Portable Optical Tweezers Kit
Chapter 7: Teaching Tips
Rev B, February 15, 2022
Page 75
Gaussian Intensity Profile
As shown in Figure 54, the cross section of a laser beam has a radius
𝑅𝑅
. The intensity
varies radially: the intensity is maximal in the center of the beam and declines towards the
edge. Comparing a ray in the middle of the profile to a ray outside, the inner one shows
the maximal intensity while the outer one exhibits a lower intensity. This is demonstrated
by the thickness of the blue lines in Figure 54.
The entire laser beam is the sum of all rays. For simplicity, we will only consider two rays
in the following which are symmetrical around the beam axis. The insights we gain with
these two rays can be transferred to the entire beam.
First, we have a look at an unfocused (collimated) laser beam that is incident on a
polystyrene bead. We have to distinguish between two cases:
•
The center of the bead is on the beam’s main axis
•
The center of the bead is not on the beam’s main axis
Note: The size of the vector arrows in the following diagrams do not match from diagram
to diagram, and instead are enlarged where possible for clarity.
Unfocused Laser Beam, Particle on the Beam’s Main Axis:
We consider two partial beams which are symmetrically arranged around the beam axis,
as shown in Figure 55. The beams are labeled
𝑡𝑡
and
𝑡𝑡
.
Summary of Contents for EDU-OT3
Page 1: ...EDU OT3 EDU OT3 M Portable Optical Tweezers User Guide...
Page 93: ......
Page 94: ...www thorlabs com...
