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.

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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

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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)