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Paul,

        The fluctuation is because the Leica has flyback
blanking, whereas your old Biorad doesn't.  You would do
better to select bidirectional scanning.  I think you can
in fact park a static beam on the Leica but I've forgotten
how to do it (not something I do very often!).

                                               Guy


> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Hi All,
> I am attempting to make direct measurements of the laser power at the
> sample plane on a Leica TCS SP2 confocal. This will be done for each of
> the visible laser lines available on our instrument (458, 488, 514, 561,
> 594 and 633nm). Determining absolute power as well as relative power
> between lines is the aim.
>
> The sensor is mounted in the specimen plane and a low NA objective is used
> in an attempt to collect as much of the laser beam as possible (thereby
> hopefully minimising the effects due to focus position on the sensor). The
> zoom is set to maximum (x32) in an attempt to get the scanned region as
> small as possible and unidirectional scanning is performed at 200Hz
> (slowest setting available).
>
> When I observe the readout power on the meter, the values fluctuate
> widely, although a maximum value can be seen. I do not see this variation
> when I do the same type of measurements on my Biorad MRC1000/1024 UV
> system. Can anyone explain what might be happening here? Could it be
> related to the function of the AOBS (or similar optical components) in the
> system? Perhaps my meter does not respond quickly enough for the blanking
> performed during laser beam flyback? How do others do this type of direct
> measurement of laser power in the sample plane on their Leica (or other)
> instruments?
>
> All comments, suggestions and criticisms welcome.
>
> Cheers
> Paul
>
> ---------------
>
> Dr Paul J Rigby
> Director and Senior Lecturer
> Biomedical Imaging & Analysis Facility (M510)
> The University of Western Australia
> 35 Stirling Highway, Crawley, WA, 6009
> Australia
> Ph (61-8) 9346 2819
> Fx (61-8) 9346 3469
>


-- 
Associate Professor Guy Cox
Electron Microscope Unit,
University of Sydney,
NSW 2006, Australia

Phone:+61 2 9351 3176    Fax:+61 2 9351 7682
http://www.guycox.net