a geant4 based engineering tool for fresnel lenses...a geant4 based engineering tool for fresnel...

A Geant4 based engineering tool for Fresnel lensesJoão Costa1, Mário Pimenta2, Bernardo Tomé2

1-Laboratoire de l’Accélérateur Linéaire, IN2P3-CNRS et Université Paris-Sud 11, Centre Scientifique d’Orsay, B. P. 34, 91898 Orsay, Cedex, France.2-Laboratório de Instrumentação e Física Experimental de Partículas, Av. Elias Garcia, 14–1, 1000-149 Lisboa, Portugal.

bernardo@lip.pt

Geant4 is a simulation toolkit including optical-photon tracking in complex 3D geometries. This ca-pability was explored to develop a simulation tool for Fresnel lenses. This tool can be used on stand-alone design and optimization studies or integrated in a full Geant4-based detector simulation.

R

∆Z

R

FRESNEL LENS GEOMETRY IMPLEMENTATIONVRML visualization of a simulated Fresnel lens consisting of a cen

tral mo

no

lithic len

s and

two

layers of p

etals

Possibility of simulating monolithic or segmented lenses

X (mm)

-30-20

-100

1020

30Y (mm)

-30-20

-100

1020

300

50

100

150

200

250

300

Lens-Detector distance (mm)1950 2000 2050 2100 2150 2200 2250

PSF

radi

us (m

m)

0

2

4

6

8

10

12

14 320 nm

400 nm

500 nm

600 nm

Radius (cm)0 10 20 30 40 50 60 70 80 90 100

Det

ectio

n e�

cien

cy

0.5

0.6

0.7

0.8

0.9

1

No bulk absorption

With bulk absorption

Realistic incident ligth spectrum;

Effects of finite groove size ;

VRML visualization of a simulated Fresnel lens illustrating the focusing of on-axis light

Each facet of the Fresnel lens is built from a piece of the original lens surface translated to the flat side of the lens

The lens geometry is described in Geant4 through a para- meterized replication of conical shaped facets (G4Cons vo-lumes)

SIMULATIONS TAKE INTO ACCOUNT:

Study of light detection efficiency and assessment of the effect of grooved lens structure onto light throughput (bottom left)

Study of point spread function (PSF) for varying focal distance and wavelength (bottom right);

PERFORMANCE STUDIESINCLUDE:

Example of simulated point spread function