Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

please log me off!!At 11:03 12/01/04 +1300, you wrote:
>Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal     Perhaps I
>missed something but in the scanning case, shouldn't the local light dose
>be about the same since it still has to destroy the same molecules in the
>focal volume? Furthermore, if new molecules can diffuse into a selected
>focal volume between scan lines, shouldn't it take _more_ energy to destroy
>the molecules in the focal volume?
>
> Cheers
>
> Kevin Braeckmans wrote:
> Search the CONFOCAL archive at
>http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal      Bericht
>Dear all,          on that from experience?           JP also asked to give
>some numbers about actual light doses in the bleach phase of a FRAP
>experiment. I'll give it a try:         area is H*t, where t is the time of
>illumination.        the bleached area and D the diffusion coefficient.
>   2) with a scanning laser beam on a confocal microscope. An example:
>   the characteristic recovery time is tau = 25 ms and hence the bleach
>time approx. 0.25 ms. For a typical bleach power of 1mW the total energy
>recieved per unit area is therefore 1mW/(pi*1mum^2)*0.25ms = 80 kJ/m^2.
>   the scanning speed of the laser beam and dy the distance between the
>adjacent scanning lines (see our article on FRAP for details). v and dy
>depend on the zoom setting of course, but will be typically in the order
>of: v = 0.1 m/s and dy = 0.2 mum. Hence, the total amount of energy per
>unit area is: 1mW/(pi*1mum^2)/(0.1m/s*0.2mum) = 6 J/m^2.       As this
>little calculation shows, it is much more likely to inflict damage to your
>live cell when doing spot photobleaching, compared to scanning
>photobleaching. Luckily, hardly anyone is still doing spot photobleaching
>experiments I guess.         To relate them to actual damage to a
>particular structure in the cell, one would have to take the absorption
>cross section (wavelength dependent) into account. Does anyone have any
>data on that?       Best regards,       Kevin           Kevin Braeckmans,
>Ph.D.   Lab. General Biochemistry and Physical Pharmacy   Ghent University
>    Belgium
>
________________________________________________________-


Daniel Mackay, B.Sc., FRMS, AIBMS
Advanced Microscopy Unit/Drosophila Laboratory
Section of Old Age Psychiatry/Department of Neuroscience
Institute of Psychiatry
De Crespigny Park
Denmark Hill
London
SE5 8AF
0207 848 0553 - office
0207 848 0554 - Microscopy Suite
0207 848 0119 - Drosophila Lab.

__________________________________________________________-