Research Highlights: September 2018

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Advances in Optical Scatter Metrology in the NASA GSFC Code 618 Diffuser Calibration Laboratory

James J. Butler1, and Jinan Zeng2

(1: Biospheric Sciences Laboratory NASA GSFC, 2: Fibertek Inc.)

Figure 1
A next generation optical scatterometer has been built and is completing full commissioning in Code 618 Diffuser Calibration Facility. In addition to providing all measurement capabilities of existing, previous scatterometer, this new instrument incorporates advances in light sources, sample stage, and detectors resulting in lower uncertainty and improved efficiency in the measurement of optical scatter in support of satellite, ground-based and airborne remote sensing projects and programs.

Name: James J. Butler, Biospheric Sciences Laboratory, NASA GSFC
Phone: 301-614-5942


Data Sources:

Technical Description of Figures

The figure shows the next generation optical scatterometer located in the NASA GSFC Code 618 Diffuser Calibration Laboratory. The suite of light sources for the scatterometer are shown in the figure on the left. These light sources include an Energetiq 99 (EQ99) laser discharge light source (LDLS) and NKT Supercontiuum Laser Source (SLS) with monochromator, two NKT SLS units with NKT Acousto-Optic Tunable Filters (AOTF), two SLS units with Photon Etc. Laser Line Tunable Filters (LLTF), an EQ99 with fixed λ uv/blue filters, five power stabilized single wavelength diode lasers, and an SLS unit operated as a white light source. The yellow line in the figure represents the common beam path for these sources with individual sources deployed using specific 90° flip folding mirrors along the beam path. These light sources enable the measurement of both specular and diffuse optical samples and materials used in instruments and spacecraft over the 250 to 2400 nm wavelength range. The detector, sample, and goniometric stages are shown in the figure on the right. Detectors include silicon photodiodes for the UV/VIS/NIR, standard InGaAS for the 1000 to 1700nm range, extended InGaAs for the 1000 to 2400nm range, and two modular scanning spectrometers from the UV through SWIR. Ultimately, the goniometric stages will be replaced by the Mitsubishi robot arm shown in the bottom right of the figure.

Scientific significance, societal relevance, and relationships to future missions:

Since its inception in May 1993, the NASA GSFC Code 618 Diffuser Calibration Laboratory (DCaL) has provided NIST-traceable, optical scatter measurements on transmissive or reflective, specular or diffuse optical elements and materials to more than 54 Earth and space remote sensing projects. As such, the laboratory is internationally recognized as a leader in measurement of optical scatter over the 250 nm to 2400 nm (i.e. reflected solar) wavelength range. In an effort to expand measurement capabilities and improve measurement efficiency in accordance with established customer launch and flight schedules, the laboratory has built and is completing full commissioning of its next generation scatterometer. This instrument incorporates advanced light sources such as supercontinuum lasers with and without acousto-optical and laser-line tunable filters and laser discharge white light sources. In addition, the instrument will be able to measure hyperspectral optical scatter using modular scanning spectrometers as detectors. The final upgrade to the instrument will be replacement of the multi-stage sample goiniometer with a monolithic robot-arm. The next generation scatterometer was recently used to provide scatter measurements to the Raytheon JPSS-1 VIIRS program and the NASA/GSFC Code 546 Contamination and Coatings Engineering Branch. The lab is currently scheduled to support the NASA GSFC PACE OCI, WFIRST, and RESTORE programs and the Raytheon JPSS-2 VIIRS and BATC JPSS-2 OMPS programs.