How does a waveplate work?

[edison]

I,m thinking of designing a module in the future with use of a waveplate to get the best beamspecs for a quad setup. Can any make a drawing to explain how the waveplate turns the beam from vertical into horizontal polarisation?

Thanks guys!!!

[andythemechanic]

Hi Edison,

I tried to outline the principle above. The waveplate is a crystal in which the speed of light depends on the direction of the electrical field. It has two axes with different propagation speeds called the fast and the slow axes. Now suppose that you look along the direction of beam propagation (like in the drawing). The axes of the crsytal are aligned at 45° to the direction of the oscillating electrical field. The incoming electrical field (red arrow ) is divided in two fields which propagate along the axes (black arrows). Now the crystal is cut at axactly the length where the field component along the slow axis is half a wavelength behind the field along the fast axis. Half a wavelength means that its direction relative to the incoming field has flipped sign. So at the exit of the waveplate you take the vector sum of both beams which gives you a rotated field (blue arrow).
Hope I explained clear enough!

Greetings
Andreas

[LaserLover]

I,m thinking of designing a module in the future with use of a waveplate to get the best beamspecs for a quad setup. Can any make a drawing to explain how the waveplate turns the beam from vertical into horizontal polarisation?

Thanks guys!!!

Hi Edison,

It sounds like your going to have fun combining 4 lasers like some members "Marconi" was doing quite a while ago.

If you want to learn more about the different types of waveplates required and their applications see this interesting tutorial here " http://www.newport.com/servicesuppor...lt.aspx?id=118 "

Good luck with your project.

[edison]

Thanks laserlover

I think i,m going to use a wave plate to get 2 of the diodes of the quad vertical polarised. If i succeed in building the quad in theorry it shoot have a beamoutput of 2mm by 2 mm and a divergence of 0.8mrad
So very excited to see if i can get that result. But first i have to focus on the groupbuy that i,m doing for the case that some members ordered. Thats my main priority at this point.

[LaserLover]

Thanks laserlover

I think i,m going to use a wave plate to get 2 of the diodes of the quad vertical polarised. If i succeed in building the quad in theorry it shoot have a beamoutput of 2mm by 2 mm and a divergence of 0.8mrad
So very excited to see if i can get that result. But first i have to focus on the groupbuy that i,m doing for the case that some members ordered. Thats my main priority at this point.

Good luck Edison,

I'd like to see the final setup and results. When you complete the project let us know and maybe post a picture or two.

Rick

[taggalucci]

This is a very new subject for me, so the question may not have a simple answer...

What circumstances define when a wave-plate must be used?

[LaserLover]

A waveplate can be used to rotate the plane of polarization and allow more or less laser light to pass. For example, If you have a Helium Neon laser which is polarized and you rotate a waveplate (at 90 degrees to the plane of polarisation of the laser) in front of the beam you will notice the beam appears dimmmer at the viewing target . This is a way to make a variable attenuator, by rotating a waveplate in the beampath of a polarized laser beam.

[taggalucci]

Cool, that make sense. Would all lasers need adapting to polarise the beam or are some like that as a product of the lasing?

I see talk about polarising vertically and horizontally in order to achieve good performance with a PBS, but I'm not sure whether one needs to do something to the diodes first in order to align their polarisation vertically or horizontally.

[LaserLover]

Cool, that make sense. Would all lasers need adapting to polarise the beam or are some like that as a product of the lasing?

I see talk about polarising vertically and horizontally in order to achieve good performance with a PBS, but I'm not sure whether one needs to do something to the diodes first in order to align their polarisation vertically or horizontally.

All lasers have some form of polarization.
You mention lasers and PBS cubes, I presume for the purpose of combining 2 lasers. That being the case, you have to rotate your laser diodes to pass the most power by aligning the laser polarization to the PBS cube polarization axis. This process is best done using a laser power meter to get maximum power and wear laser safety glasses. Once you find the peak power level you lock off the laser diodes in their holding brackets and align both laser beams in the PBS cube so they combine concentrically in one output beam. You can find a detailed description in my e-book.

[buffo]

All lasers have some form of polarization.

This is misleading at best, if not outright false. "Some form" can include random polarization, which means no polarization, strictly speaking. There are several different types of laser that have randomly-polarized output, making them unsuitable for use with PCAOM's or PBS cubes (at least for the purposes of combining two beams).

If we're talking an ion laser, then if you see brewster windows you can be certain that the output is polarized. If we're talking about a solid state laser, then the answer is "probably".

Nearly all single-emitter diodes are polarized, but with DPSS designs, the polarization efficiency is all over the map. You might have one that has a 1000:1 ratio (meaning that for every watt of light output that is polarized one way, you only have 1 milliwatt of light polarized the other way), or you might have one that has only a 5:1 ratio. Obviously the 1000:1 is the preferable case, if you plan to mix a pair of beams using a PBS.

Adam