"
Vol.
B10,
Supplement
CHINESE
JOURNAL
OF
LASERS
April,
2001
Recent Progresses in the Field
of
High Power
Diode
Lasers
(Invited)
DU
Kerning
(Frcmnhofer Institue
fUr
LasertecJmiJc
(ILT)
, Stei:nhachstr.
15,
52074
Aachen, Germany)
Abstract
At
the
moment
the available output power from a typical
200
11m
emitter is
about
2
W.
Typical
diode laser bars consist
of
about
20
emitters
and
deliver
about
40 W to
50
W with life time
of
more
than
10000
h.
The
beam
quality
after
fast axis collimation is
about
M2
= 3 along the fast axis
and
1500
along
the slow axis
and
is
extremely
asymmetrical.
For
enabling efficient fiber coupling
of
diode laser radiation
different
beam shaping techniques
have
been developed.
The
common
of
all beam shaping techniques
is
to
group the beam into sub beams along the slow direction and to rearrange
them
along the fast axis.
The
beam
quality
along both axis
can
be matched by a suitable selecting the
number
of
sub beams.
For
getting higher
power diode laser
bars
are stacked along the fast axis.
To
minimize the loss in beam quality diode laser bars
can
be mouted
by
the side
of
each other along the slow axis
and
the radiation
of
each diode laser
bar
can
be
stacked by optical means.
Using dichroitic optical
components,
diode laser beams with
different
wavelength
can be coaxial superpositioned.
In
this
way
the power
of
diode laser system
can
be scaled with the
number
of
wavelength
without
loss
of
beam
quality
in relation to it
of
a single diode laser bar. By using a wave
plate
and
a polarisation beam splitt
two
diode laser bars
can
be superpositioned without
influnence
on
the
beam quality.
Recently,
deep penetration welding
of
alloyed steel has been demonstrated.
1 Introduction
The
main
advantages
of
diode lasers
are
their small
size,
long life
time,
high efficiency
and
frequency
controllability. Table 1 shows the comaprison between diode lasers
and
nondiode lasers.
Table 1
Diode lasers N ondiode laser
-multibeam/beam
array
-single beam
output
-limited
output
power per emitter
-no
power limit
-line
shaped beam cross-section
-mostly
circular beam cross-section
-divergence
(FWHM)
-divergence
(FWHM)
typically some
mrad
-beam
quality,
Mi.
= I,M;. =
1700
-beam
quality,
M2
= 1
~
80
-compact
-large in size
-efficiency up to
50
%
-efficiency up to 15 %
-polarization ratio
1:
10
-to
be determined
-wavelength
selectable
780~
1
000
nm
-determined
by
active element
-low
energy
storage capacity
At
the
moment
the obtainable
output
power
from
a typical
200
I-lm
emitter is
about
2
W.
Typical
diode laser
bars
consist
of
about
20
emitters
and
deliver
about
40
W.
The
beam
quality
after
fast axis
collimation is
about
M2
= 3 along the fast axis
and
1500
along the slow axis
and
is
extremely
asymmetrical.
For
enabling
efficient
fiber coupling
of
diode laser radiation
different
beam
shaping
techniques
have
been developed.
The
common
of
all beam shaping techniques is to
group
the
beam
into