[Laser] Re : Re : Strange effect

[Garnier Yves]

Hi Tim

A pyroelectric detector is not able to détect a very slow optical decreasing and the silicon layer of the Pin photodiode used as LED has a rather small thermal inertia.

My pyroelectric detector with two reverse side cristals for thermal compensating (one of them is absorbing) is mounted as a classical K3PGP optical receiver.

A K3PGP receiver also works as a charge amplifier with the FET drain to gate capacitor as a Miller capacitance.

This enhances greatly the rising or decreasing slope of the output signal !

73

Yves F1AVY
http://f1avyopto.wifeo.com



________________________________
 De : Tim Toast <toasty256 at yahoo.com>
À : laser mailinglist <laser at mailman.qth.net> 
Envoyé le : Vendredi 16 mars 2012 12h38
Objet : [Laser] Re : Strange effect
 
Dave,
That is probably the reason. Without looking it up, that seems to ring a bell somewhere 
about silicon emitting in the deep IR. I hadn't fully realized till now that all LEDs might not 
have the near same detect + emit wavelengths. It makes me wonder how some of the 
other LED compositions  wavelengths are arranged too. I think i've read, in the 
UKnanowaves group, they had used green and blue LEDs in their (single led type) 
transceivers with good results. Those both may use gallium arsenide though, i don't 
know. I was thinking the blue LEDs used a nitride based construction.
 
Yves, 
You may be able to tell whether the pyrodetector is seeing the actual 1.1 micron 
radiation or the 10 micron heat, by turning the silicon detector on and off rapidly. 
If the pyrodetector is just seeing the heat generated, then the silicon detector should 
continue to "glow" for a short time after it is turned off (as it cools off) rather than a 
crisp instant on/off responce.. It may be sensitive to a combination of both even.
 
-toast
 
 
 
 
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