confocal scanning

[POUVREAU SANDRINE]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

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!

[Craig Brideau]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

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
<[hidden email]>wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> 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!
>

[Guy Cox-2]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Just to add to Craig's post, AOTF-equipped confocals do blank the beam
on the return trace, which significantly reduces bleaching.  Someone in
the early days - I think it was Watt Webb's lab - added a high-speed
shutter to a regular confocal to do the same thing, but I don't think
any microscope manufacturer took it up.  How fast your flyback can be
depends, in principle, on your scan speed but I think a lot of systems
actually scan both directions at the same speed, and of course resonant
scanners can only do that, so the bleaching on flyback can be
significant.  And many years ago I did a bleach test and the vertical
line at the 'turn-round' was quite visible - but I think that's
atypical.  

                                     Guy

Optical Imaging Techniques in Cell Biology
by Guy Cox    CRC Press / Taylor & Francis
     http://www.guycox.com/optical.htm
______________________________________________
Associate Professor Guy Cox, MA, DPhil(Oxon)
Australian Centre for Microscopy & Microanalysis,
Madsen Building F09, University of Sydney, NSW 2006

Phone [phone]     Fax [phone]
             Mobile [phone]
______________________________________________
      http://www.guycox.net
 


-----Original Message-----
From: Confocal Microscopy List [mailto:[hidden email]]
On Behalf Of Craig Brideau
Sent: Friday, 1 July 2011 4:49 AM
To: [hidden email]
Subject: Re: confocal scanning

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

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
<[hidden email]>wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> 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!
>

[POUVREAU SANDRINE]

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

Thank you for these explanations. Very helpfull!


________________________________________
De : Confocal Microscopy List [[hidden email]] de la part de Craig Brideau [[hidden email]]
Date d'envoi : jeudi 30 juin 2011 20:49
À : [hidden email]
Objet : Re: confocal scanning

*****
To join, leave or search the confocal microscopy listserv, go to:
http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
*****

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
<[hidden email]>wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> *****
>
> 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!
>