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Question a question about gps/pos for gaussian beam geometry 

Forum: Space Applications
Date: 10 May, 2017
From: <Claire>

Hello I have a question about : gps/pos/ I would like to model a monochromatic beam with a Gaussian geometry (Gaussian symmetric shape in a XY plane perpendicular to the direction of propagation Z). The FWHM is the same in both directions X and Y, of 1 micrometer. So sigma = 1/2.355 =0.4246 micrometers. The beam is purely Gaussian, there is no central circular plateau.

Example 31 of the Gant4 toolkit is very close to what I would like to do:

# the beam spot is centered at the origin and is

# of 1d gaussian shape with a 1 mm central plateau

/gps/pos/shape Circle

/gps/pos/centre 0. 0. 0. mm

# Should I comment this line? /gps/pos/radius 1. mm

/gps/pos/sigma_r .4246 um

So my question is: Should I comment the line with radius, since our beam does not have a central plateau? Or should I take a radius with a very small value compared to sigma_r ? (otherwise we would define a circle shape without radius, which would maybe be not possible ?)Or is there another shape than "circle" for a pure Gaussian shape ? Thank you

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