philippe hering [email protected] october 30, 2007 drive laser commissioning results and...
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Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
1
Drive Laser Commissioning results and plans
Philippe HeringOctober 30, 2007
Outline
• New oscillator
• Improvements of laser performances
• New transport beam line
• Beam stabilization and diagnostics for the transport beam line
• More remote control
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
2
Great Up Time!
20 weeks of commissioning
Three 8 hour downs – Hot swappable parts available now
One 3 hour down during a night shift
2 hours per week for locking problems
98% up time !
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
3
New master oscillator from Femtolasers
• Narrower bandwidth requested to have higher spectral intensity and get a better seeding in the Regen (before FWHM = 30 nm).
• Crystal is sealed in airtight cavity to avoid contamination (no more weekly cleaning, endurance test made during > 200 hours).
• Remote starting capability.
• One pump mirror is remote controlled with picomotors.
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
4
New Femtolock driver for the oscillator
• Oscillator is first locked to 119 MHz and then to 476 MHz : no more 476 MHz bucket ambiguity.
• Lock button added to be lock always on the same bucket.
• RF- locking loop and lock button can be run remotely.
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
5
Reconfiguration of the stretcher• Regarding the central wavelength of the Regen seeding beam.
• Grating and concave/convex mirrors reorientation.
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Wavelength (nm)
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Stretcher output spectrumDazzler output spectrum
Central wavelength of the oscillator
Central wavelength of the Regen seeding
Bandwidth of the stretcher
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
6
New set-up of the Dazzler
DAZZLER• Single pass configuration (instead of two before).
• More accurate spectral shaping with the Dazzler.
• After further studies from the vendor (Fastlite), quadratic phase correction cannot be added in a big amount and so 4th and 6th orders are not possible.
Only spectrum filtering is accurate for our shaping purposes (FWHM < 4 nm).
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
7
• Pulse shaping with the Dazzler is made with the spectral filtering parameters : we fix the central wavelength of the Regen seeding beam and shape the spectrum with a 3rd order super-Gaussian. A “hole” in the spectrum can also be done to compensate spectrum distortions in the amplifiers.
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Wavelength (nm)
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Super Gaussian Order 3
FWHM = 2 nm
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
8
Change in the REGEN cavity amplifier
• The Lyot filter (wavelength tuning element) has been removed.
• One of the end cavity mirror has been changed with an “edge” mirror : low pass filter coating cutting at ~750 nm.
• Remark : remaining modulations are coming from the fibered input of the spectrometer.
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Wavelength (nm)
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Regen output spectrum with the new Dazzler set-up and edge mirror
Dazzler output (Regen seeding)
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
9
Improvement of the temporal shape of the pulse
• Ps pulse duration is obtained by adding quadratic phase with the compressor (distance between gratings shorter than full compression).
• Super-Gaussian temporal profile is obtained with the Dazzler but only with spectrum shaping (no more with phase orders).
•You can also dig a “hole” in the spectrum to compensate the spectrum red shift in the multipass amplifiers after the Regen.
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Wavelength (nm)
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Compressor output spectrumwith Dazzler hole OFF
FWHM = 2 nm
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Compressor ouptut spectrumwith Dazzler hole ON
FWHM = 2 nm
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
10
• We measure the temporal beam profile directly in the UV with our scanning cross-correlator. A flat top spectrum in the IR doesn’t give a flat top temporal profile in the UV because of saturation in the Tripler : asymmetric IR leads to flat top in the UV.
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Compressor output spectrumwith Dazzler hole OFF
FWHM = 2 nm
BEFORE
Typical temporal shape during last commissioning
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
11
Improvement on the IR input spectrum shape for the Tripler has increased UV yield :
UV yield went up from <10% to >15% .
To get the same UV energy in front of the clipping iris, we decided to decrease the IR input ( ~18 mJ instead of ~28 mJ ): main IR amplifier is running with less pumping energy. Save JEDI 2 diodes (half of nominal current value) !!
Safer operation of the Tripler at short pulse duration (<6 ps).
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
12
Beam qualityTypical beam image on the clipping iris
during last commissioningChanges to be made :
• Work done on the pulse shaping has
improved a little the homogeneity of the
beam (to be investigated) ? • Replacement of 6 mm thick fused-silica
dichroics in UV tripler by 2 mm thick MgF2
(to lower B-integral)• Replacement of all Substrate transmissive
fused-silica optics by CaF2 (to lower
fluorescence and absorption).
Beam image on the clipping iris before transport after working on the pulse shaping (Preliminary results !)
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
13
Beam stability on the cathode
Jitter in x-axis = 35.4 m rmsJiiter in y-axis = 39.2 m rms
Beam position on the cathode (on VCC camera) Beam size on the cathode (on VCC camera)
Jitter in x-axis = 14.4 m rmsJiiter in y-axis = 18.9 m rms
Laser Beam on VCC camera
Instabilities in the electron beam !
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
14
We move the BCS shutter onto the laser table : before it was attached to the side of the table after the mirror folding the beam down through the transport tube.
We extended both ends of the vacuum transport tube : upstairs up to the laser table level and downstairs down to the laser box cover.
Jitter in x-axis = 11 m rmsJiiter in y-axis = 11 m rms
Beam position on the cathode (on VCC camera) Beam size on the cathode (on VCC camera)
Jitter in x-axis = 3.6 m rmsJiiter in y-axis = 4.7 m rms
Improvement by a factor of 3 !
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
15
Shot-to-shot energy stability
1.1% charge stability at 1nC
Laser energy stability vs. time < 1.5% rms
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
16
Original Transport Layout for 2007 Injector Commissioning F1=200
F2=120
F3=-150
F4=F5=5000
F6=1500
Beam shaper
Vacuum cell Zoom
Transport tube
Table in the
tunnel
Photocathode
Virtual Cathode
Steering system
Active Steering
Stabilization
L1
L2
L3
L4
L5
L6
WaveplatePolarizer
Powermeter
Camera
Shutter
Zoom Telescope
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
17
Changes in the Upstairs LayoutNo Gaussian Beam ShaperAdjustment of beam size on the cathode is accomplished by changing the magnification of the input telescope and the size of the imaged irisFirst relay stage (L1 – L3) is removed.
Input telescope has 3X higher magnification No vacuum cell is needed Iris is the object plane of the L4 and L5 imaging system
Image of the L4-L5 system is virtual L6 relay image the output of the L4 – L5 system to the cathode 4:1. L6 has remote Z-adjustment
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
18
Beam
Attenu
ator
Pulse Stacker
Iris Wheel
Zoom Telescope
Insertable
Power Meter
Insertable
Power Meter
Active Steering
Stabilization
New Transport Layout
UV BeamOutput
Vacuum Tube
to Gun
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
19
The iris diameter is adjusted by a remotely controlled aperture wheel
Laser Beam
•Wheel houses 12 apertures•Beam sizes on cathode
• 0.25 - 2.0 mm• Smaller diameters can be done
•Design allows for rapid change
for additional apertures •Wheel is controlled via Epics
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
20
Option of Focusing the Beam on the Cathode
Transport tube
Table in the
tunnel
Photocathode
Steering system
Active Steering
Stabilization
F4=F5=5000
F6=1500
L4
L5
L6Shutter
LCleaning
Removable Lens LCleaning F=3m
Z-adjustment of L6 changes the beam size on the cathode
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
21
No Major Changes to Vault Transport
M5
L5
M4
L6 M3
M2
VC Power Meter
Cathode
M1
C1
C2 UV plates for Cameras
Cathode Cleaning Lens
Philippe Hering
October 30, 2007
Drive Laser Commissioning Results and Plans
22
Work in progress before next commissioning
Vacuum Transport CleaningLayout and Alignment of New Optical TransportInstall New Controls Hardware
Power MetersCameras and UV platesIris Wheel
Beam quality still needs to be improvedSoftware Installation and Certification of ControlsCertification of Laser OperationTraining of Operators before LCLS restart