1 Femtosecond Laser Filamentation Induced Phenomena and Applications
13
Besides, to make multiple parts on a piece of glass, certain margins need to be
kept so as to avoid cross cracking. For example, on a piece of glass whose size
can accommodate 7 mirrors, only 5 can be cut by diamond because of the margins
between two mirrors. Finally glass needs to get grinded by 300–400 µm to remove
micro cracks from the edges. This also uses a lot of machinery and DI water. As to
the quality, let us look at an example. Soda lime glass with a thickness of 1.6 mm
will have 30–40 MPa bending strength right after diamond cut. This test is done by
a machine called 4-bend testing. It uses two base rods as glass holder then two other
rods from the top to push the glass to bend. The pressure at which the glass cracks is
measured. This number is not acceptable to Motor vehicle authorities. They thus need
to grind the edges to remove the cracks. After this process, they reach 70–80 MPa.
Using fs laser filament cutting, without using water, a cutting speed at 500 mm/s is
used; it is twice faster than diamond rollers. The edges are free from micro cracks
and chips; therefore, it doesn’t need grinding and that means saving water. Bending
test results in 120–130 MPa. Now if only 4–5 µm of the sharp edge gets dry grinded
(no water and just one grinder touching the glass edges to chamfer it) it will result in
220 MPa! Also, on the same piece of glass whose size can accommodate 7 mirrors,
7 parts can be cut instead of 5. The yield jumps from 70 to 99.9%; that is a huge
glass saving. This helps the reduction of CO 2 emission in glass production.
In another aspect, cutting glass less than 500 µm thick with diamond was a big
challenge up until 2012 because thinner glass couldn’t resist the diamond roller
pressure. No one could cut 400 µm thick glass. Previously, using diamond cutting,
4 layers of glass each 550 µm thick are used on a cell phone. Using filament cutting
technique, each layer becomes 150–200 µm thick. Suddenly the total thickness drops
by about 800 µm or becomes about three times thinner. That means about 63%
reduction in glass production; this also means less CO 2 emission. Also, the yield in
cutting is better; i.e. more saving in the cost. This is why smart phones get thinner,
lighter and cheaper.
1.9 Wood Cutting
Similar to cutting brittle materials discussed in Sect. 1.8, an air filament was used
to cut wood surface there-by exposing the cell structures under an electron microscope [62, 63]. The intense light in the filament zone exploded the cellulose material
‘instantaneously’ without oxidation (i.e. no burning). Each cell’s interior structure
was exposed. This ‘clean’ cut would never be achieved using even the sharpest
mechanical knife to cut the wood. Mechanical cutting will always result in a significant squeezing of the wood cells thus blocking the view of the interior of the cell
[63].
The physics of interaction has not been studied systematically by the author’s
group and probably not by other groups to the limited knowledge of the author.
A speculation is the following. Similar to the case of glass or metal, multiphoton
transition from the valence to conduction band followed by inverse Bremsstrahlung
13
Besides, to make multiple parts on a piece of glass, certain margins need to be
kept so as to avoid cross cracking. For example, on a piece of glass whose size
can accommodate 7 mirrors, only 5 can be cut by diamond because of the margins
between two mirrors. Finally glass needs to get grinded by 300–400 µm to remove
micro cracks from the edges. This also uses a lot of machinery and DI water. As to
the quality, let us look at an example. Soda lime glass with a thickness of 1.6 mm
will have 30–40 MPa bending strength right after diamond cut. This test is done by
a machine called 4-bend testing. It uses two base rods as glass holder then two other
rods from the top to push the glass to bend. The pressure at which the glass cracks is
measured. This number is not acceptable to Motor vehicle authorities. They thus need
to grind the edges to remove the cracks. After this process, they reach 70–80 MPa.
Using fs laser filament cutting, without using water, a cutting speed at 500 mm/s is
used; it is twice faster than diamond rollers. The edges are free from micro cracks
and chips; therefore, it doesn’t need grinding and that means saving water. Bending
test results in 120–130 MPa. Now if only 4–5 µm of the sharp edge gets dry grinded
(no water and just one grinder touching the glass edges to chamfer it) it will result in
220 MPa! Also, on the same piece of glass whose size can accommodate 7 mirrors,
7 parts can be cut instead of 5. The yield jumps from 70 to 99.9%; that is a huge
glass saving. This helps the reduction of CO 2 emission in glass production.
In another aspect, cutting glass less than 500 µm thick with diamond was a big
challenge up until 2012 because thinner glass couldn’t resist the diamond roller
pressure. No one could cut 400 µm thick glass. Previously, using diamond cutting,
4 layers of glass each 550 µm thick are used on a cell phone. Using filament cutting
technique, each layer becomes 150–200 µm thick. Suddenly the total thickness drops
by about 800 µm or becomes about three times thinner. That means about 63%
reduction in glass production; this also means less CO 2 emission. Also, the yield in
cutting is better; i.e. more saving in the cost. This is why smart phones get thinner,
lighter and cheaper.
1.9 Wood Cutting
Similar to cutting brittle materials discussed in Sect. 1.8, an air filament was used
to cut wood surface there-by exposing the cell structures under an electron microscope [62, 63]. The intense light in the filament zone exploded the cellulose material
‘instantaneously’ without oxidation (i.e. no burning). Each cell’s interior structure
was exposed. This ‘clean’ cut would never be achieved using even the sharpest
mechanical knife to cut the wood. Mechanical cutting will always result in a significant squeezing of the wood cells thus blocking the view of the interior of the cell
[63].
The physics of interaction has not been studied systematically by the author’s
group and probably not by other groups to the limited knowledge of the author.
A speculation is the following. Similar to the case of glass or metal, multiphoton
transition from the valence to conduction band followed by inverse Bremsstrahlung