Laser World of Photonics
Hall A2, Booth 542
www.industrial-lasers.com MAY/JUNE 2017 Industrial Laser Solutions 23
lasers will drive down the cost-per-watt
curve while enhancing capability to con-
tinue the expansion of its usage in volume
Comparing nanosecond lasers to picosecond lasers, early work [ 1] shows that
reduced melting of stainless steel occurs
when processed using picosecond laser
pulses instead of nanosecond pulses.
Many other studies have shown that
machining quality—defined as width of
HAZ, debris formation, and molten material
buildup and splatter around the laser-ma-chined edges—improves when a picosecond laser is used for micromachining. Also,
the material removal threshold, defined as
minimum fluence measured as energy per
area (mJ/cm2), required for material removal
is much lower for a picosecond laser pulse
than a nanosecond pulse.
The higher peak power achieved
because of the shorter picosecond
pulse width clearly helps initiate material
removal at a much-lower energy per pulse.
However, from a practical viewpoint, a
majority of cutting or drilling processes are
executed at a much higher fluence than the
material removal threshold, and a nanosecond laser with the same average power
provides higher throughput than a picosecond laser. If higher quality is an important requirement for the process, then using
a picosecond laser instead of a nanosecond laser is necessary.
Once that choice is made, a picosecond
laser with the appropriate power level will
need to be selected to meet the throughput
requirement. FIGURE 2 shows 0.7mm-thick
Gorilla Glass scribes created using UV
nanosecond and green picosecond lasers
under similar process conditions, with the
lasers operating at the same 30W average
power and 1MHz pulse repetition frequency.
The ~70µm scribe depth was achieved using
a UV nanosecond laser, whereas ~40µm
scribe depth was achieved using a green
picosecond laser. However, edge chipping
for the UV nanosecond laser processed
glass was ~18µm compared to ~9µm
achieved using a green picosecond laser.
In addition to the quality benefit and
throughput disadvantage of picosecond vs.
nanosecond lasers, the economics must
also be considered since picosecond lasers
are usually significantly more expensive for
both upfront cost and cost of ownership.
Spectra-Physics’ IceFyre industrial picosecond lasers, which offer widely adjust-
able repetition rates, a programmable burst
mode capability, and high reliability, will
enable advances and new applications in
micromachining that were previously impossible because of process flexibility, reliability, cost-performance, or size constraints.
Moving to even shorter pulse widths, the
choice between picosecond and femtosecond laser pulse widths for micromachining
depends on the material to be machined,
quality requirements, and economic con-
siderations. A femtosecond laser may provide quality improvement over a picosecond
laser, but the higher laser cost is a serious
consideration. Both picosecond and femtosecond lasers provide high peak power and,
therefore, lower material removal threshold fluence. The removal threshold flu-
ence for femtosecond laser pulses is lower
than picosecond pulses for many materials. However, at fluence levels higher than
the threshold where most of the practical