Near Infrared Spectropolarimeter NIRSP Design Status August 2004

  • Slides: 16
Download presentation
Near Infrared Spectro-polarimeter (NIRSP) Design Status August 2004 Don Mickey Jeff Kuhn Haosheng Lin

Near Infrared Spectro-polarimeter (NIRSP) Design Status August 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

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. August 11– 13, 2004 NIRSP 2

NIRSP Requirements Specification Requirement Wavelength Range 900– 5000 nm 1 Spectral Resolution 50, 000–

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 August 11– 13, 2004 NIRSP Goal Priority 1 3

NIRSP Coudé Unit • Feed at f: 40 – Spatial scale 0. 776 mm

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 72 µm to match telescope spot size – Spatial sampling 0. 092 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 August 11– 13, 2004 NIRSP 4

NIRSP Coudé, more • Collimator focal length 4. 0 m – Geometric pupil diameter

NIRSP Coudé, more • Collimator focal length 4. 0 m – Geometric pupil diameter 100 mm – Linear dispersion 10. 2 µm/pm at = 1. 565 µm • Grating width 300 mm (projected width 135 mm) – Diffraction image width at focal plane is 76 µm (line width) – Slit diffraction overfills grating; 15% light loss at = 1. 565 – Ruling frequency TBD • Detector TBD – – – Assume 24 µm pixels, 20 x 20 mm, array 4 h x 1 w Field 105 arc sec along slit Spectral sampling 7. 0 pm Resolving power 222, 000 at = 1. 565 Rmax is 340, 000; can narrow slit and bin 2 x, grating spill goes up to 23%. August 11– 13, 2004 NIRSP 5

Coudé layout August 11– 13, 2004 NIRSP 6

Coudé layout August 11– 13, 2004 NIRSP 6

Coudé Spot Diagram August 11– 13, 2004 NIRSP 7

Coudé Spot Diagram August 11– 13, 2004 NIRSP 7

Multiple Slits • At Coudé, the FPA width covers 2 nm at 1. 565.

Multiple Slits • At Coudé, the FPA width covers 2 nm at 1. 565. The optical quality is good over the entire field, so we might think of using a narrow-band blocker and two slits. • This design is adaptable to different pixel sizes, and the focal length could be shortened if needed. August 11– 13, 2004 NIRSP 8

NIRSP Nasmyth • Feed at f: 13. 08 (same as Gregorian image) – Spatial

NIRSP Nasmyth • Feed at f: 13. 08 (same as Gregorian image) – Spatial scale 0. 254 mm / arc sec • Build spectrograph 2 x faster, and compact: focal length one meter, f: 6. 5. – Permits fiber-feed IFU • Field lens near entrance slit – Makes beam telecentric • Slit nominal 96 µm for coronal observations, 24 µm for disk observations – Spatial sampling 0. 38 arc sec to 0. 09 arc sec • Grating is R 2 (tan = 2) echelle – Angular dispersion 4/ µrad/pm (near-Littrow) • Reflective Littrow layout, off-axis parabola August 11– 13, 2004 NIRSP 9

Nasmyth Layout, f: 6. 5 August 11– 13, 2004 NIRSP 10

Nasmyth Layout, f: 6. 5 August 11– 13, 2004 NIRSP 10

NIRSP Nasmyth, more • Collimator focal length 1. 0 m – Geometric pupil diameter

NIRSP Nasmyth, more • Collimator focal length 1. 0 m – Geometric pupil diameter 76 mm – Linear dispersion 2. 56 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; 8% light loss at = 1. 565 with 24 µm slit (2% loss with 96 µm slit) – Ruling frequency TBD • Detector: 20 x 20 mm, array 1 x 4 – – 24 µm pixels, bin 4 6 (or more!) for corona Field 315 arc sec Spectral sampling 9. 4 pm photosphere; 26 pm corona 1. 07 µm Resolving power 167, 000 at = 1. 565 August 11– 13, 2004 NIRSP 11

Nasmyth Encircled Energy, f: 6 August 11– 13, 2004 NIRSP 12

Nasmyth Encircled Energy, f: 6 August 11– 13, 2004 NIRSP 12

Nasmyth Encircled Energy, f: 13 August 11– 13, 2004 NIRSP 13

Nasmyth Encircled Energy, f: 13 August 11– 13, 2004 NIRSP 13

Scanning • Scan the slit. – Image moves on the detector, but the image

Scanning • Scan the slit. – Image moves on the detector, but the image is curved anyway so we have to locate the line in data reduction. – Scan range is about 10 mm at coudé. – At Nasmyth, dispersion is 2. 56 mm/nm, so there’s room for five or six slits if 1 nm filters are available. The scan range is also smaller, 2. 5 mm. – Optical performance supports scan over entire field. August 11– 13, 2004 NIRSP 14

Wish List • More room for pre-slit activities. Can we modify the Nasmyth relay

Wish List • More room for pre-slit activities. Can we modify the Nasmyth relay to get the image 500 mm beyond instrument attachment, instead of 210? • Fast camera • Fast modulator August 11– 13, 2004 NIRSP 15

Polarimetry • Polarizing beam-splitter at slit is possible. Can get 5 mm separation in

Polarimetry • Polarizing beam-splitter at slit is possible. Can get 5 mm separation in a Savart plate. Takes a cylindrical lens (f=62 m) in f: 13. This would help if we need to do slow modulation. • Nasmyth relay has modest polarization effect. • Should we consider PEM phase-locked modulator? May have some hope. Spherical aberration from 2 cm Ca. F 2 in f: 13 is negligible. August 11– 13, 2004 NIRSP 16