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For mono-directional scanning, the return to the start of line is called the
'flyback' time.  Usually it is quite short as the galvo typically moves at
top speed to 'snap' back to the start of the next line.  Unless your laser
powers are extremely high, the flyback exposure the sample receives is
probably negligible.  You do get a bit of lag time at the start of the line
though.  What happens is the galvo snaps to the position, but then has to
reverse direction to begin sweeping out the line.  One way to deal with this
is to have an edge clipping the beam off just before the start of a line.
 That way when the galvo is reversing direction and the laser is dwelling
for a little bit, the beam just strikes the blocking edge before it starts
sweeping out the line.  Some scan heads are designed this way, others do it
through clipping off the inherent apertures in the system rather than having
a dedicated edge.

Craig



On Thu, Jun 30, 2011 at 7:47 AM, Sandrine
<[log in to unmask]>wrote:

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>
> Hello
> One quick question about bi and mono directional scanning in confocal
> microscopy. In mono directional scanning, what happen to the laser light
> when
> the galvanometer mirror brings the beam back to the beginning of the line?
> My
> understanding is that it does not reach the sample if the system is
> equipped
> with an AOM or EOM, but I am not absolutely sure about why. And what
> happens during a dual color bidirectional scan?
> Thanks a lot!
>