Development of an Ultrafast Accumulative X-ray Streak Camera

Mahendra Shakya , Jinyuan Liu, Bing Shan And Zenghu Chang

J.R.Macdonald Laboratory

Kansas State University, KS

OBJECTIVE

To Design Camera With Resolution 100fs

Motivation

• Study of physical process requires fast detector

• Auto correlation and Cross correlation require material with efficient non-linear effect.Not applicable for X-ray

• X-ray Streak Camera Provides Intensity, Time and Space information

Streak Camera

Convert time into space

Mirror Film

Slit

t =x/v

x

vt

X-ray Signal

CCD

Deflection Plate

Electrostatic Lens

Switch

AnodeCathode

Phosphor Screen

Slit2Slit1

Streak Tube

MCP

Laser Pulse GaAs

1975 first demonstration

1990 2ps resolution

1996 0.5ps resolution in single-shot mode, Z.Chang (Appl.Phys.Lett.69,1(1996)

2001 0.7 ps in accumulation mode (G.A.Naylor, et al.) by improving laser stability

2002 0.8 ps (Belzile et al.) by using multiplephotoconductive switches

2003 Jinyuang Liu 590 fs in accumulation mode Appl. Phys Lett. 82, pp. 20 (2003, )

Developments

Factors Affecting Temporal Resolution in Accumulative Mode

• Transit Time Dispersion Velocity distribution, Angular distribution

• Scanning Speed

t s= x/v x

• Timing Jitter

psE

t ps

63.2 E

V

176fs 135fs

Au

E

Anode

Cathode

Collimating slit

psE

t ps

63.2

Effect of E field on Transit Time Dispersion

•Collimating Slit

10.6V/mm 13.75V/mm

•High electric field

tps Reduced By 23%

x Reduced 50%

Factors Affecting Temporal Resolution in Accumulative Mode

• Transit Time Dispersion Velocity distribution, Angular distribution

• Scanning Speed

t s= x/v x

• Timing Jitter

psE

t ps

63.2 E

V

rr oe148.1

re= radius of the electrode

r0= radius of the gap

Reducing x by Changing Electrode Geometry

The best focused static image width, x = 175 m(25pixels)

+/2+/2

-/2

-/2

ro

y x

re

500 1000 1500 2000

0

10

20

30

40

50

FWHM 175m

Inte

nsity

mVb=0V , Vf = 85V, Laser energy = 60 J , 6600 Shots, Exposure time = 6s

Static Image

Images with re/r0 = 1.9

FWHM, x = 560m

Factors Affecting Temporal Resolution in Accumulative Mode

• Transit Time Dispersion Velocity distribution, Angular distribution

• Scanning Speed

t s= x/v x

• Timing Jitter

psE

t ps

63.2 E

V

43200 43600 44000 44400

-200

-100

0

60 ps

Am

plit

ude

(V

)

Time (ps)

43200 43600 44000 44400

0

100

200

60psA

mp

litu

de

(V

)

Time(ps)

Effect Of Cables and Switch on Scanning Speed

RL

+V0 -V0

RLDP arm 1 DF arm 2

Es

GaAs switch

RbRb

2GHz cable, t = 90ps, 18GHz cable , t =60 ps

49600 50000 50400 50800

-300

-200

-100

0

120ps

Am

plit

ud

e(V

)

Time(ps)

Deflection Plate Output With 18GHz Cables

+V0 -V0

RbRbRLRL

DP arm 1 DP arm 2Es

GaAs switch

t1/

Factors Affecting Temporal Resolution in Accumulative Mode

• Transit Time Dispersion Velocity distribution, Angular distribution

• Scanning Speed

t s= x/v x

• Timing Jitter

psE

t ps

63.2 E

V

0 20 40 60 80 1000

20

40

60

80

100

120

140

160

Ris

e tim

e A

mpl

itude

(V)

Laser Energy (J)

The pulse amplitude of GaAs switch changes with trigger laser energy

Photoconductive Switch

Laser Energy Vs Pulse Amplitude of the Switch

0 20 40 60 80 1000

500

1000

1500

2000

2500

3000

Amplitude/Rise time fluctuation = 13.66%

Am

plitu

de/R

ise

time(

V/n

s)

Laser Energy

f=150mmf=100mm

CCD

267nm

L1L2

800nm ,25 fs

Streak Camera Calibration Setup

STREAK CAMERA

GaAs

STREAK

CAMERA

6000 7000 8000 9000 10000 11000

5.5

6.0

6.5

7.0

7.5

8.0

D Linear Fit of Data1_D

S

peed

X 1

08 m/s

ec

Cathode voltage (V)

Cathode Voltage Vs Scanning Speed

40 50 60 70 80 90 100 110

80

90

100

110

120

130

140

S

pee

d(P

ixel

s/p

s)

Bias voltage(V)

Bias Voltage Vs Scanning Speed

Vf = 85V, Vc=8.5 kV, Laser Energy = 60 J

6000 7000 8000 9000 10000 11000

0.5

0.6

0.7

0.8

0.9

1.0

Tem

po

ral R

eso

luti

on

(p

s)

Cathode Voltage (V)

Cathode Voltage Vs Temporal Resolution

Vb= 68.3V, Vf= 85V , Laser Energy = 60J, 6600 shots, Exposure time = 6.6sec

Temporal resolution

470fs at –8.5kV

Electron Sweep Speed

Vb= 68.5V, Vc= -8.5kV, Vf= 8.5V, Laser Energy = 60J

0 500 1000 1500 2000 2500 3000 35001

2

3

4

5

6

7

Speed = 1.97c

1/speed = 1.7x10-9sec/m

time

(ps)

m

0 1 2 3 4

0

5

10

15

20

25

30

FWHM 470fs

Inte

nsi

ty(a

rbitr

ary

)

time (ps)

Vc= -8.5kV, Vb= 68.3V, Vf= 85V,Exposure time = 6s, 6600 Shots.Laser energy = 60J

Time Resolution with Variable Slit

-0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.00

50

100

150

200

250

Image with 400average frame FWHM = 500fs

Inte

nsi

ty (

arb

itra

ry)

Time (ps)

6600 Shots average sub-picosecond pulse width streak image, Exposition time= 6.6 sec, Vb= 68.3v,Vc=-11kV, Vf= 90 Laser Energy=60J

Intensity Vs Time at -11KV Cathode Voltage

•Introducing variable slit to collimate electron beam

•Qudrupolens Geometry. Changed re /r0 from 1.9 to 1.147

Modification Made

• High deflection sensitivity: 20 cm/kV

•Photoconductive Switch: 60ps rise and fall time

• Fast response time: 120 ps rise and fall time

• High scanning speed: 2c

•Current Status 470fs

• Camera Potential 200fs

Summary