AOM's and PCAOM's

Hi there,

I've been in contact with Gogu recently about purchasing an AOM chip for my argon laser, and he sent me a very intriguing link to a lab at Niagra college in Ontario that uses an AOM chip as a PCAOM by driving it with a tuneable RF source.

http://technology.niagarac.on.ca/cou...SwitchAOM.html

I'm wondering if anyone here has any idea how this can be done. I'd really like to be able to select a line from my ALC68.

Here's what i (think i) know about AOM chips:
The beam passes through the chip at the bragg angle. Depending on some property of the input waveform to the piezoelectric crystal attached to one end of the crystal a portion of the incident wave is diffracted. The primary beam that passes through the crystal is the 'zeroth mode' beam, the first diffracted beam is the 'first mode' beam, etc.

The output from the driver to the piezoelectric chip is an RF modulated signal at some frequency, with some waveform, and with some signal modulated on top of it.

What i'm guessing:
If I can use a pair of tuneable RF sources, one for each of the lines from my argon, sum their outputs together and amplify them as needed, they would be able to drive a suitable AOM chip as a 2-channel PCAOM chip... that's a total guess tho.

My questions basically are:
What are the properties of this waveform and how do they affect the output of the crystal?
What are the differences between AOM and PCAOM crystals and drivers?
What would the requirements of a AOM driver be to allow it to act as a PCAOM, and could such a beast be constructed from off-the-shelf or surplus RF components?

Steve (Mixedgas on PL) is the person you want to talk to about this. He has mentioned something about a 4 channel in a past thread I didn't find in 30 seconds.... This thread should be of some help: http://www.photonlexicon.com/forums/...s-a-PCAOM-work

If you are looking to buy an AOM gogu can hook you up! http://www.photonlexicon.com/forums/...river?p=130641

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Originally Posted by sugeek

Steve (Mixedgas on PL) is the person you want to talk to about this. He has mentioned something about a 4 channel in a past thread I didn't find in 30 seconds.... This thread should be of some help: http://www.photonlexicon.com/forums/...s-a-PCAOM-work

If you are looking to buy an AOM gogu can hook you up! http://www.photonlexicon.com/forums/...river?p=130641

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Thanks very much for the tips :) I'll have another good search around the forum for more about PCAOM's, It seems at the very least the driver's going to be something like 2x VCO's, RF mixer and amp, and since the AA crystal is TeO, it should technically work as a PCAOM... After that it's just a matter of tuning the driver, of course none of these things are easy, but hey, such is life.

Always with the questions i know, but do AOM's work for multiline argon lasers? (i.e. until i try sorting out this PCAOM business will the AOM blank the whole beam even if it's got more than one wavelength component?)

Gogu is the one that tipped me off to the lab i posted a link for, like i mentioned he's the one i've contacted about purchasing the AOM's, word on the street is they're a good deal and he's good to deal with :)

Steve is the original don of all things related to my laser, he's already helped me out HUGE with info about this argon laser, so i'm reluctant to harass him again until he recovers from my previous inquiries :)

Kvant have the same aoms with different drivers for the 440-480nm here:
http://www.lasershow.sk/bazzar
more $, but it might be of interest..

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Originally Posted by gogu

Kvant have the same aoms with different drivers for the 440-480nm here:
http://www.lasershow.sk/bazzar
more $, but it might be of interest..

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Yeah, for sure! I'm going to look into getting a multichannel driver going, but until then i'll stick with just a single channel.

Gogu i'll be in touch with some money this week :)

[QUOTE=robotarmy;130821]Thanks very much for the tips :) I'll have another good search around the forum for more about PCAOM's, It seems at the very least the driver's going to be something like 2x VCO's, RF mixer and amp, and since the AA crystal is TeO, it should technically work as a PCAOM... After that it's just a matter of tuning the driver, of course none of these things are easy, but hey, such is life.

The angle of the crystal is different in a pcaom then a AOM. You can get a AOM to select 1-2 lines at a time at low transmission.

BY angle in this case, I mean the angle to the crystal structure, in x,y, and z.
They use X ray crystallography to orient the AOM and PCAOm crystals. PCAOM also has a sort of prism face cut into the crystal.

If you insist on doing it the hard way, a patent is here:

http://www.google.com/patents?id=N3A...age&q=&f=false

note that crystal is 4 inches long...

and here: http://www.google.com/patents?id=I0M...age&q=&f=false

you can select 1 (one) color at a time using a plain jane AOM if you FM modulate the carrier.

Steve

[QUOTE=mixedgas;131173]

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Originally Posted by robotarmy

Thanks very much for the tips :) I'll have another good search around the forum for more about PCAOM's, It seems at the very least the driver's going to be something like 2x VCO's, RF mixer and amp, and since the AA crystal is TeO, it should technically work as a PCAOM... After that it's just a matter of tuning the driver, of course none of these things are easy, but hey, such is life.

The angle of the crystal is different in a pcaom then a AOM. You can get a AOM to select 1-2 lines at a time at low transmission.

BY angle in this case, I mean the angle to the crystal structure, in x,y, and z.
They use X ray crystallography to orient the AOM and PCAOm crystals. PCAOM also has a sort of prism face cut into the crystal.

If you insist on doing it the hard way, a patent is here:

http://www.google.com/patents?id=N3A...age&q=&f=false

note that crystal is 4 inches long...

and here: http://www.google.com/patents?id=I0M...age&q=&f=false

you can select 1 (one) color at a time using a plain jane AOM if you FM modulate the carrier.

Steve

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Gah, i thought there might be a difference in the physical orientation of the crystal...

Is the university lab i posted just going ahead with theirs and taking huge losses in beam power then?

[QUOTE=robotarmy;131188]

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Originally Posted by mixedgas

Gah, i thought there might be a difference in the physical orientation of the crystal...

Is the university lab i posted just going ahead with theirs and taking huge losses in beam power then?

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reread the experiment. The hene is done with a CT AOM. The megadollar RGB hecad (Dr Cesele gets folks to fund his hobby while teaching, must be nice!) goes to a PCAOM. The writeup should say," You learned to do a Bragg angle once, now dont let the PCAOM intimidate you....."

Now, the older xerox aoms have a slightly tilted prism face on them and a VCO input, I have, in the lab, some years ago, gotten them to easily select lines with the built in electronics. The angle is small, and you need a long beam path, but it can be done. That older xerox driver tunes from 100-130 mhz. can you route two vcos into a mixer and get two lines, yes, but the total power might be low as you cant overdrive the crystal. more then 2 lines ina short AO, fergetttabout it...

My saying NO, DOES NOT mean you should not try the experiment. It just might say I know what you get......


NOW if you were to have 4 oscillators (AND YOUR SEEING THIS IDEA PUBLISHED HERE FOR THE FIRST TIME EVER FOLKS) and broke each image point down into 4 or 8 time slices, and you gated the RF for each color from each oscillator to the AOM during its own time slice, plus or minus a little delay for propogation, you could have a standard AO modulate colors. BUT you need a cooperative point clock from the software to do it right.. considering 1/30,000 = .000333 second div by say 4 then inverted means = 120 kilohertz, still within the bandwidth of the AO, you now get 1/4 the total power, but you would get color control. IE this is the rough idea of field sequential color used in TV, adapted for laser using a simple AO.

The above paragraph is copyright 2010, all rights reserved, O. Steven Roberts

Steve

[QUOTE=mixedgas;131244]

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Originally Posted by robotarmy

reread the experiment. The hene is done with a CT AOM. The megadollar RGB hecad (Dr Cesele gets folks to fund his hobby while teaching, must be nice!) goes to a PCAOM. The writeup should say," You learned to do a Bragg angle once, now dont let the PCAOM intimidate you....."

Now, the older xerox aoms have a slightly tilted prism face on them and a VCO input, I have, in the lab, some years ago, gotten them to easily select lines with the built in electronics. The angle is small, and you need a long beam path, but it can be done. That older xerox driver tunes from 100-130 mhz. can you route two vcos into a mixer and get two lines, yes, but the total power might be low as you cant overdrive the crystal. more then 2 lines ina short AO, fergetttabout it...

My saying NO, DOES NOT mean you should not try the experiment. It just might say I know what you get......


NOW if you were to have 4 oscillators (AND YOUR SEEING THIS IDEA PUBLISHED HERE FOR THE FIRST TIME EVER FOLKS) and broke each image point down into 4 or 8 time slices, and you gated the RF for each color from each oscillator to the AOM during its own time slice, plus or minus a little delay for propogation, you could have a standard AO modulate colors. BUT you need a cooperative point clock from the software to do it right.. considering 1/30,000 = .000333 second div by say 4 then inverted means = 120 kilohertz, still within the bandwidth of the AO, you now get 1/4 the total power, but you would get color control. IE this is the rough idea of field sequential color used in TV, adapted for laser using a simple AO.

The above paragraph is copyright 2010, all rights reserved, O. Steven Roberts

Steve

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Still a bit over my head but i'll read it a few more times and try to digest it! I could have sworn gogu said the AOM he was selling was used as a PCAOM in that lab, maybe we're both mistaken. The thing is, i'm not going to be trying to select any more than two lines from this laser, as it's just an argon and there's only two lines worth selecting from. Do you think it's still worth learning about RF and lasers at the same time and trying the experiment with a two-channel driver? :)

yes, RF is a useful skill, at VHF its fairly easy, and worth learning. I will help you.
This can be done cheaply.

Steve

Got me reading over and over too :p

Possibly a mistake, but he does refer to the AA aom as a aotf/pcaom a number times

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For the AOM / Q-Switch part of the lab:
Crystal Technology 3080-120 AO Modulator

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For the PCAOM part of the lab:
AA Optoelectronics AA.MTS.110/A3-VIS AOM used as a PCAOM in this experiment

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PCAOMs:

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This part of the lab examines the use of an AOM element as a tunable filter (called an AOTF or a PCAOM: PolyChromatic AOM) - this device can be used to select a single laser line from a multi-wavelength laser.

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For the AA Optoelectronics AOM (used as an AOTF), f is variable (set by the VCO) and v is different (it is in shear mode). Of course the wavelengths are different as well.

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Another reason i "think" that it can be used as an Aotf, haven't actually tested it. (Was hoping Steve would find some time to take a look at one. :) ) is the Kvant bazzar section has 2 listings for the same model AA aom listed as aotf.
http://www.lasershow.sk/bazzar

I have bought a book recently, "understand and use high frequency electronics" from publitronic/elektor (Jon B. Hagen) which, I think, contains everything needed for learning the basis

it contains everything you need to know about filters, amplifiers, couplers, modulation and so on, and I was planning to read and experiment as well

it is true that a 2 channel AOM would be awesome, you'd only need 2 to have a pristine linear modulation on a RGBV laser projector...

simply the fact that an acoustic wave is standing in that crystal and diffracting the beam makes me dream...

now, if I follow another idea, if I was to produce a slight deviation of the beam with an AOM, would it be possible with that said acoustic wave to vary that deflection? I was willing for a time now to try mounting two AO crystals orthogonally and make a beam traverse them to get a small X/Y motion, but have never investigated further (though I know there are AO deflectors based on that principle)

AOM noob question: Is it the 1st or 0th order beam you use as output?

I had always assumed it was the 0th, but now I'm starting to think that the 0th order beam probably can't be completely extinguished.

I'm seriously considering investing in an AOM to use with my green laserwave, because modulation is simply too poor on it now. It only works well at full power CW. Would it be hard to use one of gogu's AOMs for this?

You have to use the first order beam if I'm not wrong

I have one of gogu's AOMs and it behaves really well under 532nm light

I'll try to separately modulate my 532 and 642 lasers before combining, in order to have a colourful demonstration, as I have two AOMs

I already made some videos of the modulation process but they are really crude and the modulation input was only 3V instead of 5V, so the beam is not entirely modulated (also, the mounting and setup was very crude)

part 1:
http://www.youtube.com/watch?v=sczuM...eature=channel

part 2:
http://www.youtube.com/watch?v=fQmp-...eature=channel

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Originally Posted by tocket

AOM noob question: Is it the 1st or 0th order beam you use as output?

I had always assumed it was the 0th, but now I'm starting to think that the 0th order beam probably can't be completely extinguished.

I'm seriously considering investing in an AOM to use with my green laserwave, because modulation is simply too poor on it now. It only works well at full power CW. Would it be hard to use one of gogu's AOMs for this?

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Yes, check the polarization. If linear polarized, things are awesome with a modern isomet 1205. If linear, you can hit 90% according to the data sheet. If random polarized, and your laser has orthogonal polarizations like a hene, You'll get roughly 80% of one and 40-60% of the other.

I'm running that experiment on a sample Gogu sent me, sometime this weekend.

If the laser were all one polarization, data sheet spec on that Isomet is 90% power into the first order beam with a TEM00 mode laser. Mind you, the power you get is determined by the quality of your mounting scheme. Tilts in the plane of the baseplate can come back to haunt you. For various reasons, I'd be happy at the traditional 82% with my polarized system, but it looks like isomet has improved things.
I'm testing with a 80 pitch screw on my angle adjust.

One thing that is worth it with AOM, no matter what, having your reds and greens turn on within a few microseconds of each other, with stable power. You WILL see the difference in the graphics.

Steve

Before this spirals out of control, lets define a few things

AOM
AOBD
AOTF
PCAOM

AOM accousto-optic modulator. Modulates by deflecting the beam off its normal path. Can if specially designed, be used as a scanner, called a AOBD, ie acousto-optic beam deflector. AOBDs are very fast, but are expensive and scan very small angles

AOTF, accousto-opticly tuned filter. There are 3 or 4 variations, a PCAOM is one. NOT all AOTFs act exactly like a pcaom.

A PCAOM passes all diffracted beams in a colinear beam using a slow shear wave crystal. A AOM uses a compression wave, not shear. Shearing the crystal vs compressing it allows the designer to use polarization changes in the crystal to deflect the beam. AOMs are cut from the crystal along its INACTIVE optical axis, it might as well be water for all polarization purposes. PCAOMS and MOST AOTFs are cut along a birefringent axis and are thus active with regards to polarization. If you hold a polarizer up to a AOM and look through it, all polarizations go through the crystal when the driver is OFF. If you hold a polarizer up to a inactive PCAOM, it acts as a waveplate.

A PCAOM has a broad band transducer array of often more then one transducer that can handle high power, because you can have up to 125 mW of power per beam times 8 beams in a neos, or 1 watt. This by definition means a PCAOM is about 8 times more efficient in mW of laser transmitted per milliwatt of RF, because a normal AO needs a quarter watt to one watt for ONEwavelength. This is the downfall of using a normal AO as a polychromatic modulator, your power limited so you dont blow the driver off the crystal and the power per mW is less. Not to mention you are not creating two gratings, when you modulate AOM with two RF carriers, your creating a grating with spacing that changes periodically. If you took the 88-109 mhz FM radio band and amplified it and launched it into a 110 mhZ AOM, you'd see a spot for each radio station, the width of the spot is the bandwidth of the station and the brightness of the spot is the signal strength. So a AOM with a linear CCD detector can be, and is, used for RF spectrum analysis.

You can select a wavelength with the AOM, when it is energized. When it is not driven, a whitelight beam goes straight through, unchanged. When the AOM is energized, its a grating. when its not driven, its a block of glass. If its not overdriven and its driven with a sine wave, its a special case of grating where most power goes into the first order, ie Bragg diffraction. If its overdriven, the amplifier is clipping, or if its driven with a sqaure wave, or if its misaligned, you get RAMAN-NATH diffrraction, multiple orders, and most of the power does NOT go into the first order. In that case its the same as using a unblazed diffraction grating.

If you aim a whitelight beam into a PCAOM or MOST AOTFS, you get a spectrum out at a angle of 5-20 degrees from the entry beam path when the CRYSTAL IS NOT DRIVEN. If you apply a carrier to the PCAOM it will deflect ONE wavelength per carrier back into the entry beam path, colinear to the entrance beam. IE a selected beam goes straight through.

SO when DR CESELE tells his students to use the device, the questions are, 1. does it deflect when NOT energized. 2. Does it normally deflect a white beam off into a spectrum when NOT energized. If the answer to both questions is NO, its a AOM.

Since he tells them to align the red beam from the hecad at 68 mhz to a diffraction, my guess is NOT a AO. He may be misusing or interchanging the term PCAOM with the term AOTF.
A AO can act as a poor to moderate quality AOTF, but a real AOTF can select a beam with MUCH greater resolution then a AOM.

The reason this gets confusing is most scientists only would want to deflect one wavelength at a time. That one wavelength is interest to them, hence the term tunable filter. We display folks use more then one wavelength at any time.

Most older AOTFs are the same slow shear wave design developed at Brevard College in Florida for the PCAOM. So the question I have never had answered is: Which came first, the AOTF or the PCAOM. My bet is BOTH at the same time.

Steve

[QUOTE=tocket;131375]AOM noob question: Is it the 1st or 0th order beam you use as output?

I had always assumed it was the 0th, but now I'm starting to think that the 0th order beam probably can't be completely extinguished.
end quote

oth doesnt go 100% out. for active HIGH high deflection, ie RF on means unblanked laser show projector, you use the first order. If you want to do something like Qswitch, which means you prevent the laser from lasing(blank it) by deflecting the beam out of the cavity, you use the oth order path.

Steve

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Originally Posted by mixedgas

yes, RF is a useful skill, at VHF its fairly easy, and worth learning. I will help you.
This can be done cheaply.

Steve

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Thanks a lot for all your rad info, i'll dig around and do some reading about RF circuitry. I studied the math behind AM and FM synthesis in university, but we never got our fingers dirty with any hands-on RF board layouts or circuits...

Do you think it'd be worth getting in touch with the prof that wrote that lab and see what the deal is?

Quote:

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Originally Posted by robotarmy

Thanks a lot for all your rad info, i'll dig around and do some reading about RF circuitry. I studied the math behind AM and FM synthesis in university, but we never got our fingers dirty with any hands-on RF board layouts or circuits...

Do you think it'd be worth getting in touch with the prof that wrote that lab and see what the deal is?

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I think a better exercise is to look at the part numbers he gives and go to the AA and Isomet/CT websites and look up what he is using.

Start also with Wenzel techlib scroll down to RF. Look at measuring RF voltages with a V.O.M and the 1 watt class c RF amplifier pages. Dr Wenzel was kind enough to write the RF voltage measurement stuff many years ago when I was a student and asked him for help, as I could not afford a RF millivoltmeter back then. www.techlib.com

Steve