Blake G. Crowther

Qualification of quantum cascade lasers for space environments

Laser-based instruments are enabling a new generation of scientific instruments for space environments such as those used in the exploration of Mars. The lasers must be robust and able to withstand the harsh environment of space, including radiation exposure. Quantum cascade lasers (QCLs), which are semiconductor lasers that emit in the infrared spectral region, offer the potential for the development of novel laser-based instruments for space applications. The performance of QCLs after radiation exposure, however, has not been reported. We report on work to quantify the performance of QCLs after exposure to two different radiation sources, 64 MeV protons and Cobalt-60 gamma rays, at radiation levels likely to be encountered during a typical space flight mission. No significant degradation in threshold current or slope efficiency is observed for any of the seven Fabry-Perot QCLs that are tested.

Thermo-opto-mechanical analysis of a cubesat lens mount

A potential cubesat payload for low resolution study of planet Earth from space is an optical imaging system. Due to budget, space, and time constraints, commercial photographic lenses of the double Gauss type are prime candidates for limited duration cubesat optics. However, photographic objectives are not designed to operate in a space environment and modifications are usually necessary. One method of improving optical performance of the objective over large temperature variations is by replacing the stock lens mount with a different material. This paper describes the thermo-opto- mechanical analysis of several lens mount materials for a double Gauss imaging system suitable for a cubesat.

Sensor design and capabilities for the Russian American Observational Satellites (RAMOS)

RAMOS, the Russian American Observational Satellite program, is a cooperative space-based research and development program between the Russian Federation and the United States. The planned system configuration is a constellation of two satellites orbiting in approximately the same plane at an altitude of about 500 km, separated from one another by a variable distance centering on about 500 km. These satellites are equipped with passive electro-optical sensors, both US- and Russian-built, that operate over a range from infrared (IR) to ultraviolet (UV) and are designed for near-simultaneous stereo imaging capability. The sensor suite will include visible, IR and UV imaging radiometers, an IR spectrometer, and a short-wave infrared (SWIR) polarimeter. The projected launch date is 2008 with a planned minimum on-orbit lifetime of two years, and a five-year lifetime possible. This paper summarizes the program objectives, anticipated measurements and expected data, and presents the basic system design, expected performance characteristics, and the capabilities of each of the sensors.

Toward end-to-end optical system modeling and optimization: a step forward in optical design

Optical system modeling is interdisciplinary by its very nature. Optics, thermal engineering, structural engineering, control systems, electrical engineering, and data analysis are among the disciplines required to perform such modeling. Each discipline tends to have various software tools at its disposal to perform the required design and analysis but the software tools have had only limited ability for interdisciplinary use. Optical design software can form the core for optical systems modeling in many instances but its capabilities must be extended, or it needs to be used in a non-traditional way, depending on the problem at hand. We have used optical design software to assist in or form the basis for solving a number of interdisciplinary optical systems modeling problems. As an example, we present our method of dynamic optical ray tracing here and show its application. We also mention an example of linking optical design software to external code to solve optical systems modeling problems. Although these modeling efforts were successful, they illustrate the associated difficulty and need for integrated software modeling tools.

Cryogenic optical design and testing of the focal plane optomechanical assembly for the Tropospheric Emission Spectrometer

The Tropospheric Emission Spectrometer (TES) is one of the instruments slated to fly on the EOS Aura satellite in 2003. TES is a Fourier transform spectrometer designed to measure the concentration of various tropospheric chemical species. The Focal Plane Opto-Mechanical Assemblies (FPOMAs) are situated at the end of the TES optical train and are comprised of cryogenic telescopes, reimaging optics, and focal planes. We present the cryogenic optical design of the FPOMA units and discuss optimization parameters and predicted performance. We present measured performance data and compare it with the predicted performance.

DIAL System for Fugitive Gas Detection at Energy Production Sites

A mobile DIAL system capable of measuring carbon dioxide (CO2), methane (CH4), and aerosols has been developed. A system overview of the DIAL instrument and some representative results will be presented.

Optical system materials selection using performance indices in a simultaneous optimization approach

Optical systems are designed for a great variety of purposes and are influenced by significantly differing requirements. Due to these differences, material trade studies are part of almost all optical system designs. These trade studies must use objective comparative parameters in order to choose the best optical and structural materials for the optical system. Material figures of merit such as specific stiffness and thermal stability are traditional figures of merit used in materials trade studies. In this paper, we explore additional material figures of merit arising from both technical and programmatic concerns. We show how to use all of these figures of merit simultaneously in a systematic approach to optimum materials selection.

Cryogenic infrared radiometer for transferal of NIST radiometric standards

The Space Dynamics Laboratory at Utah State University designed and constructed two identical cryogenic mid- infrared radiometers that will be used as NIST-traceable radiometric calibration transfer standards. The radiometer design is similar to the NIST BXR radiometer and thus may be calibrated at NIST using the same sources and procedures used with the BXR. Important features of these radiometers include a single element, chopped indium antimonide detector cooled by a Stirling-cycle cryocooler, two 8-position filter wheels populated with spectral and neutral density filters, and an indium antimonide focal plane array (FPA) that can be temporarily positioned at the field stop for alignment and diagnostics. This paper presents the design and results of the as-built optical and thermal performance of these radiometers. It also presents the testing set up and calibration philosophy and approach.