----- Original Message -----
From: "Jon Baker" <jon@HAYSEED.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Friday, January 18, 2002 12:12 PM
Subject: Re: [EE]: photodetectors ( tag changed from OT)


> The wavelengths I am looking for are:
>
> 545nm 570nm 600nm and 620nm if this might make any difference to the best
> way to proceed..

You could probably find LEDs with peak output very close to those
wavelengths (many flavours exist in the yellow through red range).
Connect a LED with anode to ground and measure current at the cathode caused
by photons hitting the LED. You will need to amplify the signal a lot with
op-amps. I have not tried this...You may end up just measuring thermal noise
and ionizing radiation events.
/\/\/\/*=Martin

>
> > Jon Baker wrote:
> > >
> > > I am working on a similar but slightly more complex project at the
> moment
> > > which needs to detect 4 different wavelengths of light emitted from a
> sample
> > > luminescing. The amplitude ( brightness??) of the light at each
> frequency
> > > must be measured independently so I can draw 4 graphs- each frequency
> > > corresponds to a particular molecule and the graph is to show the
> > > concentrations ( brightness ) with time of each. I am positive this
> can't be
> > > done with filters over photo detecetors becuase the number of photons
I
> need
> > > to detect is so small it would be absorbed into the filter. What would
> be
> > > ideal is a several photodetectors each of which is sensitive to a
> > > (different) narrow band of wavelengths. Does anyone have any pointers
> where
> > > I could look for such specific devices?
> > >
> > > I had thought of using a CCD, but with all 4 wavelengths being
measured
> by
> > > the same device I think it would be almost impossible to extract the 4
> sets
> > > of data I need from the RGB value the CCD would give me.
> > >
> > > Any help much appreciated.
> > >
> > > --
> > > Jon Baker
> > >
> >
> > --
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