Finding top of silicon wafer

[Jerry Sedgewick]

Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

Hi All,

I am working with a graduate student on a home built 2 photon. In the past
he had routinely used 750nm on a Tsunami (5 watt) and was able to see a
reflection off the surface of a silicon wafer in order to determine the
bottom of his sample (the sample itself is polymer beads which do not
fluoresce at non-polymerizing wavelengths). Now we have gone to another
laser system (the 10 watt MaiTai)and he is not able to see the reflection
with the same precision (this probably has nothing to do with the new
laser, but with spot size in the back aperture or something else: it's very
well aligned).

Before the new laser (and shorter laser path) he could see the reflection
with .2 micron accuracy (the reflection fades rapidly with .2 micron
z-resolution). Now he sees the reflection at about a 2 micron accuracy.

I have been noticing that the z-resolution in general seems not quite up to
par with thin focal volumes expected with a multiphoton. This new setup
seems to have about the same z-resolution as a single photon, though I have
never measured the actual z-resolution. I don't generally use a lens in the
light path to converge the beam: when I do, it's a 1000mm focal length
plano-concave lens which creates a narrower diameter spot on the back
aperture of the lens. I do use a lens to narrow the diameter of the back
projected image onto the PMTs.

Any thoughts?

Jerry Sedgewick
University of Minnesota

[Mark Cannell]

Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

Hi Jerry

There is no reason why resolution should change except that the rear
aperture is not filled and/or the light does not have the correct degree
of collimation so that sperical aberration may be present. You must
overfill the rear aperture to get good z-resolution -don't focus the
light through the rear aperture. I note that your original figure of  z
resultion of 0.2 um for reflected mode sounds very unlikely -that's way
above the diffraction limit.

Cheers Mark

. Jerry Sedgewick wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Hi All,
>
> I am working with a graduate student on a home built 2 photon. In the
> past he had routinely used 750nm on a Tsunami (5 watt) and was able to
> see a reflection off the surface of a silicon wafer in order to
> determine the bottom of his sample (the sample itself is polymer beads
> which do not fluoresce at non-polymerizing wavelengths). Now we have
> gone to another laser system (the 10 watt MaiTai)and he is not able to
> see the reflection with the same precision (this probably has nothing
> to do with the new laser, but with spot size in the back aperture or
> something else: it's very well aligned).
>
> Before the new laser (and shorter laser path) he could see the
> reflection with .2 micron accuracy (the reflection fades rapidly with
> .2 micron z-resolution). Now he sees the reflection at about a 2
> micron accuracy.
>
> I have been noticing that the z-resolution in general seems not quite
> up to par with thin focal volumes expected with a multiphoton. This
> new setup seems to have about the same z-resolution as a single
> photon, though I have never measured the actual z-resolution. I don't
> generally use a lens in the light path to converge the beam: when I
> do, it's a 1000mm focal length plano-concave lens which creates a
> narrower diameter spot on the back aperture of the lens. I do use a
> lens to narrow the diameter of the back projected image onto the PMTs.
>
> Any thoughts?
>
> Jerry Sedgewick
> University of Minnesota

[Guy Cox]

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

I agree with all Mark says, but I would point out that the

precision with which one can profile a surface in reflection

is way better than the actual Z resolution (it's a different

question) so 200nm is not at all unrealistic.

 

                                                                    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)
Electron Microscope Unit, Madsen Building F09,
University of Sydney, NSW 2006
______________________________________________
Phone [phone]     Fax [phone]
Mobile [phone]
______________________________________________
http://www.guycox.net

---

From: Confocal Microscopy List on behalf of Mark Cannell
Sent: Tue 23/10/2007 7:33 AM
To: [hidden email]
Subject: Re: Finding top of silicon wafer

Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

Hi Jerry

There is no reason why resolution should change except that the rear
aperture is not filled and/or the light does not have the correct degree
of collimation so that sperical aberration may be present. You must
overfill the rear aperture to get good z-resolution -don't focus the
light through the rear aperture. I note that your original figure of  z
resultion of 0.2 um for reflected mode sounds very unlikely -that's way
above the diffraction limit.

Cheers Mark

. Jerry Sedgewick wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Hi All,
>
> I am working with a graduate student on a home built 2 photon. In the
> past he had routinely used 750nm on a Tsunami (5 watt) and was able to
> see a reflection off the surface of a silicon wafer in order to
> determine the bottom of his sample (the sample itself is polymer beads
> which do not fluoresce at non-polymerizing wavelengths). Now we have
> gone to another laser system (the 10 watt MaiTai)and he is not able to
> see the reflection with the same precision (this probably has nothing
> to do with the new laser, but with spot size in the back aperture or
> something else: it's very well aligned).
>
> Before the new laser (and shorter laser path) he could see the
> reflection with .2 micron accuracy (the reflection fades rapidly with
> .2 micron z-resolution). Now he sees the reflection at about a 2
> micron accuracy.
>
> I have been noticing that the z-resolution in general seems not quite
> up to par with thin focal volumes expected with a multiphoton. This
> new setup seems to have about the same z-resolution as a single
> photon, though I have never measured the actual z-resolution. I don't
> generally use a lens in the light path to converge the beam: when I
> do, it's a 1000mm focal length plano-concave lens which creates a
> narrower diameter spot on the back aperture of the lens. I do use a
> lens to narrow the diameter of the back projected image onto the PMTs.
>
> Any thoughts?
>
> Jerry Sedgewick
> University of Minnesota

[Mark Cannell]

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal OK, let me clarify that, you may be able to decide the centroid of the PSF to better than 200nm but the width of the actual PSF will still be greater than 200nm

Cheers Mark

On 24/10/2007, at 2:05 AM, Guy Cox wrote:

Search the CONFOCAL archive at http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

I agree with all Mark says, but I would point out that the

precision with which one can profile a surface in reflection

is way better than the actual Z resolution (it's a different

question) so 200nm is not at all unrealistic.

 

                                                                    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)
Electron Microscope Unit, Madsen Building F09,
University of Sydney, NSW 2006
______________________________________________
Phone [phone]     Fax [phone]
Mobile [phone]
______________________________________________
http://www.guycox.net

---

From: Confocal Microscopy List on behalf of Mark Cannell
Sent: Tue 23/10/2007 7:33 AM
To: [hidden email]
Subject: Re: Finding top of silicon wafer

Search the CONFOCAL archive at
http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal

Hi Jerry

There is no reason why resolution should change except that the rear
aperture is not filled and/or the light does not have the correct degree
of collimation so that sperical aberration may be present. You must
overfill the rear aperture to get good z-resolution -don't focus the
light through the rear aperture. I note that your original figure of  z
resultion of 0.2 um for reflected mode sounds very unlikely -that's way
above the diffraction limit.

Cheers Mark

. Jerry Sedgewick wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Hi All,
>
> I am working with a graduate student on a home built 2 photon. In the
> past he had routinely used 750nm on a Tsunami (5 watt) and was able to
> see a reflection off the surface of a silicon wafer in order to
> determine the bottom of his sample (the sample itself is polymer beads
> which do not fluoresce at non-polymerizing wavelengths). Now we have
> gone to another laser system (the 10 watt MaiTai)and he is not able to
> see the reflection with the same precision (this probably has nothing
> to do with the new laser, but with spot size in the back aperture or
> something else: it's very well aligned).
>
> Before the new laser (and shorter laser path) he could see the
> reflection with .2 micron accuracy (the reflection fades rapidly with
> .2 micron z-resolution). Now he sees the reflection at about a 2
> micron accuracy.
>
> I have been noticing that the z-resolution in general seems not quite
> up to par with thin focal volumes expected with a multiphoton. This
> new setup seems to have about the same z-resolution as a single
> photon, though I have never measured the actual z-resolution. I don't
> generally use a lens in the light path to converge the beam: when I
> do, it's a 1000mm focal length plano-concave lens which creates a
> narrower diameter spot on the back aperture of the lens. I do use a
> lens to narrow the diameter of the back projected image onto the PMTs.
>
> Any thoughts?
>
> Jerry Sedgewick
> University of Minnesota