PBS cube - What am I doing wrong?

[allthatwhichis]

Now I repeated the above but turned the cube (sat a top a rotary stage with angular markings). Again I get different results depending on the orientation of the diode.
First as before with the beam reflecting within the cube, I turned the cube through a massive 29 degrees and get 94.0mW reflected and 0.13mW thru.
Second test with the useful beam going thru I found the null at around 15 degrees which gives 92.4mW thru and 0.53mW reflected.

That is why the cube in my dual red is canted!

Discuss.

Rob

Do you have any pictures of this experiment?

[stanwax]

I did think about it though I think the numbers speak for themselves, however its all still set up so I will snap some - but it will be tomorrow as Im off to bed now - late night from last night to catch up with
Rob

[smogthemog]

Rob, can you take a picture of your reds/PBS set up so we can see exactly what you mean - I/we know what you mean, I am sure, but it will all come clear once seen

[allthatwhichis]

I don't mean pictures to prove your work. I just like to see lasers, and with the quality of your work, the pictures will look that much better.

[stanwax]

Good mornin all - i will get on it later and get some piccies posted.
I only wanted a set of 'this thread is worth nothing without pictures' smileys

Rob

[xntrix]

Thanks for all the input.
Rob-I will try out your suggestions tonight and report back.
Regards, David

[smogthemog]

Hi David.
That mirror and mount you have there, is that one from one of those 'job lot of optics' from mi-lasers off of EBay?
If it is then it looks exactly like one I have here. The ones I have here however don't have full reflect mirrors on them - they have, what look to be, coated mirrors on them. Maybe your mirror is a coated mirror that isn't reflecting 650 red too well??
Do you have a power meter? If so, measure the output from the LD after the mirror and before the PBS.

Just a thought

[stanwax]

here are the images as promised
you can see the dots that should be nulled are dimmer when the cube is angled. Im sure there is a prefectly reasonable explanation for this but I dont know what it is as the black art of polariastion goes over my head.

Rob

[drlava]

Hi David.
That mirror and mount you have there, is that one from one of those 'job lot of optics' from mi-lasers off of EBay?
If it is then it looks exactly like one I have here. The ones I have here however don't have full reflect mirrors on them - they have, what look to be, coated mirrors on them. Maybe your mirror is a coated mirror that isn't reflecting 650 red too well??
Do you have a power meter? If so, measure the output from the LD after the mirror and before the PBS.

Just a thought

That's what I was thinking too. The mirror may be affecting the horizontal polarization of the beam. Try having the beam come out of the other cube face, so that the beam reflecting off the mirror is vertically polarized and the beam straight passing through the cube is horizontally polarized.

[xntrix]

Results of playing with set up tonight.
Jim - yes they are those MI job lots, it is some sort of coating, but can not detect any noticeable loss through it.
i do not have a power meter, but using a variant of Rob's "PeakyMeter" (mine is just a solar cell conected to a DVM), I can at least make comparative measurements of (approximate) power.

In the attached picture Beam 1 is fine.
Beam 2 is the problem. The measured power at point 1 does not vary significantly if the diode is rotated 360 deg - approx 488 on my meter.
At point 2 the power varies from 190 to 390 - this is what I don't understand.
Tommorow I will try the cube at an angle.

David