Visible Spectropolarimeter Vi SP Conceptual Design David Elmore

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Visible Spectro-polarimeter (Vi. SP) Conceptual Design David Elmore HAO/NCAR Elmore@ucar. edu

Visible Spectro-polarimeter (Vi. SP) Conceptual Design David Elmore HAO/NCAR [email protected] edu

Vi. SP Mission* • Precision measurements of full state of polarization – Simultaneously at

Vi. SP Mission* • Precision measurements of full state of polarization – Simultaneously at diverse wavelengths – Visible spectrum range – Fully resolved line profiles • Provides quantitative diagnostics of – Magnetic field vector as a function of solar height – Variation in thermodynamic properties *From Instrument Science Requirements 2001, Sept. 17, B. Lites, C. Keller May 27 -28, 2004 Vi. SP 2

Vi. SP Requirements from ISRD Specification Requirement Goal Priority Wavelength range 380 nm –

Vi. SP Requirements from ISRD Specification Requirement Goal Priority Wavelength range 380 nm – 900 nm 296 nm – 1090 nm 1 Wavelength diversity 3 simultaneous lines Spatial Resolution 0. 05 arc sec Diffraction limit 1 Spatial field of view 3 arc min square 5 arc min dia. 1 Spectral resolution <3. 5 pm @600 nm 2. 0 pm @600 nm 1 Spectral sample <2. 5 pm @600 nm 1. 5 pm @ 600 nm 1 Polarimetric precision 10 -4 Icontinuum 10 -5 Icontinuum 1 Operation with NIRSP Within 5 sec. Simultaneous 2 May 27 -28, 2004 Vi. SP 2 3

Spectrograph Specifications Feed focal ratio f/40 Focal Length 2250 mm Slit Width 24 mm

Spectrograph Specifications Feed focal ratio f/40 Focal Length 2250 mm Slit Width 24 mm Pixel Size 24 mm Slit Height 140 mm Grating Height 196 mm Grating Length 200 mm Grating Blaze Angle 57º Based on VSP Coupling to Telescope. doc, Elmore (April 2003) May 27 -28, 2004 Vi. SP 4

Compact Spectrograph Design May 27 -28, 2004 Vi. SP 5

Compact Spectrograph Design May 27 -28, 2004 Vi. SP 5

Compact Spectrograph Features • Accessible: all in one plane • Selectable gratings mounted on

Compact Spectrograph Features • Accessible: all in one plane • Selectable gratings mounted on a turntable • Spectrum scanned by translating the entire spectrograph, or optionally by preceding spectrograph with beam scanning mirrors • Dimensions 2. 5 m x 2. 0 m x 0. 5 m • Mass 230 kg May 27 -28, 2004 Vi. SP 6

Compact Spectrograph Spot Diagram May 27 -28, 2004 Vi. SP 7

Compact Spectrograph Spot Diagram May 27 -28, 2004 Vi. SP 7

Compact Design Problems • Aberrations grow rapidly off axis (yes cylindrical lenses could be

Compact Design Problems • Aberrations grow rapidly off axis (yes cylindrical lenses could be added) • Very compact focal plane with small optics • Numerous mirrors or beam splitters • Large moving mass May 27 -28, 2004 Vi. SP 8

Refractive Spectrograph Background • Based upon Horizontal Spectrograph designed by Dick Dunn at DST

Refractive Spectrograph Background • Based upon Horizontal Spectrograph designed by Dick Dunn at DST • More automation • Single fixed beam plus adjustable beams May 27 -28, 2004 Vi. SP 9

Refractive Spectrograph Design collimator camera lenses fold mirror grating slit May 27 -28, 2004

Refractive Spectrograph Design collimator camera lenses fold mirror grating slit May 27 -28, 2004 Vi. SP 10

Refractive Spectrograph Design May 27 -28, 2004 Vi. SP 11

Refractive Spectrograph Design May 27 -28, 2004 Vi. SP 11

Refractive Spectrograph Design Fixed beam May 27 -28, 2004 Vi. SP 12

Refractive Spectrograph Design Fixed beam May 27 -28, 2004 Vi. SP 12

Refractive Spectrograph Design May 27 -28, 2004 Vi. SP 13

Refractive Spectrograph Design May 27 -28, 2004 Vi. SP 13

Refractive Spectrograph • Smaller moving mass • Larger spacing allows for more easily selecting

Refractive Spectrograph • Smaller moving mass • Larger spacing allows for more easily selecting spectrum lines • Excellent optical performance for every wavelength May 27 -28, 2004 Vi. SP 14

Refractive Spectrograph Motions • Slit scan stage – Range: Continuous motion over 5 arc

Refractive Spectrograph Motions • Slit scan stage – Range: Continuous motion over 5 arc minutes @ f/40 = 233 mm – Accuracy: Absolute encoding to ~. 001 arc seconds = 3. 5 mm (16 bits) • Slit width – Range: Continuous motion 0 to 1 mm – Accuracy: 1 mm • Slit rotation – Range: Continuous motion over ± 5° – Accuracy: ± 1 pixel over slit length = ± 18 arc seconds • Grating selector – Range: Discrete motion with N=3 positions – Accuracy: Position accuracy to 8 arc seconds (10 pm at 630. 2 nm) May 27 -28, 2004 Vi. SP 15

Refractive Spectrograph Motions • Grating a (selects wavelength) – Range Continuous motion over -90°

Refractive Spectrograph Motions • Grating a (selects wavelength) – Range Continuous motion over -90° to 90° – Accuracy: 10 pm @ 630. 2 nm = 8 arc second (16 -bits) • Grating b (tip) – Range: Continuous motion 140 mm field at 2. 25 m = ± 1. 8° – Accuracy: ten 12 mm pixels @2. 25 m = 11 arc seconds • Grating g (tilt end to end) – Range: Continuous to correct gross mechanical error of ± 1 mm – Accuracy: 10 pixels across 10° range of a angles = 12 arc seconds = 6 mm at the end of a 200 mm long grating May 27 -28, 2004 Vi. SP 16

Refractive Spectrograph Motions • Camera lens X-Y motion (translation) – Range: Continuous to fix

Refractive Spectrograph Motions • Camera lens X-Y motion (translation) – Range: Continuous to fix gross mechanical error ± 5 mm – Accuracy: 1 pixel = 12 mm • Camera lens Z motion (focus) – Range: Continuous motion to correct chromatic aberration ± 12 mm – Accuracy: to << 240 micron circle of confusion @ f/20 and 12 mm pixel = 25 mm • Filter wheels (one per camera) – Range: Discrete motion with N=8 positions – Accuracy: 1° May 27 -28, 2004 Vi. SP 17

Suggested Adjustment Modes • Qualification Mode (‘One time’ alignments) – Values are saved in

Suggested Adjustment Modes • Qualification Mode (‘One time’ alignments) – Values are saved in system tables for ‘reset’ if needed – Examples • Grating b, g • Slit rotation • Setup Mode (Once per observing run) – Values are saved in system tables for ‘reset’ if needed – Examples • Grating a • Camera lens X, Y, Z • Observing Mode (Changed during observations) – Example • Slit scan position May 27 -28, 2004 Vi. SP 18