phin activities at lnf

34
-Care 2008- CERN 2-5 December 2008 Giancarlo Gatti Giancarlo Gatti Phin activities at LNF

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Giancarlo Gatti. Phin activities at LNF. Outline. SPARC project overview SPARC drive laser system IR shaper comparison for flat top laser pulse IR/UV-pulse shaping Laser to RF synchronization schemes Trasverse shaping considerations Conclusive remarks. - PowerPoint PPT Presentation

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Page 1: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Giancarlo GattiGiancarlo Gatti

Phin activities at LNF

Page 2: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Outline

•SPARC project overview

•SPARC drive laser system

• IR shaper comparison for flat top laser pulse

• IR/UV-pulse shaping

•Laser to RF synchronization schemes

•Trasverse shaping considerations

•Conclusive remarks

2

Page 3: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

: MiUR Strategic Research Programs

Goals: High brightness linac to drive advanced FEL experimentsAnd further experiments

Page 4: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

SPARC commissioning phase 1: SPARC commissioning phase 1: low energy e-beam characterization low energy e-beam characterization

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Page 5: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Sparc phase 2

• After gun commissioning in 2006:

-Commissioning of downstream linac in progress.

-Variable gap undulators installed and ready.....

Last minute breaking news:First beam inside undulators

Page 6: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Photocathode drive laser

Demands:

Solutions:• Emittance minimization

• Flexibility (Long./Trasv.)

• Stable reliable operation

• High current (100 A) from Cu cathode

Synchronization rf laser < 1ps rms stable laser performance

6

High energy laser (50-500 uJ) pulses at 266 nm

Uniform time and and transverse laser profile: 6-12 ps duration, rise time, 2 mm hard edge

Page 7: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

SPARC laser system: topology

Ti:Sa laser composed by:

•12 nm bandwidth oscillator

•IR pulse shaper

•CPA amplifiers

•third harmonic generator

•UV stretcher (used as

shaper)

•Transport to the cathode

7

Proc. PAC 2007 TUPMN040

time shaper

Page 8: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

SPARC laser system

oscillatorpumps

amplifiers

Harmonics generator

UV stretcher

Pulse shaper

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• The laser delivers 5-12 ps, 100 J pulses at 266 nm with a rep. rate of 10 Hz.

• Energy jitter (5% rms), pointing stability (<50 m) and synchronization respect to the RF (<2ps rms)

• Several subsystems have been integrated: IR pulse shaper, tranverse unifom pulse selection and imaging system to the cathode.

Page 9: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Laser temporal pulse shaping

M. Petrarca S. Cialdi C. Vicario

Outline:-IR shaper comparison (a.o. Filter, LCM)-Overall system performances-UV shaper

Page 10: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Tests of two IR pulse shapers10

Dazzler

Half-wave plate

Dazzler

Half-wave plate

From oscillator

Into amplifierTelescopes

Phase mask

Lens

Lens

Grating

Grating

From oscillator Into amplifier

60 c

m

15 cm15 cm

DAZZLERDAZZLERLC-SLMLC-SLM

Page 11: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

IR programmable pulse shapers

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DAZZLERDAZZLER

LC-SLMLC-SLM

Fast mode

Slow mode

Acoustic grating

Acousto-optic interaction in a TeO2 crystal

Page 12: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

The UV time profiles the two shapers:DAZZLER LC-SLM

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Rise and fall time ~ 2.6 ps Rise and fall time ~ 2.1 ps

Opt. Lett. 31, 19 (2006) 2885-2887

LC-SLMLC-SLMDAZZLERDAZZLER

The spectral shape after the UV stretcher is very similar to the temporal profile

Page 13: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

IR shapers Features:

DAZZLERLC-SLM

• Compact

• Easy alignment

• Simultaneously phase &

amplitude modulation

• Losses within 50%

• Resolution = 0.3 nm

• Slow optimization

• Not-compact

• Not easy alignment

• Phase only

modulation

• Losses within 50%

• Resolution<0.1 nm

• Fast optimization

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Page 14: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

THG distortions: main limitation for fast rise time

A large enough pulse width (≥0.6 ps) is needed to preserve the square spectrum throughout the THG

0.10.5

1

IR p

ulse len

gth

[ps]

Measured (solid) and simulated (dots) harmonics spectra

C. Vicario et al, Opt. Lett, 31,2006, 2885

The UV spectral shape as function of the input IR pulse length

Page 15: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

UV pulse shaper

The UV stretcher was designed to perform several tasks

1. Lengthen the laser pulse proportional to bandwith up to 20 ps.

2. In the Fourier plane an amplitude filter, such as an iris, can be applied to cut the tails of an almost square spectrum produced bu the DAZZLER or LC-SLM, the obtained spectrum profile is transferred into the time profile by the stretcher

3. A on-line spectrometer is integrated.

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1

23

Appl. Opt. 46, 22 (2007) 4959

Page 16: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Picture of the UV shaper

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SpectromCCD

Focusinglenses

Filter plane

input

output Gratingpair

Page 17: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Cross-correlated UV profile 117

Simulationexperiment

Simulationexperiment

FWHM 10 ps: experim. vs simulation

FWHM 15 ps rise time 1.5 ps

Page 18: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Measured UV profile 2 for several pulse length

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UV shaper allows for fast rise timedespite of different chirp factors in the stretcher

Page 19: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Shaping without the IR filter

When a proper sharp cut is applied to the natural UV

Gaussian laser spectrum, a flat top profile in time can be

produced.

Results are comparable to the two stages pulse shaping.

Price to pay 20% higher energy losses

Cheaper and simpler respect to the other IR pulse shapers

The rise and fall time are reduced to ~1.5 ps (limited by the

bandwidth)

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Page 20: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

No IR shapers: simulations20

spectra

Time shape

IR shape No IR shape

Page 21: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Experimental results

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Appl. Opt. 46, 22 (2007) 4959-4962

Spectra

No-cut

TimeMeasured (red) and

Simulated (black)

Cut applied

Page 22: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Exotic applications: UV multipeaks generation

• With a grid in the fourier plane we obtained 4 peaks pulse (FEL microbunching enhancement)

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Page 23: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Laser to RF synchronization

M. Bellaveglia, S. Gallo, C. Vicario

Page 24: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Synchronize the laser and RF

• Laser to RF synchronization is needed to have photoinjector optimal and stable operation

• Photoelectron gun phase < 1 deg rms for emittance compensation

• Velocity bunching, pulse compression and laser acceleration demands for a tighter specification (100 fs)

Laser oscillator

Cavity length control

Pulse selection amplification

THG+stretcher

Laser to the cathode

L

cf

2

Measure Δf

Masterclock

RF chain

Page 25: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Phase noise at oscillator level

Measurements set up and results

350 fs rms

Page 26: Phin activities at LNF

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UV time jitter: measure at 10 Hz

wavereference

Activefeedback

RF phase shifter Time of arrival jitter estimated

with the RF deflector is 390 fs

0.67 ps rms over 6 hours

Pill box cavity

HV Photo diode

mixer

Laser

Phase noise detection

acquisition

Page 27: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Toward next step: Laser-driven RF

• To reduce the time jitter we can To reduce the time jitter we can synthesize the RF frequency from synthesize the RF frequency from a photodiode excited by the a photodiode excited by the oscillator pulses.oscillator pulses.

• The value measured can be The value measured can be affected by the apparatus affected by the apparatus resolution, shortly more detailed resolution, shortly more detailed characterizationcharacterization

• This technique is applicable to This technique is applicable to lock for 1 laser systemlock for 1 laser system

• All-optical synchronization system All-optical synchronization system and clock distribution to go at sub and clock distribution to go at sub 100 fs level100 fs level

Page 28: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Sparc P1 highlights

B=6*1013 A/m*rad

First ever emittance oscillation

Square laser at the cathode

PRL 99, 234801 (2007)

Opt. Lett. 31, (2006) 2885 Appl. Opt. 46, 22 (2007) 4959

REV. SC. INSTR. 77, 093301 2006

PRST- AB 11, 032801 (2008)

Page 29: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

E:beam experimental results• The flat top pulse shape allowed the observation of the

double-minimum emittance evolution at SPARC (only predicted by the theory).

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+18°RF phase

0.45 mmrms spot size

5, 1.5 psDuration, rise time

5.5 MeVenergy

100 Acurrent

PRL 99, 234801 (2007)

UV LASER

Page 30: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Gaussian vs flat beam:comparison

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Page 31: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Recent advances: Trasverse shaping

Main demands:

-Squared beam -Power efficiency Final choice:

Telescope system to map Gaussian into flat top

Pros: above 70% efficiency (up to 95%)Cons: exact matching of TEM00 gaussian alignment stability filtering cuts real efficiency

2 kinds of commercial refractiveSystems probed.

Page 32: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

OUTPUTBEAM

300 400 5000

10

20

30

40

50

60

70

Inte

nsity

(a.

u.)

X (pixels)

IRIS CUT

200 250 300 350 400 450 500 550 6000

10

20

30

40

50

60

70

Inte

nsity

(a.

u.)

X (pixel)

line 150 line 100 line 200

NO IRIS

INPUT BEAM

Our choice:No spatial filter

Page 33: Phin activities at LNF

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0 50 100 150 200 250 300

700

800

900

1000

1100

1200

1300

1400

Inte

nsi

ty (

a.u

.)

Pix

SHAPERON CATHODE

Trasportation up to cathode

Shape is preserved through relay imaging trasport (10 mt.)

Page 34: Phin activities at LNF

-Care 2008-CERN 2-5 December 2008

Conclusions

• Extensive development on laser pulse shaping has been Extensive development on laser pulse shaping has been done at LNF-SPARC within the PHIN collaboration done at LNF-SPARC within the PHIN collaboration ▫ The two stages pulse shaping for 1.5 ps rise time▫ Demonstration of UV-only pulse shaping▫ Work on faster rise time and reduced losses

• Sub ps synchronization with upgrade at < 200 fs has been Sub ps synchronization with upgrade at < 200 fs has been demonstrateddemonstrated

• E-beam results encouraging the search of flat top pulse, E-beam results encouraging the search of flat top pulse, definitive comparison at higher energydefinitive comparison at higher energy

• Complete shaping in the next future when charge issues Complete shaping in the next future when charge issues will be overcome.will be overcome.

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