2
A. Hu et al.
1.1 Introduction
Laser has become a powerful and versatile tool for manufacturing various mechanical, energy, optoelectronic and biomedical devices with a precision down to a microand nano-size [1–3]. To enable a precise engineering and manufacturing it is a
linchpin to understand the fundamentals of laser-matter interaction, specially at a
small scale [4–6]. Due to the scaling law and the size effect, many materials will
behave quite different from their bulk counterparts. Meanwhile, the principles of
micro-optics and nanophotonics, which govern the propagation and further manipulation of light and laser (i.e., high single color, extremely strong and aligned light)
and the optics at a macro scale are fundamentally disparate. This point has to be
considered for micro-to-nano manufacturing. Due to the blooming development of
both nanotechnology and nanophotonics, micro- and nanomanufacturing based on
laser technology is demonstrating the bright perspective for the extensive application
in emerging consumable electronics, flexible, portable and wearable electronics, big
data, Internet of things (IoTs).
Traditionally, a pulse period shorter than a nanosecond (10
−9 s) is named as ultrafast laser. Since the invention of chirped pulse amplification, femtosecond (10
−15
s) lased laser has attracted extensive interests for precision machining [7]. It has
found that limited heating diffusion on the surrounding region of the processed area
is one of pronounced features of ultrafast laser processing [8, 9]. By employing
a femtosecond ultraviolet laser, polymethyl methacrylate was ablated without the
formation of a heat-affect zone [10, 11]. Comparing to the ablation with a nanosecond
pulsed laser, the ablation threshold using a femtosecond and or a picosecond laser
was also reduced significantly. These features encourage the high-precision manufacturing using various materials, such as biological tissues, semiconductors and other
dialectical materials [12]. For an ultrafast interaction, the absorption of photons stimulates the carriers within hundred femtoseconds (fs), which is too short to disturb
lattice since the electron-phonon coupling typically occurs in range of 1-100 ps [13,
14]. Meanwhile, an ultrafast pulse width is less than 1 ps. Thus, in an ideal case,
ultrafast excitation only occurs within the focal spot. However, for a laser pulse
with duration of nanoseconds or longer, the thermal diffusion cannot be neglectable
[15]. On the other hand, the nonlinear multiphoton absorption is another important
aspect of ultrafast laser processing. The probability of multiphoton absorption can be
significantly increased with the extremely high laser peak intensity of tightly focused
ultrashort laser pulses since the probability is a power function of the peak intensity [16, 17]. The highly localized nonlinear effect of ultrashort laser may lead to a
super-resolution processing beyond the optical diffraction limit and thereby strong
absorption can even occur in a transparent material [18, 19]. This multiphoton absorption of ultrafast laser not only permits the surface processing, but also permits the
internal microfabrication of transparent materials, such as glass and polymer [20,
21]. Due to the unique multiphoton excitation and the aforementioned highly localized thermal processing, ultrafast laser is found unprecedent application for precise
micro-to-nanomanufacturing.
A. Hu et al.
1.1 Introduction
Laser has become a powerful and versatile tool for manufacturing various mechanical, energy, optoelectronic and biomedical devices with a precision down to a microand nano-size [1–3]. To enable a precise engineering and manufacturing it is a
linchpin to understand the fundamentals of laser-matter interaction, specially at a
small scale [4–6]. Due to the scaling law and the size effect, many materials will
behave quite different from their bulk counterparts. Meanwhile, the principles of
micro-optics and nanophotonics, which govern the propagation and further manipulation of light and laser (i.e., high single color, extremely strong and aligned light)
and the optics at a macro scale are fundamentally disparate. This point has to be
considered for micro-to-nano manufacturing. Due to the blooming development of
both nanotechnology and nanophotonics, micro- and nanomanufacturing based on
laser technology is demonstrating the bright perspective for the extensive application
in emerging consumable electronics, flexible, portable and wearable electronics, big
data, Internet of things (IoTs).
Traditionally, a pulse period shorter than a nanosecond (10
−9 s) is named as ultrafast laser. Since the invention of chirped pulse amplification, femtosecond (10
−15
s) lased laser has attracted extensive interests for precision machining [7]. It has
found that limited heating diffusion on the surrounding region of the processed area
is one of pronounced features of ultrafast laser processing [8, 9]. By employing
a femtosecond ultraviolet laser, polymethyl methacrylate was ablated without the
formation of a heat-affect zone [10, 11]. Comparing to the ablation with a nanosecond
pulsed laser, the ablation threshold using a femtosecond and or a picosecond laser
was also reduced significantly. These features encourage the high-precision manufacturing using various materials, such as biological tissues, semiconductors and other
dialectical materials [12]. For an ultrafast interaction, the absorption of photons stimulates the carriers within hundred femtoseconds (fs), which is too short to disturb
lattice since the electron-phonon coupling typically occurs in range of 1-100 ps [13,
14]. Meanwhile, an ultrafast pulse width is less than 1 ps. Thus, in an ideal case,
ultrafast excitation only occurs within the focal spot. However, for a laser pulse
with duration of nanoseconds or longer, the thermal diffusion cannot be neglectable
[15]. On the other hand, the nonlinear multiphoton absorption is another important
aspect of ultrafast laser processing. The probability of multiphoton absorption can be
significantly increased with the extremely high laser peak intensity of tightly focused
ultrashort laser pulses since the probability is a power function of the peak intensity [16, 17]. The highly localized nonlinear effect of ultrashort laser may lead to a
super-resolution processing beyond the optical diffraction limit and thereby strong
absorption can even occur in a transparent material [18, 19]. This multiphoton absorption of ultrafast laser not only permits the surface processing, but also permits the
internal microfabrication of transparent materials, such as glass and polymer [20,
21]. Due to the unique multiphoton excitation and the aforementioned highly localized thermal processing, ultrafast laser is found unprecedent application for precise
micro-to-nanomanufacturing.