Determination of photoelectron counts from the ARPES signal

[Swapnil Patil]

Hi,

I am keen to know how the photoelectron counts (or count rate) is determined from the measured ARPES signal in the detectors used by ScientaOmicron Hemispherical electron energy analyzers? These detectors consist of Micrchannel Plates (MCP)- Phosphor screen (PS)- CCD Camera setup. The photoelectrons hitting the PS after getting amplified by the MCP, create scintillations which are then imaged by the CCD and then 'counted' by various algorithms within the pulse counting mode or the ADC mode. The ADC mode is the most commonly used mode in Scienta analyzers. I am interested in knowing the details of how the CCD output signal is finally converted into photoelectron counts in both the modes, especially the ADC mode, since the Scienta technical manual is not at all detailed in this regard.

In this context the Scienta data acquisition software defines something known as 'multiple counting factor' during photoelectron counts determination. What is this factor? What does it do?

I would be glad if someone could answer me.

Thanks a lot,

Regards,
Swapnil

 

[ZapperZ]

Hi,

I am keen to know how the photoelectron counts (or count rate) is determined from the measured ARPES signal in the detectors used by ScientaOmicron Hemispherical electron energy analyzers? These detectors consist of Micrchannel Plates (MCP)- Phosphor screen (PS)- CCD Camera setup. The photoelectrons hitting the PS after getting amplified by the MCP, create scintillations which are then imaged by the CCD and then 'counted' by various algorithms within the pulse counting mode or the ADC mode. The ADC mode is the most commonly used mode in Scienta analyzers. I am interested in knowing the details of how the CCD output signal is finally converted into photoelectron counts in both the modes, especially the ADC mode, since the Scienta technical manual is not at all detailed in this regard.

In this context the Scienta data acquisition software defines something known as 'multiple counting factor' during photoelectron counts determination. What is this factor? What does it do?

I would be glad if someone could answer me.

Thanks a lot,

Regards,
Swapnil

This is a technical calibration that you need to find out directly from Scienta. Unless you are adapt at dismantling the housing that contains the phosphor screen and the CCD camera (not recommended) and do your own calibration of the screen intensity, there is no way to find out how this is calibrated.

This aspect is not something that one typically use the analyzer for. As long as the response is flat across the entire viewing screen, all one cares about are the relative signal intensity, rather than an absolute signal. Is it why, I believe, Scienta and most vendors of such devices do not typically include information on such calibration. But if you are thinking of using this as a quantum efficiency measurement device (and a very expensive one too for such a simple measurement) then my only suggestion is to contact Scienta and ask.

Zz.