Stray light characterization of an InGaAs anamorphic hyperspectral imager

Mike Lin,Steven W Brown,Rand Swanson,Keith R Lykke,Thomas Moon,Michael Kehoe,Casey Smith

doi:10.1364/oe.18.017510

Abstract

Compact hyperspectral sensors potentially have a wide range of applications, including machine vision, quality control, and surveillance from small Unmanned Aerial Vehicles (UAVs). With the development of Indium Gallium Arsenide (InGaAs) focal plane arrays, much of the Short Wave Infra-Red (SWIR) spectral regime can be accessed with a small hyperspectral imaging system, thereby substantially expanding hyperspectral sensing capabilities. To fully realize this potential, system performance must be well-understood. Here, stray light characterization of a recently-developed push-broom hyperspectral sensor sensitive in the 1 microm -1.7 microm spectral regime is described. The sensor utilizes anamorphic fore-optics that partially decouple image formation along the spatial and spectral axes of the instrument. This design benefits from a reduction in complexity over standard high-performance spectrometer optical designs while maintaining excellent aberration control and spatial and spectral distortion characteristics. The stray light performance characteristics of the anamorphic imaging spectrometer were measured using the spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS) facility at the National Institute of Standards and Technology (NIST). A description of the measurements and results are presented. Additionally, a stray-light matrix was assembled for the instrument to improve the instrument's spectral accuracy. Transmittance of a silicon wafer was measured to validate this approach.

Highlights

The emerging class of lightweight and inexpensive small uninhabited aerial vehicles (UAVs) has advantages over larger platforms due to smaller radar cross-sections, increased air maneuverability, greater portability and decreased monetary and personnel risk if lost
This paper describes measurements taken at National Institute of Standards and Technology (NIST)’s SIRCUS facility that were used to construct stray light correction matrices to remove measurement errors introduced by scattered light [6,7,8]
The anamorphic imaging spectrometer eliminates the focus along the long axis of the slit by using anamorphic optics that have no optical power along the long dimension of the slit

Summary

Introduction

The emerging class of lightweight and inexpensive small uninhabited aerial vehicles (UAVs) has advantages over larger platforms due to smaller radar cross-sections, increased air maneuverability, greater portability and decreased monetary and personnel risk if lost. Advances in the design of small, lightweight hyperspectral imagers are necessary to meet the payload requirements of small UAVs. systems utilizing un-cooled InGaAs focal plane arrays (1μm – 1.7 μm) provide access to much of the Short Wave InfraRed (SWIR) spectral regime. Systems utilizing un-cooled InGaAs focal plane arrays (1μm – 1.7 μm) provide access to much of the Short Wave InfraRed (SWIR) spectral regime To meet these needs, a small, high-performance imaging spectrometer with an InGaAs focal plane array (FPA) has been developed [1]. A small, high-performance imaging spectrometer with an InGaAs focal plane array (FPA) has been developed [1] To our knowledge, this is the first system that utilizes anamorphic optics (i.e., optics such as cylindrical lenses and mirrors that have different optical power along their two radial axes) that match the asymmetry of pushbroom imaging spectrometers [2]. Validation of this approach was demonstrated by measuring the transmission through a wafer of silicon

Imaging spectrometer description

Optical characterization

Constructing Stray Light Matrix

Corrected measurement

Discussion and conclusions