12
S. L. Chin
1.8 Industrial Application: Cutting Brittle Materials Using
Filaments
This section deals the repetitive effect of using a train of high repetition fs or ps
laser pulses to interact with a solid transparent and brittle material such as glass. A
train of sufficiently powerful fs or ps pulses, when focused onto the surface of the
material, will form filaments from the surface into the material as if they ‘pierce’ into
the surface successively. These pulses are not powerful enough yet to form filaments
in air. When a filament is formed inside the solid surface, a plasma will be created
through multiphoton transition of electrons from the valence to the conduction band
followed by inverse Bremsstrahlung and partial avalanche ionization [7]. After each
interaction with a filament in the fs/ps time scale, the material will relax thermally
in the ms time scale. But before the thermal relaxation of the material is complete;
i.e. back to room temperature, a second filament will be formed in the material at
the same position. This second filament will see the material modified by the first
filament. The interaction physics will become different. In general, the preceding
pulse will ‘soften’ the material for the second pulse to interact with. This thermal
softening would mean less abruptness in the interaction, (hence, avoiding shockwave
cracking of the material) thereby resulting in a clean ‘cut’.
This technology is based upon the finding of a new class of interaction using
high repetition rate (>100 kHz) pulse-train bursts of ps to fs laser pulses [50]. Each
pulse-train burst contains tens of pulses with about 10 ps duration or shorter [51].
The pulses are spaced by a few ns. The focused pulses in each burst interact with the
material from the surface inward. These pulses are spaced by a short time interval
such that before the thermal and other slow relaxation inside the interaction zone
have completed, the second pulse arrives. That is to say, each pulse prepares the
material surface or bulk so as to alter the interaction with the subsequent pulse
thereby improving or optimizing the interaction [51].
Based upon the above mentioned findings [50, 51], S. Abbas Hosseini added the
advantage of fs laser filaments to efficiently cut brittle materials such as glass in a way
that is superior to diamond cutting (see later). Because of intensity clamping inside
the filament, the interaction is almost constant from shot to shot even if the laser
energy fluctuates a bit. A variety of cutting techniques was thus invented by Hosseini
[52–60] to deal with the change of materials and the change of cutting contours,
shapes, etc. In no time, the technology spread into many industries that use brittle
windows or surfaces. Almost all major companies such as Corning, Asahi, Siant
Gobain and Schott, etc. that manufacture or use glass for automobile (car mirrors,
dashboards), Aerospace (airplane windows), microelectronics, cell phones (cover
windows) use this technology.
The technology is superior to diamond cutting from the economic and environmental point of view. The following is adapted from a private communication with
S. Abbas Hosseini [61].
Glass cutting by diamond uses de-ionized (DI) water while doing the rolling.
Micro cracks and chips could develop into major cracks and this reduces the yield.
S. L. Chin
1.8 Industrial Application: Cutting Brittle Materials Using
Filaments
This section deals the repetitive effect of using a train of high repetition fs or ps
laser pulses to interact with a solid transparent and brittle material such as glass. A
train of sufficiently powerful fs or ps pulses, when focused onto the surface of the
material, will form filaments from the surface into the material as if they ‘pierce’ into
the surface successively. These pulses are not powerful enough yet to form filaments
in air. When a filament is formed inside the solid surface, a plasma will be created
through multiphoton transition of electrons from the valence to the conduction band
followed by inverse Bremsstrahlung and partial avalanche ionization [7]. After each
interaction with a filament in the fs/ps time scale, the material will relax thermally
in the ms time scale. But before the thermal relaxation of the material is complete;
i.e. back to room temperature, a second filament will be formed in the material at
the same position. This second filament will see the material modified by the first
filament. The interaction physics will become different. In general, the preceding
pulse will ‘soften’ the material for the second pulse to interact with. This thermal
softening would mean less abruptness in the interaction, (hence, avoiding shockwave
cracking of the material) thereby resulting in a clean ‘cut’.
This technology is based upon the finding of a new class of interaction using
high repetition rate (>100 kHz) pulse-train bursts of ps to fs laser pulses [50]. Each
pulse-train burst contains tens of pulses with about 10 ps duration or shorter [51].
The pulses are spaced by a few ns. The focused pulses in each burst interact with the
material from the surface inward. These pulses are spaced by a short time interval
such that before the thermal and other slow relaxation inside the interaction zone
have completed, the second pulse arrives. That is to say, each pulse prepares the
material surface or bulk so as to alter the interaction with the subsequent pulse
thereby improving or optimizing the interaction [51].
Based upon the above mentioned findings [50, 51], S. Abbas Hosseini added the
advantage of fs laser filaments to efficiently cut brittle materials such as glass in a way
that is superior to diamond cutting (see later). Because of intensity clamping inside
the filament, the interaction is almost constant from shot to shot even if the laser
energy fluctuates a bit. A variety of cutting techniques was thus invented by Hosseini
[52–60] to deal with the change of materials and the change of cutting contours,
shapes, etc. In no time, the technology spread into many industries that use brittle
windows or surfaces. Almost all major companies such as Corning, Asahi, Siant
Gobain and Schott, etc. that manufacture or use glass for automobile (car mirrors,
dashboards), Aerospace (airplane windows), microelectronics, cell phones (cover
windows) use this technology.
The technology is superior to diamond cutting from the economic and environmental point of view. The following is adapted from a private communication with
S. Abbas Hosseini [61].
Glass cutting by diamond uses de-ionized (DI) water while doing the rolling.
Micro cracks and chips could develop into major cracks and this reduces the yield.