National Ignition Facility (NIF), the largest, most energetic
laser in the worldwith 60 times more energy than any laser
in existencewill be coming on line at Livermore in the next
few years. In this laser, energy will be stored in special glass
and later extracted as high-power optical pulses. High-energy
lasers such as NIF need large pieces of optical-quality glassand
lots of themto operate as designed. NIF will be about the
size of a football stadium and will require more than 3,000 pieces
of laser glass, each about 1 meter long, 0.5 meter wide, and 4
A revolutionary process
developed by Lawrence Livermore and two industrial partners produces
meter-size plates of laser glass at a rate 20 times faster and
5 times cheaper than is possible with the previous technology,
and the glass itself has 2 to 3 times better optical quality.
This work is the culmination of a 6-year research and development
project between Livermore and the two leading (and competing)
laser glass producers, Schott Glass Technologies of Duryea, Pennsylvania,
and Hoya Corporation USA of Fremont, California. Physical chemist
Jack Campbell of Livermore led this team.
The Continuous Laser Glass
Melting Process developed by the collaboration replaces the only
other way to manufacture large pieces of laser glassthe
batch method, a one-at-a-time process that produces at most three
pieces of glass per week. Not only is this method too slow to
meet the demands of NIF, but it is also more expensive, and the
optical quality of the glass is not consistent. Practically speaking,
continuous glass melting is the only method that can be used to
produce the large quantity and high quality of laser glass necessary
for NIF. Without this technology, it would be extremely difficult
to build a huge solid-state laser such as NIF.
this process was extremely difficult technically, says Campbell.
In fact, we had a saying, laser glass knows no friends,
to describe our frustrations. Now that the process has worked
out successfully, frustration has given way to pride. But believe
me, there were many anxious moments.
River of Glass
The Continuous Laser Glass
Melting Process, shown schematically below, converts high-purity,
powdered raw materials into one continuously moving strip of high-optical-quality
laser glass. Plates of laser glass are then cut from the end of
the strip as it leaves the production system.
The laser glass melting
process requires seven operations carried out in separate vessels.
The vessels are interconnected to make the process continuous.
The first process unit is designed to mix and dry the high-purity
raw materials with minimal contamination.
The second unit is the
melter system, which dissolves the powdered raw materials into
a pool of molten glass and mixes these ingredients using convection
currents.The melter consists of custom-designed, high-purity refractory
materials and uses a proprietary electrical heating system.
All units beyond the melter
are lined with high-purity platinum, as are the interconnecting
pipes. Platinum is required to achieve the fine-scale (parts-per-million)
optical homogeneity necessary for laser applications. However,
the platinum can contaminate the glass with microscopic metallic
inclusions. When a high-power laser beam hits an inclusion, the
beam causes it to vaporize, generating small fractures within
the glass. To overcome this problem, the team developed a unique
conditioner unit that uses oxygen and chlorine to remove platinum
inclusions as well as any residual water. The conditioner unit
is perhaps the most complex part in the whole system.
The glass from the conditioner
next moves to a refiner section, where bubbles are removed using
a combination of high temperature and proprietary additives. From
here, the glass enters the homogenizing unit, where it is thoroughly
mixed to achieve the one-part-per-million chemical uniformity
required to meet optical homogeneity specifications. Finally,
molten glass flows through a platinum tube to a mold, where it
is formed into one continuously moving strip about 5 to 8 centimeters
thick, 0.5 meter wide, and nearly 30 meters long. The glass strip
passes through a custom-designed annealing oven where it is gradually
cooled from more than 600°C to room temperature. Annealing
the laser glass strip is difficult because of the size of the
strip and the unusually high thermal expansion and low inherent
strength of the glass. Laser glass is five times more sensitive
to fracture by thermal shock than most other optical glasses.
of the continuous laser glass melting system. The glass product
leaving this system is shown in the background of the opening
Process Not Adequate
phosphate laser glass can be manufactured by either the batch
method, a one-at-a-time melting process, or this new continuous
melting method. Schott and Hoya are the only companies in the
world making meter-size plates of phosphate laser glass, either
by a continuous or discontinuous process. Thus, the only competitor
for the new process is the old, discontinuous technology for producing
The former technology,
which has been used for over 25 years, involves first melting
raw materials in a refractory vessel and then manually transferring
the melt to a second platinum-lined vessel. Finally, the pieces
of glass are individually cast in a large mold. The entire operation
is repeated for every piece of glass. Product quality can vary
from one melt to the next simply because of small, run-to-run
variations in processing conditions. The costmore than $5,000
per liter of glassis also high.
glass melting, however, has a much greater production rate of
70 to 300 pieces per week, and little, if any, measurable variation
in glass properties from one glass plate to the next. Plus, the
cost is less than $1,000 per liter.
Hoya and Schott will also
be manufacturing large pieces of glass using the continuous melting
method for the Laser Megajoule (LMJ) in France. The LMJs
requirements are similar to those of NIF.
Both Hoya and Schott are
applying several new technologies developed for the Continuous
Laser Glass Melting Process to the manufacture of other optical
glasses. Most notably, some of this technology is being used to
manufacture the most common optical glass, BK-7, in large sizes.
BK-7 is commonly used to manufacture optics for cameras, binoculars,
and precision optical instruments. Other aspects of the process
are being used to improve the manufacture of glass used in digital
cameras, hard-disk-drive substrates, liquid crystal displays,
projector lenses, and telecommunication devices.
success of this venture is illustrated by the fact that neither
company is willing to openly discuss the details of the other
applications for the new technology, says Campbell. The
bottom line here is that everyone is a winner from this partnership.
NIF gets the laser glass it needs, and our industrial partners
get a technology that is a springboard to new glass products.
Continuous Laser Glass Melting Process, National Ignition Facility
(NIF), neodymium-doped phosphate laser glass, platinum inclusions,
R&D 100 Award.
information contact Jack Campbell (925) 422-6497 (firstname.lastname@example.org).