Preliminary Performance Measurements for Streak Camera with

Large-Format Direct-Coupled CCD Readout*

15th Topical Conference on High-Temperature Plasma DiagnosticsSan Diego, CA April 19 - 22, 2004

R. A. Lerche, J. W. McDonald , R. L. Griffith, D. S. Andrews,G. Vergel de Dios, A. W. Huey, P. M. Bell, O. L. LandenLawrence Livermore National Laboratory

P. A. Jaanimagi, R. BoniLaboratory for Laser Energetics, University of Rochester

* This work was performed under the auspices of the U.S. Department of Energy by University of California Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

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Abstract

Livermore’s ICF Program has a large inventory of optical streak cameras built in the 1970s and 1980s. The cameras are still very functional, but difficult to maintain because many of their parts are obsolete. The University of Rochester’s Laboratory for Laser Energetics is leading an effort to develop a fully automated, large-format streak camera that incorporates modern technology. Preliminary characterization of a prototype camera shows spatial resolution better than 20 lp/mm, temporal resolution of 12 ps, line-spread function of 40 m (fwhm), contrast transfer ratio (CTR) of 60% at 10 lp/mm, and system gain of 101 CCD electrons per photoelectron. A dynamic range of 175 for a 2 ns window is determined from system noise, linearity and sensitivity measurements.

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Summary: We have characterized a new prototype streak camera (ROSS)

1. The streak camera ROSS (Rochester Optical Streak System) Design effort led by Laboratory for Laser Energetics LLNL collaborated on design Streak tube: Photonis P-510 Direct coupled CCD (2K x 2K E2V 42-40 backside) LLNL input optics used for these tests

2. Camera performance Spatial magnification: 1.3 Spatial resolution: > 20 lp/mm (limiting visual) Temporal resolution: 12 ps @ 2 ns window Sensitivity: 101 CCD e- / photoelectron System noise: 5 e- / pixel Dynamic range: ~225 (at best resolution)

3. Camera appears to meet NIF optical streak camera requirements

HTPD-2004-SC - 4ral 040418

The compact streak camera has a direct-coupled large-format CCD readout

Prototype camera configuration

S-20 Streak tubePhotonis P-510

CCD

Input optics (for our tests*):LLNL input hardwareTek C-27 lens1-mm slitMag: 1.167

Streak tube: Photonis P-510S-20 photocathode

CCD:Spectral InstrumentsSI-800E2V 42-40 backside2K x 2K (13.5 m pixels)

Prototype streak camera (ROSS)(12” x 7” x 28” without input optics)

* The prototype input optics module for the ROSS is not yet available.

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Prototype camera magnification is 1.35, field-of-view is 20.5 mm

Sample image for magnification and FOV measurements

Test conditions:Light: Collimated (532 nm)Mask: 10-m slit every 1.5 mmCCD: 2K x 2K (13.5-m pixels)

Time (CCD pixels)

Sp

ace

(CC

D p

ixel

s)

0 20480

2048

Notes:CCD (27 mm square) records central (high-res) region of 60-mm dia streak tube image.

Magnification and FOV are referred to photocathode of the streak tube.

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System line-spread function (LSF)shows a 40 m resolution (fwhm)

1. Measure system magnification

2. Illuminate 10-m mask

3. Take spatial lineout

Mask: 11 um (at photocathode)

Binning: 2x2

FWHM: 2.0 super pixels (40 m)

40 mfwhm

Line-Spread Function

Gaussian

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We calculate the system contrast-transfer function (CTF) from the line-spread function

Calculation convolves LSF with square wave at various frequencies * =

Contrast Transfer Function

- Ronchi ruling measurements

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Ronchi ruling measurements at 8.6 lp/mm confirm 70% CTR estimated from LSF

Spatial Lineout and CTR

CTR @ 8.6 lp/mmMeasured: 68%LSF Prediction: 70%

8.6 lp/mm Ronchi Ruling

Space

Tim

e

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Contour plots show position dependence of spatial resolution in the streak camera image

1-mm slit 100-m slit

2x2 binningSuper-pix = 20 m

FW

HM

(C

CD

su

pe

r p

ixe

ls)

Po

sit

ion

(C

CD

su

pe

r p

ixe

l)

1000

020

0

10

Position (CCD super pixel)

8

0

4

Position (CCD super pixel)

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Contour plot shows position dependence of time resolution in the streak camera image

Contours showing position dependence of time resolution Test conditions:

Collimated light (530 nm)Slit: 100 mCCD: 2K x 2KSweep: Static (no sweep)Binning: 2x2

Time resolution:< 4 super pixels (fwhm)

over 90% of image

Position (CCD super pixel)

FW

HM

(C

CD

su

pe

r p

ixe

ls)

Po

sit

ion

(C

CD

su

pe

r p

ixe

l)

1000

0

0

5

10

Sweep (ns) t (ps)

2 126 23

12 4630 112

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Camera gain is high enough to detect individual photoelectrons

• Determine total ADUs in signal •Convert with CCD gain

• Determine number of pe- generated• Energy at photocthode times QE• Correct for streak camera time window

Gain = 101 CCD e- / pe-

2x2 = 6 CCD e-

* CCD gain = 1.09 e-/ADU

FWHM: 11.3 = 4.81 pix

Laser pulse

Time (ns)

Am

p

Noise for 2 sec exposureBinning Noise(e-)

1x1 5.132x2 5.973x3 6.694x4 7.92

Histogram of Background

Nu

mb

er o

f p

ixel

s

Counts (ADUs)

FWHM: 11.3 ADUsnoise: 4.81 ADUs

Image of swept slit(3 mm x 0.5 mm)

Tim

e

Space

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We use 20% temporal broadening to define the maximum usable current density

J0 = 2.2 amp/cm2

2. C-L current depends on geometry and voltage

1. 20% broadening occurs near 1% of Child-Langmuir space-charge limited current (J0) for laser pulse t = 45 ps

FWHM vs Current

1% C-L

Window

pc-15 kV

Extraction grid -12.5 kV

x

Expect reduced performance for J > 1% of C-L current (J0)

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We use SNR versus photoelectrons per resolution element as a figure-of-merit

SNR = s2N / [s2N (C/C)2 + (s/sb)2(b/C)2]1/2

s2 = # of detector pixels / image resolution elementN = # of photoelectrons per detector pixelsb

2 = number of detector pixels per binned pixelb = read plus dark current noise for one binned pixelC = # of CCD electrons / photoelectronC = standard deviation in C

For the ROSS streak camera we have:s2 = 32 pixels (4 space, 8 time)sb

2 = 1, 4, 9, 16b = 5.13, 5.97, 6.69, 7.92C = 101 CCD e- / pe-

C = Unknown

Time

Sp

ace

1 pixelsb2

(2x2)

Image PSF(32 pixels)

Maximize SNR by:Increasing s (more averaging)Increasing N (reduce sweep speed)

Increasing C (more efficient pe- detection)Decreasing read (improve CCD)

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A SNR plot establishes the dynamic range (DR) at ~60 for an image resolution element

SNR too low (avoid to ensure quality data)

SNR versus Photoelectrons per Detector Pixel

Sweep DR*2ns 1756ns 40512ns 855

* Binning: 2x2

Dynamic Range = f(s, sweep speed)

>1% C-L

2ns6ns

12ns

C = 101

HTPD-2004-SC - 15ral 040418

Summary: We have characterized a new prototype streak camera (ROSS)

1. The streak camera ROSS (Rochester Optical Streak System) Design effort led by Laboratory for Laser Energetics LLNL collaborated on design Streak tube: Photonis P-510 Direct coupled CCD (2K x 2K E2V 42-40 backside) LLNL input optics used for these tests

2. Camera performance Spatial magnification: 1.3 Spatial resolution: > 20 lp/mm (limiting visual) Temporal resolution: 12 ps @ 2 ns window Sensitivity: 101 CCD e- / photoelectron System noise: 5 e- / pixel Dynamic range: ~225 (at best resolution)

3. Camera appears to meet NIF optical streak camera requirements