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Chantal Wang, Madeline Dawes, Advisor: Lawrence Wiencke, Patrick Reardon
Analyzing Optical System for Cherenkov Telescope for NASA EUSO-SPB2
Introduction/Background
1m Beam System
Model Creation and Analysis Objectives
Results:
Analysis
The Extreme Universe Space Observatory on a Super Pressure
Balloon II (EUSO-SPB2) mission will fly two telescopes
detecting high energy astroparticles. The Fluorescence
telescope will measure Ultra High Energy Cosmic Rays
(UHECRs) The Cherenkov telescope will search for neutrinos.
The launch is planned for 2023 from New Zealand.
2
The test beam system features a parabolic 1m mirror to
produce a 1m beam of parallel light to fully illuminate the
aperture of the flight telescopes during lab testing. This works
like a backwards Newtonian telescope with a fiber bundle at
the focus. The 1m test beam system collimation was tested by
Madeline Dawes.
In the Cherenkov telescope
system, light from the fiber
bundle is collimated by a
parabolic mirror, then sent
through the ACP and to a
spherical mirror which
focuses it to the sensor
array.
EUSO-SPB2 Opto-Mechanical
PMPrimaryMirrorACPAchromaticCorrectorPlate
PMRadiusofCurvatureis1659.8mm
The fiber bundle outputs light in nine beams of INSERT
WAVELENGTH light. This was modeled as nine fields of light,
and displaced both on and off axis for analysis. The 1m test
beam system uses a reverse Newtonian telescope system with
a parabolic mirror to collimate the light for the Cherenkov
system
The ACP is a fourth order lens that minimizes the chromatic and spherical aberration
the spherical mirror creates. Tests were run without ACP to see its effect on the
system.
1. The Pierre Auger Collaboration. The Cosmic Ray Energy Spectrum and Related
Measurements
with the Pierre Auger Observatory. The Pierre Auger Observatory: contributions
Submissions to
the 31st International Cosmic Ray Conference, June 2009.
2. FSU High Energy Physics, “What Are Cosmic Rays?” http://www.hep.fsu.edu/
wahl/Quarknet/summer2015/lectures/CosmicRayIntrod.pdf, date accessed 27 September
2020
3. T. Dorigo, The Highest-Energy Cosmic Rays From Auger, date accessed 27 September
2020
4. Pierre Auger Observatory, “How many cosmic rays strike the ground each second?”,
date
accessed 1 October 2020
5. University of Chicago, “EUSO-SPB Project”,
https://eusospb.uchicago.edu/instrument.php, date
accessed 29 September 2020
6. L. Wiencke, A. Olinto, ”The Extreme Universe Space Observatory on a Super-
Pressure Balloon II Mission”,https://pos.sissa.it/358/466/pdf, date accessed 29 September
2020
2
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1) Verify the optics design by simulating the point spread function (PSF) using the
industry standard ray tracing Zemax OpticStudio software
2) Incorporate the 1m Test Beam system into the simulation and estimate the sensitivity
of the PSF to the fiber bundle positioning, to test mirror’s light source
3) Estimate the sensitivity of focusing to positioning of the sensor array
4) Explore other aspects of system, and provide PSFs for points along optical axis of
sensor array
Sensor array displacement: focus sensitivity
Fiber bundle displacement: how fields
change focus
OpticStudio provides a few types of Point Spread Function (PSF) analyses, which
allows the user to see the spot diagrams of how light is absorbed by the image
surface (sensor array), and a 3D histogram of how many rays hit at each point across
the image surface. P
The
Fluorescence
telescope has
previously been
modeled by Dr.
Reardon.
Spot Diagram results at the
sensor array, using 355 nm
light. Spot size is approximately
0.4 mm in diameter.
Analysis also repeated with all
expected wavelengths.
Observing a point on the PSF
assumes the optics and
alignments are perfect.
The spot diagram type of point spread function
analysis was chosen as it will reproduce what
the scanner will produce when the system is
built and tested with a camera scanner over the
summer. The radius of the spot also allows for
focal point determination.
Another option was this histogram that can
be used in the future for analysis of
specific shapes of detected light.
1m Test Beam SystemCherenkov Flight Telescope
ACP
Sensor Array
Primary Spherical Mirror
References
Analysis Objectives
This graph shows that the
smallest spot diagram radius,
and thus the best focal point,
does not occur where the
design has placed it. For the
best focus, the fiber bundle
should be moved on- axis
about 4mm away.
The PSF functions provide a
Root Mean Squared (RMS)
radius for where most of the
light is in the spot, and a
Geometric radius (GEO) which
encompasses all rays of light.
The RMS radius is more
efficient for our analysis
purposes.
PM = Primary Spherical Mirror
IMA = Image Plane (Sensor
Array)