Near Infrared Spectro-polarimeter (NIRSP) Conceptual Design

Don Mickey

Jeff Kuhn

Haosheng Lin

August 25-28, 2003 NIRSP 2

NIRSP Mission

• Measure polarization state of spectral lines– Near infrared, 900–5000 nm wavelength– Very wide range of observational parameters

• Science– Sunspot, active region magnetic fields– Network, internetwork magnetic fields– Coronal magnetic fields– Filament, prominence magnetic fields– Waves and dynamics, coronal heating

August 25-28, 2003 NIRSP 3

NIRSP Requirements

Specification Requirement Goal PriorityWavelength 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 ViSP Flexible setup 1

August 25-28, 2003 NIRSP 4

Design Drivers

• Required spectral and spatial resolution• Field of view• Grating availability• Detector availability• Flux budget

August 25-28, 2003 NIRSP 5

Disk vs. Coronal Observations

• Disk observations:– High spatial and spectral resolution – High polarimetric precision– Good temporal resolution– “Plenty” of flux

• Corona:– High polarimetric precision– Flux is lower by 106

– Give up some spatial and spectral resolution

August 25-28, 2003 NIRSP 6

NIRSP Has Two Subunits

• NIRSPC: Coudé Unit– Disk observations– High resolution– Littrow, parabola– Multiple cameras possible

• NIRSPG: Gregorian Unit– Coronal observations– Limited spatial and spectral resolution– High throughput– Littrow, parabola– Cryogenic

August 25-28, 2003 NIRSP 7

Distributed NIRSP Concept

• Common Elements– similar optical design– Hawaii-1RG arrays or -2RG HgCdTe camera– Interchangeable mechanism designs (all warm

steppers)– Common hardware and software control/interface

structure

• Distinct Elements– NIRSPG uses cooled grating/optics (warm steppers)– NIRSPC warm optical bench

August 25-28, 2003 NIRSP 8

Baseline NIRSP Status

• Spectrograph design proof-of-concept– Fiber bundle IFU desirable– Multislit mode desirable– Optomechanical and cryogenic designs TBD

• Polarimeter concept designs beginning– NIRSPG favors SAP concept w/ polarizing

beamsplitter– NIRSPC...

• Exploring trades – Multiple or single HgCdTe camera modules – 2.5 vs 5 micron cutoff)

August 25-28, 2003 NIRSP 9

NIRSPC Layout

• R2 echelle• Littrow configuration, off-axis parabola• 3 m focal length

August 25-28, 2003 NIRSP 10

NIRSPC: Coudé Unit Specifications, f/40

Feed focal ratio f/40

Focal length 3040 mm

Slit width 39 m

Pixel size 39 m

Slit height 140 mm

Grating height 102 mm

Grating length 306 mm

Grating blaze angle 63.5°

August 25-28, 2003 NIRSP 11

Grating Illumination, f/40

• Grating illumination pattern– Feed f/40, slit 39 m, focal length 3.04 m– Grating 102 x 306 mm, tan = 2– Illumination height is from f/40; width is from slit diffraction– Light loss in wings is 14%

August 25-28, 2003 NIRSP 12

Coudé Characteristics, f/40

Spatial resolution 0.05 arc sec

Spatial field 3.0 arc min along slit

Spectral resolution 5.0 pm at 1565 nm

Size 3.5 x 1.2 x 0.6 m

August 25-28, 2003 NIRSP 13

NIRSPC: Coudé Unit Specifications, f/20

Feed focal ratio F/20

Focal length 2350 mm

Slit width 20 m

Pixel size 20 m

Slit height 70 mm

Grating height 204 mm

Grating length 410 mm

Grating blaze angle 63.5°

August 25-28, 2003 NIRSP 14

Grating Illumination, f/20

• Grating illumination pattern– Feed f/20, slit 19 m, focal length 2.35 m– Grating 204 x 408 mm, tan = 2– Illumination height is from f/20; width is from slit diffraction– Light loss in wings is 18%

August 25-28, 2003 NIRSP 15

Coudé Characteristics, f/20

Spatial resolution 0.055 arc sec

Spatial field 3.0 arc min along slit

Spectral resolution 3.3 pm at 1565 nm

Size 3.0 x 1.0 x 0.5 m

August 25-28, 2003 NIRSP 16

NIRSPC Background Estimates

Disk brightness

Coronal Brightness

Warm Bkg

Cold Bkg

F/20, R=475,000, pix=0.05” x 20 micron

August 25-28, 2003 NIRSP 17

Gregorian layout

August 25-28, 2003 NIRSP 18

NIRSPG: Gregorian Unit Specifications

Feed focal ratio F/13.1

Focal length 1300 mm

Slit width 250 m

Pixel size 250 m

Slit height 70 mm

Grating height 102 mm

Grating length 206 mm

Grating blaze angle 63.5°

August 25-28, 2003 NIRSP 19

NIRSPG Background Estimates

F/13, R=20,000 pix=1”x250micron

Disk

Corona Cold Bkg

Warm Bkg

August 25-28, 2003 NIRSP 20

Gregorian Characteristics

Spatial resolution 1.0 arc sec

Spatial field 4.7 arc min along slit

Spectral resolution 52.5 pm at 1075 nm

Size 1.5 x 0.5 x 0.4 m