Transcript Document

Preliminary Performance Measurements
for Streak Camera with
Large-Format Direct-Coupled CCD Readout*
R. A. Lerche, J. W. McDonald , R. L. Griffith, D. S. Andrews,
G. Vergel de Dios, A. W. Huey, P. M. Bell, O. L. Landen
Lawrence Livermore National Laboratory
P. A. Jaanimagi, R. Boni
Laboratory for Laser Energetics, University of Rochester
15th Topical Conference on
High-Temperature Plasma Diagnostics
San Diego, CA
April 19 - 22, 2004
* 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.
HTPD-2004-SC - 1
ral 040418
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, largeformat 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, linespread 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.
HTPD-2004-SC - 2
ral 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
HTPD-2004-SC - 3
ral 040418
The compact streak camera has a
direct-coupled large-format CCD readout
Prototype streak camera (ROSS)
(12” x 7” x 28” without input optics)
Input optics (for our tests*):
LLNL input hardware
Tek C-27 lens
1-mm slit
Mag: 1.167
Streak tube:
Photonis P-510
S-20 photocathode
Prototype camera configuration
S-20 Streak tube
Photonis P-510
HTPD-2004-SC - 4
ral 040418
CCD:
Spectral Instruments
SI-800
E2V 42-40 backside
2K x 2K (13.5 m pixels)
CCD
* The prototype input optics module
for the ROSS is not yet available.
Prototype camera magnification is 1.35,
field-of-view is 20.5 mm
Sample image for magnification
and FOV measurements
2048
Space (CCD pixels)
Test conditions:
Light: Collimated (532 nm)
Mask: 10-m slit every 1.5 mm
CCD: 2K x 2K (13.5-m pixels)
0
Notes:
CCD (27 mm square) records
central (high-res) region of
60-mm dia streak tube image.
0
2048
Time (CCD pixels)
HTPD-2004-SC - 5
ral 040418
Magnification and FOV are
referred to photocathode of the
streak tube.
System line-spread function (LSF)
shows a 40 m resolution (fwhm)
1. Measure system magnification
Line-Spread Function
2. Illuminate 10-m mask
3. Take spatial lineout
40 m
fwhm
Mask: 11 um (at photocathode)
Binning: 2x2
FWHM: 2.0 super pixels (40 m)
HTPD-2004-SC - 6
ral 040418
Gaussian
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
HTPD-2004-SC - 7
ral 040418
=
Ronchi ruling measurements at 8.6 lp/mm
confirm 70% CTR estimated from LSF
Time
8.6 lp/mm Ronchi Ruling
Space
CTR @ 8.6 lp/mm
Measured: 68%
LSF Prediction: 70%
HTPD-2004-SC - 8
ral 040418
Spatial Lineout and CTR
Contour plots show position dependence of
spatial resolution in the streak camera image
100-m slit
1-mm slit
FWHM
(CCD super pixels)
Position (CCD super pixel)
1000
2x2 binning
Super-pix = 20 m
0
20
8
10
4
0
0
Position (CCD super pixel)
HTPD-2004-SC - 9
ral 040418
Position (CCD super pixel)
Contour plot shows position dependence of
time resolution in the streak camera image
Contours showing position
dependence of time resolution
Position (CCD super pixel)
1000
Test conditions:
Collimated light (530 nm)
Slit: 100 m
CCD: 2K x 2K
Sweep: Static (no sweep)
Binning: 2x2
Time resolution:
< 4 super pixels (fwhm)
over 90% of image
FWHM
(CCD super pixels)
0
10
Sweep (ns)
2
6
12
30
5
0
Position (CCD super pixel)
HTPD-2004-SC - 10
ral 040418
Dt (ps)
12
23
46
112
Camera gain is high enough to
detect individual photoelectrons
Histogram of Background
Number of pixels
FWHM:11.3
11.3
FWHM:
ADUs
s
:
4.81
ADUs
s =noise
4.81 pix
• 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
Image of swept slit
(3 mm x 0.5 mm)
Noise for 2 sec exposure
Binning Noise(e-)
1x1
2x2
3x3
4x4
5.13
5.97
6.69
7.92
Amp
Time
Counts (ADUs)
Laser pulse
Time (ns)
Space
Gain = 101 CCD e- / pes2x2 = 6 CCD e* CCD gain = 1.09 e-/ADU
HTPD-2004-SC - 11
ral 040418
We use 20% temporal broadening to define
the maximum usable current density
1. 20% broadening occurs near 1% of ChildLangmuir space-charge limited current (J0)
for laser pulse Dt = 45 ps
FWHM vs Current
2. C-L current depends on
geometry and voltage
Window
x
1% C-L
pc Extraction grid
-12.5 kV
-15 kV
J0 = 2.2 amp/cm2
Expect reduced performance
for J > 1% of C-L current (J0)
HTPD-2004-SC - 12
ral 040418
We use SNR versus photoelectrons per
resolution element as a figure-of-merit
SNR = s2N / [s2N (sC/C)2 + (s/sb)2(sb/C)2]1/2
s2 = # of detector pixels / image resolution element
N = # of photoelectrons per detector pixel
sb2 = number of detector pixels per binned pixel
sb = read plus dark current noise for one binned pixel
C = # of CCD electrons / photoelectron
sC = standard deviation in C
Maximize SNR by:
Increasing s (more averaging)
Increasing N (reduce sweep speed)
Increasing C (more efficient pe- detection)
Decreasing sread (improve CCD)
HTPD-2004-SC - 13
ral 040418
Image PSF
(32 pixels)
Space
For the ROSS streak camera we have:
s2 = 32 pixels (4 space, 8 time)
sb2 = 1,
4,
9, 16
sb = 5.13, 5.97, 6.69, 7.92
C = 101 CCD e- / pesC = Unknown
sb2
(2x2)
Time
1 pixel
A SNR plot establishes the dynamic range (DR)
at ~60 for an image resolution element
SNR versus Photoelectrons per Detector Pixel
2ns
C = 101
Dynamic Range
= f(s, sweep speed)
6ns
12ns
>1% C-L
SNR too low
(avoid to ensure quality data)
Sweep
2ns
6ns
12ns
DR*
175
405
855
* Binning: 2x2
HTPD-2004-SC - 14
ral 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
HTPD-2004-SC - 15
ral 040418