Design of a Laser beam polarization rotation apparatus

[Tyler184]

TL;DR Summary

I’m swinging an experiment to measure the change polarity of em waves by modulating them with a rotating polarizer. However before I follow through with this experiment I would like to check the mechanics of this experiment.

Hey guys, I’m a high schooler designing an experiment to test polarity modulation for em waves. Before I study complex methods of polarity modulation that involve the use of crystals I want to use a simple laser and rotating a polarizer while the laser differs in its intensity for brief intervals indicting I hit its polarity meaning it’s rotating properly.


Anyhow, let’s review the parts involved in this process: this experiment consists of a simple laser, a main tubing, a magnetized tube, two bearings, a stand, and a polarizer, and two inductors (called the varying and neutral inductor respectively).

Next, let’s review the theory(although this is a bit less relevant): the varying inductor and neutral inductor are parallel to the magnetized tube. I send a varying current (AC) through the varying inductor, a simple way of this is fully powering the inductor and then letting it decay so for a few seconds it drops in current. While initially, the magnetized tube (which is thin) would align with the varying inductors magnetic field, eventually it would loose alignment due to the varying inductor decaying, now this is where the neutral inductor comes into play. When the varying inductor begins to decay, to ensure it doesn’t stay in the same spot, the neutral inductor induces an opposite static magnetic field direction to ensure it slowly goes the opposite way. Now, this is the baseline so if it goes up or down that depends on if it’s greater or less than the static magnetic field (that means I’m only doing 180 degrees for this experiment).

Now most importantly the mechanics: the magnetized tube is broken up into two separate tubes, each connecting to opposite sides of the main tubing. As it rotates up and down according to the varying inductors magnetic field, it would rotate the main tubing connected to the bearings at each end and would spin the polarizer glued to the end of the main tubing thereby changing polarity.


Now lastly, the process: the laser goes through the main tubing, which then goes through the main tubing, and reaches the end where a polarizer is glued on. It then will hit a wall where we can view if it intensity increases or decreases.

Here’s a cad drawing of it from four different angles:

They’re color coded as such: red: stand, light blue: varying inductor and neutral inductor, black: bearings: grey: main tubing, dark blue (although it’s difficult to see): magnetized tube.

One thing I would like to say is the polarizer is not in the cad as it would simply be glued to the end of the end of the main turning. The laser is not in it for the same reason, as it’s just connected to the other end of the main tubing where the bearings is.

Mechanically, im worried magnetized tube won’t rotate due to the size of the main tubing and friction.

Here’s the size of the parts
main tubing: 49mm OD with a 1.5mm thickness length= 838.2mm (hollow)
Laser diameter: 2.5mm
Magnetized tube (only one of the two parts): 4mm OD, 457.2mm length (solid)
Varying and neutral inductor (same size): 35mm OD, 1066.8mm length (solid, although could be hollow)
Stand:70mm X 130mm base, 609.6mm height (solid)
Bearings(6210 bearings): 90mm OD, 20mm thickness

 

[berkeman]

Before I study complex methods of polarity modulation that involve the use of crystals I want to use a simple laser and rotating a polarizer

I'm not understanding your description or drawings of the rotation mechanism. Why not just use a simple stepper motor setup, or even a solenoid actuator to do the 180 degree rotation?

 

[Tom.G]

...Or even simpler, use you hand(s) to rotate whatever it is that needs rotating.

 

[DaveE]

If you are thinking of using the Faraday Effect, then your B-field should be parallel to the beam , not perpendicular.

Using two inductors seems much harder to me than using one and driving the current (or B-field) as desired. Charging the inductor and then letting it "decay" while a similar inductor is driven in the opposite phase seems inefficient compared to simply switching the polarity on the drive to a single inductor. Those fields simply add, if you have the geometry right. Increasing one is the same as decreasing the other.

My geometry would look more like this (using a magnetic core to increase the flux density):

The diodes, resistor, and capacitor are there to keep from killing your switches; the relay in this drawing, but everyone would actually use MOSFETs in a bridge configuration.

 

[DaveE]

...Or even simpler, use you hand(s) to rotate whatever it is that needs rotating.

Yes. Or permanent magnets (not electricity!!!) to make a B-field that you rotate by hand, or with a cheap motor, to change polarity? Hint: buy really good magnets!