ULTRASPEC detector page

Vik Dhillon, Liam Hardy, version: 29 November 2013


This page collects together all relevant information on the ULTRASPEC EMCCD detector.


  1. e2v datasheet for the CCD201-20 device used in ULTRASPEC
  2. Richard Hickman's ULTRASPEC detector page
  3. NORMAL output: bias level, readout noise, electronic gain, flatfield noise
  4. AVALANCHE output: bias level, readout noise, electronic gain, flatfield noise, avalanche gain, clock-induced charge
  5. Linearity
  6. Dark current
  7. Pumping the cryostat
  8. Cooling the cryostat
  9. Flat fields



NORMAL output


METHODRatio of two flats (17/04/2013)Photon transfer curve (25/04/2013)
(click on links for plots)
CLEAR BIN 1x1SLOWMEDIUMFASTSLOWMEDIUMFAST
BIAS (ADU)8339761089   
RNO (ADU)2.93.95.52.93.95.4
RNO (e-)2.32.74.42.32.74.3
GAIN (e-/ADU)0.80.70.80.80.70.8
FLATFIELD NOISE (%)   0.30.30.3

NOTE: The above measurements were obtained in CLEAR mode. However, tests show that similar results are obtained if NOCLEAR mode is used (see table below).


METHODPhoton transfer curve + bias frame
(01/05/2013 click on links for plots)
NO CLEAR BIN 1x1SLOWMEDIUMFAST
BIAS (ADU)8339741092
RNO (ADU)2.94.65.8
RNO (e-)2.33.24.6
GAIN (e-/ADU)0.80.70.8
FLATFIELD NOISE (%)0.20.20.2

NOTE: Changing the binning factor makes little difference, as shown in the two tables below:


METHODPhoton transfer curve + bias frame
(01/05/2013 click on links for plots)
BIN 2x2SLOWMEDIUMFAST
BIAS (ADU)811920845
RNO (ADU)3.04.65.8
RNO (e-)2.43.24.6
GAIN (e-/ADU)0.80.70.8
FLATFIELD NOISE (%)0.20.20.2

METHODPhoton transfer curve + bias frame
(01/05/2013 click on links for plots)
BIN 3x3SLOWMEDIUMFAST
BIAS (ADU)822932863
RNO (ADU)3.14.15.8
RNO (e-)2.52.94.6
GAIN (e-/ADU)0.80.70.8
FLATFIELD NOISE (%)0.20.20.2

NOTE: The above measurements were obtained in NON-DRIFT mode. However, tests show that similar results are obtained if DRIFT mode is used (see tables below).


METHODPhoton transfer curve + bias frame
(01/05/2013 click on links for plots)
DRIFT BIN 1x1SLOWMEDIUMFAST
BIAS (ADU)8329731085
RNO (ADU)2.93.95.0
RNO (e-)2.32.74.0
GAIN (e-/ADU)0.80.70.8
FLATFIELD NOISE (%)0.30.30.3

METHODPhoton transfer curve + bias frame
(01/05/2013 click on links for plots)
DRIFT BIN 2x2SLOWMEDIUMFAST
BIAS (ADU)810918843
RNO (ADU)3.54.45.4
RNO (e-)2.83.14.3
GAIN (e-/ADU)0.80.70.8
FLATFIELD NOISE (%)0.20.20.2

METHODPhoton transfer curve + bias frame
(01/05/2013 click on links for plots)
DRIFT BIN 3x3SLOWMEDIUMFAST
BIAS (ADU)821932860
RNO (ADU)3.64.35.3
RNO (e-)2.93.04.2
GAIN (e-/ADU)0.80.70.8
FLATFIELD NOISE (%)0.20.20.2

Below are links to example bias frames taken in the lab in Sheffield and at the TNT. Both are taken in normal slow readout mode and are provided in ucm format.





AVALANCHE output


METHODRatio of two flats (17/04/2013)Photon transfer curve (30/04/2013)
(click on links for plots)
CLEAR BIN 1x1SLOWMEDIUMFASTSLOWMEDIUMFAST
BIAS (ADU)439648393695   
RNO (ADU)2.84.63.32.95.93.6
RNO (e-)5.67.816.55.59.414.4
GAIN (e-/ADU)1.91.64.11.91.64.0
FLATFIELD NOISE (%)   0.30.30.3

NOTE: The above measurements were obtained in CLEAR mode. However, tests show that similar results are obtained if NOCLEAR mode is used (see table below).


METHODPhoton transfer curve + bias frame
(30/04/2013 click on links for plots)
NO CLEAR BIN 1x1SLOWMEDIUMFAST
BIAS (ADU)439448413695
RNO (ADU)3.16.93.7
RNO (e-)5.911.014.8
GAIN (e-/ADU)1.91.64.0
FLATFIELD NOISE (%)0.30.30.3

NOTE: Changing the binning factor makes little difference, as shown in the two tables below:


METHODPhoton transfer curve + bias frame
(30/04/2013 click on links for plots)
BIN 2x2SLOWMEDIUMFAST
BIAS (ADU)443348223673
RNO (ADU)2.95.13.3
RNO (e-)5.58.213.2
GAIN (e-/ADU)1.91.64.0
FLATFIELD NOISE (%)0.20.20.2

METHODPhoton transfer curve + bias frame
(30/04/2013 click on links for plots)
BIN 3x3SLOWMEDIUMFAST
BIAS (ADU)444748373677
RNO (ADU)3.25.23.8
RNO (e-)6.18.315.2
GAIN (e-/ADU)1.91.64.0
FLATFIELD NOISE (%)0.20.20.1

NOTE: The above measurements were obtained in NON-DRIFT mode. However, tests show that similar results are obtained if DRIFT mode is used (see tables below).


METHODPhoton transfer curve + bias frame
(30/04/2013 click on links for plots)
DRIFT BIN 1x1SLOWMEDIUMFAST
BIAS (ADU)439348343695
RNO (ADU)2.94.63.8
RNO (e-)5.57.415.2
GAIN (e-/ADU)1.91.64.0
FLATFIELD NOISE (%)0.20.30.2

METHODPhoton transfer curve + bias frame
(30/04/2013 click on links for plots)
DRIFT BIN 2x2SLOWMEDIUMFAST
BIAS (ADU)443348213673
RNO (ADU)2.95.23.4
RNO (e-)5.58.313.6
GAIN (e-/ADU)1.91.64.0
FLATFIELD NOISE (%)0.10.20.1

METHODPhoton transfer curve + bias frame
(30/04/2013 click on links for plots)
DRIFT BIN 3x3SLOWMEDIUMFAST
BIAS (ADU)444748373677
RNO (ADU)3.05.03.9
RNO (e-)5.78.015.6
GAIN (e-/ADU)1.91.64.0
FLATFIELD NOISE (%)0.10.10.1


A note on gain in avalanche mode. We use the following definition:

system gain (e-/ADU) = electronic gain (e-/ADU) / avalanche gain

where:


METHODHVGAIN=9 BIAS HISTOGRAM (25/04/2013)
(click on links for plots)
CLEAR BIN 1x1SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0020.0010.004
AVALANCHE GAIN116511091116
CIC (e-/pix/frame)0.0380.0210.018

METHODHVGAIN=9 BIAS HISTOGRAM (30/04/2013)
(click on links for plots)
NO CLEAR BIN 1x1SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0010.0010.003
AVALANCHE GAIN133212631267
CIC (e-/pix/frame)0.0680.0440.027

METHODHVGAIN=9 BIAS HISTOGRAM (30/04/2013)
(click on links for plots)
BIN 2x2SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0020.0010.003
AVALANCHE GAIN126612411238
CIC (e-/pix/frame)0.0510.0420.035

METHODHVGAIN=9 BIAS HISTOGRAM (30/04/2013)
(click on links for plots)
BIN 3x3SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0010.0010.003
AVALANCHE GAIN130411901181
CIC (e-/pix/frame)0.0680.0620.052

METHODHVGAIN=9 BIAS HISTOGRAM (30/04/2013)
(click on links for plots)
DRIFT BIN 1x1SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0020.0010.004
AVALANCHE GAIN120211641127
CIC (e-/pix/frame)0.0430.0290.021

METHODHVGAIN=9 BIAS HISTOGRAM (30/04/2013)
(click on links for plots)
DRIFT BIN 2x2SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0020.0010.003
AVALANCHE GAIN114810671158
CIC (e-/pix/frame)0.0590.0490.035

METHODHVGAIN=9 BIAS HISTOGRAM (30/04/2013)
(click on links for plots)
DRIFT BIN 3x3SLOWMEDIUMFAST
ELECTRONIC GAIN (e-/ADU)1.91.64.0
SYSTEM GAIN (e-/ADU)0.0010.0010.002
AVALANCHE GAIN129715902495
CIC (e-/pix/frame)0.0740.0500.028

NOTE: Values in the final two tables come with significant uncertainties, due to the frames having small areas, thus fewer pixels. This means the histograms produced are less accurate, as can be seen in the plots.

NOTE 11/06/13: After several fixing several problems and opening up the cryostat on a number of occasions, the avalanche gain has dropped significantly to values closer to ~700, rather than ~1200 as before.





Linearity

This was measured using the artificial star in the lab at Sheffield. The data were taken unbinned, using the normal output in clear mode with slow readout. The first plot below shows the total counts measured within the aperture centred on the star as a function of exposure time. Note that the peak counts per pixel at exposure times of 16, 17, 18, 19 and 20 seconds were 59733, 62133, 65535, 65535 and 65535, respectively. The second plot shows the residuals, where the data have been divided by the fit. It can be seen that the device is linear to better than 1% across its entire dynamic range, with the exception of the shortest exposure times, where the effect of the frame transfer is apparent. The data used to make this plot are available here.






Dark current

Immediately after powering on the SDSU controller (both hardware and software), the dark current decreases with time as follows:

TIME SINCE PON (mins)DARK CURRENT (electrons/pix/hr)
0148
+1024
+2019
+3019
+4014
+5014
+6014
+7010
+8010
+9010
+10010
...+18010

The above data were measured on 07/06/2013 with the chip at 160 K, using normal, clear, slow read-out mode and 600 s exposures. The data are shown graphically below:

The linearity of dark current with time was also measured, and the dark current per unit time was found to remain constant for varying lengths of exposure longer than 5 minutes.

The dependence of dark current on temperature was also investigated. As expected, the dark current increases with temperature, as follows:

Temperature (K)DARK CURRENT (electrons/pix/hr)
1553.2
16013
16538
170106
175288
180659
1851389
1902682

The above data were measured on 08/06/2013 using multiple 15 minute exposures in normal, clear, slow read-out mode. A graph of the dark current dependence on temperature is shown below:


Below is an image of a typical dark frame taken in the lab in Sheffield on 3rd October 2012 with a chip temperature of approximately 160 K. The corresponding ucm file can be downloaded here.





Pumping the cryostat

The plot below shows the values of cryostat pressure as a function of time after vacuum pumping begins. Different colours represent different pumping sessions.





Cooling the cryostat

The plot below shows the values of cold finger (cooler values) and chip temperatures as a function of time after cryo-cooling begins. Different colours represent different cooling sessions.





Flat Fields

We include links here to example flat field frames taken at the NTT in June 2009 and at the TNT in November 2013. Both png and ucm files are available here. The flats have been bias-subtracted, and a suitable number of individual frames were combined to create each one.