Snake Creek Lasers
materials offer unprecedented size laser average power was the genera-scaling for lasing crystal elements tion of large amounts of heat from
with optical, lasing, spectroscopic flashlamp-pumping and the sub-and other physical properties that sequent removal of heat from the
are nearly identical to bulk single lasing element. The spectral output
crystals grown by more classical of Xe flashlamps typically extends
methods. This technology promises from 300 to more than 1,000
to spawn new laser materials or nm. For Nd, in which pumping
combinations of laser materials and occurs even in the ultraviolet, the
the possibility of tailoring the dop- average quantum defect between
MicroGreen 532-nm DPSS laser first produced by Snake
ant profile—a development the absorbed and lasing photons
Creek Lasers in 2004. This laser will enable more visible align-
that can be important in suppress- ment tools and small personal projection display products. was very large, and this was the
ing parasitic oscillations and gener- primary cause of the typically low
ating more uniform gain and thermal profiles, for example. efficiencies of early solid-state lasers.
Also, researchers and engineers have made much progress For crystals that utilize dopant ions like Yb—whose absorp-
in their ability to manipulate crystals through the use of vari- tion occurs only near 940 and 975 nm—pumping using
ous bonding methods to form very small devices or integrated flashlamps resulted in very low efficiencies. The large amount
devices that offer simplicity and ease of use. Diffusion-bonding, of heating that occurred contributed to significant ground-state
as pioneered by Onyx Optics, can be used to bond un-doped absorption, reducing the obtainable gain and increasing the
end caps, for example, on rods or slabs to minimize strain- laser threshold. The first commercial diode-laser-pumped laser
induced distortion at lasing surfaces, or to create unique laser products were introduced in the mid-1980s. The motivation
waveguides. Crystals that are difficult to diffusion-bond, such as for this development was spurred by the recognition that bright
Nd:YVO and KTP, are used in green lasers. They can be contact- quasi-monochromatic sources with bandwidths measured in
bonded or, for low-power lasers, glued together to form minia- a few nanometers were far superior as a pumping source for
ture devices whose dimensions are measured in millimeters. A solid-state lasers than a low-brightness broadband flashlamp. The
new bonding technique that uses chemical diffusion-bonding or higher efficiency achieved by laser pumping of a solid-state laser
indium promises to extend this trend and allow even more dis- produced better quality lasers in much smaller packages. This
similar materials to be combined into complex structures. technology allowed the development of diode-pumped lasers,
Solid-state lasers have evolved from their initial discrete wave- where previously small microchip lasers were not feasible.
length coverage of the infrared, visible and ultraviolet spectral In the mid-1970s, there were no commercial laser diode sup-
regions. Enormous progress has also been made in developing pliers, and the technology to produce reliable devices and tailor
new nonlinear crystals, and solid-state lasers are now routinely the output wavelength to specific solid-state laser absorption
made to be much more frequency-diverse. Laser systems are bands was in its infancy. By the mid-1980s, significant programs
commercially produced that span the mid-infrared to the ultra- were in place—at General Electric and RCA David Sarnoff Labs,
violet range using frequency doubling and tripling and optical for example—to demonstrate high-power GaAs laser diodes suit-
parametric oscillators, respectively. In the past decade, we’ve able for pumping Nd:YAG. Around the same time, a start-up
seen the emergence of periodically poled nonlinear crystals that company, Spectra Diode Laboratories (SDL), was beginning to
eliminate walk-off between the fundamental and harmonic wave offer low-power single-emitter diode lasers whose output was
in the crystal and offer high nonlinear coefficients, thus further measured in tens or hundreds of milliwatts. The laser group at
enabling high-efficiency operation in processes such as sum- Stanford University led by Robert Byer was just beginning to
frequency mixing and optical parametric generation. develop low-power diode-pumped solid-state lasers, and they
Another significant trend is the production of devices that pioneered many advancements in compact high-performance
are increasingly compact and efficient. Many technologies have solid-state lasers.
made this trend possible. Devices are now routinely produced The field is now dominated by diode-pumped devices. In
whose power density (watts per unit volume) is orders of magni- rapid succession, high-power single-emitters, high-power laser
tude greater than those of even a decade ago. bars, and quasi-CW and CW stacks of diode bars became avail-
able, largely driven by military laser projects. Accompanying
these advances has been the development of high-power fiber-
coupled diode laser sources. Recently, every year has brought
news about higher levels of output power and brightness.
Diode-pumping has had a profound effect on solid-state laser
development. In fact, we can now say with confidence that the
technology has lived up to its early promise. Not only has diode-
pumping led to more efficient lasers, and enabled pumping
Laser diode technology
The single most important change that has taken place in
solid-state lasers over the past 30 years is the development of
laser diode sources, especially those that have been specifically
developed for pumping solid-state lasers. Even during the first
decade of solid-state laser development, it was well known that
the factors that were most impeding the scaling of solid-state
