2-axes mirror calibration

[Joe Ping-Lin Hsiao]

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Hi,

I am using a 2-axis mirror to cast lasers onto specimens, and I am looking
for a mathematical procedure to convert the voltage inputs of the mirror
over the positions in the specimen space. Presumably it would take care of
the rotation and nonlinearity.

Thanks,
Joe

[Joe Ping-Lin Hsiao]

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I am afraid that I was not clear in my first email. I am using a 2-axis
tilt mirror that has voltage controlled tilt. This mirror is set up to be
conjugate with the back focal plane of the microscope objective for point
illumination positioning within the specimen. When I specify an array of
points on a square grid in the voltage space of the 2 axis mirror, the
pattern of spots in the specimen plane shows that the axes are rotated and
are nonlinear. Unfortunately, I cannot physically rotate the mirror.
Therefore, I want to do all corrections for rotation and nonlinearity
through a software algorithm that maps the mirror voltage command space to
the 2d space of the specimen. Then I can use the reverse transform to
specify the needed voltages to achieve a desired beam path within the
specimen space. I would think that there are algorithms available perhaps
from the confocal laser scanning imaging literature, but have had trouble
locating these. Any help would be appreciated.

On Wed, Mar 30, 2016 at 5:07 PM, Joe Ping-Lin Hsiao <[hidden email]>
wrote:

> Hi,
>
> I am using a 2-axis mirror to cast lasers onto specimens, and I am looking
> for a mathematical procedure to convert the voltage inputs of the mirror
> over the positions in the specimen space. Presumably it would take care of
> the rotation and nonlinearity.
>
> Thanks,
> Joe
>
>
>

[Craig Brideau]

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The easiest way is to image a grid and apply a transform after the fact.
Otherwise you need to calculate a distorted sine/ramp function to adjust
the position of the galvo mirror to accommodate the field stretching at the
edges of the angle. You should be able to get what you need with basic
trig; just keep the delta spacing of the legs of the triangle constant then
back-calculate the required angle. You will probably need to do a fit to
find the exact transfer function you need to input into the driver.

Craig

On Thu, Mar 31, 2016 at 2:23 PM, Joe Ping-Lin Hsiao <[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.
> *****
>
> I am afraid that I was not clear in my first email. I am using a 2-axis
> tilt mirror that has voltage controlled tilt. This mirror is set up to be
> conjugate with the back focal plane of the microscope objective for point
> illumination positioning within the specimen. When I specify an array of
> points on a square grid in the voltage space of the 2 axis mirror, the
> pattern of spots in the specimen plane shows that the axes are rotated and
> are nonlinear. Unfortunately, I cannot physically rotate the mirror.
> Therefore, I want to do all corrections for rotation and nonlinearity
> through a software algorithm that maps the mirror voltage command space to
> the 2d space of the specimen. Then I can use the reverse transform to
> specify the needed voltages to achieve a desired beam path within the
> specimen space. I would think that there are algorithms available perhaps
> from the confocal laser scanning imaging literature, but have had trouble
> locating these. Any help would be appreciated.
>
> On Wed, Mar 30, 2016 at 5:07 PM, Joe Ping-Lin Hsiao <[hidden email]>
> wrote:
>
> > Hi,
> >
> > I am using a 2-axis mirror to cast lasers onto specimens, and I am
> looking
> > for a mathematical procedure to convert the voltage inputs of the mirror
> > over the positions in the specimen space. Presumably it would take care
> of
> > the rotation and nonlinearity.
> >
> > Thanks,
> > Joe
> >
> >
> >
>

[Peter Rupprecht]

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I would support Craig's solution (do a calibration).
The trigonometric way to calculate the displacement of the focus that Craig mentioned would be
displacement     d = f1/f2 * f3 * tan( alpha )
with alpha being the scan angle, f1, f2 and f3 being the focal lengths of scan lens, tube lens and objective. So it's basically a tan(alpha)-non-linearity, if I'm not completely wrong. However, if your axial alignment of the lens system is not perfect, you can get some differing results.
Peter

    Craig Brideau <[hidden email]> schrieb am 22:32 Donnerstag, 31.März 2016:
 

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The easiest way is to image a grid and apply a transform after the fact.
Otherwise you need to calculate a distorted sine/ramp function to adjust
the position of the galvo mirror to accommodate the field stretching at the
edges of the angle. You should be able to get what you need with basic
trig; just keep the delta spacing of the legs of the triangle constant then
back-calculate the required angle. You will probably need to do a fit to
find the exact transfer function you need to input into the driver.

Craig

On Thu, Mar 31, 2016 at 2:23 PM, Joe Ping-Lin Hsiao <[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.
> *****
>
> I am afraid that I was not clear in my first email. I am using a 2-axis
> tilt mirror that has voltage controlled tilt. This mirror is set up to be
> conjugate with the back focal plane of the microscope objective for point
> illumination positioning within the specimen. When I specify an array of
> points on a square grid in the voltage space of the 2 axis mirror, the
> pattern of spots in the specimen plane shows that the axes are rotated and
> are nonlinear. Unfortunately, I cannot physically rotate the mirror.
> Therefore, I want to do all corrections for rotation and nonlinearity
> through a software algorithm that maps the mirror voltage command space to
> the 2d space of the specimen. Then I can use the reverse transform to
> specify the needed voltages to achieve a desired beam path within the
> specimen space. I would think that there are algorithms available perhaps
> from the confocal laser scanning imaging literature, but have had trouble
> locating these. Any help would be appreciated.
>
> On Wed, Mar 30, 2016 at 5:07 PM, Joe Ping-Lin Hsiao <[hidden email]>
> wrote:
>
> > Hi,
> >
> > I am using a 2-axis mirror to cast lasers onto specimens, and I am
> looking
> > for a mathematical procedure to convert the voltage inputs of the mirror
> > over the positions in the specimen space. Presumably it would take care
> of
> > the rotation and nonlinearity.
> >
> > Thanks,
> > Joe
> >
> >
> >
>