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The APD-Based 16-Channel Single-Photon Counting Unit

I had my first encounter with the Single-Photon Counting Technology when I came to the DNA Lab.  The work on The 16-Channel Unit had been conducted before my arrival, and I joined the team and learned how to change and tune its temperature controller and quenching circuit after their latest upgrade and, also, how to set up experiments with the Unit.

Although the Unit's layout was not perfect Ė to access the circuits that needed to be tuned, the Unit had to be taken apart Ė it was fully compensated by the Unitís high performance.

The unit is based on APD manufactured by Perkin Elmer Optoelectronics (model C30902S-DTC).  During my work in the Lab, we tested the APDs supplied by other manufacturers against our APD, in order to compare their characteristics. The testsí results testified that our sensor served our purpose best.

The APD-Based Single-Photon Counting Module (SPCM)

Each time the electronic engineer Georgiy Gudkov modified the circuit for generating precise quench and reset delays, the circuitís characteristics had to be tested. To facilitate the testing, I assembled the SPCM and afterwards participated in the experiments with the module. Later, I was gratified to see that the SPCM was used in our Labís DNA sequencing experiments on a par with the commercial SPCM-AQR-12.

The APD-Based 32-Channel Single-Photon Counting Unit

It was my pleasure to assemble this unit The unitís design comprised several attractive ideas generated by the electronic engineer Georgiy Gudkov, who, first, offered to include the APD, temperature and quenching controller into a module, built separately for each of the 32 counter channels, and then install all modules on the front panel of the Counting Unit.  Inserting or taking out modules is almost as easy now as inserting or taking out PC cards.  One can take out a module for tuning it up while the other modules continue working. 

Another idea was to install PC-104 into the Unit, for the obtained from channels data to be transferred through the Ethernet to the usersí data base by using PCís LPT.  The number of channels can now be increased by just increasing the number of Counting Units.  Thus, the problem of increasing the number of channels (up to 1024) was elegantly solved. After my assembling and tuning the Unit, it was fulfilling to participate in the experiments with it.

 

The PMT-Based 32-Channel Single-Photon Counting Unit

The PMT-Based Unit had already gone down in history by the time I came to the Lab.  The PMT sensors had been replaced by APDs in the Lab's projects.  Professor Vera Gorfinkelís new idea called for the use of much larger frequencies (up to 2 HGz) than those in our APD-based devices.  To set up the experiment for comparing the APD and PMT-based 32-channel counters, all we needed was to change the shield on the PMT sensor.  The fabrication of a new shield did not present a difficulty.  The problem we had to do away with was the 32-channel amplifierís self-excitation caused by the shield's partsí fitting that was not tight enough and, also, by the induction between the two flat cables connected to the sensor.  That problem solved, we conducted the experiment to compare the counters. 

 

Temperature Controller

 
 

APD Based Single-Photon Counter

 

Amplifier

 

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