1. Laser Source for the g-g Collider Presented to: Snowmass 2001
July 6, 2001
SPLAT
Short Pulse Lasers,
Applications & Technology
Jim Early
Lawrence Livermore National Lab
Laser Science and Technology

2. Laser Pulse Formats for TESLA and NLC LLNL
Laser wavelength (1mm), pulse energy (1J) and pulse duration (2ps) are
the same
NLC macro-pulse consists of 95 sub-pulses separated by 2.8 ns
Hz macro-pulse repetition rate
TESLA macro-pulse consists of 2800 sub-pulses separated by 300 ns
- 5 Hz macro-pulse repetition rate

3. TESLA g-g laser based on Mercury technology LLNL
Mercury laser modified from 100J at 10 Hz to 200J at 5 Hz
- 22 Mercury amplifiers required for TESLA ( versus 12 for NLC )
Series of pockell cells used to sequence single Mercury pulses with
38ms separation
- significant technology challenge in pockell cell development
Pulse string generation optics split single Mercury pulses into 128
subpulses separated by 300 ns
- total pulse train now 2816 pulses
Compression Pulse Amplification still use to convert 3 ns pulses to 2 ps
Laser system size might be reduced by multiple use of optical pulses

4. Architecture for TESLA g-g laser LLNL
22 laser chains
Switch network
Optical splitting & timing lines
Pulse compression grating
3ns pulses
3ns pulses
2ps pulses
3ns pulses
22 pulses with 38ms separation
22x128 pulses with 300ns separation
2816 pulses with 300ns separation
Spectral shaper
Stretcher grating
OPA Pre-amplifier
Mercury power amplifier
oscillator
Laser chain

5. Pockell cell switches required for TESLA LLNL
Laser pulses are 200J and 3ns at wavelength of 1mm
Pulses are separated by 38ms (switch time < 20ms)
Will need a total of 21 switches all operating at 5Hz
- switches handle different number of pulses
number of pulses per joules per Kw per
switches switch switch switch

6. The transverse electrode with transverse gas cooling allows scaling in aperture and average power
Utilize Mercury gas cell technology for high average
power pockell cell
9 cm x 34 cm x 1.6 cm KD*P crystals allow 4.4 kJ
operation at 5kHz
- requires some extension of crystal technology
SF6 is gas is utilized for cooling and voltage standoff
Device uses 3-5 crystals including a single rotator dependent upon specific deuteration level of KD*P

7. We have assembled and tested a half-aperture
high average power Pockels cell
Dual crystal configuration allows compensation for thermally-induced birefringence (Less than 1% depolarization at thermal loading exceeding 250 W/cm2
Scaling beyond kW average power level requires gas cooled faces (GCF) as opposed to transverse cooled architecture (as shown)
A Pockels Cell uses the voltage dependent birefringence of some crystals to control polarization. Voltage applied to KD*P crystals
changes polarization state of incident beam. 20 40 60 80
100 10 30 50
Uncompensated
Depolarization (%)
Compensated
Thermal loading (W)

8. Optics design for splitting pulses LLNL
50/50 beam splitters are used to first split and then recombine
beams
Optical delay line used to create combined beams with delayed
pulses forming a pulse train with 2n pulses
- for TESLA the delay line vacuum chamber is around 1 km
Two beams are finally recombined using a polarizer
- polarization of pulses in combined beam will alternate
beam splitter optical delay line
wave plate
polarizer