Newport Spectra-Physics
produce 1 PW. The first petawatt
laser, built at Lawrence Livermore National Laboratory, used a
hybrid Ti:sapphire and Nd:Glass
approach, and the laser was significantly impaired in throughput
by the low repetition rate of the
Nd:Glass amplifiers. The average
power of a Ti:sapphire ultrafast
system is currently limited to less
than 50 W, primarily because the
high-energy/pulse green lasers used
to pump the Ti:sapphire amplifiers
have limited average power as well.
Many applications do not
require femtosecond pulses. Thus, All-solid-state ultrafast Ti:sapphire laser system Millen-
in the past decade, researchers and
nia/Tsunami, with the current state of the art, hands-free ultrafast Ti:sapphire laser Mai Tai in the inset.
engineers have been aggressively
developing ultrafast sources based
on materials other than Ti:sapphire. In particular, important
work has been reported on room-temperature Yb-based sources, particularly Yb:KY W and Yb:KGW. The average power of
non-Ti:sapphire ultrafast lasers is now approaching 100 W.
For materials processing and micromachining applications that require a pulsewidth of around or less than 10-15 ps
where thermal effects are minimized, the development of these
alternative ultrafast sources is driven by the simpler resulting
laser architecture (particularly where CPA is not necessary)
and cost, as well as simpler scaling of the laser average power.
This is an important consideration for many applications, since
process throughput is proportional to average power. While
the ultrafast solid-state laser field has reached maturity, in the
coming years we expect advances in the average power as well
as a continual scaling-up of peak power in excess of the exawatt level.
c
The best properties of bulk and fiber
solid-state lasers will be fused together
by the development of crystalline rather than glass fiber lasers. This exciting
development is under way, and much
progress has been reported recently.
c
Integrated lasers in which the diode
pump source and laser crystals are substantially integrated together to form
very small devices will be developed.
c
Solid-state lasers will become smaller,
higher density, and more efficient
devices. Engineering limitations posed
by the aggressive removal of heat from
small spaces will be addressed by micro-and nano-electronic cooling techniques.
c
Cryogenically cooled lasers will become
substantially more important because
of the very significant cooling and
scalability advantages, lasing advantages, elimination of
thermally induced aberrations, and operation in a parameter
space that may offer substantial benefits not yet realized.
c
Additional lasing and nonlinear crystals will be discovered
and lead to further wavelength diversity and perhaps higher
efficiency.
After decades of steady progress, it would be easy to come
to the conclusion that most of the important discoveries in
solid-state lasers have already been made. We disagree. While the
trends we predict for the future may or may not come to pass,
surely the combination of a vast technological database and the
hard work of creative individuals around the world will lead to a
vibrant future for solid-state laser technology. t
The authors are grateful for the expertise and assistance provided by
Victoria Vitali, optical engineer at Snake Creek Lasers.
Future trends
What may we expect from solid-state lasers in the coming
decades? While some trends seem apparent now, we cannot
often foresee surprise developments. An example would be the
discovery of laser materials whose lasing ions could be directly
excited by electron impact, enabling optical pumping to be
eliminated entirely. More likely, however, the field will progress
as it has for decades, with each incremental advance building
upon previous work. We predict the following trends:
c
Higher average and peak powers will be achieved, with solid-state laser average power exceeding the megawatt level, and
peak power the exawatt level.
c
Fiber and bulk laser technologies, which have evolved separately,
will become entwined to form even more powerful and diverse
devices. Recent work on direct-pumping into the upper laser
level of bulk mid-infrared solid-state lasers with fiber laser sources shows that such combinations can be profitably employed.
David C. Brown ( DBrown@snakecreeklasers.com) is the founder, president
and CTO of Snake Creek Lasers LLC in Hallstead, Pa., U.S.A. Jerry Kuper
is a senior consulting laser physicist.
[ References and Resources ]
>> Visit Optics InfoBase ( www.opticsinfobase.org) for easy access to
the latest publications.
>> W. Koechner. Solid-State Laser Engineering, Springer-Verlag, 1976.
>> P.F. Moulton. JOSA B 3, 125-33 (1986).
>> T. Y. Fan and R.L. Byer. IEEE J. Quantum Electron. 24, 895-912
(1988).
>> M. Yamada et al. Appl. Phys. Lett. 62, 435 (1993).
>> V. Dominic et al. Electron. Lett. 35, 1158–60 (1999).
>> J. Lu et al. Journal of Alloys and Compounds 341, 220-5 (2002).
>> M.E. Fermann, A. Galvanauskas and Gregg Sucha, eds. Ultrafast
Lasers, Technology and Applications, Marcel Dekker, New York,
2003.
>> A. Mooradian. United States Patent #4,860,304.
>> J. Marmo et al. SPIE Photonics West 2009, paper 7195-06.
