source (Fig.2.1). In this process, the key is the photon having exactly the same
wavelength as that of the emitted light [ 4 ]. Application of laser machining for
micro-channel fabrication and mask making is discussed in the following sections.
2.1.1 Application of Laser Machining for micro-channel making
Laser Photo-ablation was first introduced in 1997 by Roberts’s group for making
polymer microfluidic channels [ 5 ]. The integration of laser micro-beams with
micro-fluidic devices is beneficial for rapid throughput fabrication strategies par-
ticularly for Lab on chip applications to achieve the manipulations of biological
entities and biological fluids within micro-fluidic platforms [ 6 , 7 ]. One specific
advantage of pulsed laser micro-beam irradiation is that it does not require any
specialized instrumentation except a XYZ stage which would follow commends
from a drawing software. This reduces the design complexity and cost of the
individual micro-devices tremendously while increasing the speed of their fabrica-
tion by several folds. So it is economical to dispose the devices so made after a
single use. Secondly, the laser micro-beam can be positioned to any optically
accessible location within the micro-device thus provides high flexibility in
designs, enables potential parallelization of cellular analysis at multiple device
locations etc. [ 7 ].
In laser machining processes, a high power laser is used to break the bonds of
polymer molecules thereby removing the decomposed polymer parts from the
region being ablated by the laser. Excimer laser has been successfully used for
making micro-channels with 193 or 248 nm pulses with a pulsing frequency range
of 10 to several kilo-hertzs. Micro-channels can be made by a maskless direct laser
etching process or through lithographic patterning processes [ 8 ]. Laser etching is
suitable for machining a wide range of polymeric materials including polymethyl
methacrylate (PMMA) [ 9 ], polystyrene (PS), polycarbonate (PC), polyethylene
terephthalate (PET), polyethylene terephthalate glycol (PETG), polyvinylchloride
(PVC) and polyimide [ 10 ]. Surface chemistry can be modified due to the formation
Fig. 2.1 Schematic of Laser process
36 G. Bhatt et al.