Tuesday, November 21, 2017

JOST: assembled testbed and its components

JOST, the James Webb Space Telescope (JWST) Optical Simulation Testbed, was designed to test wavefront sensing and control algorithms on segmented apertures. Its optical properties model the key optical aspects of the JWST, as it provides JWST-like optical quality over a field equivalent to a NIRCam module. It successfully produces images extremely similar to NIRCam images from cryotesting in terms of the point spread function (PSF) morphology and sampling relative to the diffraction limit. The components of JOST are detailed below.

  • Fiber launch & off-axis parabola (OAP): The OAP collimates the beam from a fiber launch.
  • Beam Capture Mirror: Capturesthe beam from the OAP and sends it onto the steering mirror.
  • Steering Mirror: Controls the field position of the laser beam.
  • Pupil aperture: JWST-like pupil, conjugated with the deformable mirror (DM) with struts and a hexagonal central obscuration.
  • Cooke Triplet of L1, L2, L3: The three custom lenses build a refractive analogue to the JWST three mirror anastigmat (TMA). L2 is motorized for movement in x, y, z translation and tip and tilt.
  • Fold mirror: Folds the beam to fit the testbed on the optical table.
  • Iris AO segmented DM: 37 hexagonal segments that can be individually controlled in piston, tip, and tilt. The pupil limits the beam to 19 active segments and the segment gaps are 10-12 um (~0.1% of the 1.4 mm segment size), which makes them to scale with the actual JWST geometry.
  • CCD camera: A CCD camera is mounted on a translation stage to allow for the acquisition of focused and defocused images.

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