Posted by
Matthew Nicholas-2 on
Jul 29, 2010; 7:59pm
URL: http://confocal-microscopy-list.275.s1.nabble.com/Scattered-light-from-AOTF-tp5352866.html
Hi All,
I have what seems like a trivial question, but I cannot seem to sort it
out, and wondered if others have experience/solutions to offer. I have
two excitation lasers combined (i.e. overlapped) via a dichroic mirror
and directed into an AA AOTF (
opto.braggcell.com).
The AOTF is used to shutter the beams and control their
intensities. Overall, the system works well. Back reflections from the
front face of the AOTF are very nearly colinear with the incoming beams
(purposely slightly mis-aligned to prevent back-reflection into the
lasers), as are first-order diffracted beams. The zero-order beams are
reflected by a pick-off mirror into a light trap. Following the AOTF,
the first-order beams are expanded by a 10X beam expander (i.e.
telescope), after which they enter our microscope. The faces of the
crytsal in the AOTF and dichroic mirror are free of dust, fingerprints,
etc. The input beam diameter is approximately 1-2 mm, and strikes the
AOTF input aperture very nearly at the center.
The problem is, even when all laser lines are off (or when the AOTF
itself is powered-down), there is minimal, but noticable scattered
light exiting the AOTF. Some of this light is collected by the beam
expander and enters the microscope (this is what I want to eliminate).
I've more or less ruled-out that the scattering occurs after the AOTF,
and believe it may be due to reflections at the front surface
(entrance) of the AOTF or within it. Since it occurs even when the AOTF
is off, it does not seem to be an acousto-optic effect. My current
thought is to move the AOTF farther from the telescope, and to use a
smaller aperture lens at the telescope input, but what I'd really like
to do is eliminate the scattered light. I've also thought of using a
pinhole as a spatial filter at the telescope focus, but since the
scattered light is focused at more or less the same spot, the hole
would have to be fairly small, and I'd like to avoid adding another
element to the system that is time-consuming to align.
Any advice or ideas would be much appreciated!
Thanks in advance,
Matt
--
Matthew Nicholas
Medical Scientist Training Program Student
Laboratory of Arne Gennerich
Department of Anatomy and Structural Biology
Albert Einstein College of Medicine
Forchheimer Building, Room 628
1300 Morris Park Avenue
Bronx, New York 10461
718.430.3446
[hidden email]