2 Industrial Laser Solutions MAY/JUNE 2015 www.industrial-lasers.com
New CO laser offers high-power, 5–6µm output
Carbon monoxide (CO) laser technology was developed in
the mid-1960s at the same time as CO2 lasers. The CO laser
was attractive because it had the potential to be 2x more
effcient than CO2 lasers. However, the CO laser presented
challenges: Early CO lasers needed to be cooled to get high
powers with high effciency (very high-power versions were
actually cryogenically cooled) and the laser output power
would degrade quickly; typical lifetimes were tens of hours
at most. Consequently, CO2 laser technology “won” and
has been the gas laser standard since.
Coherent has developed proprietary technology that
allows for CO lasers that operate at very high output powers
in the 5–6µm range at high effciencies at room temperature and that last for thousands of hours. The new Coherent CO laser employs much of the same technology developed over many years for Coherent’s CO2 laser products.
Coherent is developing CO lasers using waveguide and
slab designs that will offer high average continuous-wave
(CW) power and high-peak-power pulsed operation. Typical output power for CO lasers yields roughly 70 percent
of that of a CO2 laser. The CO laser version of the Coherent
J- 3 laser, for example, produces roughly 230W at ~5µm (at
room temperature), while the same J-3-based CO2 laser
produces 340W at 10.6µm.
There are many benefts when materials processing at
5µm, the foremost of which is the “light-material” interaction
advantage. At 5µm output, it will have signifcantly different
interactions compared to CO2 laser output simply due to the
different absorption coeffcients. It has stronger absorption
in many flms, polymers, PCB dielectrics, ceramics, and
composites. Very low attenuation of the 5–6µm laser light
in chalcogenide and heavy metal fuoride fbers open the
potential for fber delivery.
One application in which this difference in absorption
coeffcient has a signifcant impact is in glass cutting.
In CO2 laser-based glass cutting, the 10.6µm output is
absorbed very strongly at the surface. The heat generated at the surface must then diffuse into the bulk material; subsequent water jet cooling is then used to produce
a thermal shock, which creates a scribe line in the glass.
For thicker glass substrates,
this is followed by mechanical breaking. The overall process is the same with
the CO laser; however, glass
absorption of the 5µm output is much lower. Thus, the
light penetrates directly and
further into the bulk material, inducing heating more
evenly throughout the thickness of the glass. Testing at
Coherent has shown this to
produce several important
benefts, including no surface
melting, no cracks, and zero
residual stress in the glass.
The result is a better-quality cut, stronger glass, and a
wider cut process window (FIGURE).
Another important advantage is that the CO laser
enables radial (free-form) glass cutting. In contrast, CO2
lasers can only produce straight-line cuts because the
inherently round output beam must be reshaped into a
long, thin line beam to distribute the heat generated at the
surface. Curved cuts are particularly important in smartphone display applications because curved corners or
shaping to accommodate buttons and controls are often
required. Curved and free-form cuts are possible with the
CO laser, where the round beam penetrates directly into
the glass without adverse heat effects caused by the dif-fcult-to-control diffusion process.
The other major beneft of the 5µm wavelength of the
CO laser output is that it can focus to a much tighter
spot size with a longer depth of focus that allows drilling smaller holes and cutting with narrower kerf widths.
The smallest spot size that can practically be achieved
for a CO2 laser is roughly 55µm, where the limit for the
Cross-sections of 0.7mm-thick Corning CT24 glass, taken with a Nomarski
differential interference contrast microscope. The piece cut with a CO2 (~10µm)
laser (a) shows residual stress, while the cut produced with the CO (~5µm) laser
(b) is defect-free.