From: Merle Hirsh <plasma@pop3.frontiernet.net>
Newsgroups: sci.physics.plasma
Subject: Re: I need help on spectroscopy!
Date: Wed, 13 Aug 1997 10:18:08 -0400
Organization: Plasma Resources



Neodimium wrote:
>
> I need your help on spectroscopy!
>
> I’m designing a device to measure the intensity of a impurity line of a
> plasma.
> The value of the intensity line do no need to be absolute, but have a nice
> time resolution, at least 1 micro second.
>
> I have and old spectrometer, a good one, made by Mcpherson Ins. Corp.
> (model 2051)
> I do not have any output optics. But it have and old input optics, I think
> that match the f-number…
> I have either an avalanche silicon photodiode with internal amplifier, made
>
> by Hamamatsu.
>
> Obviously it look easy: only I need to do it is to buy an output lens and
> insert the light on the photodiode.
>
> But How I know that I’m capturing all the impurity line?
> How I know the proportion of background light to impurity line?
> Any advice will be thanks given
>
> My Best Regards
>
> Neodimium
>
> I speak by my self. telf: +351-1-8417696
> peres@cfn.ist.utl.pt fax: +351-1-8417819

If the impurity line and the background light have the same spatial
dependence, You can expect the ratio of impurity intensity to total
background light to be a function only of the impurity oncentration.
Then you can use the ratio of impurity line intensity to total light as
a relative measure of impurity concentration.

Do you expect the impurity line to have a different spatial dependence
than the background plasma emission? In other words, does the impurity
originate in the gas, or on a spatially localized surface? If it comes
from the background gas, then you can probably expect the impurity to
represent a fixed fraction of the background light, independent of
viewing geometry - unless you are using dc excitation, which could lead
to cataphoresis, segregating the impurity near the cathode.

If the background light is dominated by one strong line, you might use
the ratio of the impurity line to that strong line as a RELATIVE measure
of impurity concentration. Otherwise, you might integrate the total
area under the background spectrum and use that as your reference.

I will be happy to talk with you more about this.


Merle Hirsh