HELMHOLTZ GEMEINSCHAFT VUV FEL EO systems at the DESY VUV-FEL Stefan Düsterer for the VUV - FEL Team F. Van den Berghe, J. Feldhaus, J. Hauschildt, R

HELMHOLTZ GEMEINSCHAFT VUV FEL

EO systems at the DESY VUV-FELEO systems at the DESY VUV-FEL

Stefan Düsterer

for the VUV - FEL TeamF. Van den Berghe, J. Feldhaus, J. Hauschildt, R. Ischebeck, K. Ludwig, H. Schlarb, B. Schmidt, S. Schmüser, S. Simrock, B. Steffen, A. Winter

and all the others

Adrian Cavalieri, David Fritz, Soo-Heyong Lee, David Reis (Michigan University Ann Arbor, Michigan)


The 2 EOS systemsThe 2 EOS systems

Experiments

EOSEOS

„Electro Optical Sampling“

chirped laser pulse

EOSEOS

„Electro Optical Sampling“

chirped laser pulse

TiSa

fs-oscillator

TEOTEO

„Timing Electro Optical sampling“

45° - geometry

TEOTEO

„Timing Electro Optical sampling“

45° - geometry

pump-probe fs-laser

for FEL-experiments


TTimingimingEOEO

Timing monitor for the FEL-optical pump-probe Experiments

•optimized for electron bunch ARRIVAL TIME measurements

•part of the pump-probe laser system

•final goal:final goal: provide timing data to users

delaydelay + jitter


Layout: pump-probe experimentsLayout: pump-probe experiments

opticallaser

FEL pulseFEL pulse

Optical pulseOptical pulse

to TEO


TEOTEO

FEL beam Experim ent

Am plifier

fs-laser oscilla tor(50 fs, 3 nJ, 800 nm ) Optical diode

Feedback signal for changes in fiber length

Grating com pressor:com pensation for first order dispersion

Pulse shaper:Higher order com pensation

Fiber lengthcom pensation

150 m long glass fiberto transport laser pulsesinto the accelerator tunnel

Pockelscell:Pulses needed for E OS can pass- the others are reflec ted provid ing signal for the fiber length stabilization

150 m to experiment

UndulatorLinac

Am

plifi

ed la

ser

beam

(150

fs,1

00µJ

, 800

nm

)

30 m

to e

xper

imen

t

Com pressor + pulse shaper + 150 m glass fiberhave

laser pulses after the fiber are short againtogether no dispersion:

puls length: 50 fs(~ 0.3 nJ)

Electrons

CCD

ZnTe crystal= actual EO-sam pling

Pockels cell

50 % beam splitter


The laser hutchThe laser hutch

overview picture - CDR layout

TEO


The TEO layout - in the laser hutchThe TEO layout - in the laser hutch

laser hutch - CDR layout


The TEO layout - in the tunnelThe TEO layout - in the tunnel

tunnel - CDR layoutHigh degree of automation

19 motors 19 motors

6 cameras 6 cameras

3 photo diodes / PMTs3 photo diodes / PMTs

every important parameter can be

controlled and changed

from the control room

- fully integrated in the control system -- fully integrated in the control system -

High degree of automation

19 motors 19 motors

6 cameras 6 cameras

3 photo diodes / PMTs3 photo diodes / PMTs

every important parameter can be

controlled and changed

from the control room

- fully integrated in the control system -- fully integrated in the control system -


TEO - first steps...TEO - first steps...

Laser hutch

Accelerator tunnel


TEO - simulationsTEO - simulations

critical parts like

the compressorthe compressor

the phase-shaperthe phase-shaper

the imaging of the crystalthe imaging of the crystal

the interaction between laser and el. field in the crystalthe interaction between laser and el. field in the crystal

were simulated in order to optimize TEOs performance


introducing LAB II simulation softwareintroducing LAB II simulation software

Simulation of fs-pulse propagation by Th. Feurer and groupTh. Feurer and group (Jena / MIT /Bern)

time - frequency domain (no spatial calculations)

linear and nonlinear effects / three wave mixing

various materials

compressors, strechers and phase shaper

auto- / cross-correlation, FROGs

and much much more

Based on LabView

Free download at

Free download at

www.lab2.de

www.lab2.de


Lab II - simulation of TEOLab II - simulation of TEO

~ 70 fs FWHM


The compressorThe compressor

compensate for dispersion induced fs-pulse broadening by the 170 m glass fiber

compensates the huge Group Velocity Dispersion (GVD)

(second order deriv. of phase)

BUT induces third (and higher) order phase distortions (TOD)

optimization dilemma bandwidth transmission (constant grating size)

induced TOD

highly dispersive gratings

(1800 lines / mm) low dispersive gratings

(1200 lines / mm)

TOD induced by fiber: 0.5 107 fs3 / TOD by compressor: 1-2 107 fs3


the phase shaper - actual designthe phase shaper - actual design

Geometry is entirely on-axis. ( design by G. Stobrawa, U. Jena)

folding mirror

algorithms for LCD-matrix

- start with genetic algorithm (Soo / Michigan)

-next step:

parameterization with to Taylor coefficients . of the phase (about 100 times faster - Jena)

algorithms for LCD-matrix

- start with genetic algorithm (Soo / Michigan)

-next step:

parameterization with to Taylor coefficients . of the phase (about 100 times faster - Jena)


TEO - imagingTEO - imaging

ray tracing well below diffraction limit

wave front propagation

1:2 imaging

using achromatic lenses

Tilted object → tilted camera

diffraction limited resolution diffraction limited resolution

< 10 µm < 10 µm

for 2 mm field of view


0.5mm

10mm

The wedged crystal The wedged crystal (ZnTe)(ZnTe)

Signal Temporal resolution

Thick crystal Thin crystal

Change sensitivity vs. temporal resolution online online


Wedged crystalWedged crystal


Simulation of EO-Response FunctionSimulation of EO-Response Function

First reflectionof THz field e-beam

Linear diode array1000 pixel

• incidence angle of laser• freq. dependent refraction• freq. dependent EO-coeff.• group velocity mismatch• multiple reflection


Simulation of EO-Response FunctionSimulation of EO-Response Function

T=-50 fs

20% shorter bunch

5% more charge

origin

100 pixel

17%


Challenge: detection at 1 MHz

ELIS photo-diode array (silicon video inc.):

Pixels: 1024 / 8 µm Readout: 30 MHz

1000 pixel -> 30 µs 128 pixel -> 4 µs

Gating 15 ns

Low cost ns

15 ns


Differences between TEO and SPPSDifferences between TEO and SPPS

Pockels cell behind fs-oscillator ~ 100% of laser power available

all reflective shaper

70 fs pulses (FWHM) at crystal are possible

60 nm transmission through the whole system

jitter: no regenerative laser amplifier - but larger distance to experiment

gating by detection (line camera)

wedge crystalwedge crystal – change temporal resolution continuously and online

More than 20 motors / 6 cameras – TEO can be entirely remote controlled More than 20 motors / 6 cameras – TEO can be entirely remote controlled


EOSEOS

Timing monitor for the FEL-optical pump-probe Experiments

• Flexible EOS system to test various concepts

•scanning EO

•chirped pulse EO

• Electron bunch diagnosticElectron bunch diagnostic

•longitudinal bunch structure

Sub 15 fs Femtolaser

Located in container close to the accelerator

15 m beamline (future upgrade: amplified pulse / single shot correlation)

Container electrically isolated / RF shielding

Temperature stabilized RF cable

Beamline for CTR -> EOS in container ( test of crystals …)


EOS - SetupEOS - Setup

To spectrometerOTR

ZnTe crystal

300 µm

electrons

TiSa fs pulse

65 nm FWHM / 15 fs


ConclusionConclusion

• 2 EOS systems 2 EOS systems – to test different EO schemes – Cross-check

• (Goal) Measure at 1 MHz – each pulse – Machine diagnostics– Essential for user pump-probe experiments

• TEO– 50 fs arrival time monitor– Highly automated (standard diagnostics)

• EOS– 100 fs longitudinal electron bunch resolution


Dies ist eine Dies ist eine

schöne vorlage ...


TEO in numbersTEO in numbers

shaper:shaper:

• 640 element LCD matrix, 1800 l/mm grating , 500 mm focal distance

•wavelength transmission: 800 +- 30 nm

•TOD compensation = 1.2 107 fs3

compressor:compressor:

• 1500 l/mm gratings / 140 mm wide / 1.2m separation

•wavelength transmission: 800 +- 30 nm

•TOD induced = 1.4 107 fs3

fiber:fiber:

•170 m long

•Single mode polarization maintaining

•TOD induced = 0.5 107 fs3

• cutoff wavelength < 780 nm


Er

Principal ofelectro-optical

samplingPD

Sampling:• simple analysis• balanced detector allows high sensitivity• good synchronization required• multi-shot method• arbitrary time window possible

Er

Principal oftemporal-

wavelength correlationcamera

Chirp laser method:• single shot method• some more effort for laser and laser diagnostics required • resolution due to laser ~ √t0· tchirp • time window ~ 1-20ps


Space -time correlation methodSpace -time correlation method

Timing o.k.Timing o.k.

EO-Crystal

v

Er

camera

v

laser is „late“laser is „late“

v

laser is „early“laser is „early“

laser


the phase shaper - principlethe phase shaper - principle

actual shaper


Time structure and energy budgetTime structure and energy budget

Ti:Sa oscillator pulses

fiber

108 MHz

OPA

SHG10%

PM

0.01%

Pockels cell 1 MHz

Rotator

SHG

92%

5%

91%

stretcher

SLM

~ 800 ns

t = 1600 ns

9.3 ns

1 MHz

tunnel

t = 0 ns

gated detectorEO-crystal

e-bunch

0.6%

10%

90%

X 1000

0.6%0.6%

~ 800 ns

~ 1600 ns

Synchronized to electron beam at EO-crystal

Synchronized to VUV-FEL beam at sample

Pulse for SHG sampling the fiber length

Pulse for SHG for reference

50%

50%

50%

50%

92%

130 pJ

2.5 nJ

90%

10%

2*40 pJ

15 pJ

98%

FeedbackFiber length

Pump-probe experiment

PM

Documents

HELMHOLTZ GEMEINSCHAFT VUV FEL EO systems at the DESY VUV-FEL Stefan Düsterer for the VUV - FEL Team F. Van den Berghe, J. Feldhaus, J. Hauschildt, R