University of Rochester
Expansion of the
engineering database
Before the mid-1970s, those in
the field worked hard to collect
critical laser design parameters,
such as stimulated-emission
cross-section information and
absorption cross-section data, as
well as the physical and thermal
parameters needed to generate
credible laser designs. Because
lasers were flashlamp-pumped,
with output typically from the
ultraviolet to the near-infrared
spectral region, lasing ions that
efficiently absorbed the broad-
100
band light from Xe and Kr lamps
Xenon flashlamp
100
were preferentially investigated,
80
80
and yttrium aluminum garnet
(Y Al O ) or YAG became the
Intensity [a.u.]
60
3 5 12 3,000 A/cm
2
60
gold standard of crystalline laser
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materials. Nd:Glass was also
important because of its broad-
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band absorption characteristics,
although Nd:Glass lasers were
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either single-shot devices or
1,000 A/cm
2
devices operated at low repeti-
0
tion rates due to poor thermal 0 . 2
conductivity and low thermal
shock resistance.
Nd:Glass lasers were the
primary tool of the laser fusion
community; that is one of the
few things that has not changed in three decades. The first comprehensive book devoted strictly to engineering solid-state lasers
was written by Walter Koechner and published by Springer-Verlag in 1976. It heralded the arrival of solid-state lasers as a
distinct discipline, and contained a wealth of information about
fundamental laser physics, laser materials, flashlamp-pumping,
thermal effects, nonlinear optics and damage effects in solid-state
lasers. At the time, the book was a most-welcome development
that began filling in some of the missing information and database needed for intelligent solid-state laser design.
Today, the field is considerably more mature and complex.
In the past two decades, dozens of books have been published
about solid-state lasers, lasers and related materials. In addition,
we now have a detailed knowledge of the energy-level structure, spectroscopy and crystalline properties of laser materials
for a large number of laser crystals, including entirely new
crystals that did not exist two decades ago, or whose development was delayed until the arrival of a new pump source: the
laser diode. The majority of laser and nonlinear crystals in use
today were improved or made possible due to diode-pumping;
these include Nd:YVO , Nd:YALO, Ti:sapphire, alexandrite,
4
Cr:LiSAF, Cr:BeAl O , Nd:GGG,
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Cr,Nd:GSGG, Co:MgF ,
2
Nd:GdVO , KTP, BBO, LBO,
4
PPLN, PPKTP, and many others.
Within the past 20 years,
researchers have made a number
of significant discoveries and
improvements in laser materials.
We now have a richer understanding of heat generation in
solid-state lasers, the important
role that excited-state absorption and up-conversion play in
some solid-state laser materials,
and the best designs to maximize
laser performance, beam-quality
Diode laser
and efficiency. The management
of thermal effects in solid-state
lasers—once a major impedi-
ment to their advancement as
high average power devices—has
gradually yielded to improve-
ments because diode-pumping
delivers the pump energy in a nar-
row spectral band that is efficient
in 1) exciting the desired optical
transition, 2) developing the low
quantum defect laser materials, 3)
managing and reducing thermal
gradients through the use of
clever designs like zig-zag slab or
thin-disk amplifiers, 4) cryogenic
cooling, and 5) incorporating
adaptive-optic elements into laser resonators.
The development of ultrafast lasers has enhanced our
understanding of the physics and engineering of solid-state
lasers and related optical materials in which the management of
dispersion and nonlinear effects is of paramount importance.
Peter Moulton’s discovery of titanium sapphire (Ti:Al O ),
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with its unprecedented broad-gain bandwidth, set the stage for
the development of few-cycle mode-locked femtosecond laser
sources. These devices have allowed the investigation of entirely
new physical phenomena and the elucidation of complex atomic
and molecular dynamics down to the attosecond regime.
This work has given us a detailed understanding of the many
nonlinear processes that can either enhance or seriously degrade
the performance of a solid-state laser. In fiber lasers, for example,
the threshold for stimulated Raman scattering must be addressed
in the system design to control this higher-order nonlinear process. Self-focusing can be used to self-mode-lock ultrafast lasers
and can also seriously damage laser crystals or glass in other
high-peak-power systems.
The past decade has witnessed the development of new
ceramic laser materials in Japan based on nanotechnology. These
University of Rochester Laboratory for Laser Energetics
flashlamp-pumped glass development laser. The picture, taken
around 1975, was used in fusion laser design experiments.
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Diode
0
0.802 0.804 0.806 0.808 0.81 0.812 0.814
Wavelength [µm]
λ = .8085 µm
0
∆ λ = .002 µm
. 4. 6. 8 1.0 1. 2 1. 4 1. 6 1. 8 2.0
Wavelength [µm]
Comparison of the broad spectral output of a flashlamp oper-
ated at 3,000 A/cm and 1,000 A/cm current densities and the
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narrow output of a diode laser.
