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Dear Ian
this is a real good operative description.
One of the main advantages in having compact ultrafast light sources is
given by the possibility of reducing the optical lever between laser
output and the microscope.
Microscope manufacturers should make this real with proper attachments
and when aligning the systems for the final users.
Usually they provide good assitance when required .
All my best
ALberto
On 24 giu 2004, at 21:13, Ian Read wrote:

> Search the CONFOCAL archive at
> http://listserv.acsu.buffalo.edu/cgi-bin/wa?S1=confocal
>
> Dear Greg:
>
> I tend to agree with Prof. Diaspro in that alignment should be
> considered /
> eliminated as the primary cause.  First thing to recognize is that
> Ti:sapphire oscillators typically have a divergent beam.  (This is one
> reason why it was mentioned that the laser being positioned close to
> the
> microscope is advantageous.)  So, to compensate for this divergence, we
> laser manufacturers typically include a focusing lens into the direct
> coupling optics. The lens also gives the user some flexibility on the
> degree of over(under)filling the objective aperture.  To first order, I
> would remove the both this collimating lens and the objective lens and
> optimize the beam throughput using the method described by Prof.
> Diaspro (I
> wouldnt' use an average power measurment here since the throughput
> will be
> affected by the larger beam size)  Pay special attention that the beam
> height entering the scan head is parallel with the table and traveling
> along the optical table's hole pattern.  Basically, the beam needs to
> be
> very straight going into the scan head.  This can be tricky if you
> have an
> upright scope because the periscope adjustments do some funny things if
> you're not used to it.  At any rate, once the beam is visible on a
> piece of
> paper, you can properly center it through the scope and perform .  Once
> you've done this, you can optimize the throughput using the collimating
> lens (Spectra-Physics provides a long focal length lens for this
> purpose)
> Now, be sure that everything is straight entering the scan head.  Keep
> in
> mind that the lens will change the beam position if it's not centered
> properly.  Now that you have the beam centered at a single wavelength
> (use
> 720nm since you can see it) through the collimating lens and the scope,
> replace the objective lens.  Here's where you can run into trouble.
> If you
> were present during the microscope installation, much effort is placed
> on
> aligning the beam relative to the confocal laser beam.  The first step
> is
> to place a mirror under the objective lens.  This serves to reflect the
> visible laser out through the scan head so that the Ti:sapphire beam
> will
> overlap with the confocal beam.  Now, if adjustments to the beam
> position
> are made with the collimating lens in place then you will have problems
> because the beam is not passing through the center of the lens
> anymore, and
> the beam will be coming into the objective (potentially) at an angle.
> To
> avoid this problem, remove the collimating lens while the necessary
> adjustments are being made to overlap the two beams.  Once the beams
> are
> overlapped, you can then replace the mirror with a real sample.
> Things to
> watch for if your alignment is off are: uneven illumination of the
> sample
> and more importantly the image will shift both relative to the confocal
> image and as the laser is tuned.  You can minimize these effects by
> overfilling the back aperture so that the beam profile entering the
> objective is more consistent.  I hope this helps to understand where
> the
> problem may be coming from.  Before you embark on this relatively
> involved
> procedure, I would check with Zeiss as they may feel more comfortable
> handling this themselves.  In that case, I hope that you can use this
> information as reference for getting the best images possible.
>
> Ian
>
> -----------------------------------------------------
> Ian Read, Ph.D.
> Product Manager
> Spectra-Physics
> Mountain View, CA 94043
> (650) 966-5346    :voice
> (650) 969-3546    :fax
> [log in to unmask]
> -----------------------------------------------------
>
>
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Alberto Diaspro, Department of Physics, University of Genoa
Via Dodecaneso 33, 16146 Genova, Italy
facsimile +39-010314218 - voice +39-0103536426/480/309
URL: http://www.lambs.it
http://www.wiley.com/WileyCDA/WileyTitle/productCd-0471409200.html
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