Omega Volume VII-System Description, Руководство по эксплуатации

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Volume VII–System Description
OMEGA EP Operations Manual Page 1 of 35
1. Laser Sources Subsystem
The Laser Sources Bay is located between the north and south Capacitor Bays on the first floor
of the facility. Each beamline in OMEGA EP has its own dedicated set of laser drivers, referred to as
laser sources. Beamlines 1 and 2 have the capability to produce both short- or long-pulse seed pulses
for their dedicated beamline. Thus, there are six independent laser sources.
1..1 Laser Sources 1 and 2
Different architectures are used for generating the long-pulse and short-pulse laser sources, as
indicated schematically in Figs. 1.5 and 1.6. The long-pulse (LP) source is largely based on existing
OMEGA technology with some modifications made to the regen to allow for 10-ns pulses. The short-pulse
source is based on optical parametric chirped-pulse amplification (OPCPA) because existing long-pulse
technology lacks the bandwidth needed.
The short-pulse beams start with a commercial Time Bandwidth Products mode-locked oscillator
that produces pulses with an ~200-fs duration. These pulses are stretched to ~2.4 ns (FWHM) in an optical
system that uses a diffraction grating to impose different delays on different frequency components.
The resulting “chirped” beam is spatially shaped before being amplified using an optical parametric
amplifier. This OPCPA stage is critical to the performance of the short-pulse beams. Attractive features
of OPCPA include a broad gain bandwidth, high gain in a short optical path, and reduced amplified
spontaneous emission. These are exploited to preserve the bandwidth of the signal beam and provide a
gain of ~10
9
.
Optical parametric amplification is a nonlinear optical process whereby energy is down-converted
from a (pump) beam of higher frequency into two beams of lower frequency, known as the signal and
idler beams. For OMEGA EP, the pump beam is a frequency-doubled, 527-nm-wavelength, Nd:YLF laser.
LBO (lithium tri-borate) crystals are used as the parametric-amplification media. The signal beam is
the input to the OPCPA stage, and the amplified signal beam is the output. The idler (1053 nm, like the
signal) is generated in the LBO crystals and separated after the OPCPA stage. The sum of the (chirped)
Table 1.3: Performance parameters of the 351-nm long-pulse beams (quantities refer to a
single beam). The “baseline” UV energies are what can be obtained with exist-
ing technology. The “potential” UV energies are possible with reasonable optical
technology developments. The quoted intensities are averages over the focal spot
and use the “baseline” UV energies.
Square pulse width (ns) 0.1 1.0 4.0 8.0 10.0
UV on-target energy (kJ):
Baseline
Potential
0.25
0.25
2.5
2.5
3.7
4.8
4.5
6.0
5.0
6.5
Intensity (W/cm
2
)
for 1-mm spot diameter 3
#
10
14
3
#
10
14
1.2
#
10
14
7
#
10
13
6
#
10
13
Intensity (W/cm
2
)
for 100-
n
m spot diameter 3
#
10
16
3
#
10
16
1.2
#
10
16
7
#
10
15
6
#
10
15