Gas Laser Safety

[Trevor]

...other than the actual beam of course.

I'm speaking about HeNe lasers specifically; I'm curious because I'm procuring one soon, and most of the fun (read: dangerous) facts I know about gas lasers apply to argon. Like their habit of arcing to a carelessly placed hand, which nearly rivals our habit of building and buying obscene amounts of lasers. But I digress.

I knew that any gas laser was going to have high enough voltage to vaporize anyone's fillings - but I didn't know much about HeNe's in particular, so I pulled up Sam's Laser FAQ.

However, unlike those for laser diodes, HeNe power supplies utilize high voltage (several kV) and some designs may be potentially lethal. This is particularly true of AC line powered units since the power transformer may be capable of much more current than is actually required by the HeNe laser tube - especially if it is home built using the transformer from some other piece of equipment (like an old tube type console TV or that utility pole transformer you found along the curb) which may have a much higher current rating.

The high quality capacitors in a typical power supply will hold enough charge to wake you up - for quite a while even after the supply has been switched off and unplugged. Depending on design, there may be up to 10 to 15 kV or more (but on very small capacitors) if the power supply was operated without a HeNe tube attached or it did not start for some reason. There will likely be a lower voltage - perhaps 1 to 3 kV - on somewhat larger capacitors. Unless significantly oversized, the amount of stored energy isn't likely to be enough to be lethal but it can still be quite a jolt. The HeNe tube itself also acts as a small HV capacitor so even touching it should it become disconnected from the power supply may give you a tingle. This probably won't really hurt you physically but your ego may be bruised if you then drop the tube and it then shatters on the floor!

...

After powering off, use a well insulated 1M resistor made from a string of ten 100K, 2 W metal film resistors in a glass or plastic tube to drain the charge - and confirm with a voltmeter before touching anything. (Don't use carbon resistors as I have seen them behave funny around high voltages. And, don't use the old screwdriver trick - shorting the output of the power supply directly to ground - as this may damage it internally.)

Any words of wisdom in terms of handling the tube (...other than not handling the tube) and the laser in general? I believe this one is in the neighborhood of 2-3mW so (I hope at least) the epic shocking potential would be less than that of an argon.

I'm planning on building some sort of enclosure.

-Trevor

 

[photonaholic]

Just be gentle and use common sense.

Enclosed tubes with Alden connectors pose very little to no risk.

Open tubes with clips and exposed ballast resistors are a different story...

I have one of each...

 

[daguin]

...other than the actual beam of course.

I'm speaking about HeNe lasers specifically; I'm curious because I'm procuring one soon, and most of the fun (read: dangerous) facts I know about gas lasers apply to argon. Like their habit of arcing to a carelessly placed hand, which nearly rivals our habit of building and buying obscene amounts of lasers. But I digress.

I knew that any gas laser was going to have high enough voltage to vaporize anyone's fillings - but I didn't know much about HeNe's in particular, so I pulled up Sam's Laser FAQ.



Any words of wisdom in terms of handling the tube (...other than not handling the tube) and the laser in general? I believe this one is in the neighborhood of 2-3mW so (I hope at least) the epic shocking potential would be less than that of an argon.

I'm planning on building some sort of enclosure.

-Trevor

Get in the habit of handling such things with only one hand. Also short out the PSU and/or tube before handling them. If the tube is in an enclosure (aluminum tube) you are pretty well protected from the tube shocking you (except at the plug)

One of the most important things to remember is that BOTH the PSU AND the tube act as capacitors. They WILL bite you after they are turned off and disconnected from power.

Peace,
dave

 

[photonaholic]

A lyden jar filled with HeNe..

 

[Trevor]

Thanks for the replies, guys...

@daguin: So use the technique mentioned in Sam's Laser FAQ to short the PSU and tube?

-Trevor

 

[daguin]

Thanks for the replies, guys...

@daguin: So use the technique mentioned in Sam's Laser FAQ to short the PSU and tube?

-Trevor

The method depends on your particular set-up. Just remember to do it

The shock won't kill you, but it could make you drop or throw your tube

Peace,
dave

 

[bryce007]

Always have a trained professional handle your gas lasers

 

[Trevor]

The method depends on your particular set-up. Just remember to do it

The shock won't kill you, but it could make you drop or throw your tube

Peace,
dave

I'll post pictures once it actually arrives.

Thanks for the replies.

-Trevor

 

[Trevor]

Attached is the layout of the inside of the laser. Any suggestions for a shorting technique? :beer:

EDIT: Two other things - are HeNe's like Argons in that you shouldn't turn them on and run them for a short period due to useless wear on the tube? Also - will shorting the tube with a regular wire be an issue - and does the act of shorting the tube cause undue wear?

-Trevor

 

[HIMNL9]

just get an old 1Kohm 5W resistor (ceramic ones), and use it for short both, keeping it connected some seconds, 5 or 10, if you want to be sure ..... high enough for have no sparks, and low enough for discharge the caps

The tube, once shorted, must give you no more problems ..... the PSU, having a ladder multiplier, can get partially recharged from the other caps (there's moe than one P), so once you've discharged the tube, you can simply short the psu and let the resistor connected, til you're working on it, and take it away when you reconnect all.

 

[Bluefan]

I work with a spectra physics model 256 exciter. What I do is discharge the caps with a 1K power resistor before fiddling with connections. I always keep my distance from any powered unit. Enclosed lasers are usually very safe, but may keep their charge. Always discharge before plugging. In normal use, common sense gets you everywhere.