NIM Camera/Polarimeter Run, 16-27 Sep 2002

Tests at NSO/KP McMath-Pierce Telescope

27 Sep 2002 (cooling tests and tear-down)

Possible problems with the LN2 vacuum attachment? Pressure and dark counts stay high; cool-down in 3 hours.
Same asymptotic limit value as yesterday; same filter wheel settings used. This value 470-bias=284.4 divided by 2 sec exposures and multiplied by the gain determined from 25 Sep implies 51,620 photo-electrons per second looking at cold aluminum plate in dewar.

Here is the log of data.

26 Sep 2002 (cooling test)

Cooling tests show cool-down in 2 hours.
NOTE: asymptotic limit of tests today not the same as the test on 24 Sep 2002: could be different filter wheel set-up.

Here is the log of data.

25 Sep 2002 (light transfer tests with lamps)

Array tests with lamp for gain and read noise evalution. Plot shows log(noise) vs log(intensity). Equation which describes this (in ADU units) is:
log(noise)=1/2 log ( I/gain + readnoise^2)
At low intensity signal, log(noise)=1/2 log (readnoise^2) = log (readnoise) log(readnoise)=0.096, readnoise=1.24738 ADU
At high signal, log(noise)=1/2 log (I/gain) = -1/2 log(gain)+1/2 log(I)
Best line with slope = 1/2 was eyeball fit, intercept =-1.28 => gain = 363 photons/ADU
readnoise = 453 photons

Here is the idl data reduction script.

NOTE: NO INFO FOUND IN MANUALS RE: GAIN, READ NOISE

24 Sep 2002 (polarimeter tests)

Cooling test looking at dark stop on outer filter wheel Cooling tests show cool-down in 2 hours.

Here is the idl data reduction script.

Move to 1550 nm with filter wheel, test Meadowlark retarder. Beamgate electronics box outputs a 2kHz square wave.

--- Tests "polar_..." have linear polarizer 90 degrees, variable retarder 45, linear polarizer 0, slit 0 at 1550nm

Reproducibility problems? after scanning voltage once, the 2-4 volt region was rescanned and appears to have an offset compared to the first scan.

Looks like about 1/4 wave retardance at high voltage limit.
Here is the idl data reduction script.

--- Tests "polarb_..." have linear polarizer 90 degrees, fixed 1/4 wave at 45, variable retarder 45, linear polarizer 0, slit 0 at 1550nm

--- Tests "polarc_..." have linear polarizer 90 degrees, variable retarder 45, linear polarizer 0, slit 0 at 1083nm

--- Tests "polard_..." have linear polarizer 90 degrees, fixed 1/4 wave at 45, variable retarder 45, linear polarizer 0, slit 0 at 1083nm

23 Sep 2002 (long pump-down, tests of off-limb background)

Disk center flux is 6.92 ADU/millisecond
Strange flux tests - perhaps changing background during different exposures?

Negative flux at r=1.4?

Here is the idl data reduction script.

20 Sep 2002 (TIA tests, flux tests)

TIA offset nominal value is 148.
Bias is linearly related to TIA value
Flux rates constant within linear part (fits range from 0.968 to 1.005)
bias=-20968.2+142.948*(TIA offset)
bias =0 @ tia offset = 146.68

Here is the idl data reduction script.
Flux tests: solar flux is 5.98 adu per millisecond.
Darks look steady:

However solar flux has a non-zero y-intercept, implying there is a problem in the exposure time. Exposure time = exposure + 14.1 milliseconds.

Is there some non-linearity in the response or just an error in the fit coefficient? Making a linear fit with the first three points shows that longer exposures have greater values than expected by a percent or so.

Here is the idl data reduction script.
Background measurements normalized by disk flux.
Background at 1.10Rsun is 734 millionths (from single frame, not flux sequence).
Background at 1.30Rsun varies greatly as a function of time, 220 to 580 millionths.

Here is the idl data reduction script.

19 Sep 2002 (Flux measurements, slit size tests)

Tests with a cold allen wrench over the open shutter are the same as "spectrograph" darks.
Mean dark shows intercept of 201 counts, slope 0.98 ADU/millisecond

Differences in the mean dark frames are small; scatter decreases as counts increase (less susceptible to read noise?).

Disk flux tests show 6.49 ADU / millisecond flux.
Also show a non-zero y-intercept implying 8.37 millisecond exposure overhead.

Here is the idl data reduction script.
Different slit sizes: 100, 200 and 400 microns used at 4010nm. Flux varies.
At 400 micron slit flux is 6.48 ADU/millisecond, but 100 micron slit normalized gives only half that flux.
Is this diffraction from the slit overfilling the spectrograph optics?

Here is the idl data reduction script.

18 Sep 2002 (Windy: did not open, sample darks)

Darks look ok: bias = 187, slope is 1.01 ADU per millisecond

Here is the idl data reduction script.

17 Sep 2002

Filter center wavelength at 4010nm, not 3950nm? Very little light at 3934 at disk center; not worth any effort looking for coronal line with this prefilter.
Center the spectrograph at the hydrogen line at 4051.5nm. Sample image at limb.

Here is the idl data reduction script.
Mirrors are dirty, no special cleaning done for this run. Background measurements and disk center measurements made at 100 micron slit ("b" filenames) and 200 micron slit (no "b").
No coadding, rather 64 raw files stored to disk.
Measurements made at 1.1, 2.0 and 3 solar radii.
No dark images taken. Instead images at 200 and 100 micron slits subtracted then divided by solar flux at disk center with 100 micron slit. Error bars are variation during 64 images (during 5 minutes time?).

Here is the idl data reduction script.

16 Sep 2002 (set-up and dewar pumping)

Inventory NIM polarization optics:
1 variable retarder in black housing, (should be another one in a blue housing),
2 quarter-wave plates in black housings,
1 quarter-wave plate in a rotating housing,
2 linear polarizers in black housings,
miscellaneous sheet polarizers.
Quarter-wave plates a thin film based and not achromatic.