Laser system schematic
2ω 4ω
1.55 μs
200 μs, 5-50 Hz
15 kW 10 μJ 270 μs
~2332 pulses 370 nJ/pulse
~2332 e- bunches
2.33 nC/bunch Beam conditioner 1.5 GHz Nd:YLF oscillator
400 μs, 5-50 Hz
Diode pump 18 kW pk
3 kW 2 μJ 3-pass Nd:YLF
amplifier x300 CW
preamp
3 pass Nd:YLF amplifier
x5
200 μs, 5-50 Hz
Diode pump 22 kW pk
Optical gate (Pockels cell) Energy stabiliser (Pockels cell) Feedback stabilisation Phase coding
Practical layout
High Q preamp
High Q oscillator Coding
Faraday isolator Amp 1
Amp 2 1.54 μs
slicing Noise control
1 pulse slicing
HG HG
Thermal
lensing correction
Amplifier head design
Laser head assemblyNd:YLF rod
• 7mm diameter 8 cm long – Amp. 1 • 10 mm diameter 11 cm long – Amp. 2 • 1% doping level
• Deep surface etching for higher fracture limit
Glass tube The rod
water
Diodes
Lens
5 Diode laser stucks
• 18 kW total peak power – Amp. 1 • 22 kW total peak power – Amp. 2 • 400 μs – Amp.1
Amplifier 1
• Amp 1 operational and tested at 5 Hz and 50 Hz
• Rod failure at 50 Hz may be due to non-saturated operation • Expected output has been delivered (actually slightly exceeded) • Near-field uniformity should improve with better rod
Amplifier 1
Near-field profile is flattened by saturation but shows some effects of rod inhomogeneities0 100 200 300 400
Time (μs)
0 200 400 600 Ga in 0 1000 2000 3000 Po w e r (W )
• Measured output from Amp 1 exceeds target power
(3 kW from 3 passes)
• Output saturates in agreement with model
0 50 100 150 200 250 300 350 400
0 1000 2000 3000 4000 100 200 300 400 500
Diode current: 90A
Time (microsec)
Pow
er (W)
Gain
Amplifier 2
0 100 200 300 400
Time (μs)
0 1000 2000 3000 Ga in 0 3000 6000 9000 12000 P o w e r (W ) 22.8 kW 21.5 kW
2 passes 20.2 kW 1 pass 20.2 kW
• 10kW from Amp 2 corresponds to 6.7μJ/pulse • Beam uniformity is better than Amp 1 (fine
fringes are an artefact) but rod is underfilled
• Overfilling improves saturation so steady state is reached but energy is reduced
0 100 200 300 400
Time (μs)
0 1000 2000 3000 Ga in 0 2000 4000 6000 8000 10000 P o w e r (W )
Pulse slicing
-0.2 0 0.2 0.4 0.6 0.8 1
-0.4 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
• Risetime is ~4ns
• Extinction ratio, throughput and level of induced noise remain to be optimised (noise level in above trace is misleading)
• Power handling, with additional AOM, remains to be confirmed
6 8 10 12 14
Time (ns) -0.01
0 0.01 0.02 0.03 0.04 0.05
PD S
ig
n
al
(
V
)
Frequency multiplying
• Crystals are available for two frequency quadrupling schemes:
2 × type I in BBO (preferred) Type II in KTP + type I in BBO (allows two IR polarisations, perhaps for 3 GHz
multiplexing)
• Tests with Amp 1 (low energy) showed an IR-UV conversion efficiency of up to 7%
Extrapolation to Amp 2 should allow system specification to be met
Task listing
Oscillator & preamplifier Complete – April 2005 Amplifier 1 (5 Hz) Complete – April 2006 1.54 μs slicing (no AOM) Demonstrated – July 2006 Amplifier 2 (5 Hz) Demonstrated – July 2006 Phase coding Designed
Frequency multiplying Demonstrated with Amp 1 – August 2006
Safety and machine protection After delivery
Coding finalisation After delivery
Frequency multiplying finalisation After delivery
Amplitude stabilisation After delivery
Single-pulse and AOM slicing After delivery
50 Hz testing After delivery
50Hz thermal lensing correction After delivery
Lasers at CERN
• Oscillator in operation – September 2006
• Preamplifier in operation after service by High Q Laser – November 2006
• Amplifier 1 in operation – November 2006
• Amplifier 2 assembled and tested (beams not optimized) – January 2007
2nd amplifier
Pockels cell
Breadboard
Laser beam to cathode
Phase coding
Faraday isolator 1st amplifier
HighQ oscillator HighQ amplifier
Flipping mirrors
Beam dump f = 300 mm
f = - 250 mm
f = -100 mm λ/2
f = 100 mm
f = - 150 mm f = 400 mm
f = - 100 mm BBO SHG f = 800 mm
BBO FHG f = 300 mm
Laser beam to CALIFES
Oscillator Preamplifier Amplifier 1
Amplifier 2
Pulse slicing Pockels cell
Fiber-optics coding system
Amplifiers hardware
Amplifier 2 Chillers for amplifier diodes
55 l/min and 75 l/min Drivers for 5 diode laser
stucks of Amplifier 2 120 A each
Pulse coding
EO Modulator
140.7 ns
macropulses Variable
delay
Variable attenuator 140.7 + 0.333 ns delay 320 mW in
from oscillator ~30 mW out
to preamp
• Fibre modulation, based on telecoms technology, is fast but lossy and limited in average power
• Measurements on the High Q system suggest 10dB loss before the preamp results in <3dB output reduction
• Delay can be adjusted by varying the fibre temperature (~0.5ps/°C) • Attenuation can be controlled by varying the fibre bending losses
Pulse slicing with AOM
AO Deflector
Output to doubler Pockels
cell Input from
Amp 2
RF Driver
Pockels Driver
AO deflector could reduce power loading on Pockels cell by up to 80% for most of
the macropulse
Laser-room ÎDB gun 15 m 0.05 μs Laser-room ÎPB gun 75 m 0.25μs Photo-injector ÎDelay Loop 85 m 0.2833 μs PB macro-pulse length 0.021312μs Delay Loop 42 m 0.14 μs
TL Delay Loop ÎComb. Ring 30 m 0.1 μs TOTAL time 0.271312μs Combiner Ring 84 m 0.28 μs Conv. 1.5 GHz to 3 GHz 0.021312μs TL Comb. ring ÎProbe Beam 48 m 0.16 μs PB selection after DB 1.860709μs
Total with 1 DL and 4.5 C. Ring 598 m 1.9933 μs Macro pulse length 0.14 μs Filling time of PETS+Acc. 0.02 μs TOTAL time 2.1533 μs
First pulse of the Drive beam Probe Beam
