Cold stop target

I installed a target in the cold stop last week- something that can tell us scale and orientation.

It was made with 0.65mm diameter wire, held in place with Al tape. Errors in parallelism are less than 0.3mm from end-to-end of any wire, but it remains to be seen how the whole thing cools down.


Added on 6/17/2013: CD015 COLD STOP TARGET:

Bounce back angle from the slit wheel mirror

Now that there is an Al flat mirror in one of the slit wheel positions, we wanted to see at what angle it returns the beam. These photos show the laser bumper where the tip of the red laser fiber lies. A card held over the input beam clearly shows the input beam shining through. What the second photo is *supposed* to show is that the beam returned from the mirror can only be clearly seen by partially obstructing the input beam (there is a bright dot in the middle of the glow from the input beam -- hard to see in this image.) So basically, the mirror returns the beam almost to the point of the laser fiber tip.

preliminary slit mechanism repeatability

The files used here are from a B_12_03_01/. (b208-217)

To look for slit mechanism repeatability, we moved the slit wheel by -12000 steps, then 12000 steps to see if the apparent positions of spectral lines changed after the motion. We only did 10 frames for this test, discarding the first image, in which we brought the slit to 3.6341 V.
by hand turning the mechanism knob.

EXES was looking at the gas cell, targeting 1335 cm^-1 H20 lines.
filter: 7.466um
decker: central arc
V_echelle: 7.9809 V
flip: high medium
lens: OPEN

A sequence of four 3-second images were taken at each iteration. I combined these by doing a linear fit to the pixel values across the frames, and recording the slope into a single 1024^2 array (using [3,6,9,12] seconds as the x-axis for the fit).

 10 x 100 pixel box around a H20 spectral line, used to track changes in the slit wheel position after -12000 step,+12000 step motions.

Figure: jagged line is the sum of a 10x100 pixel box around a water vapor line. Top curve is the smoothed version of this, with a 6-param Gaussian fit. 

Then for this very preliminary test, I focused on just one line, at [128, 516], and summed a 10x100 pixel box of this line to have a 1-d cut. Even though the line was strong, a ~20 adu amplitude sawtooth pattern (probably from 60 Hz noise in the readout) made fitting a Gaussian problematic. I smoothed the 1-d array with a 4pixel boxcar, and then fit a 6 param Gaussian.

The fit centers of the Gaussian (along the y-axis)  
   52.975
   53.021
   52.796
   52.839
   52.767
   52.777
   52.841
   52.876
   52.948
   52.808

For a stddev of 0.09 pix and a maximum difference from the mean of 0.16 pix.

We probably want to know a great deal more about out repeatability than this - longer time baseline, effects of changes in cabin temperature ...

And as far as measuring it, I want to try to correct the 60 hz noise (or whatever it really is) without using the smooth function. But at least the mechanism seems very repeatable over short time baselines.

Instructions to start most recent previous working acq and exesgui combination.

How to switch the basic asriocfg windows driver used to communicate to the eBox.

1. First, make sure the "new" or current driver is unloaded
2. Reboot "gus" the PC.  Hard boot preferable.
3. Load the new driver OR just start acq.

1.  Unload the current driver.  For example:

cd \mikework\nexes\acq\drivers
drvs remove

drvs.bat is a batch file which will load and register a driver with the operating system or if the parameter "remove" is provided it removes the driver.  The sc.exe command of Microsoft Windows XP is used (Microsoft XP reference).

In that directory is the newest driver (at date of this writing) provided by Justin.  asriocfg.sys with the date 8/22/2012, 8:43 AM and size 44,288.  This was unloaded above.





2.  Rebooted the PC.  TURNED OFF AND ON.

3.  Starting the "old" standard acq icon on the desktop starts the program c:\exes\exes.exe.

Since it checks if the service(driver) is available and loads it if it is not available, this works fine. I do not know if this is as permanent as using drvs or not.  I will try to check this.

After the driver was removed, I am not sure what Mark did.  But I believe it is simply to start the "old" acq from the desktop.

I started the gui by going to the directory c:\exes\acq and double-clicking on the exesgui.exe application.

Lens wheel configuration for CD014

Here's the layout of the lens wheel for CD014, looking in from the Dbox wall side. I will update this drawing to include the pot voltages and the position of the UKIRT filter at a later point (I'm keeping the UKIRT filter in vacuum storage until the last minute).

This time we wanted to have the 38 mm KRS5 lens focus the grating onto the detector at its new position (0.125" closer to the grating).
The nominal EFL for the 38mm KRS5 lens is 38mm -- however, it is a 8mm thick meniscus lens and i wasn't sure where the EFL is referenced. So I carefully measured the back FL at optical wavelengths (0.63um, n=2.57) in the lab. I got an average of 31.1 mm. The EFL would have been closer to something like 31.1+4 =35.1mm. At 10.6um (n=2.37), then the EFL is 40.2mm, and the BFL=36.2 mm.

To focus the grating 1000mm away, the back of the lens should be 37.9 mm from the detector.

The distance from the new detector position to the lens barrel is 27.2, so the back of the 38mm KRS5 lens was placed at 10.7 mm into the lens wheel (or 13.8 into the lens barrel).

For the ZnSe lens, I picked a closer distance to the detector of 31.9 mm from the back of the lens.

Note: Drawing updated to actual CD014 configuration on 5/13/2013.

Mounting the square UKIRT 20um filter

Here's some pictures of the holder for the UKIRT 20um filter, which will be installed in the lens wheel for CD014. The black rings are made from delrin, adapted from the stock rings with threaded outer diameter. I milled out the inside of one ring to hold the filter. The white rings are 0.01" teflon sheets with 0.875" holes punched out. The filter is 0.06" thick; the delrin slot is 0.0815" deep. One teflon ring fits into the slot. The other has the same ID, but will be sandwiched between the two delrin pieces. (so the total material in the slot is just 0.06"+0.01" --> i.e. no compression on the filter).
 

CD 14 tasks: V 1.0

UPDATED: 11/30/12 (ver 1.1)

Changed some blocker notes.  changed lens wheel notes.

UPDATED: 11/2/12 (ver 1.0)

I've added a bit more to the list:
Filled in filter slots, filled in decker slots, added imaging tests, added fast framerate tests, added generic data taking tests.

Configuration:

1. Tilted focal plane at detector.  
2. Incorporate directional/size indicator at cold stop.
3. Lens Wheel (note: order isn’t important, but having these components is required)
1. Mirror (will always have mirror and make it position 1)
2. open
3. 1.5” diameter ZnSe lens (note distance of lens edge relative to detector side of lens mounting barrel - would like it to be about half as much as KRS5 lens)
4. 1.5” diameter KRS5 lens (note distance of lens edge relative to detector side of lens mounting barrel - use numbers for IR focus from blog post in May 2012)
5. 1.5” diameter ZnSe blocker 
6. UKIRT filter
4. Slit wheel should have mirror in place (only 1 open position)
5. Decker Wheel filters (note: order isn’t important, but having these components is required)
1. BBP_8000_11000 + BaF2 Blocker - NEW
2. BBP_4700_5615 (no blocker) - New
3. BBP5030_5720 (filter list suggests blocker is not needed. No blocker is mentioned for CD13.  If blocker is present, should be CaF2)  CD13: decker wheel 3
4. BBP5500_6000 (filter list suggests blocker needed, but no blocker is mentioned for CD13.  If blocker is present, should be CaF2) CD13: decker wheel 4
6. Filter Wheel (note: order isn’t important, but having these components is required) 
1. Open CD13: Slot 3
2. 18a (add KBr blocker) CD13: slot 1
3. Soifer Filter - Move from Decker wheel CD13: decker wheel 1
4. 6.2 + MgF2 blocker - New
5. BP14100_850 CD13: slot 12
6. N04679-4 + CaF2 blocker.  Note that this could be N04769-4 (dyslexia) For throughput testing, this need LONG integrations or the blackbody heated up. CD13 slot 2
7. N10247-9 + BaF2 blocker - New
8. OCLI Q + BaF2 blocker - New
9. OCLI R + BaF2 blocker CD13: slot 9
10. BP6000_250 + CaF2 blocker - New
11. BP6600_320 + CaF2 blocker - New
12. N04582-8 + CaF2 blocker - New

Tasks:  As much as possible, use Mike's GUI and ND sampling schemes with any number of S's thrown in to make the integration time as desired.   

There are a couple zeroth order tests relating to the detector and how the data taking software behave

1. see if the array behaves at 0.5 second frametime, which we would like to make our default.  If it doesn't behave at 0.5 second frametime, adjust frametime by 0.1 second intervals to see at what frametime we get good behavior.  Defining good behavior may be hard, but perhaps "repeatable" is more important than absolute performance. We want there to be no (or <1%???) echos from pixels with strong emission.
2. Verify some basic readout patterns and timing.  Assuming framerate is 0.5 seconds, every integration (time between Destructive reads "Ds") will be integer multiple of 0.5 seconds.  For all integrations of two or more frametimes, we will use a combination of a non-destructive read and a destructive read for the integration (ND).  The exact integration time will be achieved by including spins (S's) where we clock through the array, but do not reset or convert.  
1. Verify that doing something like 20 D's takes 10 seconds (0.5second frametime).  Ideally, this would result in a single FITS file with naxis3 = 20.  
2. Verify that doing 20 ND's takes 20 seconds (0.5 second frametime).  Ideally this would result in single FITS file with naxis3 = 40.  Every second frame from FITS file (corresponds to the D's) should have twice the signal of the other frames.
3. Verify that we can do integrations of arbitrary length up to 30 seconds and that timing and fluxes seem accurate.  For 0.5 second frametime, 30 seconds would be "N, 58 S's, D"

Optical tests to be done are:

1. Focus in Med mode at 13.7 microns
1. Investigate whether image size depends on location on detector.  With tilting, we expect ~2500 micron difference in path length from one end of detector to the other (Based on my memory that we’re getting 6 degree tilt with a 25 mm detector -> 25000*cos(6 deg) = 2526).  Orientation should be such that adjusting echelle grating to move a spot from one side of the detector to the other results in different path lengths.
2. Adjust echelle mirror to bring gas cell pinhole spots in center of array to best focus.
3. Assuming it is measurable, determine how many turns of echelle mirror required to go from best focus at one edge of detector to best focus at the other edge.  Assuming the number in 1.1 for path length difference across the full array (2500 microns), and the 80 turns/inch pitch of the mirror screws (317.5 microns per turn), and a 2:1 change in movement at the focal plane compared to movement at the mirror, we would expect 2500/317.5/2 = 4 turns.
4. Return to best focus at center of array.
5. Measure line profile at center of array using slits 1-6 (not flux slit).
2. Focus in High res mode at 13.7 microns
1. Minimize spot size in high res mode at center of array by adjusting echelon mirror while keeping echelle mirror fixed.  Hope is that we go through focus.
2. See if possible to reduce spot size by moving echelon and echelle mirrors in opposite directions.  Hope is that we go through best focus.
3. Map spot size around best focus with +-2 turn grid on both mirrors.  
4. Measure line profile at center of detector at best focus through slits 1-6 (not flux slit).
5. If echelle mirror is at different position from med mode best focus, than measure med mode resolving power at current mirror position.
3. For those filters that have not been tested, map filter transmissions looking at continuum source with short slit.  Adjust integration time so that good signal where light comes through well, but does not drive response >1% non-linear. We will be looking for grating positions that show 1% leaks.
4. Map 18a filter with ZnSe blocker in beam and with KBr blocker in beam
5. Investigate alignment of fore-optics ellipsoid compared to entrance window. 
6. Test imaging photon rate through N04679-4 filter and through N10247-9.
7. Image cold stop in pupil mode.  Use both KRS5 and ZnSe lenses.  Experiment with how moving optics impacts pupil image.  Restrict aperture at slit plane to sharpen image and cut down photon flux.  Try N04679-4 and N10247-9 filters
8. Mount to TAAS 
1. In pupil mode with restricted aperture at slit plane, use small chopped hot plate (SCHP) to map EXES beam.  Determine size of cold stop compared to size of SCHP and location of EXES beam center.  If EXES beam is good relative to entrance window (Item 5 above), then try “walking” beam via shimming at flange to SCHP position matching SOFIA.
2. Investigate alignment compared to large chopped hot plate in pupil mode.   Goal is to see image of LCHP at cold stop.  
3. Switch to FCLS and imaging mode.  Try imaging spot.  See if can get a spectrum of it.  Move FCLS so it matches slit location (don’t move slit around).

Honey-comb bumpers

I installed the 4 honey-comb bumpers.
Here are some pictures:

The left side pedestal is attached to the He can. I covered the flat surface with a layer of Kapton electrically insulating tape as a precaution against touches. I drilled holes and bolted the honey comb material to the cover plate with two 2-56 screws. It was situated so that it would be flush to the LN2 side of the bumpers, shown on the right in the picture.

There is about 3.5 mm of air space between the honey comb and the He side.

18a filter holder

The 18a/20a filter holders are made from 2 Al washers, sandwiched together. The inner hole of each washer has a lip on it, just slightly smaller in diameter than the 18a/20a filters, and recessed deep enough so that the filter is flush with the top of the washer when the filter is inserted.

The washers are 1.65 mm thick.
The depth to the lip is about 0.94 mm. (it is at least as deep as the filters).
The second washer is identical and directly in contact with the other washer, so that it acts as a retaining plate.

Together the two washers completely occupy the 1" filter hole, so that the retaining plate on the top of the filter wheel is in contact with the top washer. The retaining plate is about 0.8-0.9mm thick.

The filter wheel itself has at least 3mm of clearance to the SDF assembly lid.  

EXES lookout angle

The X in this image from CD013/B_12_02_28/b170.fits shows the position of the center of the window. EXES is in echelle-side, imaging mode, filter=7.4um, decker=slit=OPEN, ctdelay=10.

The "X" is mode of strips of masking tape oriented up-down and left-right with respect to the floor. (The mounting screws on the window holder were used as a guide to getting the angle right.)

The center of the X is (567,472), +/- 5 pixels on each coordinate.

The center of the illuminated region (defined by the SDF on the right, and probably LN2 baffles and window edge on the left)  is 515,488.

So we would like to move the EXES outlooking angle +52 pixels in x and -16 pixels in y.

To get the orientation and scale on the window, we placed a screw in front of the window (with the bare MUX), backlit by a quartz lamp at the end of the TAAS.

As viewed from the front, the screw was coming in from the right, level to the ground. The orientation of the ellipsoid is shown with the overlaid box. The long axis represents the side with the mounting screw plates.

The screw pitch is clearly visible and gives us the plate scale on the window-- averaging 54 pixels for each thread, which is physically 0.113".

So in terms of magnitude of deflection, we need to move the ellipsoid by sqrt(52^2+16^2)=54 pixels (coincidently, the same as a screw thread). The window to ellipsoid distance is 1200mm, so this angle is 0.00239 rad. This is on the order of 0.011", for the 4"-4.5" ellipsoid. We currently have about 0.025" of shim on the right side of the ellipsoid (as pictured above) and 0.005" on the top.

It was confusing to establish the orientation, so I'm going to try to get someone else's opinion. 

Update: I think this is the real orientation:

 Therefore, the operation will be primarily removing 0.01" of shim from the right side of the ellipsoid.

Imaging the Chopped Hot Plate

Can we image the Chopped Hot Plate (CHP)?

To answer this I used a Zemax model of the medium resolution mode of EXES (echelle chamber only) where the echelle grating is turned into a flat mirror and a 'pupil imaging' KRS5 lens of focal length 38mm (at 633nm wavelength) is placed between the last turning mirror and the detector.

This layout is sketched below:

I placed an 88mm object 2760mm away from the entrance lens to simulate the CHP and I used wavelengths of 633nm and 13.7microns.

Imaging at the Detector

The quick answer to the initial question is that EXES will image the CHP if we move the pupil imaging lens away from the detector:  perhaps about 3mm for 633nm wavelength and about 12mm for 13.7microns wavelength.  The figure below shows the 88mm object imaged at 633nm wavelength into a roughly 2mm image while the 13.7micron wavelength is defocused. (This all depends on where the lens really is and how you measure the distance from the lens to the detector.  I measured from the center of a 5mm thick lens to the face of the detector.)



 

In the image below I show the effects of moving the pupil imaging lens away from the detector in two 3mm steps.  I've indicated the changing distance from the detector to the outboard vertex of the biconvex lens.  I've kept the total distance from the turning mirror to the detector constant at 191.23mm - which may or may not be accurate.

New Pupils and New Foci

I defined the entrance lens as the aperture stop, which created pupils at the turning mirror before the slit and also about 12mm before the pupil imaging lens.

At 633nm wavelength foci within the instrument now occur about 112mm beyond the cold stop, also about 1/3 of the way from the grating toward the second hit on the paraboloid and on the detector.

At 13.7microns wavelength foci occur about 280mm beyond the cold stop, about 100mm beyond the second hit on the paraboloid and on the detector.

Caveats

Although this system will image the CHP, it is extremely inefficient.

Probably the biggest loss is due to small entrance lens and long distance to the CHP, but, in addition to that, the beam becomes quasi-collimated at the slit (about 14mm in diameter) which will cause losses if any slit is in place (see image to right.)

In addition, as always, the model is not the instrument and distances in the model may not always correspond to their counterparts in reality.

No optical light from SCHP

We tried to see if we could get light from the SCHP, set at temperatures of 23C, 100C and 200C.

We set the ctdelay to 150 (exptime=4s) and took 16 coadded frames, and repeated for 10 images for each setting.

All images were taken in imaging mode or pupil imaging mode; echelle at face-on, echelon bypassed, slit/decker/filter OPEN.

In B_12_07_25/

b000
b001-b010, T=23C, imaging mode
b011-b020, T=100C, imaging mode
b021-b030, T=100C, pupil imaging (25.4mm KRS5 lens)
b031-b040, T=200C, pupil imaging (25.4mm KRS5 lens)
b041-b050, T=200C, imaging mode

Taking only good pixel values (between 8125 and 10625 for coadded frames / 16.0)
We get:

Setting                          mean pixel value +/- stddev(pixel value)
T=23 C , imaging        9243 +/- 3
T=100 C, imaging       9244 +/- 3
T=100 C, pupil            9245 +/- 3
T=200 C, pupil            9244 +/- 3
T=200 C, imaging       9242 +/- 3

TAAS SCHP instructions

Al Howard installed the Small Chopped Hot Plate (SCHP) on TAAS and gave this rundown of how to use it.

1) turn on the motion control box on the TAAS E-rack.
2) turn on the AC Power to the hot-plate, located on the hot plate stage (the tub must be removed).
3) Open SCHP1.vi to control the motion of the SCHP.
           - Press "Home" and wait for motion to complete
           - Load "Mid-position 144X 144Z" to center the plate.
           - the plate has a full range of motion of 288mm in X and 288mm in Z.
4) Open "Temperature control.exe" to control plate temperature.
           - make sure port is set to COM7, and hit "Open COM Port"
           - enter desired plate temperature
           - plate has range of temperature of ~23 C (room temperature) to 200 C.
 
For shutting down, the only essential thing is to turn off the AC power to the hot plate (located on the SCHP stage, under the tub).

      

Skype the Tub

More alignment images, this time via iPhone and Skype.

Taped an iPhone to the tub-side of the 41-inch flange, positioned so that its camera could look in toward the instrument's KRS-5 window without obscuring too much of the TAAS beam.  Surprising that Skype works in the closed up tub, but whaddyaknow.

Pictures below correspond to ~diametrically opposed positions on the 'mystery' aperture corresponding to the dotted green line two posts back, just where the TAAS image starts to clip on it.

It seems conclusive that the  mystery aperture is in fact the black ring holding the window in its mount.  Why this isn't exactly concentric with the flange opening (dotted red line two posts back) is something to ponder....

About the TAAS/EXES images

If we put a 0.5 degree artificial 'sag' in the TAAS/EXES instrument at the SI flange, effects similar to what you're seeing show up as illustrated in the attached composite image from Zemax models.  It's not clear to me that the magnitude of the effect is the same as what you're seeing, or that the direction of the sag is the same.  Or it might be something else altogether!

The obvious things I see are the beam displacement at the cold stop and at the detector.

The sketch at the bottom shows what TAAS/EXES looks like with a 5.0 degree 'sag' at the SI flange to show you the sense of the tilt that I induced.

More Alignment

We continued to investigate the irregularity of the field of view. A webcam was dropped inside the EXES/TAAS junction and yesterday's pattern was repeated. The webcam took pictures of the pattern relative to the hole in EXE's 41-inch flange. These images were then composited and aligned with yesterday's results. Two more dotted perimeters were also added. The red perimeter indicates the edge of the 41-inch flange hole, while the green perimeter is an extrapolation of whatever is restricting the field of view in the lower left of this image. The blue perimeter is, as it was yesterday, the s/d/f perimeter.The centers of each circle are color-coded accordingly. This image confirms that the assembly has coaxial alignment issues.

TAAS Field of View Measurement

We carried out a search procedure to ascertain the exact size and shape of the TAAS field of view as seen from EXES.  We selected the largest aperture opening available to us on TAAS, 5 mm, and positioned it at various points where we saw the TAAS aperture clipped in the FOV.  Each exposure was saved as an image file, which we later compiled into one image. The resulting image is shown here, along with a dotted line showing the observed position of the s/d/f wheel aperture.  The observed FOV did not appear to be perfectly round, nor did the bootstrapped TAAS boresight center position (the dim white circle near the center of the image) correspond to neither the center of the FOV nor center of the s/d/f/ aperture (the overlaid red dot). We will continue to investigate why these patterns are non-concentric.

TAAS/FLCS Startup

We had a repeat session with Al Howard on using the TAAS with the FCLS-- this time we wrote things down...

Turning on the hardware
      a) first turn on the temperature controller
      b) then, turn on the amplifier
 At any time, turn on computer and TAAS motor controller box.

Software/files for running TAAS.
------------------------------------------
TAAS_Aperture.vi
When started, the aperture motors automatically home after a 10-15 second delay. Afterwards, select the aperture size and it will automatically be slewed into place in front of the light source.

FCLS.vi
         a) press "HOME"- entire FCLS stage will move
         b) press "LOAD" and select "FCLS X-Z Slides Aligned2" -- this is the best bore-site representation of the SOFIA telescope, transferred from DAOF TAAS using one of the SOFIA instruments.

Robofocus
The value of the focus is given in steps.
The button "A/R" toggles whether the focus is given in absolute or relative step numbers. It defaults to display relative, but absolute is far more useful, so select "absolute" as soon as you open the program.
The step numbers can be converted to absolute focus position by converting steps to mm with the excel spreadsheet,  "FCLS #2 Focus Calibration Curve 02-14-2011.xls", also located on the desktop.


FCLS #2 Focus Calibration Curve 02-14-2011.xls
find the distance from the mounting flange to the TAAS focus using the conversion from steps to mm given in this spreadsheet. Negative mm values mean the focus is inside TAAS; positive mm values mean the focus is on the instrument side of the flange.

Other notes:
The beam is thought to be close to f/10.


The light source is located inside a glass envelope. The temperature is controlled with a PID loop, and heated by a long, horizontally-oriented filament. The filament is likely to be the only thing producing light in visible bands: for example, if the temperature setpoint of the black body is suddenly turned down, the filament will completely shut off, and the spot on the bare MUX will disappear until the temperature of the glass envelope falls below the new set point and the amplifier turns on again.


Current Performance:
Currently,  with the bare mux in place in the warm instrument,we see a ~ 70 pixel spot, regardless of the aperture selected or the focus position. 

More Stray Light

I looked at files that were darks (detector blanked off) along with high and low flux images from  5 different filters (18a,  bp14100, N10692-9, Ocli O, BBP5030_5725).  I corrected for number of coadds and took the ITIME parameter as the integration time for each frame.  There were a couple filters where the data were taken with SUTR (4 frames).  I took the last frame except for one case where the signal was going non-linear, so I took the 2nd of the 4 frames.

Comparing the 4 frames in SUTRs, there is a clear difference between the "dark" regions when there is strong light and when there is not.  For the case where very little light is coming through, getting about 2 ADU/sec at 5 microns.  When there is a fair bit of light, the "dark" regions have more signal when the orders themselves have more signal.  Values are something like 5 ADU per second (peak is around 20 ADU per second)  This suggests there is light from echelon orders spilling into inter-order regions.  Consistent with echelle scattering 20% of the light at 5 microns.  


Looking at all frames, I also see clear correlation of "dark" region signal and peak signal.  For 18a, BP14100, N10692-2, and OCLI O, the extra light is at about the same level, ~10 ADU per second.  The amount of extra light at BBP5030 is more.   This suggests the echelle scattering is not as bad at long wavelengths.  


These results are not definitive, but they make some sense given what I expect for the grating performance (more scattered light as going to shorter wavelengths).

A better test for CD14 will be to include a dark when doing filter scans and to take the data with SUTR and shortening the exposure time as needed.

Deflection estimates

To evaluate the use of the triangles, Jeff is going to do some modeling.

3 configurations: No triangles, triangles attached only to plate, triangles attached to plate and EXES

2 orientation: Triangles vertical on plate (telescope at 40 degree elevation) and SI flange rotated 20 degrees (telescope at 20 or 60 degree elevation)

2 gravity: 1g (static) and 0.9g (assuming 0.1g gets through to SI flange)

Looking at deflection in z at 300 mm forward of SI flange (nominal SOFIA focus) and at 762 mm forward of SI flange (nominal cold stop location).

Believe can evaluate sag based on motion in EXES focal plane scaled to SOFIA focal plane and motion of cold stop as fraction of secondary image.

EXES focal plane platescale is roughly 8"/mm and SOFIA focal plane platescale is ~4"/mm.  Want deflection to be <1" with roughly 4" images.   This gives 0.250 mm deflection at SOFIA focal plane.

Secondary mirror is 350 mm diameter and, from zemax file, we found it to be 4.895m from EXES entrance lens.  The entrance lens images the secondary onto the cold stop.  The cold stop is 38mm diameter and, from Autocad file, is 711 mm from entrance lens.  If the sag should be <2.5% of the cold stop diameter, then we get that a deflection of 0.95mm is acceptable.

The deflections of interest are not the static ones, but deflection between the vertical 0.9g case and the 20 degree/1g case.

Best focus position of the pupil lens

We have the laser fiber in the bumper and the stopped-down pupil mask with a bearing placed in the 1/4" hole to provide a target on which to test the focus.

The target image appeared to be very sharp on the grating and at the collimator (seen below on a card just forward of the collimator mirror).

As a starting point for the 1" KRS5 pupil lens, Joe and I placed 14 mm into its lens wheel barrel, (see post "Current Lens Wheel Configuration")

For this test, I took images with the bare-MUX and red laser with the KRS5 lens placed at different positions in the barrel.

From left to right, these distances are: 13.1 mm, 14.3 mm (closest to calculated value), 15.2 mm, 16.2 mm, 17.3 mm, 18.3 mm.
Visually, 17.3 mm seems to be the best focus. Using the 1" KRS5 lens in this position we will try to align the ellipsoid while EXES is on the TAS.

Current lens wheel configuration

When Joe was here on 4/30/12, we installed and adjusted the lenses in the lens wheel. For future reference, here's some measurements and a record of the current configuration of the lens wheel.

distances:
detector to O-box wall (CD013):   10.9 mm
detector to O-box wall (proposed for CD014) :  7.7 mm
O-box wall to lens front of wheel: 14.4 mm 
focal length of 1" KRS5 lens:  38 mm (measured at optical)
0.63um focal length of 1.5" KRS5 lens: 38 mm
0.63um focal length of 1.5" ZnSe lens: 38 mm

To calculate how deep to place the lenses in the lens barrels we calculated d_i from the lens equation:
d_i= (1/f - 1/d_o),  where we used 1000mm for the value of d_o.

For the 38mm focal lengths, this was d_i=39.5 mm

n(0.63um) =2.57
n(11um)=2.37

f_mir= 38mm * (2.37/2.57) = 35 mm

d_i=36.27 mm


For the ZnSe lens, we chose the closest possible distance to the detector,  ~ 25.3 mm in order to see the effect of an extreme case on the focus.

For the 1" KRS5, we chose the best 0.63 um focus distance for the current config (with the D-box standoffs the same as CD013),   total distance is 10.9+14.4+7.9mm = 39.5 mm

Before the next cool down (CD014) we will move the lens 3.3 mm away from the detector, to compensate for the 1/8" inward change of position of the detector.

BBP5030_5725

Same basic process as for 18a.  Images saved as groups of 4 SUTR, so photon response is easy using image differences.

First off, here is wavelength as a function of echelle angle.

Shows that when we're in main part of filter window, things are ok.  Have a light leak at near 45 degrees near center of an echelle order and near 55 degrees near edges of echelle orders.

Next is echelon order spacing as a function of wavelength and angle.  This is near the short wavelength extreme for EXES.  Note that we can get almost 50 echelon orders in a single image, which would be about 30 cm-1.

I got data numbers from the difference between the first and last images in the SUTR.  I took the 75%ile of pixels which were over 150 DN in the difference.  Plotting row 550 of all the images in the series is in the figure below.  The value I take for each image is the red dot.

Finally, assuming 9 seconds of integration between first and last images and a resolution of 4 km/s, I get throughput numbers as below.  Again, they are too high.  I wonder if they are even higher than the factor of 4 too high seen for 18a.

18a filter info

I've finally gone through the 18a filter.  From the logbook, we used ctdelay-110 (3 seconds) and the 3.5 km/s slit (which gives something more like 3.8 km/s at 18 microns).

Joe looked at the images and decided if the signal for each echelle angle was on, off, or weak.  He also recorded if the data frame was clean (only one echelle order) or not.  This info was saved in a csv file.

I read this into IDL, used quantities from the blog regarding echelle angle and wavelength for given voltage, and worked out the wavelength for each setting.  To do this I started with the assumption that the wavelength getting through was in echelle order = 3 and then adjusted the lower angle measurements to order = 2 so that the wavelengths that came through, the number of orders, and the filter warm curve made sense.

I saw that the array had some weird data behavior on the first row and last row (see blog post before this one), so I reset those, as well as pixels with extreme values, with an estimate of the median reset value.

I used a function I call ORDERSPACING to determine a single value for the number of pixels between echelon orders for each clean file (see figure below).  These can be used to check models for the instrument.

I then got an estimate of a "typical" value for each good image by looking at values where there was clearly light, requiring there to be >5000 such pixels, and selecting the 25%ile (more light means lower numbers) as "typical".  I subtracted the no-light values I found for each image to get the number of data numbers corresponding to the incident light.  The plot below shows a cut along row 510 of each good image (there are 25 good images) using the small dots.  These values go across orders near the peak of the blaze.  My typical values are shown in red with each frame having a single value.  For most of the frames, these values are not at the top, but do reflect larger than median signal.  For frames with low response, the "typical" values seem too high.  The green dots are my "no-light" values.  Note that I believe there is some light on the detector beyond what is landing in the orders (see comment to post on scattered light).

I finally calculated throughput using logbook/blog values for the integration time (ctdelay = 110 or 3 seconds), gain (35.9 e- per DN), slit resolution (3.8 km/s), and assuming emissivity =1 and temperature = 295 K.

I calculated the area*omega product in two ways.  First, I used the half angle that we measured during CD13 where we mapped a soldering iron tip across the beam and divided by an estimate for the distance to the focus (note that we had a KRS-5 lens not designed for EXES, so it just has a stock focal length that is close).  This half-angle = 0.0251 radians.  I calculate the corresponding solid angle as 2*!pi*(1-cos(0.0251)) = 0.001979 sr.  I next took EXES design numbers for performance on SOFIA.  Since area*omega should be invariant, if we had the proper SOFIA lens in place, this should be equivalent.  We didn't have that lens in place, so I view this more as a sanity check if we're close.  Using the SOFIA telescope = 2.375m diameter (accounts for undersized cold stop), EXES as an f/10 system, and 25 micron pixels, I get a platescale of 0.217 arcsecond per pixel or 1.053e-6 radians per pixel.  The net result ends up that area*omega from CD13 is about 4 times larger than using SOFIA design parameters.

Anyway, this entire digression of area*omega is possibly relevant because when I calculate the number of photons that should be incident per pixel assuming 100% throughput compared with the record number of electrons, I get unrealistically high numbers for the CD13 experimental area*omega and realistic numbers for SOFIA design parameters.  I'm hoping someone will find an error in my calculations.

Below is my plot for throughput.  White is with CD13 area*omega and red is the SOFIA design.  I wouldn't be surprised if the true throughput is even a factor of two below the red points for this wavelength.  I plot values as a function of wavelength and as a function of echelle angle.  It is apparent the echelle is more efficient at angles <55 degrees.  You can also see that we need a blocker for the filter to get the 16-17.5 wavelength region.

Some strange data values

Looking at 18a filter scan data, I noticed ALL the data frames (single destructive reads) have some funny behavior.  In the plot, the white dots are the first row of 1024 pixels, the green are row 510 (but are generally true for rows 1 to 1022), and the red dots are the last row of 1024 pixels.  

You can't really see it from this plot, but the first row clearly shows the 4 readout chains while the others don't show that imprint clearly.  

The first row, after 4 reference pixels near 15,000 ADU, jump to 16,000 ADU and slowly climb to 16,200 before a short jump down to the last 4 reference pixels.  

The middle rows look like like good data with a sharp jump on the end 4 reference pixels the only big weirdness.  It is a little weird to me that reference pixels at start have more charge than data.

The last row almost seems pinned at a saturation value (3200 ADU).  First four reference pixels are all around 14,500 ADU and last four reference pixels are 10,500; 10,500; 10,500; 2500 ADU.

Don't know if this is partially coming from ebox interacting with array, but something looks screwy.

Finding a Common Best Focus Position for High & Medium Resolution Modes


Last week I finished running scans of both Medium and High Resolution Zemax models for different settings of collimator distances. I used my Medium Res results to pick a detector distance of 95mm from the turning mirror and 35 turns on the Echelle Collimator.  The blue straight line on the graph is shows Medium Res best focus position for different positions of the Echelle Collimator.  The brown curve shows the Medium Res best focus geometric spot radius for those different Echelle Collimator positions.

  Then I went to my High Res results, found where the detector distance of 95mm and Echelle Collimator setting of 35 turns coincided (roughly) with an Echelon Collimator setting of 10 turns. The individual straight lines represent best focus detector positions for different Echelle Collimator positions at one Echelon Collimator position. The extrapolation on the High Res graph indicates about 13 turns needed on the Echelon Collimator to coincide with the Medium Res best focus position.

 So... going to my Zemax models and setting these conditions I get an RMS spot size (radius) of ~18microns in Medium Res (vs Airy radius 167microns) and an RMS spot size (radius) of ~101microns in High Res (vs Airy radius 143microns.)  The best setting for the Echelon Collimator was about 11.4 turns instead of 10 or 13 ... not wildly different considering how I got all of these numbers.

The logarithmic PSFs for both modes are essentially the same with both having FWHM of 200 microns or 8 pixels at 13.7 microns wavelength:

 

In other words, this method works pretty well - in the models.  Also, my value of 95mm is, I think, indistinguishable with the current measured value of 93mm.

Now - how do we know when we've set the real collimators at some 'n' number of turns with respect to the nominal Lacy model positions?

Distance from turning mirror to detector plane

We took advantage of having the flip mirror side-wall exposed today and measured the distance from the center of the turning mirror to detector plane.

Using calipers, the center of the turning mirror to the outer edge of the O-box wall is 3.24"~ 82mm

The detector plane is 10.9 mm from the outer edge of the O-box wall.
This value was obtained using the SolidWorks drawing of the D-box, and adjusting/assuming the following values:
        1) The G-10 standoffs are 4.445mm in the drawing, but for CD013 are actually 3.82mm.
        2) Assumed that the detector plane is 6.35mm behind the front cover of the detector socket.

Our calculation puts the detector plane 10.9 mm away from the outer edge of the O-box wall or
93 mm (3.66") from the center of the turning mirror (for CD013).

Echelon parameters

I've been looking at the echelon parameters so we can predict which echelon order lines will end up in.  The best data I have are with the filter open and the gas cell (see below) so we know what wavenumbers fall in echelon orders that are divisible by simple integers.  The order in the center has two clear lines in it.  I know from previous observations with appropriate filters in place that the line closest to the center of the detector is 600.103 cm-1 seen in echelle order = 3 and the line in the same order near the bottom is 400.2217 cm-1 seen in echelle order = 2.  There is also a line near the top near column 400 that I know is 400.48451 cm-1. The central order is much stronger than all the other orders and also much cleaner at the ends of the slit (horizontal).  This makes it apparent that the echelon orders overlapping in the central order are multiples.  To the right and left of the central, clean order are various less intense, less contrasting orders.  Eventually, we see a clean order on both sides.  Again, this is an order where different echelon orders overlap exactly.  Mid-way between the clean orders are somewhat intense, somewhat clean orders.  These locations are echelon orders that are multiples of 2, but not of 3.  Since the echelon order separation is inversely proportional to the echelle order number, we can figure out the location of echelon orders divisible by 4 as well.

Starting with the TEXES echelon parameters for the echelon groove spacing (7589 microns), R number (tan of incidence angle: 9.8), and gamma angle (0.025 radians), I varied the parameters to have the 600.103 line near the center of an echelon order (near M1.00, the 400.2217 cm-1 in the lower half of an echelon order (>M2.00,<M2.40), and the 400.48451 cm-1 line in the upper half of an order (>M3.50,<M3.75).  Further more, M1 = 3/2. M2 and M3 = M2 + 1.

Results will be better when we do this at other wavelengths (13.7 microns? 1315 cm-1?), but currently have:

echelon groove spacing: d = 7589.0 microns
echelon R number (tan of incidence angle): R# = tan(theta) = 9.8
echelon gamma angle: gamma = 0.20


Working on IDL routine to simulate gas cell spectra using HITRAN files with these parameters (and echelle parameters).

Changes to the detector box for the tilted detector experiment

We are considering tilting the detector by ~9 degrees in the echelle dispersion direction for the next cool-down, CD014.  This would allow us to move a spectral line along different focus values (+/- 2 mm) and find the optimal detector position for EXES. In addition to a tilt, we also wish to move the center of the detector forward (toward the camera) by 0.125", since we believe that to be equivalent to the 5 turn difference in the echelle collimator mirror position between best focus in med and high res modes that we uncovered in CD013.

This drawing shows the current configuration.
To do the tilt operation, we will add spacers to the posts marked "A", and we will need to make the standoff spacers at "B" and "C"to be 0.00" and 0.73", respectively. The latter results in pulling the detector center back by 0.24"-- so the length of the spacers at "A" needs to be 0.24+0.125=0.365". 

These requirements create a few spots for mechanical interference in the current D-box.

The chimney baffle will have to be widened from 2.46" to > 2.56", and rear plate of the D-box will have to have a alcove toward one side to accommodate the tilted heat-sink block.

Ryan from Emmett's shop needs about a few days on the CNC to remake the plate with the chimney - and he said that they could get to it before May 1.

In addition we will need 4 of the detector standoff spacers at "A" of ~0.365", 2 of the 0.73" head sink block standoff spacers at "C", and a new rear plate with an alcove built into it. I didn't get a chance to ask about the lead time for these parts.

(As for their recent delivery record: last Friday and early this week they have managed to get us the new cassette cover plate and add screw holes on the window holder to hold the window cover).

Tomorrow, I am meeting with Ryan to edit the solid works drawing to double check all the above measurements.


In the mean time, we should discuss this. If this effects when the next cool-down begins, at what point will it better to simply try +0.125 to the detector position with no tilt, rather than waiting for new d-box parts?

System Power Draw

Did a rough measurement this morning of the current drawn by the EXES racks as various items were turned on.

Bottom line:  Lots of headroom on the 2kVA UPS supply.

System draws about 6.5A total (absent the cal source supplies), which would be ~0.78kVA if we just multiply by 120V.

Here's a rough listing:

PC Host computer:  2A (momentary 4A on startup)
eBox supply:  2A
macmini + monitor:  1A
Lakeshore:  0.5A

Pot power supply + agilent + motor boxes + network switch < 0.5A total

The resolution on the current meter was only 0.5A, so these numbers are not precise below that level.  Hard to see where we'll have a problem that would require us to use any of the non-UPS power.

Slit feature resolutions at 14um in low mode

Echelle Voltage: 0.9062 V
files are from B_12_02_27

#filenum slitfeature   1             2              3
b061 1.5km/s          6.50        6.25         7.60
b060 2.0km/s          6.72        6.72         7.42
b059 2.7km/s          7.40        8.80         9.08
b058 3.5km/s          8.98        9.12         11.90

The scale is: R=36400/N_pix or 8.24 km/s per pixel

Resolutions:
Slitwidth     R
1.5     5600
2.0     5500
2.7     4130
3.5     3990

Slit feature resolutions at 7.5um in medium mode

The picture above shows the line IDs for the H20 band near 1315 cm-1 in medium resolution mode.

I calculate a velocity per pixel of:  2.53 km/s/pix

I was forced to only use frames 1 and 2 of the SUTR data to avoid saturation.

And below is a table of the FWHM of the lines, which were calculated by fitting 5-parameter Gaussian functions across the 20 central-most rows of each line. The values below are the median(sigma*2.355) for the 20 fits across each line.
The line pair at 1313.5 and 1313.6 were partly blended, even with 1.5 km/s, so I didn't record their widths. Where other entries are missing, it is either due to blending, or to saturation.

#slit            file    1        2         3      6      7       8
1.5 km/s        b032    7.77     6.81    6.88    6.36    6.10    6.22
2.0 km/s        b031    8.68     7.58    7.80    7.30            7.32
2.7 km/s        b030    9.70     8.85    8.97                    8.78
3.5 km/s        b029   11.75    11.26   11.59                   10.81               

4.5 km/s        b038            13.89                           13.54          
6.0 km/s        b037            18.30                                                 

flux slit       b036       

 For the mean values of FWHM, the resolutions are: 
#slit            mean(FWHM)    v_res(km/s)    R
1.5 km/s        6.69            16.9        17700
2.0 km/s        7.74            19.6        15300
2.7 km/s        9.08            23.0        13100
3.5 km/s        11.35           28.7        10400
4.5 km/s        13.72           34.7         8600
6.0 km/s        18.30           46.3         6500

Also, it seems clear that the right side is in better focus than the left. This was not clear to see in the high res modes. See the plot below.