Post on 31-Dec-2015
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 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