Volume VII–System Description
OMEGA EP Operations Manual
Page 20 of 35
Within the GCC, full-aperture calorimeters may be inserted to measure the energy of the
high-intensity pulses. Additionally, each compressor line has a “leaky” mirror (~1%) that samples the
compressed pulse and, with other optics, directs the beam to the short-pulse diagnostic package (SPDP)
table for characterization. The SPDP table is located just south of the GCC on the Laser Bay floor.
For experiments requiring long-pulse (1 to 10 ns) beams, the 1053-nm beams are frequency
tripled to 351 nm using potassium dihydrogen phosphate (KDP) and deuterated potassium dihydrogen
phosphate (KD
*
P) frequency-conversion crystals (FCC’s) and then transported to the OMEGA EP target
chamber. They cannot be directed to the OMEGA target chamber. Each beam is focused onto the target
using an
f
/6.5 aspheric lens followed by a vacuum window and a thin debris shield. An option to smooth
the target-plane profile is to place a distributed phase plate (DPP) just before the lens. In the baseline
configuration, the beam is directed to the ports at a 23º angle of incidence with respect to a common
central axis of the target. Beam transport to a 48º angle of incidence ports is a future option.
The frequency-conversion performance is diagnosed with a 4% diagnostic pickoff located after
the FCC’s in an arrangement similar to that used successfully on OMEGA. The pickoff diagnostics also
include alignment sensors for co-aligning a UV alignment source to the IR alignment source. Each of
the four beamlines has its own UV diagnostics (UVDP) and alignment table (UV-ASP) that are located
near the target chamber on the target area structure (TAS). The UV alignment source is located on its
own table (UVAT) located on the Laser Bay floor in front of the TAS, and its output beam is introduced
just before the FCC’s with the periscope mirror assembly (PMA). The placement of the FCC’s before
the target chamber (rather than on the target chamber as in the NIF) permits more convenient beam
diagnostics and allows for the separation of unconverted light.
1.5.2 Grating Compressor Chamber
The pulse-compression grating systems are located in a large rectangular vacuum chamber, 15 ft
(inside) square and 70 ft long, known as the grating compressor chamber or GCC. The vessel is located
in the northwest corner of the Laser Bay. An equipment entry door on the south end facilitates insertion
of large pieces of equipment, while two smaller entry doors located on the north and south ends provide
personnel access. A conceptual drawing of the GCC is shown in Fig. 1.8.
The GCC houses two independent pulse compressors, deformable mirrors, compressor alignment
mirrors (CAM’s), transport mirrors, full-aperture calorimeters, a beam combiner, and the transport
chain optics to the SPDP table. In addition, a pair of interferometers is used to align the tiles of each
tiled-grating assembly (TGA). The pulse compressors are each comprised of four TGA’s. Each TGA is
comprised of three tiled MLD gratings. A diagram of the internal components of the GCC illustrating
the 14 optical tables, 8 TGA’s, and target chamber selection mirror is shown in Fig. 1.9.
The optical path of the upper compressor is shown in Fig. 1.10. Beam 1 or 2 from the switchyard
enters via a vacuum window located on the east side of the GCC and is directed toward the first TGA,
G1. The beam-incidence angle on G1 is 72.5º. The refracted beam is directed toward TGA G2 then TGA
G3 and finally TGA G4. At G4, the pulse has been temporally compressed by up to 300 ps/nm.
Emerging from G4, the pulse reflects off the compressor deformable mirror (DM). This DM is
used to correct for aberrations in compressor optics and the short-pulse transport and focusing optics. The
diagnostic mirror allows 1% of the pulse to be directed to the SPDP table. The remainder of the pulse
Summary of Contents for Volume VII-System Description
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