Tech Briefs Magazine - May 2021 - PIT-12

TECHNOLOGY LEADERS Test & Measurement Systems

Laser power density is
defined as the power per
unit area (watt/cm2). A
change in the focus diameter - for example, due to an
incorrectly cooled lens or a
dirty protective window -
exerts a direct influence on
the power density of the
laser beam and can have
multiple consequences:
* The travel speed may have
to be reduced.
*
The quality of the maFigure 3. A schematic comparison of camera-based and beam-based
measurement techniques.
chined part in the cutting
or welding process may
2. Replace the protective window.
suffer.
3. Check the beam path adjustment.
* Production times and power consump4. Check the laser's output beam for its
tion can increase, as can the need for
power and beam profile.
expensive gases used in processing.
The central parameters to be meas* The heat-affected zone (HAZ) will be
ured are laser power, focus diameter,
larger, requiring more post-process finfocus position (x, y, z), focus shift, beam
ishing like straightening, deburring, or
profile and divergence, beam quality M2,
polishing. Under certain circumas well as BPP (beam parameter prodstances, an undetected loss in product
uct). However, for all these measurequality can lead to diminished
ments, the question of which measuring
strength - a defect that, once recogtechnology to use should not be decided
nized, may result in costly recalls.
solely based on laser power; it is essential
These technical effects inevitably take
to also know laser power density.
a significant toll on costs and sustainabil-

Figure 4. The Ophir BeamWatch integrated instrument shows the focus shift caused by dirty glass (below), as
compared with the measurement when the glass is clean (above).

ity. The greater the deviation in the
beam quality at the processing point, the
more spent on energy and process gases.
Efficient Power Measurement
Even with these clear correlations,
critics often claim that measuring the
laser beam is too expensive and the
instruments too fragile. But new technologies are available that are optimally
adapted to industrial applications.
MKS Instruments, for instance, recently introduced a new power gauge
that not only covers a wide range of laser
applications, but is also quite small, compact, and robust. The Ophir Ariel determines laser power up to 8 kW based on
a quick measurement of the energy.
Even in continuous mode, power levels
up to 500W can be measured. Different
wavelength ranges - 440-550nm, 9001100nm, 10.6 μm and 2.94 μm - can be
calibrated and measured with one
device. The included diffuser can be easily attached so that the instrument also
works with high power densities, such as
when the beam diameter is small.
Given the kinds of industrial settings
in which laser measurement is used, the
system design needs to be robust; preferably shockproof, dustproof and splashproof; with no need for cooling with
water or air. This allows for measurements in closed construction chambers,
as is often the need in additive manufacturing or robot cells. Measurements
should be readable via Bluetooth using
an app or on a PC, and shown directly
on a high-resolution display. Alternatively, they can be stored in the internal
memory and transferred over a USB-C
interface. Developers, operators and
service technicians can get a first impression of the process quality by quickly
determining the laser power with such
compact instruments.
Automated Processes
For performance measurement in
automated laser production systems,
there are also compact and robust systems available that operate without the
need for water cooling. Such systems
measure the laser beam quickly and reliably, and they transmit the data to a central data storage system via an appropriate network interface. Such systems
include a standard RS232 interface. More

Photonics & Imaging Technology, May 2021

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Tech Briefs Magazine - May 2021

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