Re: spurios transmission artefatcs

its the back-thinned detector, due to the silicon becoming semi-transparent
when you go into the near IR. The thin silicon layer in back thinned
devices, then acts like a rather
poor etalon. Apparently I need a "deep depletion" CCD to get around this,
or use a front illuminated device and sacrifice quantum efficiency.

Will have a go at calibrating it out, or removing it using Fourier
filtering.




"Helpful person" <rrllff@xxxxxxxxx> wrote in message
news:1195048476.796502.80860@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Nov 13, 1:47 pm, "davros" <smartin...@xxxxxxxxxxx> wrote:
Hi

I am building an optical system, a spectrometer to be precise, it is to
work
between 800 and 1000 nm. The problem I am having is when I introduce
broadband light from a filament bulb into the system, instead of seeing a
smooth curve, there is a 10 % modulation on top of the signal which
varies
across the range of the spectrometer. The period of this is about 10 nm.

The system consists of 3 lenses (currently AR coated and optimised for
the
visible). A diffraction grating optimised for 800 nm, 2 protected gold
mirrors, and some long pass filters (dichroic).

I am not sure which of the components is causing the modulation. Its'
not
the dichroic's as I have swapped those out for colour glass filters, and
the
modulation remains.
I wondered is AR coated achromats could cause this when not used at the
correct design wavelength, or is it an artefact of the diffraction
grating
which is being used at about 10 degrees more than the blaze wavelength

cheers

davros

Is the pixel separation of your detector equivalent to our ripple
frequency?

www.richardfisher



.

Quantcast