Multimode illumination for speckle reduction and angle neutrality in millimeter wave active imaging: range and time-resolved mode averaging.

Abstract

Active illumination is an attractive approach for millimeter and submillimeter wave imaging because of its generally larger signal margins and capacity for range determination. However, the resultant speckle from diffuse targets and the requirement that specular targets have strategic angular alignment are significant shortcomings. As a result, many, if not most, demonstrations of active imaging have involved the use of strategically oriented specular targets. We have previously shown [J. Opt. Soc. Am. A29, 2643 (2012)10.1364/JOSAA.29.002643JOAOD61084-7529] that spatially time-resolved modulated multimode mixing approaches mitigate these issues. In this paper, we extend this work to demonstrate the use of range resolved multimode mixing as an alternative means to provide statistically independent images for speckle reduction averaging. We also demonstrate the use of systematic illumination of spatial modes in a "grassy field" geometry.