Fabrication of Biosensor Chips - From Bioimaging to Biosensors: Noble Metal Nanoparticles in Biodetection - page 130

of picoseconds (picosecond, ps = 10 −12 s). If this laser comes up
short, the femtosecond laser has a pulse width of femtoseconds
(femtosecond, fs = 10 −15 s). Using a focused femtosecond laser,
the pulse energy can be lowered to achieve a very high power
density, with a high power output of 10 GW. When the laser pulse
irradiates the processing surface, the instantaneous high power
causes a high absorption of laser energy in the material, allowing it
to be stripped as part of the processing mechanism [42]. The main
processes on the material are femtosecond multiphoton absorption
and multiphoton absorption material produced after avalanche
ionization, so it can break through the fused silica material's light
absorption properties in the 400~1500 nm wavelength. In addition,
due to its very short laser pulse width, the material absorbs this
energy so quickly that almost no heat is transferred, and the
material in the processed area is almost entirely unaffected by
heat. Unlike in continuous laser processing, the femtosecond laser
pulse does not cause a plasma effect, resulting in high processing
eficiency. In addition, unlike with traditional laser focusing spots,
the femtosecond laser processing threshold value is clear and, if
precise control is maintained of the femtosecond laser pulse power
density, only a very small Gaussian beam centre area of energy is
higher than the threshold value. The result is that, unlike with a
traditional laser, the processing of the nonlinear absorption effect,
optical diffraction limit, realization of submicron particles or
nano-level of processing capacity, and the processing zone and the
non-processing area boundaries can be accurately controlled and
repeated.
Many researchers have used femtosecond lasers on multi-mode
optical ibers to produce window ibers [43-45]. Optical ibers
consist of three different layers. The outer jacket layer's material is
mainly made of polymer. The other two layers are mainly made of
fused silica. Therefore, the production of window iber needs to set
the laser's energy at different strengths, adjusting the energy level
to where the outer layer of the polymer jacket layer is removed,
then adjusted again when the iber cladding layer and iber core
layer are off, processing to the set side, then using the defocused
laser technique to heat the exposed core. This can improve the
roughness on the surface that was created during processing. The
femtosecond laser's high precision allows window iber to form
different shapes and arrangements, as shown in Fig. 6.19.