AOBD Beam Deflector, need some advice....

I found a beam deflector on ebay for 1064nm which has the following specs:

AOBD 4090-6 1064 nm
Scan Angle: 56 mrad
Active Aperture: 2 mm
Scan Frequency Range: 72.5-107.5 MHz
Material: Tellurium dioxide

I want a beam deflector for the output of a small 1064nm YAG with a beam diameter of about 2 to 3 mm. When I see the active aperture is only 2mm, this makes me wonder what it was used for with such a small aperture? I don't think I can use it if it barely accepts a 2mm wide beam, in that case, I don't see how it could be steered at all. Can someone please tell me how to interpret these numbers?

Thanks

Re: AOBD Beam Deflector, need some advise....

Alaskan said:

I found a beam deflector on ebay for 1064nm which has the following specs:

AOBD 4090-6 1064 nm
Scan Angle: 56 mrad
Active Aperture: 2 mm
Scan Frequency Range: 72.5-107.5 MHz
Material: Tellurium dioxide

I want a beam deflector for the output of a small 1064nm YAG with a beam diameter of about 2 to 3 mm. When I see the active aperture is only 2mm, this makes me wonder what it was used for with such a small aperture? I don't think I can use it if it barely accepts a 2mm wide beam, in that case, I don't see how it could be steered at all. Can someone please tell me how to interpret these numbers?

Thanks

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Have a link to the listing or pictures? Can PM me it if you don't want others to see it...

Edit: Think I found it, looks basically like an AOM. You'll need a driver for it too. Probably used as a modulator for a lamp pumped YAG, that or a Q-switch but that seems less likely to me. Could have been for very fast scanning too I guess, that is the intended use afterall. IIRC you'll want a beam <2mm for best results - although it should still work with larger beams I think, just less efficiently. You'll want a Bragg mount for it too, AOMs are sensitive to angle. You can always reduce the beam before the modulator and expand afterwards, no reason that doesn't work. Or have it near the focal point of a 0x expander, i.e. an expander where both lenses are the same power.

What are you planning on doing with it?

AODs are essentially the same as acousto-optic modulators (AOMs). In an AOM, only the amplitude of the sound wave is modulated (to modulate the intensity of the diffracted laser beam), whereas in an AOD, both the amplitude and frequency are adjusted, making the engineering requirements tighter for an AOD than an AOM.

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Re: AOBD Beam Deflector, need some advise....

Alaskan said:

Maybe there are better less cumbersome methods of doing that, like simply having a mirror on a mechanical arm?

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That's how they do it in large lamp pumped YAGs like the Laserscope 800. There are two output couplers, one for 1064nm and one for 532nm. A mirror is placed into the cavity that switches to the 1064nm OC for 1064nm operation.

Here's a diagram of the cavity I grabbed from the manual and labeled (neglected to mark the 532nm OC as HR@1064nm):



You can see the unit with the switching mirror and 1064nm OC/aperture to the right side (near the middle vertically) of this image - the black block with the brass ring houses both, and adjustment hardware. The brass ring and black block to the right, right on the fold, is the 532nm OC/1064nm folding mirror.



Will your NLOC be external to the cavity? Best efficiency is achieved when power in the NLOC is highest, i.e. intracavity, beam waist inside of NLOC (see the two concave mirrors for HR@532? those focus the intracavity beam to a small spot inside the KTP). Unless you're running Q-switched/pulsed, in which case extracavity works fine. Should still work with enough power CW, just less efficient than intracavity or Q-switched/pulsed.

NLOC = Non-linear Optical Crystal for future reference.

Re: AOBD Beam Deflector, need some advise....

Alaskan said:

I was planning on Q-Switched output extracavity for the LBO. OK, I need to look into finding a small switching mirror, that helps a lot, thank you very much. Kind of you to go to this much trouble with the diagram and all

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No problem

A galvo or something like a GM20 actuator may be the best option for doing that, easier than coming up with a driver for an AOD and getting that all aligned and working... Or even a stepper with a mirror/prism attached to the end. Could set two positions for a galvo and use it as a shutter, resting goes to a beam stop, next is 1064nm out, next is LBO. Or just use a separate shutter if you want one...

Need to keep the mirror clean and the spot fairly large, that way you avoid blasting off the coating... Keep in mind LBO is hygroscopic too, you'll probably want that in a sealed container with some desiccant for long life.

Alaskan said:

Diachi, I guess I jam packed that last post with too many questions, stalled your engine for a response

Here is a video I found today showing an AO beam deflector in operation, what surprises me is there is more than one beam on the output and that the beam jumps position with a sinusoidal RF waveform input, where a sawtooth wave makes what appears to be a smooth transitioning beam deflection, but still more than one spot. Why more than one spot? Can you or anyone help me with that?

Do you or anyone here know if these can be used with the high peak power a YAG can output with 6-20 nanosecond pulses and 50-100mJ of output power? Just an example to give me a ball park idea.

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With AOMs/AODs part of the beam isn't modulated/deflected. They are inefficient devices, often with quite a lot of loss. IIRC the good ones, when properly set up, can achieve 90% efficiency - but that's top end, 50-60% is common for lower end devices and less precise setups. So that non-moving dot you're seeing as the transmitted, un-modulated beam.

You can see it quite well here to the left of the image:



Diagram from RP Photonics page (link to page below):




https://www.rp-photonics.com/acousto_optic_modulators.html

Alaskan said:

Thank you again, I had seen that drawing too, but I thought maybe it was simply illustrating the positional change. That is quite lossy, better to use a mirror unless you must use one, it appears. If they are that lossy, shooting a short pulse high energy YAG beam through it might not be such a good thing. Maybe I'm guessing wrong, have you seen them used with YAG's?

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You can use a mirror, but it is far slower than an AOM/AOD.

Not so much lossy in that the power is wasted in the crystal and turned to heat, it's just that much of it isn't deflected and simply passes straight through. You can recover the transmitted beam for other uses - that's what's happening in the picture I added above, they are using the transmitted beam for a lumia.


Ignoring Q-switches, which are essentially the same thing, I've seen them used with YAGs, but only ever AOMs and only ever for CW YAGs (Actually, doubled YAG). But I never looked into using them for pulsed systems The spec sheet for any AOM/AOD will tell you the damage threshold.

Alaskan said:

I found a spec sheet for one I was interested in on ebay, but it had no information regarding how much power the unit could take.

https://goochandhousego.com/product-categories/beam-deflectors-aobd

Here's a spec sheet for one just like it, except only a 5mm aperture, the one I found on ebay has a 15mm slot.

https://www.goochandhousego.com/wp-content/pdfs/45050_5_6_5DEG_85_56A21747.pdf

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They may be able to give you the damage thresholds/power limits if you contact them directly.


One thing I forgot to mention is polarization of the laser beam, the RP Photonics page sums it up nicely.

One may also use different kinds of acoustic waves. Most common is the use of longitudinal (compression) waves. These lead to the highest diffraction efficiencies, which however depend on the polarization of the optical beam. Polarization-independent operation can be obtained when using acoustic shear waves (with the acoustic movement in the direction of the laser beam), which however make the diffraction less efficient.

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Alaskan said:

Great, thank you much, reps coming when I can. This forum can be such a great resource and I am guessing you must work with lasers as a job to be able to respond with so many answers about what are fairly technical newbie questions, as I am, new to YAG's and these optical modulators. I have contacted Gooch and Housego, I think they bought the company who originally made the unit I am interested in, I don't find NEOS when I try to google it, but they use identical part numbers.

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Actually, I work in IT - although I did used to build projectors for a little money on the side. I just spend a lot of time reading - I was never particularly into the pointer side of things either, I always preferred the lab stuff. Spent a lot of time reading about DPSS, would love to build a >1W 532nm at some point, just don't have the funds. I've got more learning to do too... Certainly wouldn't mind a job with lasers though!

Hopefully G&H get back to you. Not sure what happened to NEOS, perhaps G&H bought them. NEOS stuff still turns up fairly frequently though.

The other one I was thinking of was AA Optoelectronics: AA Opto Electronic - Home