Oct 24, 2006 SSWG 1

Robert StobiePrime Focus Imaging

SpectrographStatus

• On-telescope throughput analysis• Ghost analysis• Repair plan• Status of other current control and mechanical issues• Commissioning progress• Budget

Oct 24, 2006 SSWG 2

RSS Optics Throughput Shortfall

• Telescope system testing found RSS optics throughput ~60% of expected in visible, < 25% below 375 nm

• Either blank absorption or coatings at fault

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Wavelength (nm)

EG 21 S litless Spec

47 Tuc Im aging

EG 21 Im aging Burst

M ar-Jun Im aging Burst

FPR D M in

R SS Throughput Shortfa ll

Oct 24, 2006 SSWG 3

Blank Absorption Investigation

• Polished and measured spare NaCl blank - good

• Remaining possibility of effect found for UVES: coating process causing development of "color centers" in CaF2. Curable by UV Flooding

NaCl %Tblank thickness: 56 mm

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Wavelength (nm)

%Tr

ansm

issi

on

In ternalN aC l % T

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Oct 24, 2006 SSWG 4

Throughput Test Apparatus

• To isolate optical subsystems with problem and narrow range of causes, develop apparatus to measure throughput of integrated optics at 375 and 635 nm

• Tests performed 23 - 30 Sept, 2006

3 7 5 n m la serp h o to d io d e/ 6 3 5 n m filter

p h o to d io d e/ 3 7 5 n m filter

en tra n ce o fcam era

sh u tter /ex it o f co llim ato r

6 3 5 n m la ser

P ico -a m m eter

la ser tilt ad ju stm en ts375 nm laser

A l "G rating B lank"(175x175x10 m m )

R eturn beam from optics

380 nm interference filter

U V Photodiode

G rating rotation

Vertica l positionadjustm ent

Oct 24, 2006 SSWG 5

Throughput Experiments

F ilte rs

C C D

C o a tin g s

C am era G ra tin g H o ld e r

Collim

ator

1 /4 W av ep la te S lid eF o ca l P lan e

C o llim a ted B eam

M g F / so lg e l2

M g F 2

M u ltilay e r

C aF 2

S ilica

Oct 24, 2006 SSWG 6

Subsystem Throughput• Throughput of 7

subsystems derived:

• MgF2 coatings, LLNL fold flat exonerated

• Visible loss in collimator main group and camera

• UV loss also in collimator doublet

• Multiplying losses consistent with on-sky system results

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easu

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6 3 53 7 5Q B LH W PQ W P

W P F LB L

M G

M IR

D B L C A M

M g F 2 M g F 2M g F 2

S o lG e l S o lG e l

S m all = In d irec t

M u lti M u lti M u ltiL L N L

Oct 24, 2006 SSWG 7

Conclusions• no common coatings

=> at least 2 separate problems.

• doublet shows transmission < 1 - reflectivity => CaF2 color center possible. Definitely multilayer coating problem.

• problem in collimator main group means instrument must come off.

C o a tin g s

C am era

M g F / so lg e l2

M g F 2

M u ltilay e r

C aF 2

S ilica

C o llim a to r

Oct 24, 2006 SSWG 8

Ghost

• Flatfield ghost with interference filter imaging and Fabry-Perot– in interference filter sky images and flat fields see ~ 10%

“doughnut” which appears to be an image of the pupil– does not show up with clear or color filters => one ghost

surface is the filter (reflection 10 – 100% depending on wavelength)

– a severe problem for FP mode– determined to be internal to RSS

• Ghost investigation– take flats with various pupil masks inserted in grating

holder, field mask at slit– raytrace analysis to find surface that forms pupil image– circular polaroid between ghost surfaces should eliminate it

Oct 24, 2006 SSWG 9

Ghost Geometry

• Mask experiments -> 2nd surface in camera• Polaroid experiment -> after filter• Raytrace -> dewar front surface

C ircu lar Polaro id -Top

C ircu lar Polaro id -Bottom

G host Path

Oct 24, 2006 SSWG 10

The trouble with the dewar window

• Predict surface reflectivity from observed ghost intensity vs wavelength: up to 20% peaking at 540 nm

• remove detector, measure and inspect window: yellow-green

• Another (different) multilayer problem

• Fix during throughput repair

W a v elen g th (n m )

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lect

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Oct 24, 2006 SSWG 11

Repair plan

Oct 24, 2006 SSWG 12

Control Issues

• Grating insertion interlock problem– not interlocked against inserting grating when etalon or articulation

is in wrong status.– this works on built-up spare at UW. Suggests wiring or board

problem in RSS electronics box. – Found error and fixed.

• Waveplate homing problem– found that we need to turn off the waveplate rotator encoder when

not moving it (stray light). Rotator homing then does not work.– again, this works on built-up spare at UW. Suspect a software or

firmware incompatibility.– hardware verified with encoder diagnostic software.

– software not waiting long enough after turning encoder on. Software problem identified

Oct 24, 2006 SSWG 13

Mechanical Issues• Slitmask mechanism

– severe reliability problems due to difficulty of aligning magazine, carrier, and focal plane chute

– temporarily removing magazine, using insertor to inset and remove a manually loaded slitmask

– SAAO redesigning slitmask assembly to make it monolithic, aligned on bench

– install during down time• Articulation fall arrestor

– safety restraint to prevent catastrophic damage in case articulation motor fails during articulation

– installation and testing within a few days• Polarizing Beamsplitter

– SAAO task to redesign and manufacture beamsplitter insertor to allow for beamsplitter removal/ rotation/ insertion in situ

– clearance issues resolved. Now installed

Oct 24, 2006 SSWG 14

Commissioning - Longslit Spectroscopy

• Mostly done. Many PV proposals used.• Autoguide setup procedure mature• Calibration procedures developed

Oct 24, 2006 SSWG 15

Commissioning - MOS

• Slitmask cutting process tested

• Manual acquisition with MOS painful (10 - 20 m), but surprisingly possible

• Orientation control issue identified with slitmask cutting/ TCS software

• Needs slitmask magazine, more automated acquisition procedure to be practical

Oct 24, 2006 SSWG 16

Commissioning - Fabry-Perot

• On 20060922, first light RSS on-sky Fabry Perot observations: two spiral galaxies, NGC 1535 and NGC 1365, at Hα through the LR etalon.

• roughly 20-step etalon scans through the line.

• An initial reduction of the data cubes shows a velocity map for NGC 1365 which compares well with data obtained on other telescopes

• throughput is within 2x of expected

Oct 24, 2006 SSWG 17

Commissioning - Continued

• Polarimetric. Next two weeks: – linear polarization lamp calibration

– spectropolarimetry on-sky first light

– linear: standards, high and low-res PV

– circular: mCV

• High speed: awaiting detector software issue• All UV commissioning: after repair (starting

May?)

Oct 24, 2006 SSWG 18

Cost to Completion

• Does not include ~50 - 100 $K for optics repair costs (mostly optomechanical)

• Predicting CTC ~20% over CDR budget

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$1,000,000

$2,000,000

$3,000,000

$4,000,000

$5,000,0002002 2003 2004

PD

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CD

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iver

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E st C ost to C om pletion

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SAAO

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Tota lExpenditures

Baseline

20% Budgeted R eserve

now

2005 2006