[RASMB] Lamp intensity fluctuations

[Tom Laue]

Hi Andrew-
You are right about being able to grab the last scan incident readings. 
The incident light detector is in the monochromator head and after the 
monochromator itself.
Best wishes,
Tom

Leech, AP wrote:
> Hi Tom, Titus, all
>
> I thought the "incident" readings come from the reference detector:
> these can be seen using the menu Scan -> Request Data -> Incident
> from the GUI, but they are only available from the last scan and
> do not seem to be collected during a run. The incident data should
> be flat across the scan, slightly noisy and slightly higher than the
> maximum reference sector data (at least, that is how they are on our
> XL/I). We once had a problem with the reference detector which resulted
> in this data being a perfect flat line, solved by replacing the
> monochromator assembly.
>
> Best regards,
>
> Andrew
>
>
> Tom Laue wrote:
>> Hi Titus, et al.-
>> I am not sure what the intensity reading is you are presenting- is it 
>> the average value across the radial scan? Is it the reading at a 
>> particular radial position? In any case, it is worthwhile getting 
>> some idea of the complexity that is behind the XLA intensity readings.
>> There are two intensity readings taken with each lamp flash- 1) 5 or 
>> 10% (can't recall which) of the lamp flash intensity itself is 
>> monitored using light bounced off of a semi-reflecting mirror and a 
>> photodiode sensor. This signal is used to correct for the inherent 
>> ~3% variation in flash intensity characteristic of the lamp. 2) The 
>> light intensity at the photomultiplier (PMT) after it has passed 
>> through the cell and slit/lens assembly. I do not believe the 
>> photodiode intensity readings are accessible to the outside world, so 
>> your readings are from the PMT.
> [...]
>

-- 
Department of Biochemistry and Molecular Biology
University of New Hampshire
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