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30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Photocathode lasers Photocathode lasers generating long trainsgenerating long trains
of flat-top pulsesof flat-top pulses
Ingo Will, Guido KlemzIngo Will, Guido Klemz
Max Born Institute BerlinMax Born Institute Berlin800 s
1 s100 ps
(10mm glass plate)
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Optical sampling system Optical sampling system for high-resolution measurement for high-resolution measurement
of the longitudinal pulse shapeof the longitudinal pulse shape
Ingo Will, Guido KlemzIngo Will, Guido Klemz
Max Born Institute BerlinMax Born Institute Berlin
100 ps(10mm glass plate)
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
The desired pulse trains and pulse energy(superconducting linac, Cs2Te photocathode)
Spacing of the pulses: 1 Spacing of the pulses: 1 ss• In future: 0.2 In future: 0.2 s = 5 MHz (XFEL)s = 5 MHz (XFEL)
and 0.11 and 0.11 s = 9 MHz (option for FLASH)s = 9 MHz (option for FLASH)
Duration of the pulse train: Duration of the pulse train: at least 800 at least 800 s, variables, variable
Very reliable synchronizationVery reliable synchronization Rectangular envelope of the pulse Rectangular envelope of the pulse
trains trains Energy:Energy:
• > 100 > 100 J in the IR J in the IR (I.e. (I.e. = 1047 nm) = 1047 nm)
– corresponds to >100 W power during the pulse corresponds to >100 W power during the pulse traintrain
• 15 15 J in the UV (I.e. J in the UV (I.e. = 262 nm) = 262 nm)
800 s
1 sDesired parameters (according to the requirements specified by DESY):
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Desired pulse shape Desired parameters Desired parameters
of the micropulsesof the micropulses• Wavelength: UV (262 nm)Wavelength: UV (262 nm)• Edges: < 2 ps (UV)Edges: < 2 ps (UV)• Noise in the flat-top region: Noise in the flat-top region:
< 10…20 %< 10…20 %• Pulse duration Pulse duration ~ 20 ps ~ 20 ps
Completely remote-Completely remote-controlled laser systemcontrolled laser system
Very reliable Very reliable synchronizationsynchronization
20 ps
< 2 ps < 2 ps
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
First completely diode-pumped pulse-train laser First completely diode-pumped pulse-train laser operational at PITZ since April 2005operational at PITZ since April 2005
photo-diode
#1
photo-diode
#3
wavelengthconversion
IR -> UV
outputpulses
photo-diode
#2
pulseshaper
boosteramplifier(2 stages)
mainpulse picker
auxiliarypulse picker
preamplifier(4 stages)
modelockedoscillator
Conclusion: The duration of the train in the amplifiers must be much larger (>1.5 ms) than the length of the output train
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Pre-compensation of changes of the pulse shape Pre-compensation of changes of the pulse shape during amplification and conversion to the UVduring amplification and conversion to the UV
flat top:17.2 ps
edges(10-90%):
4.9 psFWHM:22.5 ps
time [ps]0 20 40 8060
IR = 1.047 m
green = 0.524 m
UV = 0.262 m
flat top:16.4 ps
edges(10-90%):
6.1 psFWHM:23.3 ps
time [ps]0 20 40 8060
flat top:17.3 ps
edges(10-90%):
6.5 psFWHM:23.8 ps
time [ps]0 20 40 8060
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
The MBI setup of a generator of long flat-top The MBI setup of a generator of long flat-top pulse trains for the superconducting linacpulse trains for the superconducting linac
photo-diode
#1
photo-diode
#3
wavelengthconversion
IR -> UV
outputpulses
photo-diode
#2
pulseshaper
boosteramplifier
mainpulse picker
auxiliarypulse picker
preamplifiermodelockedoscillator
100 ps 100 ps
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
MBI setup of a generator of long flat-top MBI setup of a generator of long flat-top pulse trains for the superconducting linacpulse trains for the superconducting linac
photo-diode
#1
photo-diode
#3
wavelengthconversion
IR -> UV
outputpulses
photo-diode
#2
pulseshaper
boosteramplifier
mainpulse picker
auxiliarypulse picker
preamplifiermodelockedoscillator
Effect of all components of the laser on the micropulsesEffect of all components of the laser on the micropulsesshould be constant for a duration of 800 should be constant for a duration of 800 ss
Components of the laser should work Components of the laser should work with 1 MHz rep. rate during the trainwith 1 MHz rep. rate during the train
High average power during the train of the final amplifiers: High average power during the train of the final amplifiers: PPtraintrain > 100 W > 100 W
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Selected pulse shaping techniques: Selected pulse shaping techniques: suitability for single pulses and pulse trainssuitability for single pulses and pulse trainsTypeType MethodeMethode schemescheme effecteffect Single Single
pulses pulses Pulse Pulse trainstrains
(bursts)(bursts)
Linear Linear shaping shaping techniquestechniques
Grating pulse Grating pulse shaper:shaper:
Spectral shaperSpectral shaper
Spectral decomposition
ok ok.ok.
Grating pulse Grating pulse shaper:shaper:
Direct Direct space-to-timespace-to-time
Diffraction on a grating
ok okok
Acoustooptic filterAcoustooptic filter(i.e. DAZZLER)(i.e. DAZZLER)
Diffraction on a sound wave
package
ok Not Not suitablesuitable
Birefringent filterBirefringent filter filter with a transmission
sin()/
ok okok
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Selected pulse shaping techniques/effects: Selected pulse shaping techniques/effects: suitability for single pulses and pulse trainssuitability for single pulses and pulse trainsTypeType MethodMethod schemescheme effecteffect Single Single
pulses pulses Pulse Pulse trainstrains
(bursts)(bursts)
Nonlinear Nonlinear shaping shaping techniquestechniques
Fiber shaperFiber shaper Self-phase modulation in a
fiber
ok ok.ok.
Nonlinear amplifying Nonlinear amplifying loop mirror (NALM)loop mirror (NALM)
Nonlinear phase shift in a fiber
ok okok
Fast optical power Fast optical power limiterlimiter
Nonlinear phase shift in a bulk
medium
ok Limited, Limited, depends depends
on NL on NL mediummedium
Nonlinear interaction Nonlinear interaction in crystalsin crystals
(SHG, FHG, OPA)(SHG, FHG, OPA)
Nonlinear interaction in
3 crystals
ok okokoutputpulses
UV
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
ddapertureaperture = 9 mm = 9 mm
FWHMFWHM = 75 ps = 75 ps
ddapertureaperture = 4 mm = 4 mm
FWHMFWHM = 47 ps = 47 ps
ddapertureaperture = 3 mm = 3 mm
FWHMFWHM = 30 ps = 30 ps
output pulses recorded with a streak camera:
Flat-top laser pulsesFlat-top laser pulses• generate electron bunches
with a flat-top shape in z-direction
• -> improved brightness -> improved brightness of the electron beamof the electron beam
knifeedge
knifeedge
flat-topoutput pulses
slit
Gaussianinput pulses
grating
toamplifier
chain
master oscillator
synchroscanstreak camera
(3 ps resolution)
short-pulseNd:YLF oscillator = 7 ps FWHM
Simple DST shaper forming flat-top laser pulsesSimple DST shaper forming flat-top laser pulses
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Simple DST shaper forming flat-top laser pulsesSimple DST shaper forming flat-top laser pulses
ddapertureaperture = 9 mm = 9 mm
FWHMFWHM = 75 ps = 75 ps
ddapertureaperture = 4 mm = 4 mm
FWHMFWHM = 47 ps = 47 ps
ddapertureaperture = 3 mm = 3 mm
FWHMFWHM = 30 ps = 30 ps
output pulses recorded with a streak camera:
Flat-top laser pulsesFlat-top laser pulses• generate electron bunches
with a flat-top shape in z-direction
• -> improved brightness -> improved brightness of the electron beamof the electron beam
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Amplification of flat-top pulses from an Yb:YAG oscillator
Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength
Parameters of the pulses Parameters of the pulses shown:shown:• length of the train: 1.5 ms length of the train: 1.5 ms
(1500 pulses)(1500 pulses)• Energy in the train: 27 mJEnergy in the train: 27 mJ• Energy per micropulse: 18 Energy per micropulse: 18 J J
(at 1030 nm)(at 1030 nm)• Streak camera measurement Streak camera measurement
taken taken with SHG (at 515 nm)with SHG (at 515 nm)
Energy is ~ 4…5 times Energy is ~ 4…5 times smaller than in the present smaller than in the present Nd:YLF phothocathode laserNd:YLF phothocathode laser
Increasing this energy is a Increasing this energy is a major challenge to the laser major challenge to the laser designerdesigner
100 ps(10mm glass plate)
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
The MBI setup of a generator of long flat-top The MBI setup of a generator of long flat-top pulse trains for the superconducting linacpulse trains for the superconducting linac
photo-diode
#1
photo-diode
#3
wavelengthconversion
IR -> UV
outputpulses
photo-diode
#2
pulseshaper
boosteramplifier
mainpulse picker
auxiliarypulse picker
preamplifiermodelockedoscillator
100 ps 100 ps
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Some amplification techniques: Some amplification techniques: suitability for single pulses and pulse trainssuitability for single pulses and pulse trainsTypeType MaterialMaterial Single pulses Single pulses Amplifiers for pulse trainsAmplifiers for pulse trains
(bursts)(bursts)
Optical-parametric Optical-parametric amplifiersamplifiers
(OPA)(OPA)
BBO, LBO, KTPBBO, LBO, KTP Ok OkOk(implemented in the FLASH (implemented in the FLASH
pump/probe laser)pump/probe laser)
Laser amplifiers:Laser amplifiers: Nd:YLFNd:YLF Ok OkOk
Edges limited to > 4...5 psEdges limited to > 4...5 ps(see present PITZ (see present PITZ
photocathode laser)photocathode laser)
Ti:SaTi:Sa Ok
(regenerative amplifier required)
Unknown:Unknown:- very strong thermal lensvery strong thermal lens
- Sophisticated pump laser Sophisticated pump laser neededneeded
Yb-doped mediaYb-doped media(Yb:KGW, (Yb:KGW, Yb:YAG,Yb:YAG,
Yb:CaF)Yb:CaF)
Ok(regenerative
amplifier required)
Under development,Under development,- moderate thermal lensmoderate thermal lens
- regen required, but too low regen required, but too low saturation during a single saturation during a single
micropulse micropulse
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Part 2: OPCPA stage generating femtosecond pulses
output pulse train which output pulse train which contains 700 micropulsescontains 700 micropulses
OPCPA: OPCPA: Optical Parametric Chirped-Pulse amplification Generates femtosecond pulses Generates femtosecond pulses
150 fs FWHM 150 fs FWHM pulse energy available at present : pulse energy available at present :
EEmicromicro = 100 = 100 J (before J (before compressor)compressor)
EEmicromicro = 50 = 50 J (behind J (behind compressor)compressor)
Available wavelength: Available wavelength: • = 790…830 nm= 790…830 nm• on request: on request: = 395…415 nm = 395…415 nm
G ~ 20
Ti:Sa oscillator grating stretchergrating
compressor
outputpulse trains800 s long, = 790 ...
830 nm
three-crystalOPA
Piezo
photodiode
mixer1.3 GHz
master clockf = 1.3 GHz
primarysynchronization loop
G > 5 000
= 15 ps
picosecond-pulseoutput channel:
pulse trains, 800 s long
= 150 fs (FWHM)Emicro = 50...100 J
@ f= 1 MHz
synchronizedNd:YLF Burst-Mode laser
pumping the OPA = 523 nm
= 12 ps(FWHM)
100 fs
pulsepicker
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
= 14 ps (FWHM)Emicro = 1.2 mJJ @ f = 1 MHz
Esingle pulse > 8 mJ
G ~ 20
fastcurrent
controller
fastcurrent
controller
Ti:Sa oscillator
gratingstretcher
gratingcompressor
outputpulse trains800 s long, = 790 ...
830 nm
three-crystaloptical-parametric amplifier
(OPA)
Piezo
photodiode
mixer1.3 GHz
master clockf = 1.3 GHz
primarysynchronization loop
G > 5 000 100 fs = 15 ps
diode-pumpedNd:YLF oscillator
AOM
fround trip = 27 MHz
EOMAOM
Faradayisolator
pulsepicker1 MHz
pulsepicker
two-stage diode-pumpedNd:YLF amplifier
fastcurrent
controller
SHGcrystal
pumpdiodes
pumpdiodes
three-stageflashlamp-pumpedbooster amplifier
outputpulse trains800 s long, = 523 nm
= 12 ps (FWHM)Emicro = 600 J @ f = 1 MHz
Esingle pulse = 4 mJ
= 150 fs (FWHM)Emicro = 50...100J
@ f= 1 MHz
OP
CP
A
sta
ge
Pu
mp
lase
rScheme of the Pump-Probe laser
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Regenerative amplifiers can be made to Regenerative amplifiers can be made to work at 1 MHz repetition ratework at 1 MHz repetition rate
Specialty in burst mode:Specialty in burst mode:Each micropulse can extract only a small Each micropulse can extract only a small fraction (~ 0.2%) of the stored energy fraction (~ 0.2%) of the stored energy • Low stability (2% fluctuation during the Low stability (2% fluctuation during the
train)train)• Reduced efficiency (~50%) in Reduced efficiency (~50%) in
comparison to single pulsescomparison to single pulses• Failure in the trigger will damage the Failure in the trigger will damage the
amplifieramplifier– sophisticated software solution, (present sophisticated software solution, (present
DOOCS not save) DOOCS not save) – NL limiterNL limiter– Fast repair technology Fast repair technology
Pulse traveling in the resonator
Output pulses
20 s1ms (1000 pulses)
SHG limiter
fiber-coupledpump diode
"switch-out"Pockels cell
"switch-in"Pockels cell
Yb:YAG
Faradayisolator
Faradayisolator
outputbeam
inputbeam
polarizer
polarizer
M1
M4
M2
M3
50 ns
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Two-stage regenerative amplifier conceptTwo-stage regenerative amplifier concept
Thermal lens in the power regen Thermal lens in the power regen leads to a drop of the intensity to leads to a drop of the intensity to 50% during 2000 pulses50% during 2000 pulses
The two- or three-stage regen The two- or three-stage regen concept may enable us to apply concept may enable us to apply advanced amplifier techniques advanced amplifier techniques (i.e. thin-disk amplifiers) (i.e. thin-disk amplifiers)
First regen
Secondregen
Emicro
= 15 J
Emicro
= 3 J
2ms (2000 pulses)
Yb:KGW oscillator Yb:YAG regen
Yb:YAG power regen
DST shaper
Drop due to thermal lensing
First regen
Secondregen
Compensation of Compensation of the drop by the the drop by the drive current of the drive current of the pump diodes, pump diodes, but the but the „pumping“ „pumping“ of the beam diamter of the beam diamter remainsremains!!
2ms (2000 pulses)
Emicro
= 15 J
Emicro
= 3 J
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Amplification of flat-top pulses from an Yb:YAG oscillator
Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength
Parameters of the pulses Parameters of the pulses shown:shown:• length of the train: 1.5 ms length of the train: 1.5 ms
(1500 pulses)(1500 pulses)• Energy in the train: 27 mJEnergy in the train: 27 mJ• Energy per micropulse: 18 Energy per micropulse: 18 J J
(at 1030 nm)(at 1030 nm)• Streak camera measurement Streak camera measurement
taken taken with SHG (at 515 nm)with SHG (at 515 nm)
Energy is ~ 4…5 times Energy is ~ 4…5 times smaller than in the present smaller than in the present Nd:YLF phothocathode laserNd:YLF phothocathode laser
Increasing this energy is a Increasing this energy is a major challenge to the laser major challenge to the laser designerdesigner
100 ps(10mm glass plate)
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Amplification of long pulse trains for the Amplification of long pulse trains for the cold linac by an Yb:YAG boostercold linac by an Yb:YAG booster
Stable pulse train: control of the ramp of the current of the Stable pulse train: control of the ramp of the current of the pump diodespump diodes
Stable beam diameter: Stable beam diameter: beam-shaping aperture at the outputbeam-shaping aperture at the output• Can the beam-shaping aperture in the beamline play this role? Can the beam-shaping aperture in the beamline play this role?
Technology for lossless stabilisation of the beam diameter: Technology for lossless stabilisation of the beam diameter: fast deformable mirrorfast deformable mirror
Emicro
= 15 J
Emicro
= 3 JYb:YAG
fiber-coupledpump diodes
photodiode
Yb:YAG
inputfrom regen
outputbeam
Energy per Energy per micropulse:micropulse: ~ 15 ~ 15 JJ
Amplification Amplification (two stages): (two stages): G = 5...8 G = 5...8
5 ms(5000 pulses)
Without compensatio
nby pump current
5 ms(5000 pulses)
with compensationby pump current
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Shortest pulses and bandwidth of this Shortest pulses and bandwidth of this amplifier combinationamplifier combination
Output pulses of the KGW oscillator: Output pulses of the KGW oscillator: = 0.5 ps = 0.5 ps Output pulses of the regen combination: Output pulses of the regen combination: = 1.8 ps = 1.8 ps
Can pulses of this duration efficiently be transferred to the UVCan pulses of this duration efficiently be transferred to the UV(forth harmonics, (forth harmonics, = 258 nm) ? = 258 nm) ?
Emicro
= 2x7 J
Emicro
= 3 JYb:KGW oscillator Yb:YAG regen
Yb:YAG power regenEmicro
= 2x0.1 J
12ps
2ps
d =1.2mm
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Shortest pulses and bandwidth of this Shortest pulses and bandwidth of this amplifier combinationamplifier combination
Emicro
= 2x7 J
Emicro
= 3 JYb:KGW oscillator Yb:YAG regen
Yb:YAG power regen
Emicro
= 2x0.3 J
12ps2ps
Output pulses of the KGW oscillator: Output pulses of the KGW oscillator: = 0.5 ps = 0.5 ps Output pulses of the regen combination: Output pulses of the regen combination: = 1.8 ps = 1.8 ps
Can pulses of this duration efficiently be transferred to the UVCan pulses of this duration efficiently be transferred to the UV(forth harmonics, (forth harmonics, = 258 nm) ? = 258 nm) ?
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
> 75%of totalenergy
25%of totalenergy
thirdharmonics
tophotocathode
moderate power, large bandwidth Yb:KGW channel
sum frequencygeneration
pulse shaper(1% transmission)
rectangularly shapedmicropulses
E = 50 J, P = 50 W = 1038 nm
long micropulseswith long edge
E = 150 J, P = 150 W = 349 nm output:
rectangularly shapedmicropulses
with short edges = 260 nm
mask
pulsepicker
pulsepicker
large power, small bandwidth Nd:YLF channel
Mixing stageDiode-pumped
short-pulse oscillator < 1 ps, f = 54 MHz
amplifier chain(one regenerative andone linear amplifier)
Diode-pumpedshort-pulse oscillator = 50 ps, f = 27 MHz
Nd:YLF amplifier chain
Two-channel mixing scheme: reduced energy Two-channel mixing scheme: reduced energy requirements to the broadband laser amplifierrequirements to the broadband laser amplifier
75% of the total laser energy delivered by the Nd:YLF long-75% of the total laser energy delivered by the Nd:YLF long-pulse system pulse system
only 25% need to be delivered by broadband channelonly 25% need to be delivered by broadband channel
Broadband pulse:from Yb:KGW laser
- sharp edges- Emicro = 20J- =1038 nm
Narrowband pulse
from Nd:YLF laser
- slow edges
- Emicro = 100J
- = 349 nm
BBOcrystal
UV output pulse- sharp edges- Emicro > 20J- = 260 nm
tophotocathode
beam
stop
beamstop
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
transmission < 20 %losses > 80 %
Photocathodelaser
<--- 10...25 m --->
photo-cathode
beamline telescopeor spatial filterwith pinhole
Gaussianlaser beamD = 2 mm
overfilledbeam-shaping
apertureD = 1...4 mm
presentscheme
three times more energythan without pre-shaping
transmission ~ 70 %losses ~ 30 %
"pre-shaped"beam
asphericlens pair
Photocathodelaser withflat-top
pump profiles
<--- 10...25 m --->
photo-cathode
beamline telescopeor spatial filterwith pinhole
Gaussianlaser beamD = 2 mm
overfilledbeam-shaping
apertureD = 1...4 mm
pre-shapingby an asphericalLens pair
Pre-shaping the beam of the photocathode laser Pre-shaping the beam of the photocathode laser may significantly reduce losses in the beamlinemay significantly reduce losses in the beamline
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Summary: Long trains of flat-top laser pulses Summary: Long trains of flat-top laser pulses for the superconducting linacfor the superconducting linac Pulse shaping techniques: Only minor limitationsPulse shaping techniques: Only minor limitations
Most linear pulse-shaping techniquesMost linear pulse-shaping techniques (gratings, filters etc) (gratings, filters etc) workwork for long trains for long trains Techniques based on travelling Techniques based on travelling acoustic waves (i.e. DAZZLER) cannot be usedacoustic waves (i.e. DAZZLER) cannot be used Nonlinear techniques: limited duration of the pulse train (100...500 micropules) Nonlinear techniques: limited duration of the pulse train (100...500 micropules)
(only for nonlinear techniques using bulk materials)(only for nonlinear techniques using bulk materials)
Amplifiers: Amplifiers: 1.1. Optical-parametric amplifiers (OPA): work without restrictions, Optical-parametric amplifiers (OPA): work without restrictions,
but large pump laser requiredbut large pump laser required
2.2. For laser amplifiers: The broadband laser materials require regenerative amplifiers in the For laser amplifiers: The broadband laser materials require regenerative amplifiers in the first stages. These regens can work at 1 MHz for Yb:YAG, Yb:KGW:first stages. These regens can work at 1 MHz for Yb:YAG, Yb:KGW: With somewhat reduced stability and with slightly less less efficiency (~ 50%) than for single With somewhat reduced stability and with slightly less less efficiency (~ 50%) than for single
pulses pulses Reason: low saturation during each micropulse (0.2% energy extraction per pulse)Reason: low saturation during each micropulse (0.2% energy extraction per pulse)
3.3. Linear power amplifiers: work well with pulse trains Linear power amplifiers: work well with pulse trains Some problems arise from theSome problems arise from the thermal lens, that drifts during the train thermal lens, that drifts during the train
Solution: Solution: Dynamic correction with fast deformable mirrorsDynamic correction with fast deformable mirrors
4.4. Ti:Saphire: No solutions for long, intense pulse trains availableTi:Saphire: No solutions for long, intense pulse trains available
We have made the correct choice for the laser material: We have made the correct choice for the laser material: Diode-pumped Yb:KGW and Yb:YAG instead of Ti:SaphireDiode-pumped Yb:KGW and Yb:YAG instead of Ti:Saphire
30 Nov. 0630 Nov. 06I.Will et al., Max Born Institute: Long trains of flat-top laser pulsesI.Will et al., Max Born Institute: Long trains of flat-top laser pulses
Amplification of flat-top pulses from an Yb:YAG oscillator
Record of flat-top pulses with a synchroscan streak camera (Optronis, ~3...4 ps resolution) at 515 nm wavelength
Parameters of the pulses Parameters of the pulses shown:shown:• length of the train: 1.5 ms length of the train: 1.5 ms
(1500 pulses)(1500 pulses)• Energy in the train: 27 mJEnergy in the train: 27 mJ• Energy per micropulse: 18 Energy per micropulse: 18 J J
(at 1030 nm)(at 1030 nm)• Streak camera measurement Streak camera measurement
taken taken with SHG (at 515 nm)with SHG (at 515 nm)
Energy is ~ 4…5 times Energy is ~ 4…5 times smaller than in the present smaller than in the present Nd:YLF phothocathode laserNd:YLF phothocathode laser
Increasing this energy is a Increasing this energy is a major challenge to the laser major challenge to the laser designerdesigner
100 ps(10mm glass plate)