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Hi all,

I confess that I know nothing of the specific APDs in question.

However some years ago, I was very interested in APDs in general and, 
at that time, those that worked in the analog mode, had to operate at 
low gain (10- 100x) so that they did not run away. In this mode they 
had very high multipicative noise* and in addition, at this low field 
strength, the most likely amplification for an individual 
photoelectron (PE) was zero. (i.e., Although the photon was absorbed 
and the PE produced, the local field was insufficiently large to make 
the PE initiate a cascade). All the PE with a gain of zero 
essentially reduced the effective QE to a level much below that of 
the silicon itself.

If you increased the acceleration field enough that most PE did 
initiate a cascade, this produced a gain of maybe 10 million (+/- a 
lot, depending on where in the depletion zone the PE was produced.). 
However, you then had to quench this process (either passively, by 
putting a resistor in series with the diode, so that the current flow 
of the discharge reduced the applied voltage and terminated the 
discharge, or by using active circuits to do the same thing but with 
a shorter time-constant.) to prevent the diode from overheating.

This meant that you could only operate in a pulse-counting mode. If 
the maximum throughput of the pulse-counting circuit was 30 MHz, then 
even counting 3 photons in a 1 microsecond pixel time would lead to a 
10% chance of having missed one more pulse because of pulse pileup: a 
30% error that would become WORSE as the count-rate increased. Not 
very useful for normal confocal.

At that time, you could only get a high effective QE if you used a 
high field strength, and is you did this you had to use pulse 
counting.

It would be nice to know away around this problem but I have yet to 
hear of one.

Jim P.

*The extreme end of this trend is a single stage of the gain register 
in an EM-CCD with a gain of 1.01, a situation that produces a 
multiplicative noise almost exactly as large as the Poisson Noise 
from the same signal and effectively halves the QE.


               **********************************************
Prof. James B. Pawley,               		            Ph.  608-263-3147 
Room 223, Zoology Research Building,               
FAX  608-265-5315
1117 Johnson Ave., Madison, WI, 53706  
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3D Microscopy of Living Cells Course, June 14-26, 2008, UBC, Vancouver Canada
Info: http://www.3dcourse.ubc.ca/	         Applications still 
being accepted
	       "If it ain't diffraction, it must be statistics." Anon.


>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
>Hi Dale,
>    Yes, I contacted them in the first place, as they have the best 
>PMT (in my opinion). But the APD they recommend me is really not 
>good (C5460) -- 2-3 times weaker signal than the PMT. I think APD 
>should perform better than PMT in 800nm region, and that's why many 
>reflective confocal setup uses APD (well, also APD should be 
>cheaper).
>
>Best regards,
>Peng Xi Associate Professor
>Institute for Laser Medicine and Biophotonics
>Shanghai Jiao Tong University
>800 Dongchuan Rd.
>Shanghai 200240, China
>Tel: (86) 21-3420-4076
>http://biophotonics.sjtu.edu.cn/
>
>
>
>Dale Callaham wrote:
>>Search the CONFOCAL archive at
>>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>>
>>Have a look at hamamatsu? I'm sure they are high quality.
>>http://sales.hamamatsu.com/en/products/solid-state-division/si-photodiode-series/si-apd.php
>>
>>I have no connection with Hamamatsu.
>>
>>Dale
>>
>>Peng Xi wrote:
>>>Search the CONFOCAL archive at 
>>>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>>>
>>>Hi,
>>>
>>>     Anybody know which company produces high-quality  Avalanche 
>>>photodiode (APD)? I am planning to use it to detect 800nm signal. 
>>>I prefer high sensitivity, low noise, analog one used in confocal 
>>>reflective devices. Thank you for your advice!
>>>
>>>
>>>Best regards,
>>>Peng Xi
>>>Associate Professor
>>>Institute for Laser Medicine and Biophotonics
>>>Shanghai Jiao Tong University
>>>800 Dongchuan Rd.
>>>Shanghai 200240, China
>>>Tel: (86) 21-3420-4076
>>>http://biophotonics.sjtu.edu.cn/
>>>
>>>


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