Calculating Photomultiplier Tube Saturation Limit: A Guide

[watertreader]

Hi,

Have some query on the photomultiplier tube saturation limit(the maximum light luminosity or intensity that can be delivered to the PMT without damaging the equipment). How do we calculate it?

I have looked through the specification. The only relevant specification for the saturation problem is the maximum current produced per luminosity. Is there some other gauge we should take to measure the maximum allowable amount of input light? What's the common rating?

Wouldn't want to spoil another PMT again

 

[Topher925]

I don't think you are able to easily calculate the damage threshold of a PMT. This type of information is usually provided by the manufacturer, and as far as I know it takes a considerable amount of light flux (relatively speaking) to damage a PMT. PMTs are used for very sensitive and low intensity applications. If you are damaging PMTs with to high of a light intensity then you should look at photodiodes or phototransistors as a possible substitute.

 

[Bob S]

I have measured a peak pulse of more than 1 volt across 50 ohms (20 ma) out of a RCA 6810, but the average output should be less than 1 ma. Are you using a dynode or anode output? As for the cathode, you probably should not expose it to sunlight with no voltage on it, and never when any voltage is on it. What tube are you using, and what gain? How did you spoil the first one?

 

[watertreader]

I am using the anode output, using a Hamamatsu R928... It is sited inside a circuit box that I have fabricated(with all the accessories electrical circuits for DC Measurement and an input fiber SMA fiber port)...using a gain at around 400-500V

Guess I have pumped in round 300-500uW of laser power through the fiber onto the cathode detector area(tat's why I like to know the damage threshold)... Another fatal mistake is that I have not switched off the room's light...
(Slipped my mind to off the light)

THe PMT was working for some time... but the next time round I have used them... I can't detect any DC signal anymore...

Guess I should try to be careful the next time round...

 

[dlgoff]

Just curious. Have you ever measured the temperature inside your "circuit box"?
The tubes Operating Ambient Temperature is -30 to +50 °C. Usually devices, that are operating at a temperature above their rated value, will age much quicker. Don't know if this is a problem with your tube.

 

[watertreader]

No, I didn't. Have another one PMT(other model) in an even smaller box... seem to be working well for me...

BTW, out of interest... to monitor temperature in a box... what circuit did you used? A thermostat?

 

[dlgoff]

I would use a thermocouple with an associated meter. Or maybe just a glass thermometer.

 

[omer korech]

Hi

I am also using Hamamatsu R928 and also exposed it accidentally to fluorescent light, with about a KV on it. After one night without voltage it resumed its capabilities.

Does someone know this device intensity limitation? Do you know at which range its response is linear with intensity?

Thanks