A. Zholents, July 28, 2004

Timing Controls Using Enhanced SASE Technique*)

A. Zholents

or*) towards absolute synchronization between “visible” pump and

x-ray probe pulses

SLAC XFEL short bunch measurement and timing workshopJuly 26 – 30, 2004

A. Zholents, July 28, 2004

Pump-probe experiment concept

ion or e- detector

Laser excitation pulseX-ray probe pulse

∆tX-ray detector

sample

• Requires control/measure of t with a resolution better than x-ray pulse duration (possibly as small as 100 attoseconds)

A. Zholents, July 28, 2004

Pump-probe experiment concept con’t

Near IR

X-ray probe pulse

ion or e- detector

X-ray detector

sample

XUV

Multicolor excitation

A. Zholents, July 28, 2004

• One can hope to get a required synchronization if all sources are linked to a common origin

Master laser source

Pump-probe experiment concept con’t

controlled delay

Near IR

XUVCourtesy H. Kapteyn

laser - e-beam manipulation and “seeding”

X-ray probe pulse

• 90o Thomson scattering: Schoenlein, R.W., et al., Science, 274, (1996)236.

• “Slicing”: Schoenlein, R.W., et al., Science,. 287, (2000 )2237.

• Harmonic Cascade FEL: L.-H. Yu, et al., Science, 289, (2000)2237.

A. Zholents, July 28, 2004

Energy modulation in the wiggler at 2 - 4 GeV

Enhanced Self Amplified Spontaneous Emission (ESASE)

Only one optical cycle is shown

Required:

•Laser peak power ~ few GW

•Wiggler with 10 – 20 periods

Assumed:

•Electron energy spread ~ 1.2 MeV

Master sourceNear IR pump

A. Zholents, July 28, 2004

Acceleration to 14.35 GeV and bunching at the laser wavelength

acceleration bunching

Only one optical cycle is shown Pe

ak c

urr

ent

z /L

Pe

ak c

urr

ent

En

erg

y sp

rea

d

Peak current and energy distribution within one micro-bunch

Bz L 2/

50 fs laser pulseL= 2 microns

A. Zholents, July 28, 2004

SASE in the undulator producing x-rays synchronized to the modulating laser

The output x-ray radiation from a single micro-bunch

Power at saturation (estimate for bunching~0.5), P0~200 GW

70 as

xGx Mzz ˆ8Ln2/

• Each spike is nearly temporary coherent and Fourier transform limited.• Carrier phase for an x-ray wave is random from spike to spike.

A. Zholents, July 28, 2004

The x-ray radiation output from the entire electron bunch

Pe

ak p

ow

er

z /L

Shaping of a temporal profile of the laser pulse is a tool for shaping of a temporal profile of the x-ray pulse.

A. Zholents, July 28, 2004

e-beam based timing reference

Master sourceNear IR pump

one period wigglerisochronous

bend

x-rayswiggler radiation, ~0.5 GW

ESASE

SH correlator

Near IR pump

A. Zholents, July 28, 2004

KDP

filter

detector

laser pulse, I1(t)

wiggler pulse, I2(t)

I2(t)

I1(t)

KDP

x

S(x) = dttItI

21

c

xn

sin

SH

~0.3 mm

Single shot measurement of a time jitter using Second Harmonic intensity correlation

F. Salin, et al., Applied Optics, 26, (1987)4528

A. Zholents, July 28, 2004

Demonstration of the detector calibration by inserting 0.36 mm glass plate in either arm.(from C. Rempel and W. Rudolph, Experimentell Technik der Physic, 37, (1989)381.)

A. Zholents, July 28, 2004

Summary

1) Synchronization between pump and probe pulses is obtained by linking all pulses to the common origin.

2) ESASE provides a time mark for the x-ray pulse and allows absolute synchronization between laser pulse and x-ray pulse.

3) ESASE allows control over the duration of x-ray pulse and its temporal shape. X-ray pulses less than 100 attoseconds are feasible.

4) ESASE allows beam based monitoring for a time jitter with better than fs resolution.