Optical CAD programs are now being integrated with
mechanical programs, together with finite element
analysis capabilities to ensure highly accurate
manufacturing of laser components.
part of the scattered light will travel at slightly different angles
than the compressing-path beam and it will be focused around
the final spot. No matter how “clean” the stretched pulse is,
some temporal and spatial background will be generated by the
stray light in the compressor.
The amount of energy contained solely in the stray light
that ends on the target could exceed 0.01percent of the incident energy. If the laser output is, for example, near 100 J, the
stray light could contain as much as 10 mJ. If we assume that
half of this light will reach the target before the main pulse
and half after, that is still more than enough energy to vaporize
the target material and create a pre-plasma. The consequence is
simply that the experiment performed in this way is different
than what was intended and no clear scientific conclusion can
be reached.
One solution to this problem is to manufacture gratings
that scatter less light. Researchers have made progress with
holographic gratings that exhibit superior performance over
ruled ones. Multilayer dielectric coatings appear to scatter less
than bare gold coatings. The scattering angle and characteristics also depend on the groove density and substrate material, as well as the manufacturing process. How would laser
engineers take into account all these options and find the best
solution? They should first characterize the scattering in a small
experimental setup. Then, the resulting data can be entered
into a ray-tracing computer program that can analyze various
compressor designs without actually having to build one.
Computer screen to production
Ultrafast lasers are composed of many parts, sometimes hundreds of them. Each component needs to perform perfectly:
If one piece fails, the entire laser fails. This all-or-nothing
phenomenon was well understood in the mid-1960s when
the first mechanical computer-aided design (CAD) programs
were built for automotive and aerospace companies such as
General Motors and Lockheed Martin. Progress is being made
on CAD programs for laser design, but there is still a good
amount of work to do.
Optical CAD programs are now being integrated with
mechanical programs, together with finite element analysis capabilities, to ensure highly accurate manufacturing of laser components. Some of the traditional CAD programs can now trace
rays and work with free-form or user-defined optical surfaces.
ONLINE EXTRA: Visit www.osa-opn.org for short video
examples of a compressor and stretcher ray tracings in Zemax,
as well as a focal-spot compressor misalignment study.
G2
M4
OAP
VRR
Output M2
G1
Target
detector PS M3
Input
M1
50 mm
Horizontal [mm]
– 6 – 4 – 2 0 2 4 6
1E+0
For now, data are quickly exchanged between optical,
mechanical and analysis modules. Once fully integrated modules are perfected, optical engineers will be able to find the best
design, save time and money and avoid errors by using them
individually. Hopefully, a decade from now, engineers can use
one CAD program that incorporates all three modules to manufacture flawless lasers directly from the computer screen. t
This work was performed under the auspices of the U.S. Department
of Energy by Lawrence Livermore National Laboratory, U.S.A., under
contract DE-AC52-07NA27344.
Catalin V. Filip ( filip1@llnl.gov) is at Lawrence Livermore National
Laboratory, Calif., U.S.A. Member
[ References and Resources ]
>> E.B. Treacy. IEEE J. Quantum Electron. QE- 5, 454 (1969).
>> A. Offner. U.S. Patent 3748015 (1971).
>> D. Strickland and G. Mourou. Opt. Commun. 56, 219 (1985).
>> O.E. Martinez. IEEE J. Quantum Electron. QE- 23, 59 (1987).
>> M. D. Perry et al. Opt. Lett. 24, 160 (1999).
