Parasitic-light in NGST instruments: Issues

Scientific requirements

• Types of SED expected in 1-5 micron range: bluest/reddest
• Spectral purity: deep absorption lines
• High contrast requirements

Diffraction/scattering

This is of most relevance to the spectrographs.

• The focal plane
  • Micro-mirrors
  • Micro-shutters
  • Image slicers
  • Other devices: fibres, lenslets...
• Dispersing elements
  • Reflection gratings
    • O-order wings (~50%)
    • I-order wings (~50%)
    • Ruling profiles: blaze efficiency vs. ghosting levels
    • Emission lines in higher orders
  • Grisms
  • Prisms
• Spectrograph optics
  • Baffling
  • f-ratios

Bandpass blocking

Of relevance to both cameras and spectrographs

• Blocking/order-sorting filters
• Dichroics
• Detector sensitivity bandpass
• Bright source handling