Re: Q: aging of absorptive neutral density (ND) filter

"Barry Cense" <barry_in_boston@xxxxxxxxxxx> writes:

Could you explain us more about this effect? Why does the transmission
change as a function of time?

I assume it's a thermal effect - the power absorbed in the filter heats it
and changes the density or the transmission properties in some other
respect. The effects I'm describing are reversible. But it's definitely
annoying if using the ND filter in front of a power meter sensor!

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The bit about them being non-linear is something many people don't realize.

If you shoot a high power beam at many ND filter materials, the transmission
will change (up or down) over a few seconds depending on the power density.

Thus, using an ND filter in front of a photodiode to increase its power
handling has to be done with that knowledge. Just any old ND filter may
result in undesirable behavior.

--- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
.

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