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How I got my laser eye injury

funraniumlabs.com

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Re: How I got my laser eye injury

#311

Post by ljf »

eru wrote: post #298
sebastiennight wrote: post #249

Earlier quoted context omitted.

This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow.

> This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow. Almost all household appliances that heat (and specifically heat food or water) will operate at the limit of what your house can supply. So that's about 1800 Watt in the US and about 3500 Watt in most of the rest of the world. It's only natural that you see almost any (heating) appliance…

I found it odd that in the US most home brewers don't use electric, but as you say they are limited by the elements they can use.

Here in the UK, my home brew beer set up has a 3000w option - great for boiling 25 litres of water/wort - that said it came with a EU plug with some sort of 'fancy' UK plug convertor. After about 4 years the plug started to get so hot that it melted a socket or two - I found that inside the convertor the connection between the EU plug and the UK was really thin, which was causing it to heat up.

I cut off the end of the cable and rewired it to a heavy duty UK plug - it has been perfect since then - and no longer over heats.

Re: How I got my laser eye injury

#312

Post by eaglefield »

justinclift wrote: post #256
hinkley wrote: post #184

Earlier quoted context omitted.

I know one of the reasons we wanted pico-second and shorter pulsed lasers is that they can cut material with little to no damage of the neighboring material. There was a demo that I read about when this was all brand spanking new research, where they claimed that a laser scalpel causes no heat damage to tissue outside of a cell’s breadth from the contact point.

Is it this? https://en.wikipedia.org/wiki/Coulomb_explosion

It's related, but as i recall the reason that short pulses cut better has to do with heat transfer. Most heat transfer in metal is due to the vibration in the electrons, being much lighter than the atomic lattice they move in. Very short pulses, means that the heating in the beam path happens faster, than the electrons can transfer it out to the rest of the metal. In long pulses once the metal is vaporised, a lot of the surrounding material has melted. This molten metal cools into jagged structures and that leaves the edge weird. All this doesn't happen if the pulse is short enough. It vaporises metal before the surrounding structure has a chance to heat up.

Here's a figure showing the quite stark difference. https://www.researchgate.net/figure/SEM-image-of-the-substra...

Re: How I got my laser eye injury

#313

Post by justinclift »

eaglefield wrote: post #312
justinclift wrote: post #256

Earlier quoted context omitted.

Is it this? https://en.wikipedia.org/wiki/Coulomb_explosion

It's related, but as i recall the reason that short pulses cut better has to do with heat transfer. Most heat transfer in metal is due to the vibration in the electrons, being much lighter than the atomic lattice they move in. Very short pulses, means that the heating in the beam path happens faster, than the electrons can transfer it out to the rest of the metal. In long pulses once the metal is vaporised, a lot of…

Awesome, those photos do illustrate the difference really well.

Thanks heaps. :)

Re: How I got my laser eye injury

#314

Post by lightedman »

cwillu wrote: post #247
oh_my_goodness wrote: post #224

Earlier quoted context omitted.

If it's a 1-micron wavelength laser with a 60 micron radius spot, the divergence can't be much less than about 5.7 mrad half angle. What makes eye safety tricky is just that 2.5 million milliwatts is a lot of power. Even when you spread it out some.

‹twitches in metric prefix› 2.5 kilowatts. It's called 2.5 kilowatts. ‹calms down› 2.5 kilowatts is how much power a tea kettle in the UK draws. It's an insane amount of power to pump into a 60 micron point.

When we discuss laser power, damage begins in the milliwatts range, so those of us in the hobby prefer to state it like that so we can easily give people an idea of how fucked they can be if they treat a laser like a toy.

Re: How I got my laser eye injury

#315

Post by jaystraw »

ponector wrote: post #292
amluto wrote: post #268

Earlier quoted context omitted.

On the other hand, 2.5kW of light is not outrageous. It’s not drastically higher than some of the larger theatrical lights. (Not that being in a spotlight is pleasant , but it does not permanently blind the actors.) A lot of this comes down to wavelength. Some wavelengths get focused by one’s eye and can concentrate their power in a small spot on the retina. Other wavelengths will be absorbed before they get to the r…

But isn't stage light labeled for consumed power, not emitted power?

that's what i was going to say. and while you can use barn doors and lenses to hone the throw (the size of the beam on stage) -- it's not collimated like a laser is. even with parabolic reflectors like par cans. we're talking magnifying glass and the energy at the focal point (minus what the air absorbs for a given wavelength etc)

Re: How I got my laser eye injury

#316

Post by sgarland »

porknubbins wrote: post #250
sebastiennight wrote: post #249

Earlier quoted context omitted.

This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow.

Brits don’t mess around with tea I guess. I believe they’re mostly on 240v even for residential there. Correct me if I’m wrong but I don’t think it would even be possible to heat water that fast in the US on 120v.

Assuming perfect energy transfer (fairly reasonable for conductive heating of water) with no losses to ambient, a starting temperature of 20 C, 1 L of water (which I assume to weigh 1 kg) and a 1800W kettle (the max you’ll find in America): no.

t = specific heat capacity of water * mass of water * degC deltaT / power

4.186 J/gC 1000g * 80C / 1800 J/s ~= 186 seconds

Re: How I got my laser eye injury

#317

Post by sgarland »

ljf wrote: post #311
eru wrote: post #298

Earlier quoted context omitted.

> This seemed like a wild claim (2500 watts for a tea kettle!? As much as a microwave oven in full blast?) so I looked it up. Wow. Almost all household appliances that heat (and specifically heat food or water) will operate at the limit of what your house can supply. So that's about 1800 Watt in the US and about 3500 Watt in most of the rest of the world. It's only natural that you see almost any (heating) appliance…

I found it odd that in the US most home brewers don't use electric, but as you say they are limited by the elements they can use. Here in the UK, my home brew beer set up has a 3000w option - great for boiling 25 litres of water/wort - that said it came with a EU plug with some sort of 'fancy' UK plug convertor. After about 4 years the plug started to get so hot that it melted a socket or two - I found that inside th…

Electric is growing in popularity. It’s not overly expensive (compared to the cost of the gear, anyway) to get a dedicated 30A or 50A 240V circuit installed; or you can brew next to your washer/dryer, since there is nearly always a 240V circuit available there.

Re: How I got my laser eye injury

#318

Post by sgarland »

nayuki wrote: post #274
cwillu wrote: post #247

Earlier quoted context omitted.

‹twitches in metric prefix› 2.5 kilowatts. It's called 2.5 kilowatts. ‹calms down› 2.5 kilowatts is how much power a tea kettle in the UK draws. It's an insane amount of power to pump into a 60 micron point.

60 micrometres. "micron" is a deprecated irregular word that is unlike every other scaling of the metre.

Listen, our shoe sizes are measured in barleycorns, so we’re doing the best we can to adopt metric in places.

Re: How I got my laser eye injury

#319

Post by jaystraw »

ziofill wrote: post #234
DannyBee wrote: post #17

So I laser weld, and beyond my own PPE, interlocks (gun won't fire if it's not touching metal, etc), the most important part of the whole setup is laser safety curtains. Because it's a 2500 watt laser, if i didn't have laser safety curtains , the relections/etc could very easily blind someone at a fairly long distance. The NOHD (nominal ocular hazard distance) is something like 10km (2500 watt laser, 0.06mm spot size…

What are the curtains made of? I’m surprised 2500W on 0.06mm don’t just go through like there’s no curtains

hopes and seams

Re: How I got my laser eye injury

#320

Post by jaystraw »

trelane wrote: post #147
nocman wrote: post #141

Earlier quoted context omitted.

It depends totally on how you read it. In this case, my first thought after reading that was "play stupid games, win stupid prizes". There are plenty of people (especially on the internet) who actually do think that way -- by which I mean people that are serious when they respond with "you guys ruin all the fun" to others who bring up genuine concerns that will most likely have wide-sweeping ramifications.

> There are plenty of people (especially on the internet) who actually do think that way Sure. That's why these safety officers exist. I think some other funranium posts state.that (paraphrased) "safety rules are written in blood." That said, I suspect folks like that would tend to phrase the rule in a way to diminish the implied impact/likelihood, rather than enhance it or state as-is, as (afaict) the original did.

like finishing a comment with, "we walked away with all our fingers -- perfect to flip the safety officer the bird"
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