Laser System Upgrade Overview
RF Gun review @ 19, Nov, 2015
Requirement of laser system for RF-Gun• Laser energy
– 500 mJ for Ir5Ce cathode
– 50 mJ for Ce2Te cathode
• 50 Hz, 2-bunch (96ns spacing)=> Regenerative amplifier + 96ns delay=> Large regenerative amplifier (unstable)
=> Multi-pass amplifier (Upgrade existing underground laser )
• Temporal pulse shaping to reduce energy spread=> Broadband laser crystal (Yb or Ti:Sapphire)
=> postponded until Phase-III• Continuous operation (limited cost / human resource)
– Support cost for commertial product is very high.(1,000-2,000$/day/person + a (margin) )
– No laser system company in Japan.– Recovering time.
1.00E-10
1.00E-09
1.00E-08
1.00E-07
1.00E-06 1.00E-05 1.00E-04 1.00E-03 1.00E-02
Charge(QE=1e- 5)@266nmCharge(QE=1e- 4)@266nmCharge(QE=1e- 3)@266nm
Required laser pulse energy
5nC
Ce2Te
ATF
Offline measurementP-polarization
Offline measurementS-polarization
Normal injection (old 3-2)Inclined injection
Charge( C )
Laser power ( J )
QE=10-3QE=10-4
QE=10-5
Current laser energy(500μJ)
How to generate 2-bunch with 96 ns spacing.• Amplification time of standard regenerative amplifier
(usually adopted in commertial product) is around 1 ms.
• Regenerative amplifier and 96 ns delay (ground laser)• Large regenerative amplifier (built & failed)
– Unstable output energy due to low gain.– Difficult to compensate thermal lens.
• High gain fast regenerative amplifier (built & failed)– Difficult to reduce the ghost pulse from first bunch due to
limted extinction ratio of pockels cell.• Multi-pass amplifier (upgrade existing underground
laser)
Properties of laser medium
LD Pump(808nm)
Nd:YVO4Nd:YAG
SHG(532nm) 40%FHG(266nm) 20%5HG(213nm) 3%
τ~ 200μs, 40%Nd-doped
Yb-doped
Ti-doped
LD Pump(941/976nm)
Yb-glassYb:YAGYb:BOYS
1064nm808nm
941/976nm 1040nm
τ~ 900μs, 40%
Pump(808nm)
Nd:YAG SHG40%
1064nm808nmTi:Sapphire
532nm 800nm
τ~ 3μs, 40%τ=200μs, 40%
○ 4-state laser is easy to operate.○ High power pump LD is available.○ Large crystal is available× Pulse width is determined by SESAM. (Gaussian)
○ Wide bandwidth => pulse shaping○ Long fluorescent time => High power○ Fiber laser => Stable○ Small state difference × ASE× Absorption
○ Very wide bandwidth○ High breakdown threshold× Low cross section× Short fluorescent time => Q-switched laser is required for pumping
Pump
TW laser is based on Ti-Sapphire
SHG(520nm) 40%FHG(260nm) 20%5HG(208nm) 3%
SHG(400nm) 40%THG(266nm) 20%FHG(200nm) 10%
Material Nd:YAG Yb:YAG Ti:Sapphire
Wavelength 1064nm 1030nm 660- 1100nm
Fluorescent time 230ms 960ms 3.2ms
Spectral width 0.67nm 9.5nm 440nm
Fourier minimumPulse width
2.48ps 165fs 2.59fs
Wavelength 807.5nm 941nm 488nm
Spectral width 1.5nm 21nm 200nm
Quantum efficiency 76% 91% 55%
Fluo
resc
ence
Abs
orpt
ion
Nd laser system for 3-2 RF-Gun
Ti:Sapphire laser system for beam monitor.
Short term upgrade for laser development• Undeground Yb-Fiber(Upgraded) + Yb:YAG (Existing)
– Downgrade to 25Hz 2-loop amplifier => Fix configuration– Stability improvement : Improvements on Yb-Fiber laser.– Increase monitor points / quadrant detector etc..
• Ground Yb-Fiber + Nd:YAG / Yb:YAG– Installation of MENLO Orange oscillator(commertial)
However it doesn’t cover 1064nm.=> New stable oscillator for 1064nm was installed.
– Existing fiber amplifier is best fit to amplify 1064nm. (p.9) – Nd:YAG 10 Hz regenerative amplifier is under test.– Yb:YAG 50Hz regenerative amplifier is under construction.– Better room environment / Virtual cathode.– (Cryogenic Yb:YAG) => Postpond until Phase-III.
Collaboration / Visit• Collaboration
– Hamamatsu Laser Diode / Disk Laser– HiLASE Yb Fiber & Disk
Laser– IMS / Taira Lab. Laser Crystal / Bonding– Waseda Univ. Yb-Oscillator
• Visit– DESY / Flash Nd:YLF– J-Lab– etc,.
Spectrum compare
Upgrade of existing underground laser
Yb-doped fiber oscillator with
Transmission grating
Yb-doped fiber pre amplifier
Yb-doped fiber main amplifierPulse picker
Yb:YAG thin-disk multi-pass cavity amplifier
Yb:YAG thin-disk multipass amplifier ×3
SHG
Synchronization system
SHGRF GUN
51.9 MHz
2, 5, 25, 50 HzSingle or Double bunch
0.2 nJ @ 1037 nm
Yb-doped fiber main amplifier
Transmission grating pair
stretcher
2856 MHz triggerFrom Accelerator
Yb-doped fiber pre amplifier
>μJ @ 1037 nm
Pulse picker
10 MHz
Fix the configuration to 25 Hz operation
Improvement of Yb fiber laser• Fiber oscillator
– MENLO oscillator is installed and under operation.However it doesn’t cover 1064nm
– ANDI type oscillator was installed for the 1064nm.• Simplify and increase the pulse energy
– Semiconductor Optical Amplifier (SOA) for pulse picker (114 to 10 MHz) and amplification
• Multimode fiber amplifier– PCF fiber cutting method etc,.
Simplify the Yb:YAG solid laserNew high gain multi-pass amplifier (10-15 pass x 2 loop)
LD Laser Diode
INP
UT
OU
TP
UT
1p
ass 1
0-1
5p
ass
←
Laser stability
New laser system in the ground laser room
Menlo1030nm oscillator
Grating stretcher(Transmission)
SOApulse picker
Yb single mode fiber amp
Yb-doped double clad fiber amp
Repetition frequency114.24MHz
Wavelength selection1030nm & 1064nm
Repetition frequency 10MHz
Nd:YAG regenerative amplifier
EO modulepulse picker
Repetition frequency : 10Hz
Yb:YAG Thin diskregenerative amplifier
1030nm oscillator(ANDi type)
1064nm oscillator(ANDi type)
Output(1030nm)Output(1064nm)
ASE rejection grating pair
1030nm
1064nm
1064nm
Fiber part
96ns Delay => Combine => SHG => FHG
Strecher for Yb:YAG & Nd:YAG
2.0nm
Yb:YAG Nd:YAG
Center wavelength 1030 nm 1064 nm
Gain spectrum width ~2 ns ~0.5ns
Distance of the Stretcher 1.5 m (30 ps) 8 m (10ps)
Grating pair
10 ps
Gain spectrum of Yb:YAG
Distance of grating pair
Nd solid laser• 4-state laser is easy to operate• Small band width / Thermal lens effect• Crystal type
– Rod - Side pump: Thermal lens effect, High gain– Thin disk: Less thermal lens, Low gain
• Pumping Laser Diode– 808nm : Commercial product– 885nm : Direct pump, Higher LD power, Lower
cross section
Nd rod DPSS module○ 4-state laser is easy to operate.○ High power pump LD is available.○ High gain efficiency.○ Large crystal is available× Small gain bandwidth. (Gaussian)
1.1% Dia. 4×93mm AR/AR@1064nm
Existing DPSS module is designed for 10 Hz operation.50 Hz commercial DPSS module is available (expensive).
Nd:YAG regenerative amplifier
On going development.• Nd regenerative amplifier for the Phase-I
stable injection.• Yb regenerative amplifier is for Rui’s R&D
under collaboration with HiLASE.• Virtual cathode will be built on the optical
board.• Vacuum optical duct is under development.