73 research outputs found
Baseline Requirements For Detecting Biosignatures with the HabEx and LUVOIR Mission Concepts
A milestone in understanding life in the universe is the detection of
biosignature gases in the atmospheres of habitable exoplanets. Future mission
concepts under study by the 2020 decadal survey, e.g., HabEx and LUVOIR, have
the potential of achieving this goal. We investigate the baseline requirements
for detecting four molecular species, HO, O, CH, and CO,
assuming concentrations of these species equal to that of modern Earth. These
molecules are highly relevant to habitability and life on Earth and other
planets. Through numerical simulations, we find the minimum requirements of
spectral resolution, starlight suppression, and exposure time for detecting
biosignature and habitability marker gases. The results are highly dependent on
cloud conditions. A low-cloud case is more favorable because of deeper and
denser lines whereas a no-cloud case is the pessimistic case for its low
albedo. The minimum exposure time for detecting a certain molecule species can
vary by a large factor (10) between the low-cloud case and the no-cloud
case. For all cases, we provide baseline requirements for HabEx and LUVOIR. The
impact of exo-zodiacal contamination and thermal background is also discussed
and will be included in future studies.Comment: 15 pages, 5 figures, 1 table, accepted by JATI
Wavefront control for minimization of speckle coupling into a fiber injection unit based on the electric field conjugation algorithm
A fiber injection unit situated in the focal plane behind a coronagraph feeding a high resolution spectrograph can be used to couple light from an exoplanet to obtain high resolution spectra with improved sensitivity. However, the signal-to-noise ratio of the planet signal is limited by the coupling of starlight into the single mode fiber. To minimize this coupling, we need to apply a control loop on the stellar wavefront at the input of the fiber. We present here a wavefront control algorithm based on the formalism of the Electric Field Conjugation (EFC) controller that accounts for the effect of the fiber. The control output is the overlap integral of the electric field with the fundamental mode of a single mode fiber. This overlap integral is estimated by sending probes to a deformable mirror. We present results from simulations, and laboratory results obtained at the Caltech Exoplanet Technology Lab’s transmissive testbed. We show that our approach offers a significant improvement in starlight suppression through the fiber relative to a conventional EFC controller. This new approach improves the contrast of a high contrast instrument and could be used in future missions
Observing Exoplanets with High-Dispersion Coronagraphy. II. Demonstration of an Active Single-Mode Fiber Injection Unit
High-dispersion coronagraphy (HDC) optimally combines high contrast imaging
techniques such as adaptive optics/wavefront control plus coronagraphy to high
spectral resolution spectroscopy. HDC is a critical pathway towards fully
characterizing exoplanet atmospheres across a broad range of masses from giant
gaseous planets down to Earth-like planets. In addition to determining the
molecular composition of exoplanet atmospheres, HDC also enables Doppler
mapping of atmosphere inhomogeneities (temperature, clouds, wind), as well as
precise measurements of exoplanet rotational velocities. Here, we demonstrate
an innovative concept for injecting the directly-imaged planet light into a
single-mode fiber, linking a high-contrast adaptively-corrected coronagraph to
a high-resolution spectrograph (diffraction-limited or not). Our laboratory
demonstration includes three key milestones: close-to-theoretical injection
efficiency, accurate pointing and tracking, on-fiber coherent modulation and
speckle nulling of spurious starlight signal coupling into the fiber. Using the
extreme modal selectivity of single-mode fibers, we also demonstrated speckle
suppression gains that outperform conventional image-based speckle nulling by
at least two orders of magnitude.Comment: 10 pages, 7 figures, accepted by Ap
Baseline requirements for detecting biosignatures with the HabEx and LUVOIR mission concepts
A milestone in understanding life in the universe is the detection of biosignature gases in the atmospheres of habitable exoplanets. Future mission concepts under study by the 2020 decadal survey, e.g., HabEx and LUVOIR, have the potential of achieving this goal. We investigate the baseline requirements for detecting four molecular species, H_2O, O_2, CH_4, and CO_2. These molecules are highly relevant to habitability and life activity on Earth and other planets. Through numerical simulations, we find the minimum requirement for spectral resolution (R) and starlight suppression level (C) for a given exposure time. We consider scenarios in which different molecules are detected. For example, R = 6400 (400) and C = 5 × 10^(−10) (2 × 10^(−9)) are required for HabEx (LUVOIR) to detect O_2 and H_2O for an exposure time of 400 hours for an Earth analog around a solar-type star at a distance of 5 pc. The full results are given in Table 2. The impact of exo-zodiacal contamination and thermal background is also discussed
Demonstration of an electric field conjugation algorithm for improved starlight rejection through a single mode optical fiber
Linking a coronagraph instrument to a spectrograph via a single mode optical
fiber is a pathway towards detailed characterization of exoplanet atmospheres
with current and future ground- and space-based telescopes. However, given the
extreme brightness ratio and small angular separation between planets and their
host stars, the planet signal-to-noise ratio will likely be limited by the
unwanted coupling of starlight into the fiber. To address this issue, we
utilize a wavefront control loop and a deformable mirror to systematically
reject starlight from the fiber by measuring what is transmitted through the
fiber. The wavefront control algorithm is based on the formalism of electric
field conjugation (EFC), which in our case accounts for the spatial mode
selectivity of the fiber. This is achieved by using a control output that is
the overlap integral of the electric field with the fundamental mode of a
single mode fiber. This quantity can be estimated by pair-wise image plane
probes injected using a deformable mirror. We present simulation and laboratory
results that demonstrate our approach offers a significant improvement in
starlight suppression through the fiber relative to a conventional EFC
controller. With our experimental setup, which provides an initial normalized
intensity of in the fiber at an angular separation of
, we obtain a final normalized intensity of in
monochromatic light at ~nm through the fiber (100x suppression
factor) and in broadband light
about ~nm (10x suppression factor). The fiber-based approach
improves the sensitivity of spectral measurements at high contrast and may
serve as an integral part of future space-based exoplanet imaging missions as
well as ground-based instruments
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