NEOS PCAOM 6 ch Help

[FutureDesign]

...since, unless you have an RF watt-meter and an O-scope, you are also really kind-of 'shooting in the dark', too, with troubleshooting down the x-tal / driver path, further... one way to quickly test is to swap with a known-good x-tal / driver - If you don't have another, know anyone that does? Friend? Nearby laser-sho co? Just some thoughts...

But I'd bet it's your cube / combo-scheme, there...Or your tube is rotated, in its 'crib'... let us know..
j

Hi,
This week I went to Tesa's place to help him out with the laser. I took my frequency meter and o-scope with me.

I'm not an AOM expert so I didn't actually knew how it worked until I read the manual and this thread.
After some digging around in the driver we managed to get the driver to select the to strong lines in the krypton laser. So now a little more light was passing through the first order. However, there was still a lot of waste in the 0-order.

To the best of my knowledge the two lasers are not polarized. So we installed a filter from thorlabs that rotates V by 90* and summing the now 2 x H together.
However, this didn't make the waste beam go away.

Now we are thinking in the same direction as you guys inhere.. That the krypton might be rotated to an odd angle in the housing. How can we determine the rough angle?

We have in our possession:

1 x "combine V and H" filter.
1 x "split V and H in to directions from a cube" filter.
2 x Diffraction Gratings.
1 x laser power meter.

Can we with this equipment determine the angle?

Thank you very much in advance!

Btw. I have a side question to the AOM driver. The driver is a 6 channel driver and is build from 6 complete circuits with local oscillator, PLL, VCO and so forth. Is there a reason for not using the same local oscillator for all 6 channels. Is it important that they all run async?

/Jan

[mixedgas]

That laser is a medical surplus dual ion laser. AKA a ION SLED

Those medical Innova dual sleds are polarized, they have intracavity Brewster Windows. I know, I used to repair them for a living and have used them in labs at a university when we needed a low cost laser. The argon is vertically polarized, the krypton is at about 45 degrees or 90 degrees depending on the model. You need to rotate the krypton polarization with a waveplate.

The intracavity Brewster window has near zero loss for one polarization, and nearly 75% loss for the mode at right angles to it, so the laser will prefer one polarization. So the orientation of the windows on the tube determines the polarization.
You cannot rotate your tubes in the magnets, nor can you move the windows without ruining the tube. So you must use
external optics to rotate the KRYPTON polarization about 45 degrees, this means a RED waveplate.

I need to get on a 9 hour flight, so I just did the drawings. DSLI Jon can explain from here. I'm on a road trip for a week, so I do not know when I can post again.


The drawing explains how to slide back the window cover to see how the window is oriented on the laser tube.
The Long axis of the window ellipse is the Electric field of the light. By definition, when the long axis of the ellipse is at right angles to the laser baseplate, the polarization is vertical. You'll see the brewster window on the RED laser is rotated compared to the BLUE-GREEN laser.

DSLI Jon can explain the small hazards of this, and how to retune the laser cavity if you lose power is in Argon Ion chapter, Sam's Laser FAQ. Some times the friction of the O-Rings in the window cover can detune the laser cavity a bit. You must be gentle, and do this where there is no dust. There is HIGH VOLTAGE around the
window cover, so until you KNOW where the high voltage is, you must DO THIS WITH THE POWER OFF!.

You have two choices. You cannot easily fix this mechanically, so you can either purchase a waveplate or live with low red power.

Your RF driver is probably just fine, and there is no reason to phase the Local Oscillators on the RF driver off of one master quartz crystal. The different frequencies are simply summed to form a complex diffraction grating in the PCAOM optics. There is no beating between the different RF channels.


I'm on a airplane in 10 minutes, so out of time for now! It will be perhaps 3 days before I can post again.

Steve

[FutureDesign]

Hi, Thanks for your reply and I hope you had a nice flight :-D

That laser is a medical surplus dual ion laser. AKA a ION SLED

Those medical Innova dual sleds are polarized, they have intracavity Brewster Windows. I know, I used to repair them for a living and have used them in labs at a university when we needed a low cost laser. The argon is vertically polarized, the krypton is at about 45 degrees or 90 degrees depending on the model. You need to rotate the krypton polarization with a waveplate.

Are you sure we are talking about the same laser type? I don't seem to recognize Tesa's laser in your description. Just to clarify, the laser we are talking about is a Spectra Physics 2010 and looks like this:

http://www.repairfaq.org/sam/laserpic/sp201-1.jpg

The brewster is all internal and can't be accessed from outside. Only the reflection mirror and window is accessible.

Your RF driver is probably just fine, and there is no reason to phase the Local Oscillators on the RF driver off of one master quartz crystal. The different frequencies are simply summed to form a complex diffraction grating in the PCAOM optics. There is no beating between the different RF channels.

Yes, the driver and AOM seams fine. I was just wondering why the 6 oscillators instead of reusing the same oscillator to save cost, space and get a more reliable design.

Anyway, the big tasks is still to verify whether or not the laser is polarized, and if so, what the angle is then.

We appreciate any help we can get! Thanks in advance!

[mixedgas]

If you have a polarizing beam splitter cube, you can determine what you have. combining cubes work backwards as well, rotate the cube to use as a polarization test. You should see a peak and a null twice per rotation if your laser is polarized, four times per rotation or more if your laser is unpolarized, because in a unpolarized tube the polarization modes are orthogonal to teach other.

Steve

[mixedgas]

Also, you can see polarization in the blue sky in much of the world, as a way to test your polarization cube.

Have no idea what it will be compared to the horizon in the South Hemisphere on a given date. So All I can say is morning and afternoon sky usually shows polarization.

Steve