Question for the use of Woolaston Prism in OPTICAL TWEEZER

  • Context: Graduate 
  • Thread starter Thread starter Choi Si Youn
  • Start date Start date
  • Tags Tags
    Optical Prism
Click For Summary

Discussion Overview

The discussion revolves around the use of a Wollaston Prism in optical tweezers, exploring its purpose and functionality within the optical setup. Participants examine the role of the Wollaston Prism in relation to other optical components, such as half-wave plates and laser polarization, within the context of optical trapping and imaging techniques.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant questions the necessity of the Wollaston Prism in the optical setup, seeking clarification on its specific purpose.
  • Another participant suggests that the half-wave plate does not polarize light into a single direction, indicating that the Wollaston Prism is needed to achieve proper polarization before entering a spatial light modulator.
  • Some participants discuss the role of the half-wave plate in controlling the polarization direction of an already linearly polarized laser beam, with one noting that it cannot create linear polarization from arbitrary polarization.
  • A participant mentions that mirrors in the optical path can spoil linear polarization, suggesting the use of additional prisms to ensure good polarization before using half-wave plates.
  • Several participants indicate that the prisms are associated with differential interference contrast (DIC) microscopy and may not be necessary for the trapping effect of optical tweezers.
  • Another participant describes their experience using the half-wave plate to control laser power and the Wollaston Prism to further reduce power and polarize light.
  • There is a discussion about the output of the Wollaston Prism, with one participant explaining that it can provide two polarized beams at a significant angle, depending on the input polarization angle from the half-wave plate.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and function of the Wollaston Prism in optical tweezers, with some asserting its importance for polarization and others suggesting it may not be needed for the trapping effect. The discussion remains unresolved regarding the specific role of the Wollaston Prism in the context of the optical setup.

Contextual Notes

There are mentions of various optical components and their interactions, including the effects of mirrors on polarization and the specific configurations of optical setups. Some assumptions about the linear polarization of the Nd:YAG laser and the implications of using different optical elements are noted but not fully explored.

Choi Si Youn
Messages
7
Reaction score
0
I studied optical tweezer,
So I saw the optical path in the diagram.

Then I can't understand why they use the Wollaston Prism?

After launch the laser, the beam through the half-wave plate
So the beam polarized, I know this.

and after through the half-wave plate, the beam through the Wollaston Prism.

But this time, I can't understand why they use it.


Does they have a special purpose for using the Wollaston Prism?


^^
 
Science news on Phys.org
The half wave plate does not polarize the light into a single direction. This is why the prisim is needed, in order to polarize the light before it enters a spatial light modulator. It can also be used to reduce the power of the laser so you don't burn out anything in the path. But from my understanding it's mainly used to polarize the light either horizontally or vertically.
 
In many optics book, they explain a half wave plate to the things that make laser beam
linear polarization.
is it different your explain and book?

http://en.wikipedia.org/wiki/Wollaston_prism
I read the webpage that explain the Wollaston Prism.

anyway, I'm thank you for your answer,

but, I can't understand this sentence..
"The half wave plate does not polarize the light into a single direction."

I'm use the Nd:Yag laser, So light already linearly polarized.
So I think that sentence doesn't make sense for me anymore, right?
 
Choi Si Youn said:
In many optics book, they explain a half wave plate to the things that make laser beam
linear polarization.
is it different your explain and book?

If you already have a linearly polarized laser beam, you can rotate the linear polarization using a half wave plate, but you cannot create linearly polarized light from arbitrarily polarized light using a half wave plate.

Choi Si Youn said:
I'm use the Nd:Yag laser, So light already linearly polarized.
So I think that sentence doesn't make sense for me anymore, right?

That depends. For most real setups you will have some mirrors between your laser and your experiment. These can spoil your linear polarization pretty bad. When using my Ti:Sa laser (well, the one of my department), I always use a Glan-Thompson or Glan-Taylor prism to ensure I have a good degree of linear polarization before using half wave plates to rotate the polarization around.
 
Choi Si Youn said:
I studied optical tweezer,
So I saw the optical path in the diagram.

There are as many different designs for tweezers as there are constructed tweezers- can you provide a link to the diagram you saw?
 
http://www.stanford.edu/group/blocklab/Optical%20Tweezers%20Introduction.htm
that page's Figure 3.
I just setup for seeing the trapped particle.
So now I need more optical elements for my experiment.

I just saw that diagram, and just setup, just one part of it.

Now I studied how can I research the result,
so I concerned and study other optics...

Above answer, and my other people who answer my question help me to know and
understand the optics that align in Figure..
 
Last edited by a moderator:
That setup looks like a nightmare...

As best I can tell, the prisms are there for DIC imaging while trapping, and don't pertain to the trapping/monitoring beams- but it's difficult to tell becasue of the 1/2-wave plate and dichroic mirrors (which have a polarization-dependent performance).

Personally, I keep the prisms well away from the trapping beam to prevent damage.
 
The prisms belong to the DIC (differential interference contrast) microscope, as Andy REsnick has mentioned. I worked on a similar setup. You don't need them for the tweezers effect and I would remove them most of the time, at least during the alignment of the trapping laser.
 
Ok, so I've been working with a set up similar to this one this summer and I can kind of tell you how we used each thing. First off why do you need the Wollaston between the lamp and the specimen? We just used the half wave plate to control the amount of power that was entering the objective (an easy way to control it rather than using the laser itself). the prisim was used to polarize the light and to help further reduce the power.
 
  • #10
Split Ratio..Re: Question for the use of Woolaston Prism in OPTICAL TWEEZER

Cthugha said:
If you already have a linearly polarized laser beam, you can rotate the linear polarization using a half wave plate, but you cannot create linearly polarized light from arbitrarily polarized light using a half wave plate.

That depends. For most real setups you will have some mirrors between your laser and your experiment. These can spoil your linear polarization pretty bad. When using my Ti:Sa laser (well, the one of my department), I always use a Glan-Thompson or Glan-Taylor prism to ensure I have a good degree of linear polarization before using half wave plates to rotate the polarization around.

Yes, it is correct.
Half wave plate is used to change the linear polarization direction, by rotating.
Wollaston prism is to get 2 polarizations devided with big angle.
The application in your case:
By rotating 1/2 waveplate, get different polarization angle to input wallaston prism, in order to get different ratios of 2 polarization beam, output from wollaston.

Any more questions, may email me: charles.chen@photonik.com.sg
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
3K
Replies
12
Views
1K
  • · Replies 1 ·
Replies
1
Views
1K
  • · Replies 5 ·
Replies
5
Views
2K
  • · Replies 66 ·
3
Replies
66
Views
7K
  • · Replies 5 ·
Replies
5
Views
3K
  • · Replies 8 ·
Replies
8
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 7 ·
Replies
7
Views
2K
  • · Replies 2 ·
Replies
2
Views
4K