1 Introduction to Laser Micro-to-Nano Manufacturing
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1.7.1 Two-Photon Direct Writing
The two-photon direct writing technology based on femtosecond laser has been developed to prepare micro/nanostructures. Two-photon absorption means that organic
material molecules can simultaneously absorb two photons, with the same or different
frequencies, and then be excited from a low energy state to a higher energy state. This
two-photon direct writing technology enables the feature size of 3D printing down
to submicron, thereby promoting the trend of miniaturization. The theoretical manufacturing size of TPP is about λ/(2.7n.sinα), smaller than the single-photon diffraction limit [18]. Gissibl demonstrated the application of direct writing and testing
by two-photon direct laser writing with a target of approximately 100 μm multilens and verified its high performance and functionality for quantitative measurement of modulation transfer function and aberrations [258]. Liao proposed a technique based on two-photon polymerization (TPP) for the preparation of precise and
customizable hollow three-dimensional microstructure devices [259]. Different from
traditional manufacturing technology, direct laser writing with TPP manufacturing
scheme can better control all geometric characteristics of the manufactured architecture both interiorly and exteriorly. Two-photon printing is also used in the biological
field. Worthington used the two-photon direct writing technique to print topological
patterns with different feature sizes to study their effects on cell differentiation. This
technique demonstrates a fast manufacturing of terrain surfaces with well-defined
shapes with a resolution of less than 3 μm [260].
1.7.2 Near-Field Manufacturing
Another powerful nanofabrication using lasers with a spatial resolution beyond the
optical diffraction limit is to use near-field technology, that is, evanescent waves
manufacturing near scattering objects, which can achieve sub-diffraction limited
focusing (minimum ∼10 nm) [261]. In the near-field optical phenomenon, the evanescent wave becomes more important than free space far-field wave. The characteristic
of the evanescent wave is that its amplitude decays rapidly in at least one direction of space. The light can be confined to a lateral dimension far less than half of
the wavelength. There are a few near-field laser nanomanufacturing technologies as
follows.
Particle lens array (PLA) technology uses an array of two-dimensional (2D) small
particles as a lens array. The array is then used to convert the laser beam into a
near-field parallel focused multiple enhancement optical spot. The efficiency of this
method is very high. As the lens array covers a large area, millions of nanostructures
can be prepared by irradiating with laser pulse only once. This makes it an ideal
method for nanofabrication of large-area surfaces [262]. With 140 nm dielectric
particles and 248 nm laser light source, PLA can obtain smaller features with a
resolution as low as 30 nm [263].
59
1.7.1 Two-Photon Direct Writing
The two-photon direct writing technology based on femtosecond laser has been developed to prepare micro/nanostructures. Two-photon absorption means that organic
material molecules can simultaneously absorb two photons, with the same or different
frequencies, and then be excited from a low energy state to a higher energy state. This
two-photon direct writing technology enables the feature size of 3D printing down
to submicron, thereby promoting the trend of miniaturization. The theoretical manufacturing size of TPP is about λ/(2.7n.sinα), smaller than the single-photon diffraction limit [18]. Gissibl demonstrated the application of direct writing and testing
by two-photon direct laser writing with a target of approximately 100 μm multilens and verified its high performance and functionality for quantitative measurement of modulation transfer function and aberrations [258]. Liao proposed a technique based on two-photon polymerization (TPP) for the preparation of precise and
customizable hollow three-dimensional microstructure devices [259]. Different from
traditional manufacturing technology, direct laser writing with TPP manufacturing
scheme can better control all geometric characteristics of the manufactured architecture both interiorly and exteriorly. Two-photon printing is also used in the biological
field. Worthington used the two-photon direct writing technique to print topological
patterns with different feature sizes to study their effects on cell differentiation. This
technique demonstrates a fast manufacturing of terrain surfaces with well-defined
shapes with a resolution of less than 3 μm [260].
1.7.2 Near-Field Manufacturing
Another powerful nanofabrication using lasers with a spatial resolution beyond the
optical diffraction limit is to use near-field technology, that is, evanescent waves
manufacturing near scattering objects, which can achieve sub-diffraction limited
focusing (minimum ∼10 nm) [261]. In the near-field optical phenomenon, the evanescent wave becomes more important than free space far-field wave. The characteristic
of the evanescent wave is that its amplitude decays rapidly in at least one direction of space. The light can be confined to a lateral dimension far less than half of
the wavelength. There are a few near-field laser nanomanufacturing technologies as
follows.
Particle lens array (PLA) technology uses an array of two-dimensional (2D) small
particles as a lens array. The array is then used to convert the laser beam into a
near-field parallel focused multiple enhancement optical spot. The efficiency of this
method is very high. As the lens array covers a large area, millions of nanostructures
can be prepared by irradiating with laser pulse only once. This makes it an ideal
method for nanofabrication of large-area surfaces [262]. With 140 nm dielectric
particles and 248 nm laser light source, PLA can obtain smaller features with a
resolution as low as 30 nm [263].