photonicsproducts
PHOTONICS PRODUCTS: HIGH-POWER LASER-DIODE ARRAYS
Diode arrays are compact,
high-power light dynamos
JOHN WALLACE, SENIOR EDITOR
High-power laser-diode arrays,
which are made of stacks of individual or multistripe laser diodes, or in
some cases vertical-cavity surface-
emitting lasers (VCSELs), can put out
watts to kilowatts of optical power
for uses such as laser pumping, in-
dustrial heating, illumination, or as
the input for fiber-optic direct-diode
laser devices for materials processing
or for medicine.
Laser diodes typically have much
higher electrical-to-optical (wall-plug)
efficiencies than other types of lasers;
in fact, they are some of the most-effi-cient light emitters
known. The
disadvantage of laser-diode
arrays is
their relatively
low beam
quality—
there are no
single-mode
kilowatts-level la-
ser-diode sources in our near future.
However, there are many applications
that do not require a single-mode
beam; in addition, laser
manufacturers are con-
stantly refining beam-
combining techniques
to produce ever-bright-
er high-power laser-di-
ode sources.
From watts to kilowatts
“High-power diode lasers are com-
monly referred to as being bar-based
or single-emitter-based,” says Steve
Patterson, VP and GM of DILAS
(Tucson, AZ). “In point of fact, they
exist on a continuum with single emit-
ters on one end and bars—typically
a centimeter wide or less, consisting
of multiple emitters on a single piece
of semiconductor—on the other. The
diode lasers are then mounted to any
of a variety of heat sinks, the choice
depending upon operating conditions
and what final package the diode la-
ser bar might go into.”
DILAS produces laser bars
that range in output pow-
er from single-digit values
out to hundreds of watts
per bar. Their wavelengths
range from 635 nm (visible
red) to greater than 2300 nm and be-
yond, with electrical-to-optical effi-
ciency reaching to more than 70% in
some cases, notes Patterson.
The mounted bars can then be
packaged into arrays that produce
up to kilowatts of total output pow-
er, whether the output be a free-space
laser beam or coupled into an optical
fiber. With these sorts of capabilities,
says Patterson, “any market from the
traditional pumping of solid-state and
fiber lasers, to direct-diode applica-
tions in medicine such as dermatology
or phototherapy, to industrial process-
ing of materials such as the deposition
of laminates to emerging markets in
cinematography and enhancements in
advanced medical-imaging technolo-
gies may be addressed.”
Patterson notes that there have been
many new developments over the past
year: for example, enhancements in
visible red and blue outputs for appli-
cations in cinematography and medi-
cal photodynamic therapy; fiber-cou-
pled systems that output on the order
of 10 k W in wavelengths ranging from
around 800 nm to 1000 nm, typical-
ly used for all sorts of materials pro-
cessing, including welding; and a unit
developed to enhance magnetic-reso-
nance imaging (MRI).
“All aspects of diode-laser tech-
nology were challenged here,” says
Patterson. The challenges included
development of the basic epitaxy de-
sign of the diode laser, advances in
With their high-power density, high
efficiency, and long life, laser-diode
arrays are the essential light source
for materials processing, laser
pumping, and other applications.
