Primary objective grating telescopy & the dicer space telescope: an exploration of novel technologies and applications
Loading...
Authors
Swordy, Leaf
Issue Date
2024-05
Type
Electronic thesis
Thesis
Thesis
Language
en_US
Keywords
Physics
Alternative Title
Abstract
This thesis focuses on using large area Primary Objective Gratings (POGs) as an alternativeto the conventional lens/mirror telescope primary. Building on prior work by Thomas Ditto,
we investigate the feasibility of POG designs as compared to conventional telescope optics.
The work of this thesis is distinct from previous applications utilizing dispersive/holographic
primaries, as we attempt to utilize the high degree of chromatic distortion incurred by the
primary as a ‘feature,’ rather than a ‘bug’ in need of chromatic correction.
We begin by laying a theoretical groundwork for POG telescopy from first principles.
In doing so, we find that gratings in grazing exodus configuration (light collected from
the grating at a high exodus angle) exhibit angular resolution in the dispersion direction
that is equivalent to the grating length under the Rayleigh criterion. We define a new
figure of merit for comparison of POG architectures to conventional telescopes, termed the
‘spectral ´etendue’. We find that POG telescopes exhibit a wide array of potential benefits
including enhanced field of view, high resolution multi-object spectroscopy, and the potential
for lightweight optics deployed in space. However, these potential advantages are complicated
by difficulties of disambiguating objects in the focal plane, as well as the number of required
pixels in the focal plane to achieve the full spectral/angular resolution of the POG.
With a knowledge of these potential advantages in hand, we endeavor to find a suitable
science case for this technology. We explore the applications of Near Earth Object (NEO)
detection, as well as direct detection of Earth-like exoplanets in the local stellar neighbor-
hood. We have not yet found a ground based NEO observatory that is competitive with
conventional telescope technology. We also ruled out the use of extremely long gratings (in
isolation) as a means of detecting Earth-like exoplanets. While working on these notional
applications, a novel device for generating spatially coherent light fields is developed and
tested in the lab.
Following our failed attempts at using an extremely long grating to resolve an Earth
analogue planet, we subsequently develop an interferometric nulling coronagraph in order
to suppress the bright host star Point Spread Function (PSF). This novel coronagraph is
termed the Dispersion Leverage Coronagraph (DLC). Standard coronagraph metrics of stellar
leakage, residual optical path difference tolerance, the ‘transmission map,’ and host star PSF
leakage due to telescope pointing error/jitter are subsequently derived from first principles.
With the novel DLC technology in hand, as well as the previously developed theory for
POG telescopy, we design the POG-equipped Diffractive Interfero Coronagraph Exoplanet
Resolver (DICER), a space observatory capable of detecting Earth-like exoplanets within
a distance of 10 parsecs (pc). Our final benchmark design is shown to exhibit an angular
resolution approaching ∼ 0.1 arcseconds (the angular separation of 1AU at 10pc distance),
while plausibly being able to fit inside of a Falcon Heavy Rocket. The benchmark design
is shown to exhibit stellar leakage residuals of ∼ 10−5 for the Sun at 10pc, and a pointing
jitter limited null depth of ∼ 10−4 under the assumption of JWST fine guidance tolerances.
Ultimately, we find that thermal dust emission, both within the Solar System and
orbiting the host star, could limit the ability of DICER to detect exo-Earth candidates.
However, we find that DICER could plausibly detect up to ∼ 4 − 9 rocky planets in the
habitable zone within 10pc assuming an idealized model of dust brightness. The limitations
imposed by dust are primarily due to difficulties of overlapping background/signal spectra
in the focal plane, coupled with insufficient secondary spectroscopy to remove background
emission from exozodiacal dust.
While our benchmark DICER design ultimately fails to detect the majority of simu-
lated Earth analogue planets, it still represents a stark departure from conventional telescope
designs seeking to solve this extremely difficult science case. It may be the case that future
developments solve the current background reduction issues that put DICER at a disadvan-
tage, and the novel DLC technology may have applicability for other science cases beyond
near-Earth exoplanet detection.
Description
May2024
School of Science
School of Science
Full Citation
Publisher
Rensselaer Polytechnic Institute, Troy, NY