricated by STED-TPP. (a) Schematic diagram of the STED-TPP and the minimum longitudinal size of 40 nm[110]; (b) The relationship between the line width and the 532 nm CW laser and the fabricated nanowires with widths of 95 nm, 65 nm, 90 nm, and 145 nm[111]; (c) Cross-sectional intensity distributions of the initiation and inhibition laser beam, and the fabricated nanowires with width of 54 nm[112]; (d) Schematic diagram of improving resolution by increasing inhibition intensity and the fabricated nanowires with the minimum size of 9 nm[113]
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Figure 8.
Periodic 3D structures fabricated based on multi-beam parallel fabrication technology.(a,b) Micro-gear and micro-bull combined structures fabricated by TPP with diffractive elements[120]; (c) 2D array structure fabricated by TPP with DMD projection[121]; (d) Parabolic mirror structure based on SLM-TPP[122]; (e-g) 3D mechanical metamaterials fabricated by TPP with diffractive elements[123]
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Figure 9.
High-precision, large-scale structures fabricated by DMD TPP technology.(a) DMD holographic multi-focus 3D TPP method and the fabricated high-resolution "bridge" structure, and woodpile structures[125]; (b) The prepared Millimeter-scale structure with sub-micrometer features, micro-nano bridge structures by FP-TPL technology[126]; (c) The prepared micro-nano suspended lines and micro-metamaterial structures by projection TPP with the spatiotemporal focusing technology[127]; (d) The prepared nanowires and nanodots structures, cross-scale structures by femtosecond projection nanolithography technology[128]
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Figure 10.
Photonic crystals, metamaterials, and devices. (a) Woodpile photonic crystal[131]; (b) Diamond photonic crystal[133]; (c) Heat shrinkable woodpile photonic crystal[134]; (d) Chiral helical metamaterial[135]; (e) 3D invisibility cloak structure in optical band[136]; (f) Beam deflector[137]; (g) Composite chiral photonic crystal material[138]; (h) Circularly polarized beam splitter[139]
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Figure 11.
Metalens device. (a) Schematic diagram of the broadband focusing of the hybrid achromatic metalens[141]; (b) The structure of the hybrid achromatic metalens[141]; (c) The partial enlarged view[141]; (d) The imaging of the broadband near-infrared light[141]; (e) The broadband metalens, which combines nanoholes with a phase plate[142]; (f) Measured broadband focusing spot[142]; (g) The tunable multifocal 3D metalens[146]; (h) Measured zoom focusing spot[146]
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Figure 12.
Integrated photonics device. (a) Miniature prism coupler[148]; (b) Low-loss fiber-on-chip coupler[149]; (c) Polarization-rotated polymer rectangular waveguide[150]; (d) Fiber-on-chip connector[153]; (e) Chip-on-chip optical connector[153]; (f) On-chip device-device optical connector[153]; (g) Microdisk cavity structure and optical interconnect waveguide structure[154]; (h) 3D curved surface photonic microcavity structure[155]
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Figure 13.
Micro-nano optical lens. (a) Aspherical solid immersion microlenses[158]; (b) Ultracompact multi-lens objectives[159]; (c) Stacked diffractive microlenses[160]; (d) Graded index Lumberg lenses[161]
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Figure 14.
Inverse-designed micro-nano optics devices. (a) Free-form NIR polarizing beamsplitter[163]; (b) Spectral splitting metalens[164]; (c) 3D circularly symmetric metalens[165]; (d) Multilayer metalens[166]
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Figure 15.
Mechanical metamaterial structures and devices.(a) Pentamode metamterials and structural unit of two connected truncated cones[168]; (b) An elasto-mechanical unfeelability cloak made of metamaterials[170]; (c) A twist mechanical metamaterials[171]
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Figure 16.
Drivable micromechanical devices. (a) Remote magnetically actuated micro-rotor, micro-shield machine and 3D helical thruster[176]; (b) The pH-responsive spider micro-robot and smart micro-gripper[179]; (c) The liquid crystal elastomer-based micro-walker[180]; (d) Optical tweezers-driven micromechanical rotor[181-182]
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Figure 17.
Microfluidic device. (a) Micropump[185]; (b) Microturbines[186]; (c) Microsieves[188]; (d) Microfilters[189]; (e) Microvalve[190]; (f) Micromixer[191]; (g) Micromixer and filters[191]; (d) Micro-overpass devices[192]
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