Med mode TAAS spectrum at 6.6 um

I quickly looked through the different wavelengths at which we did medium mode TAAS FCLS spectra.  The 6.6 micron filter was first and turned out to be very interesting because of atmospheric H2O lines.

A quick look at the other wavelengths shows that the long wavelengths (18a, Soifer) are totally not worth doing unless we cut down on the light or really speed up the frame time (partial array readout).
The BP14100 wasn't that good, either.  The N07904 with slit 1 and 0.5mm FCLS was brilliant, but no interesting atmospheric lines.

The rotation and shifting used at 6.6 worked well at 7.9, which is probably because the grating angle is the same for both.  The continuum in the 6.6 is spatially offset from in the 7.9.  The FCLS parameters are:  6.6) X,Z = 43,26 and 29,14.5 with 2mm aperture, slit 6.  7.9) X,Z = 43,26 and 29,14.75 with 0.5mm aperture and slit 1.  The offset could be due to the different aperture and EXES slit.   The separation between the continua is different between the two filters -- and in the wrong sense from what the FCLS coordinates suggest -- but I'm doubtful the data are good enough to make conclusions.

There was very strange fringing in the raw files (upper left, below).  Saw enhanced DN in relatively thin bands that look like wavey lines across the detector.  They are not evenly spaced in frequency, which basically means they can not be caused by an optic before dispersion (filter, window).  Best theory is that they are from the detector.  See same basic pattern at 6.6 and 7.9, although fewer fringes at longer wavelength.

I reduced the data by taking difference of the "nod" pair with greatest extent along the slit (upper right).  I then rotated the frame using IDL new_frame = ROT(old_frame,12.0) where the rotation angle was not what made the slit vertical in imaging mode, but 1.4 degrees more than that.  This probably depends on grating angle.  With atmospheric absorption lines in the 6.6 difference, I judged the rotation by eye.  At this point the continua still ran diagonally across the detector and the spatial dimension was correct.  I then shifted the continua at each spatial position so the spectra ran along rows.   I then took a box around where all the data were good (see lower left), summed the spectral information to create a spatial weighting, and made a weighted extraction of the spectrum (lower right).

The spectrum, I later noticed, has some variation with integration time.  Not too surprising since I didn't correct for non-linearity.  We will need to look at how to do that best before continuum.  The displayed data comes from analyzing the second samples in each ramp.

The final extracted spectrum was compared with the HITRAN emission strengths for H2O at room temperature using the hitran_exes IDL procedure that lets you specify a wavenumber, a grating angle,  a mode, and a grating angle (many other things possible) and get a predicted output spectrum.  I ended up using 51.885 degrees as the echelle angle - Curtis later told me there is an offset between hi-med and med mode spectra of about 100 pixels - and overplotted the results in the lower right.  It's not perfect, but it is pretty darn close.  I don't know what causes the additional absorption near 6.51 microns.  I have since found that CH4 has a couple lines there, but don't know that we have enough CH4 to cause that.  Also, it looks more like a tight band to me at 6.51 microns, so it could be a hot band that I don't know about or just haven't stumbled across.

Below I show the impact of integrating longer.  The data had four samples in each ramp.  The black line is for the first sample, green - second, red - third, and blue - fourth.  There could be an impact due to non-linearity, but there could also be an impact in the absorbers changed.  I have trouble believing the air in the TAAS changed substantially, but the line near 1537 cm-1 really looks like a line and not a non-linearity.

CD16: FCLS quick notes

Looking at three files from CD16 where we were imaging the FCLS through the flux slit (Slit 7) with the N04679 filter.  These are simple D's and the applied bias was set to 0.5 V (to avoid saturation?).  The three images are below along with the EXES x,y that I found today and the FCLS coordinates.  The EXES x,y that I found was off by 1-3 pixels compared to what was in the lab book, but I don't think that is a big deal.

The FCLS coordinates are, according to Ted Dunham's email in Feb of 2013 and stated in a previous TAAS post, millimeters and the DAOF TAAS FCLS corresponds to a SOFIA platescale of 4.16" per mm.  From the difference between top and bottom image locations, I calculate an EXES platescale of

17.96mm / 376.2 pixels = 0.04774 mm/ pixel

or

0.04774 mm / pixel * 4.16 " / mm = 0.199" / pixel

Our design number comes assuming we are F/10 and have 25 micron pixels and is:

2.06e5 arcsec * 25 microns/pixel / 2.5e6 microns / 10 = 0.206" arcsec/pixel

Looks like we are <4% off from the design number.  Good enough.

For rotation, I first considered the angle between our slit long axis and our columns.  This comes out to be 10.6 degrees (determined by using IDL ROT(image,angle) function and seeing what angle gives best alignment of top and bottom of the slit).  Our slit is rotated -10.6 degrees clockwise from our columns

Comparing our slit to the FCLS x,z coordinates, I first plotted the FCLS coordinates for the spot and noted that the top of the slit ends up in the lower left corner of the plot.  This means our slit is rotated 

180 + atan(fcls_x / fcls_z) = 231.3 degrees

clockwise from the FCLS Z axis.  Assuming the FCLS axes correspond to +elevation (+x) and +cross elevation (+z), this means we are rotated 231.3 degrees clockwise from the cross elevation axis.  

Noise vs. Temperature

Noise vs. Temperature

MIRI detectors have shown peaks in the detector readout noise at specific temperatures, in the range of 7K where we tend to operate. To check for excess noise at our operting temperature, or to optimize the temperature at which we should operate, a series of noise runs (3 sets each of 5 ramps of 8) were taken at temperatures from 6k to 9K on the way up and then 9K to 7K on the way down. The noise results are plotted here.

There is a great deal of scatter, but generally speaking the noise seems to increase with increasing temperature. The lowest noise actually occurred at 6K rather than at 7K where we have been operating, so it may be desirable to operate the array at a lower temperature in the future.

Reference Pixel Subtraction

Reference Pixel Subtraction

In an attempt to improve linearity of the ramp and noise over the full set of scans (rather than having to ignore the first one) reference pixel subtraction was explored. Initially the simple step of averaging all reference pixels in a scan from both the leading and trailing stripe of the array gave no real improvement. The second attempt was to subtract row by row the average of the 8 reference pixels in that row. This improved the linearity of the ramps, as shown below, but worsened the noise. Scan average is plotted vs. scan number in the data cube.

First using a set of noise data, 5 ramps of 8 scans for Fowler-4 noise, that was taken during grounding scheme optimization at 2V applied bias, the initial linearity was poor (data 413 from CD016) and the noise was 1.336 DN (47 electrons) full frame, all 5 scans, or 1.168 DN full frame only the last 4 scans.

By subtracting the reference pixels row by row, the observed linearity in the following plot was improved, especially for scans 1 and 8 of each ramp, but the noise increased to 1.56 DN (55 electrons) full frame all 5 ramps.

Now trying a different set of data taken at zero applied bias to eliminate any photon generated charge noise, the initial data is a 7K run in a set of noise-temperature measurements (data 1794 from CD016). The initial ramps had larger (0.4 DN) offsets of the first and eighth scans in each ramp as shown below, and the noise was 1.336 DN.

After subtracting row-by-row reference pixels, the offsets of the first and last scans improved a lot but the noise increased to 1.544 DN (54 electrons).

So, although the scan averages fall on a better line, the fact that we are not averaging thousands of reference pixels before our subtraction makes the subtracted data noisy and contributes to the overall noise significantly.

Noise vs. Grounding Scheme

Noise vs. Grounding Scheme

In an effort to minimize the readout noise of the array, we attempted different grounding configurations external to the dewar. The internal cold fanout board configuration for CD016 was:

JP3 IN = AGND jumped to DGND

JP1 IN = AGND jumped to Clock Shields

JP6 IN = AGND jumped to Bias Shields

JP10-14 IN = AGND jumped to Preamp Shields

The external ebox configuration was:

JP1 IN = AGND DC jumped to Bias Shields

JP4 IN = AGND PRE jumped to Preamp Shields

JP9 IN = DGND LEVL jumped to Clock Shields

The ebox Power Supply (P/S) configuration to start the run was:

Jumper wires from AGND DC ro DGND LVL to AGND PRE

Data was taken in the dark, with the mirror selected in the lens wheel for lowest photon noise contribution. The following sets of variations were performed in the external circuit. In each variation, three sets of data were taken, each one 5 ramps of 8 scans (14 5 egos) in order to extract Fowler-4 noise data. The noise was lower in all cases when the first of the 5 ramps was ignored, so only the last 4 ramps are used in the Fowler average. The noise plotted is the average of all 3 data sets at each configuration.

1               Baseline configuration as above

2               Remove jumper wires between DC P/S modules in ebox P/S

3               Remove ebox jumbers JP4 and JP1 for signal and bias shields

4               Replace jumper wires between DC P/S modules in ebox P/S

5               Replace ebox jumbers JP4 and JP1 for signal and bias shields

The noise is worse with the shield jumpers removed, whether with or without P/S jumpers. The noise is much worse with shield and P/S jumpers out, and somewhat worse with just the P/S jumpers out. Noise is lowest (runs 1 and 5) with the baseline configuration as given above.

Linearity

To analyze the linearity of the detector, 20 repeat frames were taken with the following configuration: 25 1 egos (N2 S0 N3 S0 N3 S0 N1 D0), frame time = 0.5s, slit 3, center_arc_middle decker, filter BP14100, echelle angle = 37, cal source = 22 degrees, high-resolution mode.  The data can be found under the directory C:/data/CD016/cd016_2013oct/52, frames 1817 - 1836.  Frame 1823 had a dropped read and so was not used in this analysis, leaving a total of 19 repeat frames.

Each read was subtracted from the first read, which was taken as a baseline.  A 5x50 pixel array [499:503,441:490] near the center of the detector that was approximately uniformly illuminated was used for this analysis.  A 3 sigma iterative rejection was used when calculating the statistics of each read.

(Top Panel)  Flux versus integration time is plotted for each individual pixel in the 5x50 array.  A linear equation is fit to the first 6 data points for each individual pixel, while an exponential equation is fit to data points 6 through 10.  The last three data points are clearly saturated and not used for any fit.  It is obvious that there are two distinct fits for both types of equations due to the offsets between even and odd rows in the detector.  Two separate fits are listed on the right-hand side of the panel.

(Bottom Panel)  Flux versus integration time is plotted for the average of all of the pixels at each integration time.  The first frame is not included in this average, due to it typically being offset from the rest of the points.  This left a total of 18 frames for the average.  Again, a linear and exponential fit is shown.  The average fits lay somewhere in between the individual pixel fits, as would be expected.  The equations stated on the right-hand side can be used to show how the detector is approximately 1% non-linear at a flux value of ~5050 DN.  Looking at the first read for each frame, the counts value is ~ 10,850 DN in the same 5x50 pixel array, which would mean that the detector response becomes 1% non-linear at a count value of ~5800 DN.  

Thoughput Filter Curves

The throughput for the different filters was measured over several different EXES cool downs.  The specific cool down where each filter's data in the plot below were taken is listed here: 18a (CD16), BBP4700 (CD16), BBP5030 (CD14), BBP5500 (CD14), BBP8000 (CD15), BP4900 (CD15), BP6000 (CD15), BP6600 (CD15), BP14100 (CD16), N04582 (CD15), N04679 (CD16), N07053 (CD16), N07466 (CD16), N07904 (CD16), OCLI_Q (CD14), OCLI_R (CD14), Reading6.2 (CD16), Soifer (CD16).  For all of the measurements, a gain of 35.9e-/DN was assumed and the acceptance half angle was 0.028, as measured from CD16.

Dark Frames

The goal of this analysis was to examine the stability of dark frames and to compare using the slit mirror to the lens mirror.

Two different data sets were taken: One with the slit mirror in place and one with the lens mirror in place.  The data can be found in directory C:/data/CD016/cd016_2013oct/56.  The slit mirror frame numbers are 2165-2184 and the lens mirror frame numbers are 2145-2164.  The data was taken using a frame time of 0.5s and a 24 1 egos pattern (N6 S64 N5 D0) with 20 repeats.

The first read of an exposure was taken as a baseline and subtracted from all other reads.  A 3 sigma iterative rejection was used when calculating the statistics for each frame.  The results are shown below.

(Top Panel) All twenty frames are plotted with flux in DN versus integration time.  The blue triangles are the slit mirror data, while the black open circles are the lens mirror data.  The first frame has abnormally high flux compared to the rest of the images and so it is not included in the average polynomial fits shown in the bottom right.

(Bottom Panel) This plot shows the flux per time versus time.  These data points represent the average of all 19 frames (ignoring the first frame) for each integration time step.  The corresponding fits to the data are stated in the upper right-hand corner.  By the end of the frame time (~40s), the data points have flattened out at a value of ~3 DN/s.   The red circles were calculated from data that can be found in C:/data/CD016/cd016_2013oct/52, frames 1877-1896 (there were dropped reads in image 1889, so it was not used), frame time equal 0.5s with a 25 1 egos pattern (N2 S0 N3 S0 N3 S0 N1 D0) using the lens mirror.  This data is over plotted to show how well the fits work with data at integration times not present with a 24 1 egos pattern.  The error bars on all points represent the standard deviation from the mean.  The lens mirror and slit mirror data appear comparable with respect to each other.

Light Leak Analysis

The purpose of this analysis was to examine if there are any significant light leaks in between orders.

The data used for this analysis is from C:/data/CD016/cd016_2013oct/53.  The frames were taken with the following configuration with a total of 20 repeat frames: 25 1 egos (N2 S0 N3 S0 N3 S0 N1 D0); Slit 3; BP14100;  Echelle angle = 37; Cal BB source at 22 C.  For the images with light (file numbers 1958-1977) the 14 pixel decker was used so that the orders did not overlap and for the dark images (file numbers 1978-1997) the lens mirror was used.

To examine possible light leaks, the dark regions between the order were identified and then the corresponding pixels on the dark frames were used to subtract off any background.  The first read was taken as a baseline and all other reads were subtracted from the first read.  Below shows the results from the analysis.  Comments and questions are always appreciated.

• Panel A. shows the results from the light frames minus the dark frames.  The lighter grey circles shows the average value in Data Numbers for each of the individual 20 frames at each time step.  There is an obvious outlier that lies above the other frames.  This is the first image that was taken and is not used in the rest of the analysis.  The dark circles in panel A. are the average at each time step of the 19 frames.
• Panel B. displays the average values at each time step divided by the integration time, resulting in a value of DNs per second, which appears to be fairly constant.  Ignoring the first and last time step, the average value is 12.5 DN per second. *Note: not sure why the last read is off.  Has this been seen before?*
• For panel C. I found the amount of light in the orders and compared it to the amount of light in between the orders.  This analysis showed that, on average, the amount of light in between the orders is at the 3.5% level compared to the light in the orders.

Finding the position of the 28.2um H2 line

The 28.23um or 354.233cm-1 line falls near the center of the blaze of the echelon orders.



To see this, we first centered up on the 580.73cm-1 line at 3rd order (defining the V0 of the echelle to be 3.595V). Then we went to the predicted angle of the H2 line at 2nd order: 58.647 deg, and put in the Soifer filter.


The water vapor spectrum around the H2 line looks as follows:

Water Vapor lines at R=70K. 28.2um H2 line position is plotted with dashed line. 

We should see 2 water lines, so we put in the gas cell, continually pumping it.

The default position of the echelon dispersion screw shows a barely visible line at the top of the central echelon order.

A 1/4 CCW turn brings the barely visible line on the center order into plain view (-150 pix shift).

 1/4 CW turn from default position brings a second line into view at the bottom. (lower freq.)

Assuming that the H2O lines would have been ~1200 pix apart, the H2 line should be about 1000 pix below the higher frequency line, or 375 pix above the lower frequency line (bottom).
With the default dispersion screw position, the center of the lower line would have come in at about y=-75, so the H2 line should be coming in around y=300 for the default disp. screw position.

Positions of the temperature sensors in EXES

EXES has 6 thermal diodes, labeled A, C2, C4, D2, D3, D4. Their placement has been the same for CD013, CD014, CD015 and CD016. 

A: detector thermal stage

C2: X-plate (on the metal bracket that stabilizes the G10 X between the He and LN2 shield plates.

C4: base plate of the vapor shield

D2: on the outside of the echelon side wall, ~2" above the O-box circular base plate.

D3: base plate of the LN2 shield

D4: base plate of the He shield

Some temperatures during the cooldown period of CD16.

10/23 (LN2 cooling begun at 9:40AM)
11:00AM
A:  281.6K
C2 149.8K
C4 82.6K
D2 79.2K
D3 281.6K
D4 281.6K

10/24 (LN2 cooling of He and LN2 dewars, stopped He dewar fills when A<100 K)
2:30 PM
A: 92.5 K
C2 186.4 K
C4 231.2 K
D2 92.8 K
D3 77.6 K
D4 93.2 K

10/25 LN2 (cooling of He and LN2 dewars, resumed He dewar partial fills with LN2)
4:24PM
A: 83.89 K
C2: 153.4 K
C4: 225.4 K
D2: 80.0 K
D3: 77.8 K
D4: 77.5 K

10/27 He cooling begun 6:30AM
11:04 AM
A: 22.15 K
C2: 107.27 K
C4: 204.98 K
D2: 15.07 K
D3: 77.34 K
D4: 4.30 K

--------
Continued on 11/13/2013

In order to find the LHe hold time, we filled cryogens and monitored the boil-off by trying to take note of when positive pressure through the He Bunsen tube ceases. Unfortunately, it appears this isn't a great way to do it, because the LHe dewar and detector were clearly lifting off while air was still blowing through the Bunsen tube. Perhaps the continuing boil-off after He is gone is due of other gases in the neck tube, like O2?

We will continue by noting when D4 sensor lifts off a certain value.


Filled at 2:35PM on 11/12/13

at +20:00 hrs
A: 6.1068 (E-box on but detector unheated)
C2: 57.060
C4: 204.36
D2: 4.9116
D3: 77.724
D4: 4.2841

at +26:54 hrs
A: 6.9987 detector heated to 7.000 with 12mW heating.
C2: 57.059
C4 205.753
D2: 5.1200
D3: 77.745
D4: 4.3501

at +27:25 hrs
A: 7.0012
C2: 57.060
C4: 205.831
D2:5.2942
D3:77.750
D4:4.8290

at +28:10 hrs
D4: 5.57

at +28:36 hrs
A:7.2595
D4: 6.1136

Optics Configuration for CD16

Filter Wheel
1) 18a + ZnSe (no change)
2) BBP5500_6000 + CsF2 (no change)
3) Open (no change)
4) Reading 6.2 + MgF2 (removed N04582-8 + MgF2)
5) N04679-4 + CaF2 (moved BP6000_260 + MgF2 to Decker)
6) N07466-9 + CaF2 (removed BP4990_265 + CaF2)
7) BP6600_320 + MgF2 (no change)
8) Soifer (no change)
9) N07053-9 + CaF2 (no change)
10) BBP5030_5725 + blocker (no change)
11) N07904-9 + CaF2 (removed N10247-9 + CaF2)
12) BP14100_850 (no change)


Decker Wheel
1) BBP8000_1100 + BaF2 (no change)
2) BBP4700_5615 + MgF2 (added the MgF2 blocker)
3) BP6000_250 + MgF2 (removed W10692-9 + BaF2)
4) OCLI Q + BaF2


Lens Wheel
1) Mirror (no change)
2) Open (no change)
3) CaF2 38mm window (removed ZnSe 38mm window)
4) 1.5" diam KRS5 lens (no change)
5) 1.5" diam ZnSe lens (no change)
6) BaF2 38mm window (no change)

Cold Stop Target for CD16

I re-installed the pupil target, taping wires of thickness d=0.65mm to the cold stop plate. Now there are two wires running in the "sharp" direction and one in the "blurry" direction.

Pupil Imaging in CD15

While in pupil imaging mode, we scanned the position of the echelle parabaloid mirror to try to get a handle on where to move the pupil lenses to achieve better focus.

Conclusions: We see almost no difference in sharpness on the target wires over the mirror travel range for either lens.

 It is strange to see that one target wire almost 3x sharper than the pair of wires perpendicular to it.
Scaling to the pupil diameters, the sharp wire seems equally well-focused for ZnSe and KRS5. The blurry wires are imaged much more sharply by the ZnSe lens.

Here’s what we did:

The pupil target looked as follows for CD15:

Diameter and wire separations are to scale, (unlike the schematic drawings in post : http://codgermmck.blogspot.com/2012/12/cold-stop-target.html).

The resulting images at 1T on echelle look like:

ZnSe pupil image

KRS5 pupil image

Remarks:

The striations are due to the echelle grooves- they are perpendicular to the medium resolution dispersion direction.

The single wire in the echelle-echelon direction is clearly visible. Why are

the two parallel wires not?

The physical diameter of the pupil is 38mm. In pixels, the diameter is 168 pixels and 186 pixels, for ZnSe and KRS5 images, respectively. The separation between the center and clearly visible wire is  43 and 50 pixels, actually 10mm. 

The scale is therefore, on average: 

               ZnSe: 4.35 pix/mm

               KRS5: 4.95 pix/mm

In order to line things up along rows and columns, I rotated the images by 24.5 deg. 

Then I measured the Gaussian widths – to remove the profile of the pupil, I divided out a Gaussian function that approximated the profile of the pupil. 

Rotated pupil image with summed profiles in vertical and horizontal directions.

After the pupil profile was divided out, I fit a second Gaussian function to the wire features (just the central one for the blurry pair of wires.) The FWHM of that fit is shown below.
Then I scaled the FWHM by the pixel/mm scales in the second plot. The sharply imaged wire has the same width for both ZnSe and KRS5 lenses, but the blurry wires are much more sharply imaged by the ZnSe lens.

So what does it mean when the pupil image is astigmatic?
Also, it is not surprising that a motion of 14 T on the echelle parabaloid (x 2 = 9mm) would do so little to the focus of the lens. The lens has a f=38.1mm, and if the effective "object distance" was around 1000mm, then a change of 9mm would only change the image distance by a few hundredths of a mm. 

CD16 tasks (revised 10/22)

First Second pass at CD16 tests.  This reflects discussion on 10/22  This is posted mostly so people can comment and we can revise.  What else?!?

• would like to run as much as possible from GUI.  
• Should have bias we expect to fly with (2 V?).  If we need to adjust bias when higher photon fluxes, we can do it, but that would mean we need to get bias board installed for commissioning.  
• Would like to run with short frame time as much as possible.  ctdelay = 13 will give us 493 msec.  Do lots of Ns (and use lots of memory).  

1. verify focus across array with flat focal plane
1. medium mode
2. hi-med mode (slit 3 should give < 3 km/s at 14 microns)
2. Check for leaks in BBP_4700_5615 + MgF2 blocker.  
3. Calibration testing - ideal is to be able to do calibrations in the lab before/after mounting to SOFIA, but that probably won't happen.  We'd need to be able to use a model for dividing out the sky for this to work.  More likely is to do a blackbody and sky at start of each leg for the calibrations with eventual goal of only needing to do it once per flight per setting.
1. flatfield - how repeatable are blackbody images.  Good to do at wavelength with little/no atmosphere.  1230 cm-1 is one possibility (N07904 filter).  Or medium mode long slit near 1160 cm-1 (Ocli Q in decker).
1. in time series (differences with no change to setup)
2. after lunch or overnight (leave setup as is, but let time change)
3. after returning to an old setup
4. Note: want to check flatfield counts vs predictions.  
2. darks (will be subtracted from blackbody):
1. how dark is mirror in lens wheel compared to dark at slit wheel and to unilluminated parts of cross dispersed and long slit.
2. how variable is it (various time scales).
4. Linearization data - repeats of multi-Ns with D such that we can see ADU change as a function of linear increase in time.  Vary illumination by using slit width?  Have orders just slightly overlapping in hi-med mode.  
5. Check to see if ellipsoid shimming is good.
6. Check pupil imaging focus, if needed.
7. Get throughput for filters without them.  Also need throughput for at least one previous filter to see if bias has impact.
8. Noise data: verify noise floor with new fanout using series of identical darks (lens wheel mirror) at several biases.
9. Measure input angle using heat source at distance of secondary mirror.  TAAS SCHP with no SI plate (or SI plate still connected to EXES) might work.  Might use travel of SCHP to determine acceptance angle.  Distance between EXES window and secondary is (from KRS5 zemax file) 6.66 meters or 21 feet 10 inches.  Secondary diameter is 352 mm or 13.86 inches.   I think we'd like to have SCHP travel be larger than 70 mm (20% of secondary diameter) to get an accurate enough idea of our acceptance angle.  More travel is better.
10. Mount to TAAS
1. Compare alignment to SCHP on TAAS to previous iterations.  Ted Dunham says he's seen 1.5mm difference in TAAS FCLS locations.  Absolutes are, therefore, questionable.  Relative motions should, I think, be ok.    
2. Look for change of SCHP in cold stop as a function of letting EXES sag on its plate.

linearization (first pass)

I used the noise images I had from CD15 and tried to look at the linearization.  The data were 5 files with 16 repeats of NSNSNSD pattern - one was looking at the room and another was looking at a mirror.  These are the same data as used for this post.  As for the read noise, I removed the first two repeats of each file.  This left me with two (1024,1024,56,5) arrays

My goal was to produce a fit such that the ADU measured could be corrected to an ADU value as if the response was totally linear.  This means I fit ADU_linearized as a function of ADU_measured.

For the ADU_measured values, I made one correction to the room data before doing my fits.  The first N showed a pattern just like the illumination.  Since these first reads are done right after a reset, it suggests that the reset level remembers the previous illumination (stored charge).  Maybe we should hold the reset pulse a little longer?  Anyway, the magnitude on the worst pixels was around <1000 ADU out of 11500 ADU.  For each pixel, I subtracted a constant from all the room values such that the first room N and the first mirror N for that pixel had the same median in all repeats and all files.

For the ADU_linearized values, I took the ADU increase during mirror N_3 - mirror N_2 (first read is N_1) as the true measure of the ADU increase as a function of time.  Looking at plots of the ADU_measured values for a given pixel in both mirror and room and assuming room emissivity=1, it looked like mirror emissivity=0.033, which seems reasonable.  This let me create ADU_linearized values by multiplying (mirror N_3-mirror N_2)*emissivity_factor*time.  In other words, the ADU_linearized for the room D was (mirror N_3-mirror N_2) * ( 1.00 / 0.033 ) * 3.  This was done on a pixel by pixel basis.

I originally thought to fit the ADU_measured as a function of integration time.  This seemed to me to be a function of the form:

ADU_measured = A * exp(B*t) + C 

This just seemed to make sense to me in a theoretical sense.  When I decided I wanted to fit ADU_linearized as a function of ADU_measured, I worked the above equation and derived a functional form of:

ADU_linearized = A * ln(ADU_measured + B) + C

I fit pixels (150:849,150:849) for all the data (5 files, 14 repeats, 4 samples, room and mirror).  There were a number that didn't converge, but most of the 490,000 did.  The plot below shows a randomly selected 500 pixels that I fit with the data  (560 points) in red and the fit overplot in blue.

Data for 500 random pixels (ADU_measured on x-axis, ADU_linearized on y-axis) along with the fit the pixel.  There are 560 individual points for each pixel (mirror and room with 14 NSNSNSD reads with 5 files).  Linearization was done assuming mirror 3-mirror 2 was linear (it wasn't quite) and that the mirror had 3.3% emissivity, which made the counts look nice.  Also, offset rooms so that first N for room and mirror had same median.

Looking at the fit parameters, could see a difference between even and odd pixels.  The figure below uses the ADU_measured in room_2 as the X-axis and has A in top panel, B, in middle panel, and C in bottom panel.  As the signal gets stronger (right hand side of the plots), all three terms seem to have narrower ranges and a more fixed value.  There is some curvature to the parameters, which would represent a problem for linearization, I believe.  At low signal levels, the parameters seem have stranger variability.  

My main conclusion from this is that CD16 or the green Dewar should be used to provide some new data.  I think we'd like to do as many Ns as possible at a fairly short frame time (0.5 seconds).  We'd like to have a fairly low photon flux comparable to the mirror at 14 microns.  Probably 16 files would be good.  It might be good to compare the fits with the same photon flux and longer frame time, or same photon flux and same frame time, but throw in some S's, and also a higher photon flux (although not as high as room at 14 microns - maybe room at 7.5 microns or so.

CD16 optics desired

Here's the email I sent out with CD 16 optics choices.

===============================================

Hi Folks,

Here's my guess at a filter list for CD16.  I'll post it on the blog, too.  It is also in the dropbox EE/docs/EXEScomponents.xlsx

Filter slot

1) 18a+ZnSe blocker (no change)

2) BBP5500_6000+CaF2 (no change)

3) open (no change)

4) N04679-4 + CaF2 blocker (remove N04582-8+MgF2 blocker)

5) Reading 6.2 + MgF2 blocker (move BP-6000-250 +MgF2 to decker slot 3

6) N07466-9 + CaF2 (remove BP4990_265+CaF2)

7) BP-6600-320+MgF2 (no change)

8) Soifer (no change)

9) N07053+9 + CaF2 blocker (no change)

10) BBP5030_5725+blocker (no change)

11) N07904-9 +CaF2 blocker (remove N10247-9 + CaF2 blocker) 

12) BP14100_850 (no change)

Decker slot:

1) BBP_8000_1100 + BaF2 blocker (no change)

2) BBP_4700_5615 + MgF2 blocker (install MgF2 blocker)

3) BP-6000-250 + MgF2 (moving from filter slot 5)

4) OCLI Q + BaF2 blocker

Lens wheel:

1) mirror

2) open

3) CaF2 window (38 mm) (remove ZnSe 38 mm window)

4) 1.5" diam KRS5 lens (no change, but may want to move toward detector - see below)

5) 1.5" ciam ZnSe lens (no change, but may want to move toward detector - see below)

6) BaF2 window (38 mm) (no change)

Detector position:

We should be back to where we were in CD13.  I believe this is 3. mm back from where we were in CD14.  Based on the images of the pupil in CD14

http://codgermmck.blogspot.com/2013/04/taas-summary.html

I think we want to leave the lenses where they are.  My reasoning is that the ZnSe was further from the detector in CD14 and seemed to provide sharper images.  The ZnSe is currently further from the detector.  When we move the detector back, the KRS5 lens should be about where the ZnSe lens was and the ZnSe lens will be even further away from the detector.  Note that we may want to use the echelle mirror to investigate focus for the cold stop during CD16.

-matt

Remeasured Detector distances for CD13, CD14 and CD15

Detector Measurements

We measured the detector distance for the CD13 D-box and we remeasured the tilted CD14 D-box using a microscope in Emmett’s machine shop.

D= Detector distance = distance from the O-box wall to the central column detector surface.

Prior to these measurements, we thought that D= 14.5 mm for CD13, based on the mechanical drawing and adjusted for the widths of the 8 G10 spacers that were actually used.

The tilted detector box was measured with a bare-mux installed prior to CD14 by Ryan Walker, and had a central column distance of D=12.61 mm (see http://codgermmck.blogspot.com/2013/02/tilted-detector-distances.html).

Here are the new measurements:

CD13 -- new measurements: D=15.53mm (8/27/13)

CD14 -- new measurements: D=12.53mm to central column (8/26/13)

left edge(blue): d=10.58mm, right edge(red): d=14.49

(previous measurements by R.W. were 12.61 mm to central column, 10.63 and 14.59 for left and right edges respectively)

CD15 -- detector box tilted, with 1.89 mm spacer plate installed

new measurements: 12.53mm+1.89mm = D = 14.43mm to central column

left edge(blue): d=12.47mm, right edge(red): d=16.38

So the equation for the column position for CD15 is

d=0.003818*column+12.47 mm

The detector was at the CD13 distance at column x=802 during CD15. This is close to where the best focus was measured for the medium resolution mode.

Bounce Tests, CD015

Performed by Kristen and Curtis.
pp 23-24 of Lab Book VI, 8/16/13

The purpose was to evaluate EXES sensitivity to vibrations when motor hold currents are on/off and when the flip/door mirror stops are "wound" against, or when the flip/door mirrors are "hanging".

This test used 14 1 egos sequences (N6 D). We took one set as a baseline.
Then another set with a mechanical shock, executed at the beginning of frame 4.
The counts in each frame were linearized. 

The "mechanical shock" was as follows.

Using the orange plastic coated mallet from Dave Black's toolbox.
Hold handle in one hand, and lift hammer end 6" above forward end ring. At end of frame 3, let drop.

The images show double subtracted frames to show small differences in the high or medium spectra in each interval.

We call the "baseline" the sequence where there was no mechanical shock.
We call the "event" the sequence where the hammer was dropped at the end of "3"

For comparison, we show a "BEFORE" frame, that is baseline(2-1)-event(2-1) or [baseline(*,*,2)-baseline(*,*,1)]-[event(*,*,2)-event(*,*,1)]. This should just be noise in all cases, since in precedes the hammer drop for both sequences.

The After frames are baseline(6-5)-event(6-5) or [baseline(*,*,6)-baseline(*,*,5)]-[event(*,*,6)-event(*,*,5)], and these should show smearing or shifts if there is significant motion induced in the mechanisms by the hammer.

                  

HIGH-RES: These first images give an idea of the counts in a single interval (single subtraction, not double):

                                     

HIGH-RES, Wound against stop (wall). Motors Disabled

                                      

HIGH-RES, Wound against stop (wall). Motors Enabled

                                    

HIGH-RES, Flip mirror floating, Motors Enabled

                            

HIGH-RES, Flip mirror floating, Motors Disabled




---------------------------------------Medium Res Spectra-------------------------

                              

MEDIUM-RES: These first images give an idea of the counts in a single interval (single subtraction, not double):

                        

MEDIUM-RES, Flip mirror floating (aligned). Motors Enabled

                                      

 MEDIUM-RES, Flip mirror floating (aligned). Motors Disabled

                       

 MEDIUM-RES, Flip mirror wound against stop (wall). Motors Disabled

                     

 MEDIUM-RES, Flip mirror wound against stop (wall). Motors Enabled.