The Carbon Observatory Instrument Suite, or CARBO, consists of four carbon observing instruments sharing a common instrument bus, yet targeted for a particular wavelength band each with a unique science observation. They are: a) Instrument 1, wavelength centered at 756 nm for oxygen and solar-induced chlorophyll fluorescence (SIF) observations, b) Instrument 2, centered at 1629 nm, for carbon dioxide (CO<sub>2</sub>) and methane (CH4) observation, c) Instrument 3, centered at 2062 nm for carbon dioxide and d) Instrument 4, centered at 2328 for carbon monoxide (CO) and methane. From low-Earth orbit, these instruments have a field-of-view of 10 to 15 degrees, and a spatial resolution of 2 km square. These instruments have a spectral resolving power ranging from ten to twenty thousand, and can monitor columnaverage dry air mole fraction of carbon dioxide (XCO2) at 1.5 ppm, and methane (XCH4) at 7 ppb. These new instruments will advance the use of immersion grating technology in spectrometer instruments in order to reduce the size of the instrument, while improving performance. These compact, capable instruments are envisioned to be compatible with small satellites, yet modular to be configured to address the particular science questions at hand. Here we report on the current status of the instrument design and fabrication, focusing primarily on Instruments 1 and 2. We will describe the key science and engineering requirements and the instrument performance error budget. We will discuss the optical design with particular emphasis on the immersion grating, and the advantages this new technology affords compared to previous instruments. We will also discuss the status of the focal plane array and the detector electronics and housing. Finally, we report on a new approach – developed during this instrument design process - which enables simultaneous measurement of both orthogonal polarization states (S and P) over the field-of-view and optical bandpass. We believe this polarization sensing capability will enable science observations which were previously limited by instrumental and observational degeneracies. In particular: improved sensitivity to all species, better sensitivity to surface polarization effects, better constraints on aerosol scattering parameters, and superior discrimination of the vertical distribution of gases and aerosols.
To achieve and maintain excellent imaging performance, the Next Generation Space Telescope (NGST) will employ image-based phase retrieval methods to control its segmented primary mirror. In this paper, we present the experimental validation of a focus-diverse wave front sensing (WFS) algorithm with comparative interferometric measurements of a perturbed test mirror. Using sets of defocused point-spread functions measured with the NGST phase retrieval camera, we estimate the aberrations of the test optic in a perturbed and unperturbed state. Interleaved with the focus-diverse sets, we measure the surface figure of the mirror using a ZYGO interferometer. After briefly reviewing the basic WFS algorithm and describing the experimental setup, we show that we can obtain agreement that is better than 1/100th of a wave rms in the difference of the wave front estimates obtained in the perturbed and unperturbed states. Although this experiment does not establish the errors that are solely attributable to our WFS approach, it nevertheless validates the accuracy of our image-based methods for NGST, demonstrating that they are generally competitive with standard industrial optical metrology instruments.
To accomplish micro-arcsecond astrometric measurement, stellar interferometers such as SIM require the measurement of internal optical path length delay with an accuracy of ~10 picometers level. A novel common-path laser heterodyne interferometer suitable for this application was proposed and demonstrated at JPL. In this paper, we present some of the experimental results from a laboratory demonstration unit and design considerations for SIM's internal metrology beam launcher.
A novel scheme of a laser-based chemical sensor has been examined. The scheme is based on the lasing frequency shift of a DBR laser as a result of refractive index change of the sensitive coating in the presence of chemicals in question. The applicability and advantages of different schemes are discussed. The results of preliminary experiments related to the construction and stability of an external cavity DBR laser and interferometric measurements of refractive index change are presented.