Galvo Vs. Resonant mirror velocity

[Chris O'Connell]

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Hi All,

For teaching purposes, I was wondering if anyone knows of or has graphs/diagrams comparing the velocity of galvo vs. resonant scanner mirrors.  I was looking over my slides on that topic and realized it would be helpful in explaining the difference in speed.

Thanks.

Chris

[Benjamin Smith]

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The simplest way to plot it would be to assume both mirrors are running in
bidirectional mode.   This means that the galvo mirror will scan in a
triangle wave pattern and the resonant mirror would scan in a sinusoidal
wave.  In my experience the fill fraction for both mirrors tends to be
around 66% (i.e. the mirror overshoots by 1/6th of the total scan on each
end).  Type the following into the Google search bar, and you will get a
good plot of this:

y=sin((8*2*pi)*x), y=0.67, y=-0.67, y=2/pi*arcsin(sin(2*pi*x))

The first equation is for an 8 kHz sine wave (where the X axis is in
milliseconds) - this is for the angular position of an 8 kHz resonant
mirror as a function of time.
The second and third equations show the edges of the scan field during the
mirror sweep (beyond this is the overshoot/flyback)
The fourth equation is for a 1 kHz triangle wave - this is for a 1kHz
bidirectional scan with a galvo mirror.

One caveat, the plot for the galvo mirror obviously isn't the actual
angular position of the mirror, as this would require infinite acceleration
and deceleration at the turn.  Rather, this is the plot of the driving
voltage sent to the mirror drivers (which is converted by the driver to a
corresponding driving current).  The actual mirror angular position would
be rounded at the turn around points due to angular momentum.

These plots make for a good segue into the need for flyback blanking (and
hence AOTFs and Pockels cells), bidirectional registration (bonus points
for introducing detector slew rates as a limiting factor in bidirectional
imaging), resonant scanner image clock adjustments due to the constantly
changing pixel dwell time, etc.

Hope this helps,
   Ben Smith

On Tue, Oct 20, 2020 at 11:33 AM Chris O'Connell <[hidden email]>
wrote:

> *****
> To join, leave or search the confocal microscopy listserv, go to:
> http://lists.umn.edu/cgi-bin/wa?A0=confocalmicroscopy
> Post images on http://www.imgur.com and include the link in your posting.
> *****
>
> Hi All,
>
> For teaching purposes, I was wondering if anyone knows of or has
> graphs/diagrams comparing the velocity of galvo vs. resonant scanner
> mirrors.  I was looking over my slides on that topic and realized it would
> be helpful in explaining the difference in speed.
>
> Thanks.
>
> Chris
>

--
Benjamin E. Smith, Ph. D.
Imaging Specialist, Vision Science
University of California, Berkeley
195 Life Sciences Addition
Berkeley, CA  94720-3200
Tel  [phone]
Fax [phone]
e-mail: [hidden email]
https://vision.berkeley.edu/faculty/core-grants-nei/core-grant-microscopic-imaging/

[Michael Giacomelli-2]

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The spot velocity for a resonant scanner depends on the magnification
and scan angle, but is on the order of 10s of meters per second under
typical conditions.  Here is a simulation for a 24 KHz (bidirectional,
so 12khz fundamental) scanner with a 1mm FOV:

https://imgur.com/a/PqkV47Q

The peak velocity is ~500nm per laser pulse, or about 40 meters per
second. The right axis is how many pixels the spot displaces, assuming
2048 uniformly spaced pixels per line.

Mike

On Tue, Oct 20, 2020 at 2:33 PM Chris O'Connell <[hidden email]> wrote:

>
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> *****
>
> Hi All,
>
> For teaching purposes, I was wondering if anyone knows of or has graphs/diagrams comparing the velocity of galvo vs. resonant scanner mirrors.  I was looking over my slides on that topic and realized it would be helpful in explaining the difference in speed.
>
> Thanks.
>
> Chris