Diffraction, chopping, and background subtraction for LDR

Details Diffraction, chopping, and background subtraction for LDR Diffraction, chopping, and background subtraction for LDR

Aug 1988

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1988aldr.work..106w&link_type=abstract

In Jet Propulsion Lab., California Inst. of Tech., Report of the Asilomar 3 LDR Workshop p 106-109 (SEE N90-13449 05-18)

Physics

Background Radiation, Diffraction, Infrared Telescopes, Large Deployable Reflector, Transmission Loss, Fourier Transformation, Light (Visible Radiation), Sidelobes

Scientific paper

The Large Deployable Reflector (LDR) will be an extremely sensitive infrared telescope if the noise due to the photons in the large thermal background is the only limiting factor. For observations with a 3 arcsec aperture in a broadband at 100 micrometers, a 20-meter LDR will emit 10(exp 12) per second, while the photon noise limited sensitivity in a deep survey observation will be 3,000 photons per second. Thus the background subtraction has to work at the 1 part per billion level. Very small amounts of scattered or diffracted energy can be significant if they are modulated by the chopper. The results are presented for 1-D and 2-D diffraction calculations for the lightweight, low-cost LDR concept that uses an active chopping quaternary to correct the wavefront errors introduced by the primary. Fourier transforms were used to evaluate the diffraction of 1 mm waves through this system. Unbalanced signals due to dust and thermal gradients were also studied.

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