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Forum: Processes Involving Optical Photons
Re: Question question regarding PMT photocathode and quantum efficiency (Athreya Shankar)
Re: More Re: question regarding PMT photocathode and quantum efficiency (Athreya Shankar)
Date: 17 Jul, 2012
From: Gumplinger Peter <Gumplinger Peter>

Athreya,

> Thus, I can use the QE characteristics of the photocathode-cum-window
> system, provided I do NOT take into account the transmittance property
> of the window material, since this is already taken care of in the
> wavelength-dependent QE values. This I can accomplish by specifying the
> ABSLENGTH property of the window to a wavelength-independent arbitrarily
> high value.

Or not specify it at all. The default AttenuationLength = DBL_MAX for any material for which "ABSLENGTH" is not defined.

> The above solution ensures that the effect of the glass window on
> transmission is taken into account, as well as ensures that the
> possibility of reflection off the glass window-scintillator surface
> interface is not lost.

ok

> However, if the photocathode reflectivity comes
> into play and the photon is reflected back into the glass window region,
> then, since we have not set the transmittance properties, the photon may
> travel around for longer than reality.

I would set the reflectivity of the photocathode to zero. The simulation is then incorrect only for the few photons that reflect from one PMT and are detected in another PMT. I don't know how often that could happen in your setup but it is probably a higher order effect and 'in the noise' compared to some other uncertainties you have in your simulation - like wall reflectivities etc.

> Is my reasoning correct ?

yes, I'd say.

Peter

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