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Higher NA is more vulnerable to spherical aberration.  As you under fill the
lens, you reduce the NA.  This increases your laser spot size, costing you
some resolution, but in turn the lower NA beam is less vulnerable to
spherical aberration so you get a bit better penetration.

Craig


On Wed, Dec 22, 2010 at 3:44 PM, Jerry (Gerald) Sedgewick <
[log in to unmask]> wrote:

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>
> I was at the American Society for Cell Biology earlier this month and came
> across a company using adaptive optics with deformable mirrors for
> microscopy.  Their setup included a way in which the sample could be
> monitored for changes in the index of refraction as the focal plane goes
> deeper into the tissue, and then the beam shape is changed via the
> deformable mirror.  The net result is greater penetration into the sample,
> and I would suspect that this method would be an improvement over pulse
> compression.  In my experience, the diameter of the beam at the back
> aperture of the lens, particularly when it underfills, vastly improves
> penetration into the sample.  This may sacrifice the 2 photon effect, but
> it's a good solution when depth is more important than z-resolution.
>
> The adaptive optic technology is coincidentally very promising in the world
> of ophthalmic imaging because the refractive index of the eye changes from
> one person to another.
>
> I would be very interested in getting responses from this community about
> this technology.  I don't have a commercial interest at all in the company
> that is providing adaptive optics for microscopy.
>
> Cheers,
>
> Jerry Sedgewick
> --
>
> Jerry Sedgewick
> Sedgewick Initiatives
> [log in to unmask]
> http://www.imagingandanalysis.com
>
> Author of: "Scientific Imaging with Photoshop: Methods, Measurement, and
> Output"
>