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S-AD-M-005
Chapter 1: System Overview
Each temporally stretched pulse is compressed to the desired pulse width while maintaining
beam size using a pulse compressor comprised of a quad of tiled multilayer dielectric diffraction (MLD)
grating assemblies. The two pulse compressors are located in the GCC aligned atop one another, and
the upper compressor is illustrated in Fig. 1.3. The principle of pulse compression is based upon the
diffraction of light off the grating surface and the fact that different wavelengths of light travel different
distances within the compressor before being recombined at Grating 4.
G6860J1
Figure 1.3
The upper of two four-grating pulse compressors is shown inside the GCC. The lower compressor is identical. The output of
each compressor is directed to a beam combiner where the pulses are coaxially aligned. A target chamber selection mirror
(not shown) diverts pulses to either target chamber. Alternatively, the two pulses can be used to simultaneously backlight
and sidelight an OMEGA EP target.
After pulse compression, the beams can be directed to either the OMEGA or OMEGA EP target
chamber. When the beams propagate to the OMEGA target chamber, they are coaxially aligned using a
beam combining optic and a target chamber selection mirror directs them to the target chamber. They
enter the chamber through diagnostic hex port (H9) and traverse the chamber to hex port (H7) where
an off-axis f/1.8 parabolic mirror focuses them onto the target. The focal spot can be shifted to any
location within 1 cm of the center of the chamber to provide for flexible backlighting geometries. The
foci of the two beams may be separated by ~1 mm.
In OMEGA EP, two beam configurations are possible. In the first configuration, the beams
propagate along the backlighter beam path, enter the target chamber through port 33, and are focused
by an f/1.8 off-axis parabolic mirror in a nearly opposing port that focuses the beam onto the target. The
beams may be coaxially aligned in this setup. In the second configuration, the two beams can propagate
separately along the backlighter and sidelighter paths, entering the chamber through ports 33 and 69.
They are similarly focused by a pair of f/1.8 off-axis parabolas on nearly opposing ports. The focal spots
of these beams can be shifted to any location within 1 cm of target chamber center, providing for flexible
experimental geometries and configurations. An illustration of the concept is shown in Fig. 1.4.
In long-pulse mode, all four beams are diverted in the switchyard to the frequency-conversion
crystals, where they are frequency tripled to the UV (351 nm). UV high-reflector (HR) mirrors and a
focus lens (FOA) deliver the beams to the target chamber at 23º relative to the target normal. These
UV-only mirrors also serve to separate unconverted IR and second-harmonic light before the beam
enters the target chamber. A future option is to add a 48º beam path relative to target normal. The
four (or eight) ports for the UV beams straddle the f/1.8 off-axis parabola for symmetric production of
preformed plasma.
TGA 2
Input beam
TGA 1 TGA 4
January 2006—Page 11 of 35
TGA 3
Beam combiner
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