Power Meter, Bragg Mount and Oudin coil (aka-argon laser toys)

[Jem]

Hmmm... Just a thought here, and at the risk of going off on a tangent again

Don't the Ophir heads have a thermopile sensor? If so, you're not going to be able to do MPE calculations correctly as you won't be able to work out repetition rate/ pulse width (whatever you call it, it's 3:00am here and I have insomnia ). For that you'll need a fast silicon photodiode based sensor that you can connect to an oscilloscope.

Anyway... Time to get Ryan's thread back on topic

[White-Light]

Al... this is simply not true.


^ Lots of clat.

Well I couldn't find a cheaper way of doing it with a new quality head. The Ophir head alone is £140 with postage to the UK.

I guess if you self built using your own thermopile then maybe it could be done cheaper but are you really going to trust your safety to something uncalibrated? At least buying a brand new Ophir head you know its factory calibrated, stable and all you need to verify is to put it next to a meter of know calibration for a quick check.

2nd hand pretty much the same applies. You could perhaps buy an old meter but what about accuracy? You could be buying someone else's problem and with safety that's Russian Roulette. I mean what happens if you buy a 2nd hand meter that drifts? A quick check shows it to match the accuracy of a known calibrated meter, you switch it on, on another occasion, leave it for a while and then its drifted before you take the reading. I don't know if drift is possible with laser power meters but certainly 2nd hand you don't know what you're getting.

WTF as per audience scanning...??? just read what Ryan posted.
He needs to meter his argon(s!)

Al, you win Tangent of the Year Award for the "university epilogue"!

So pointing someone in the direction of where they might be able to get something machined is retarded?

In the real world Dan, not everyone has their own lathe from which they can manufacture 36mm discs from 3mm aluminium. Additionally tolerances are tight. By my calculations the central aperture needs to be 11.28mm across to give 1cm squared (√100/pi x2) (that gives 99.94mm squared when reverse calculated by my limited maths). How many people can home machine to tolerances of 1/100th millimetre? That's CNC territory.

I also didn't say he had to audience scan I was just covering all the bases, and remember the meter I'm building is for home use. I would be on a fast photo-pile meter from Coherent if I was doing professional shows.

Hmmm... Just a thought here, and at the risk of going off on a tangent again

Don't the Ophir heads have a thermopile sensor? If so, you're not going to be able to do MPE calculations correctly as you won't be able to work out repetition rate/ pulse width (whatever you call it, it's 3:00am here and I have insomnia ). For that you'll need a fast silicon photodiode based sensor that you can connect to an oscilloscope.

Jem I was thinking more in terms of using such a power meter as part of the simple method.

[robotarmy]

...you're not going to be able to do MPE calculations correctly as you won't be able to work out repetition rate/ pulse width ...

MPE? Pulse width? Repetition? Sounds like you're talking about audience scanning with a q-switched yag or similar. I'll leave that one up to you guys to do, i'll keep my stuff truly CW or far away up in the air methinks...

[robotarmy]

I can drill an 11.28

... not everyone has their own lathe from which they can manufacture 36mm discs from 3mm aluminium. Additionally tolerances are tight. By my calculations the central aperture needs to be 11.28mm across to give 1cm squared (√100/pi x2) (that gives 99.94mm squared when reverse calculated by my limited maths). How many people can home machine to tolerances of 1/100th millimetre? That's CNC territory. ...

1/100th of a mm = 1e-5 m. quick google search for coefficient of linear expansion of aluminum = 2.22e-5 m/m/K. A half degree change in temperature will cause a change in hole diameter greater than what you're quoting there as a tolerance.

If you want a thingie to go on your meter, let me know tho! I'll just drill a hole 11.3mm, what's 0.02mm between friends (i'll tell you, it's a one degree temperature change! better mount your thermopile meter on a TEC...no wait a minute, don't.)

[danielbriggs]

are you really going to trust your safety to something uncalibrated?

Yeah, well it's not like anyone's going to loose an eye over it.
Oh shit, wait...

That's CNC territory.

Pffttt... if you're so bothered just use a CD. Hole is in the middle is close enough.




Also Al, with your previous post, there are so many things wrong with it, I don't have the energy to quote them all.

All the best ol' chap,
Dan

[White-Light]

Also Al, with your previous post, there are so many things wrong with it, I don't have the energy to quote them all.

All the best ol' chap,
Dan

If there's some point regarding safety then please do. I'm always willing to learn and its best to have the correct information on a public forum.

BTW, I just measured the centre of a cd for pure devilment. Apart from them being clear, I make it 15mm diameter = 176.7mm Squared by my maths or nearly 77% oversize, that's a hell of an error factor.

If I'm wrong I'm always willing to learn Dan

[stanwax]

theres only one way to describe how this thread is going

See image
Rob

[hologeek]

Ahh yeah, i thought it might have been... Don't need the meter so much as i have an analog multimeter that should hopefully work. I was looking at this ... http://www.ebay.co.uk/itm/Ophir-OEM-...item19c3d98f8c ... but I'd rather give my money to someone on PL than some random on EBay, not sure why.

Maybe 2.5 ish watts is more realistic? If i ever buy a laserscope or some CuBr thing i just might have to fork out, but i'm sure at that point the power meter will be a piss in the ocean of my problems

Those are the Ophir meters I am selling. I have some bragg mounts from q-switch's if you're interested. These are rail mounted but you could make it work. I can include one free as a PL deal! Let me know.

[White-Light]

The Ophir head will take 20 Watts if heat sinked provided you don't exceed the average power density of 23kw/cm squared. At least that's what the pdf I have says (attached).



I also said I wasn't going to post here again in my Pm to you Robot but as I have with the spec sheet I will add what I had to say and that is my knowledge of laser safety calculation is very small and I welcome input from others on that. I was trying to be helpful above with my comments on the power meter but it seemed it was an invitation to attack.

However for completeness for any 3rd party coming to the thread, I'd like to just correct what you said above - the accepted pupil diameter is 7mm not 9mm (taken directly from references in multiple ILDA laser safety documents written by Greg Marhov, Patrick Murphy and Bill Benner - I can reference and link if anyone would like these).

Note to Rob, I've re-read these and can see where you're coming from as you do need to know that show doesn't exceed a 1ms dwell time and that the pulse width doesn't exceed the calculated maximum so yes you do need to check patterns to check the pulse width and maximum repetition rate isn't exceeded when using the simple method. I'm now planning to build a fast photo sensor device for width measurement and purchase an oscilloscope when funds allow (maybe some time though, as I'm currently totally skint and I haven't even got a hazer yet! Make no mistake safety is important to me even as a home user and I have no intention of audience scanning anyone at home until I have a full understanding of safety and all the tools to ensure I have all the relevant information to make proper safe calculations)

[robotarmy]

White-light: Thanks for that document on audience scanning, i get what you mean by pulse width now... not q-switch pulse, more "scan-past-eye-hole" pulse. Also, i get what you're talking about with the 1cm^2 aperture, you're not trying to measure power, you're trying to measure irradiance without applying a scaling factor. How big a venue do we have to rock in to get a 1cm^2 beam?! damn...

"If the beam diameter is less than one centimeter, this is already an unsafe exposure unless you are using laser powers below 15mW" god damn that! for serious? I hope my argons aren't that big, but i also hope i don't have to turn the damn things down that much!

Those are the Ophir meters I am selling. I have some bragg mounts from q-switch's if you're interested. These are rail mounted but you could make it work. I can include one free as a PL deal! Let me know.

Ahh! hah, i should have known anyone selling proper gear like that on ebay is on here too! I've had an excellent offer from Dan to work as a stop-gap while my bank account replenishes itself, but i'm sure i'll be in the market for a new shiny toy soon enough.

Do you have any pictures of the q-switch mounts? And a price? I've had a great description of how to make such a beast from mixedgas in another thread, but if your ones are nicer than i could make and the price is right i might just have to splurge and buy my first optics mount EV0R!

So, to recap -
Power meter sorted for now, but options is options
Bragg mount still interested, but might have a solution if i can't hit the price point
Oudin coil, no idea where to even START looking... should i just make one?
Oh yeah, and lasers are deadly and can blind even your third eye, don't use them for anything ever