Page 189 - High Power Laser Handbook

158 Diode Lasers High-Power Diode Laser Arrays 159

Figure 6.25 Laser
brazing of an
automotive part.
(Courtesy of
LaserLine)

6.7.2 Medical Applications
Diode lasers are used in a variety of medical applications, such as
hair removal, tattoo removal, endovenous laser treatment (EVLT),
photodynamic therapy, dental surgery, and cosmetic surgery. In hair
removal, an 810-nm laser operating in pulse mode delivers light
through a handheld device to the skin surface. The laser light is read-
ily absorbed in the dark matter (melanin) of the hair follicle, remov-
ing the hair while sparing the rest of the skin. Tattoo removal is very
similar to hair removal. The selective absorption of the laser light in
the color-embedded skin tissue leads to fragmentation of the tissue;
these fragments are then absorbed by the body and eliminated. The
main difference between the two is the use of multiple wavelengths
to remove the various colors of ink used in tattoos. A wavelength
range between 670 and 890 nm is used to remove green and blue inks,
while a range of 500 to 700 nm is used to remove red, orange, and
purple inks. Black ink absorbs all wavelengths.
In dental surgery, such as periodontal (gum) surgery, a 980-nm
fiber-coupled diode laser is used for precision cutting of soft gum tis-
sue. This allows faster healing and relatively less scarring as com-
pared with other techniques.
The treatment of varicose veins is another procedure that is now
using diode lasers. In EVLT, an 808-nm laser beam operating in the
15 to 30 W range is delivered inside the varicose vein via a microfiber
delivery. The laser destroys the varicose vein from the inside, and
the damaged vein is eventually absorbed and eliminated as waste by
the body.

6.7.3 Defense Applications
Diode lasers, by virtue of their high efficiency, small footprint, com-
pactness, robustness, and low operating costs, are widely deployed in
defense applications. Diode lasers mounted on ground and airborne
military vehicles are used as illuminators. An illuminator typically con-
sists of several stacks, with each stack consisting of both axis-collimated
diode laser bars operating in QCW mode so that lasers can be conduc-
tively cooled. These stacks can deliver multikilowatt peak power at a