[Laser] Laser Digest, Vol 87, Issue 2

Dave wa4qal at ix.netcom.com
Wed Mar 14 13:27:05 EDT 2012


On 2012-03-14 12:02 PM, laser-request at mailman.qth.net wrote:
> Date: Tue, 13 Mar 2012 12:48:27 -0700 (PDT)
> From: Tim Toast<toasty256 at yahoo.com>
> Subject: Re: [Laser] Strange effect
> To: laser at mailman.qth.net
> Message-ID:
> 	<1331668107.60289.YahooMailClassic at web37907.mail.mud.yahoo.com>
> Content-Type: text/plain; charset=iso-8859-1
>
> Hi Yves
> I would have to agree with the other responces you got and say the photodiode is emitting 1 or 2 microns and the pyrodetector is either seeing the 2 micron weakly (at the upper edge of its bandwidth) or is just responding to the heat generated near 10 microns. The germanium detector is seeing the radiation directly and so has the best responce. Makes sense :-) ...it is still strange to see a detector emit light at such a far removed wavelength, when LED's detect at almost the same wavelength - differences in construction i imagine.

As best as I remember, Silicon is not a direct-band-gap semiconductor, 
while Gallium Arsenide (etc.) are.  As such, while Gallium Arsenide will 
emit and detect at the same
wavelength, Silicon won't.  With Silicon, it will detect at near the 
band-gap energy, but
it won't emit there, due to the non-direct transition.

Please check me out on this, though.  It's been a LONG time since I've 
performed
any research with regards to Silicon and the indirect band-gap 
transition.  But, this
may give some terms to search on.

> -toast

Dave


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