Near Infrared Spectropolarimeter NIRSP Design Status May 2004

Near Infrared Spectro-polarimeter (NIRSP) Design Status May 2004 Don Mickey Jeff Kuhn Haosheng Lin May 27 -28, 2004 NIRSP

NIRSP Modules • Two spectrograph modules, one on coudé platform and the other at Nasmyth. • Common basic design; common camera. • Coudé: high spatial resolution, multi-camera capable. Warm optics on optical bench. AO observations of limited field. • Nasmyth: Coronal observations and wide-field disk observations. Cold optics. May 27 -28, 2004 NIRSP 2

NIRSP Requirements Specification Requirement Wavelength Range 900– 5000 nm 1 Spectral Resolution 50, 000– 300, 000 1 Transmission 30% 1 Modulation efficiency 90% of max attainable 1 Polarimetric accuracy 10 -4 Ic 5 10 -5 1 Spatial Resolution 0. 05 arc sec / pixel 0. 025 arc sec / pixel 1 Spatial Field 3 arc min at 0. 1 arc sec 5 arc min at 0. 1 arc sec 1 Spatial Scanning Slit, step 0. 05 arc sec Slit, step 0. 025 arc sec 1 Wavelength Diversity 3 simultaneous 5 simultaneous 2 Obs with Vi. SP Flexible setup May 27 -28, 2004 NIRSP Goal Priority 1 3

NIRSP Coudé Unit • Feed at f: 40 – Spatial scale 0. 776 mm / arc sec • Field lens near entrance slit (if required) – Makes beam telecentric • Slit nominal 36 µm – Spatial sampling 0. 046 arc sec • Grating is R 2 (tan = 2) echelle – Angular dispersion 4/ µrad/pm (near-Littrow) • Reflective Littrow layout, off-axis parabola – Coma-corrected at any grating angle – Minimal astigmatism – Spectrograph magnification = 1. 0 May 27 -28, 2004 NIRSP 4

NIRSP Coudé, more • Collimator focal length 2. 25 m – Geometric pupil diameter 56 mm – Linear dispersion 5. 75 µm/pm at = 1. 565 µm • Grating width 300 mm (projected width 135 mm) – Diffraction image width at focal plane is 26 µm – Slit diffraction overfills grating; 12% light loss at = 1. 565 – Ruling frequency 87 mm-1, or TBD • Detector like Hawaii-2 RG, 1 2 mosaic – – – 18 µm pixels, bin 2 2 Field 95 arc sec Spectral sampling 6. 3 pm Resolving power 200, 000 at = 1. 565 Increase f to 3 m and w to 400 mm gives R=270, 000 May 27 -28, 2004 NIRSP 5

Multiple Slits At Coudé, the FPA width covers 6. 4 nm at 1. 565. The optical quality is good over the entire field, so we might think of using a narrow-band blocker and up to six slits. May 27 -28, 2004 NIRSP 6

NIRSP Nasmyth • Feed at f: 13. 08 (same as Gregorian image) – Spatial scale 0. 254 mm / arc sec • Field lens near entrance slit – Makes beam telecentric • Slit nominal 108 µm for coronal observations, 18 µm for disk observations – Spatial sampling 0. 425 arc sec to 0. 07 arc sec • Grating is R 2 (tan = 2) echelle – Angular dispersion 4/ µrad/pm (near-Littrow) • Reflective Littrow layout, off-axis parabola – Coma-corrected at any grating angle – Minimal astigmatism – Spectrograph magnification = 1. 0 May 27 -28, 2004 NIRSP 7

NIRSP Nasmyth, more • Collimator focal length 1. 3 m – Geometric pupil diameter 99 mm – Linear dispersion 3. 32 µm/pm at = 1. 565 µm • Grating width 300 mm (projected width 135 mm) – Diffraction image width at focal plane is 15 µm – Slit diffraction overfills grating; 20% light loss at = 1. 565 with 18 µm slit (3% loss with 108 µm slit) – Ruling frequency 87 mm-1, or TBD • Detector like Hawaii-2 RG, 1 2 mosaic – – 18 µm pixels, bin 6 6 (or more!) for corona Field 290 arc sec Spectral sampling 5. 4 pm photosphere; 22 pm corona 1. 07 µm Resolving power 225, 000 at = 1. 565 May 27 -28, 2004 NIRSP 8

Nasmyth Scanning • How do we scan the image at Nasmyth? – Scan the telescope? – Scan the spectrograph? – Add a scanning mirror to the relay optics? May 27 -28, 2004 NIRSP 9

Tip-tilt at Nasmyth • Nasmyth observations need tip-tilt correction • T-T options – Active secondary – Active second relay mirror • Image moves 2. 5 mm for 10 arc sec; pupil moves 1. 2 mm. – Add a pupil mirror to the relay optics May 27 -28, 2004 NIRSP 10

Nasmyth Context Image • • How do we get a context image? Multiple slits make slit viewer “difficult. ” Dichroic or bandpass ahead of slit? Infrared, or visible, context image? May 27 -28, 2004 NIRSP 11