Coherent Detector for Near-Angle Scattering and Polarization Characterization of Telescope Mirror Coatings

Macenka, Steven A.; Chipman, Russell A.; Daugherty, Brian J.; McClain, Stephen C.

A report discusses the difficulty of measuring scattering properties of coated mirrors extremely close to the specular reflection peak. A prototype Optical Hetero dyne Near-angle Scatterometer (OHNS) was developed. Light from a long-coherence-length (>150 m) 532-nm laser is split into two arms. Acousto-optic modulators frequency shift the sample and reference beams, establishing a fixed beat frequency between the beams. The sample beam is directed at very high f/# onto a mirror sample, and the point spread function (PSF) formed after the mirror sample is scanned with a pinhole. This light is recombined by a non-polarizing beam splitter and measured through heterodyne detection with a spectrum analyzer. Polarizers control the illuminated and analyzed polarization states, allowing the polarization dependent scatter to be measured. The bidirectional reflective or scattering distribution function is normally measured through use of a scattering goniometer instrument. The instrumental beam width (collection angle span) over which the scatterometer responds is typically many degrees. The OHNS enables measurement at angles as small as the first Airy disk diameter.

Document ID

20120006573

Acquisition Source

Jet Propulsion Laboratory

Document Type

Other - NASA Tech Brief

External Source(s)

http://www.techbriefs.com/component/content/article/12660

Authors

Date Acquired

August 25, 2013

Publication Date

January 1, 2012

Publication Information

Publication: NASA Tech Briefs, January 2012

Subject Category

Report/Patent Number

Distribution Limits

Public

Public Use Permitted.

Available Downloads

Name

Type

20120006573.pdf

STI

No Preview Available

NTRS

NTRS - NASA Technical Reports Server

Available Downloads

Related Records