ultra-stable flashlamp-pumped laser a.brachmann, j.clendenin, t.galetto, t.maruyama, j.sodja,...
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Ultra-stable flashlamp-pumped laserUltra-stable flashlamp-pumped laser A.Brachmann, J.Clendenin, T.Galetto, T.Maruyama, J.Sodja, J.Turner, A.Brachmann, J.Clendenin, T.Galetto, T.Maruyama, J.Sodja, J.Turner,
M.WoodsM.Woods
OutlineOutline
IntroductionLaser System SetupRecent ModificationsExperimental ResultsConclusions and
Summary
IntroductionIntroduction SLAC built Flashlamp-pumped
Ti:Sapphire laser system
Installation in 1993 at the SLAC PES
Generation of polarized electrons in combination with SLAC’s Polarized Electron Gun
Recent Modifications result in increased stability and output power
Benefit of low jitterBenefit of low jitter
• Statistics of experiments
• Reduce Beam loading
• Reduction of residual dispersion and wakefields
• Facilitates beam tuning and minimizes losses
0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
500
1000
1500
2000
2500
Day
s
Jitter [%]
Time needed to achieve 100 ppbfor E-158 assymmetry statistics (for 120 Hz rep. Rate) (assumption that laser is only source of jitter)
Laser System SetupLaser System SetupCavity
CCD
HBS
Spectrometer
‘SLICE’ Photodiode
F=750mmF=500mm‘SLICE’ -PC‘TOPS’ -PC
PL PLPL
/2
flashlamps
/2Brewster Ti:Sapphire
PL: PolarizerPC: Pockels cell
‘LONGPULSE’ Photodiode
Laser system peripheryLaser system periphery
• SLAC built pulsed power supply
• SLAC built cooling water system (closed loop > 16 M)
• Commercial Pockels cell driver
• SLAC built HV power supply and control of TOPS Pockels cell
• Variety of Controls & Diagnostics integrated into control system (Power supply, Pockels cell HV, Photodiodes, Spectrometer, CCD)
Parameters of operationParameters of operation
2 4 6 8 10
2
4
6
8
10
Arbitrary Units
Arb
itra
ry U
nits
Modestructure Multimodal (higher order modes
dominate)
Wavelength Tunable (805 nm, 850 nm)
Bandwidth 0.7 nm
Repetition rate 120 Hz
Peak power of cavity(15 s pulse)
45 mJ
‘Used’ power(50 – 370 ns pulse)
60 J (~ 600 J possible)
Stability 0.5 %
Temporal pulse profile and timing Temporal pulse profile and timing setupsetup
0 5 10 15 20 250.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
0 5 10 15 20 250
2
4
6
8
10
12
14
16
18
20
A
mpl
itude
[Vol
ts]
Time [microseconds]
100 - 370 nsSlice
Slic
e R
egio
n
Sta
nd
ard
de
via
tion
/ M
ea
n *
10
0
Time [microseconds]
Recent modificationsRecent modifications Cavity optimization according to thermal
lensing included in resonator modelling results
Elimination of cavity halfwave plate reduces element sensitive to optical damage
Wavelength change to 805 nm required by new photocathode yields higher output power Operation near gain maximum for Ti:Sapphire material
Thermal lensingThermal lensing
0.7 0.8 0.9 1.0 1.1 1.2 1.3
2000
2040
2080
2120
2160
2200
2240
2280a
xis
dia
me
ter
[m]
distance from center of cavity [m]
minor axis diameter major axis diameter
Cavity simulationsCavity simulationsThermal lens
L1 L2
flat
2 mcc5 mcc
w0
Rx
wx
x
Spotsize within gain medium as a function Spotsize within gain medium as a function
of thermal lens and mirror spacingof thermal lens and mirror spacing
0.8 1.0 1.2 1.4 1.6 1.8 2.00.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.8 1.0 1.2 1.4 1.6 1.8 2.00.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
f - thermal lensf - thermal lens
2 mccw
0 [m
m]
5 mccL2 [mm]
400 500 600 700 800 900 1000 1100
Wavefront radius of curvature as a Wavefront radius of curvature as a function of thermal lens and mirror function of thermal lens and mirror
spacingspacing
0.8 1.0 1.2 1.4 1.6 1.8 2.00
1
2
3
4
5
6
7
8
9
10
0.8 1.0 1.2 1.4 1.6 1.8 2.00
1
2
3
4
5
6
7
8
9
10
2 mccC
urva
ture
of w
avef
ront
[m]
L2 [mm] 400 500 600 700 800 900 1000 1100
f - thermal lensf - thermal lens
5 mcc
Laser stability and eLaser stability and e-- beam beam stability near target are highly stability near target are highly
correlatedcorrelated
0.460.54Jitter [%]
3.95E+1141.35MEAN
TORO 488 TMIT
Slice J
(Photodiode)
(500
data points)
40.8 41.2 41.6 42.00
20
40
60
80
100
120
freq
uenc
y
Slice J3.90 3.95 4.00
0
20
40
60
80
100
120
TORO 488 TMIT (1011)
Optical damage on cavity halfwave Optical damage on cavity halfwave plate surfaces (damaged coating)plate surfaces (damaged coating)
Controlled crystallographic Controlled crystallographic orientation of laser rodorientation of laser rod
Power supply stability as a Power supply stability as a function of high voltage levelfunction of high voltage level
7600 7700 7800 7900 8000 8100 8200
8100
7600 7700 7800 7900 8000 8100 82000
5
10
15
20
25
30
fre
qu
en
cy [%
]
BACT [V]
7600
7600 7700 7800 7900 8000 8100 8200
7700
7600 7700 7800 7900 8000 8100 8200
7800
7600 7700 7800 7900 8000 8100 8200
7900
7600 7700 7800 7900 8000 8100 8200
8000
0.1497.8
0.2057.9
0.2128.0
0.2158.1
0.0597.7
0.0947.6
Jitter [%]HV [kV]
Conclusions and SummaryConclusions and Summary Stable operation of laser systems required for
polarized e-beams is achieved
‘Home built’ systems preferred over commercial systems – greater flexibility– better support– straightforward integration into existing control
system
Development laboratory with duplicate system is essential if continuous production is required
ReferencesReferences
Humensky et al.; SLAC’s Polarized Electron Source Laser System and Minimization of Electron Beam Helicity Correlations for the E-158 Parity Violation Experiment; NIM; to be published
Brachmann et al.; SLAC’s Polarized Electron Source Laser System for the E-158 parity violation experiment; Proceedings of SPIE, Volume 4632, 211-222, 2002