Metrologic ML855 HeNe Laser

Hi Folks,

I'm a high school physics teacher, and just found an ML855 HeNe Laser from

1989 in a storage closet at my school that I'm trying to get to energize. M y degree is in electrical engineering, so I'm not unfamiliar with troublesh ooting electronics, but I've never worked with laser electronics, especiall y not from the 80s. The device requires a key to activate a switch, which I cannot find, but I was able to use a paperclip, while the device was unplu gged, to attempt to rotate the lock mechanism into the "on" position. Now, I'm not sure if this rotated the actual switch or just some part of the loc k, so the source of this entire problem could be that I am missing that key . If this is so, how could I obtain a replacement key for this unit?

If this is not the case, and you think my "jimmy the lock with a paperclip" method should have turned it on, does anyone know of any common failures w ith this model laser? The power light on the back does not even turn on, so if it is a failure, I imagine it's with the power supply.

Any and all suggestions would be appreciated.

Thanks

Reply to
mpresnick
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You should be able to get a key made by a locksmith. Baring that, key switches are easy to find with new keys. You could remove the key switch and install a common toggle switch for trouble shooting the laser tube.

Most likely you will find the tube will not start. Over the years, the He gas has migrated through the glass and the seals and will be at low pressure.

If this is the case, It is possible to soak the tube in a He atmosphere and He will diffuse back into the tube. This will take a few days to do and you will need to check it frequently

tm

I'm a high school physics teacher, and just found an ML855 HeNe Laser from

1989 in a storage closet at my school that I'm trying to get to energize. My degree is in electrical engineering, so I'm not unfamiliar with troubleshooting electronics, but I've never worked with laser electronics, especially not from the 80s. The device requires a key to activate a switch, which I cannot find, but I was able to use a paperclip, while the device was unplugged, to attempt to rotate the lock mechanism into the "on" position. Now, I'm not sure if this rotated the actual switch or just some part of the lock, so the source of this entire problem could be that I am missing that key. If this is so, how could I obtain a replacement key for this unit?

If this is not the case, and you think my "jimmy the lock with a paperclip" method should have turned it on, does anyone know of any common failures with this model laser? The power light on the back does not even turn on, so if it is a failure, I imagine it's with the power supply.

Any and all suggestions would be appreciated.

Thanks

Reply to
tm

IF there is a number on the metal part of the switch, a locksmith can make you a key based on that number.

Paul

Reply to
Paul Drahn

bypass the switch.

there's no reason to have a keyswitch on some old dead laser.

You'll also find a new keyswitch from digikey or newark will cost less than talking to a locksmith.

Reply to
Cydrome Leader

Wow, you need to find a better locksmith. I needed a key for a portable pulsed x-ray source and took it to a good locksmith. He looked up the lock number and sold me two keys for $6 something.

I agree with you that the laser will most likely be dead but might be recoverable with a He soak.

I am pretty sure that a key switch is required by the FDA depending on the laser power. Considering he is a HS teacher and may be using this around students, the key switch is a good thing to have.

This space reserved for snarkey comments.

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Reply to
tm

Thanks all. I'll pop it open and hook in a rocker switch or something like that (when no students are around, of course). Maybe I'll get lucky and the tube will still work. Otherwise, I'll talk to some friends in labs about a Helium soak.

Thanks again.

Reply to
mpresnick

Well if that doesn't work. What's a HeNe do, that you can't do with a red diode laser? ~$10 or so.

George H

Reply to
ggherold

Actually quite a lot.

If it is less than about 30 years old, the tube is hard-sealed and doesn't really leak. An ML855 could be function like new.

Bypasss or replace the switch and see what happens.

Just be careful of the line voltage and high voltage inside!

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Reply to
Samuel M. Goldwasser

HeNe is cool retro-tech, laser diodes are cheating...

I have three HeNe tubes that need a new home - can test them to make sure still alive, they were for a Panasonic Laser Disc player from the early 80s...and did work the last time I tested them in 2006.

John :-#)#

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Reply to
John Robertson

bypass the switch.

there's no reason to have a keyswitch on some old dead laser.

You'll also find a new keyswitch from digikey or newark will cost less than talking to a locksmith.

----------------------------------------------------------------------------------------------------------------------------- I've worked with HeNe tubes before. The ones I've seen are a foot to 1.5 feet in length; they are usually 1 milli-watt to 5 milli-watts laser output power. You would not want to get the beam directly in your eye, it could cause some damage. I have heard that the eye very quickly turns to avoid being damaged though. The little laser pointer that you can buy all over that work off of watch batterys are in the same range of power. A HeNe tube puts out a much better quality of laser light and more coherent than a little laser pointer and it will be most likely red light. You won't see the beam at these low power levels, just a intense bright spot on what ever you aim it at. Note that the brightness of the spot is much brighter that our eyes can determine. If it is low power like I'm guessing, I don't think you need the key switch; just replace it with a toggle switch, I think US and Canada changed the rules on low power laser otherwise you wouldn't be able to by a laser pointer toy.

The power supply to power the HeNe tube run around 2000 volts and some put out a pulse to start the tube up to a voltage of around 10,000 volts. They draw a few milliamps. So watch out not to shock yourself if you touch anything inside the chassis. Also note that after the power is turned off, the laser tube holds a charge on it and if you touch the wrong area you'll get an unpleasant shock - guess how I know this :-)

Good luck!

Shaun

Reply to
Roger

Roger kom med denne ide:

Sign: Don't look into laser with remaining good eye.

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Reply to
Leif Neland

The ML855 seems to be rated as a 5 mW laser.

According to the Great Font of Trackless Factoids (i.e. Wikipedia) this is right at the upper limit of Class 3R ("considered safe if handled carefully, with restricted beam viewing"). It's well above the 1 mW limit for Class 2 lasers ("safe because the blink reflex will limit the exposure to more than 0.25 seconds") which is usually the category in which you find inexpensive laser pointers, I believe.

Anything above 5 mW is at least Class 3B, which does require a key switch and a safety interlock.

So, replacing the keyswitch with a new one, rather than with a toggle, would be prudent. Otherwise, the laser might someday end up being toggled on by someone who thought it was no brighter (or more hazardous) than a $2 laser pointer, and careless use might result in someone's eye being damaged.

Reply to
David Platt

e:

like that (when no students are around, of course). Maybe I'll get lucky a nd the tube will still work. Otherwise, I'll talk to some friends in labs a bout a Helium soak.

red diode laser? ~$10 or so.

Hi Sam, What kind of things? We sell both a HeNe and a diode laser with ou r interferometery apparatus.

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The HeNe has a fixed wavelength.... and as it warms up you can watch the co herence length 'swish' around as the different longitudinal modes cross ove r the gain curve. But that seems like a bit of an esoteric difference for t he 'normal' high school laser application.

What else do you have in mind?

George H.

is

in the

Reply to
ggherold

Hi Shaun, Certainly the beam profile is better in a HeNe.

I'm not sure what you mean by 'more coherent', but for the few diode lasers I've looked at - compared to the short cavity HeNe that I have, the diode lasers had a longer coherence length. (Which struck me as a bit weird the first time I saw it... I had this mistaken belief that the coherence length was related to the cavity length.) I'm not sure if the long cavity HeNe's have a longer or shorter coherence length when compared to the short cavities... Perhaps Sam will educate us.

George H.

Reply to
ggherold

They go soft if you don't use them. The gases get unmixed. You may get it to come back but probably not.

Reply to
dave

I worked for a company in the mid 80s that sold Pioneer Laser Disc players. A high school kid came in one day who experimented with the laser tubes from these players. He had holes burnt into the iris of one of his eyes. Chuck

Reply to
chuck

There's a lot one can do with respect to the longitudinal modes, though perhaps that is a bit of a stretch for an intro to lasers in high school.

But one can do some nice interferometry experiments with not much additional equipment.

In fact, I see you your Web site that you do some of these things.

A Fabry-Perot with a common random polarized HeNe laser is a work of art. ;-)

The beam quality is also a lot better than most diode lasers (divergence, beam profile).

With some you can put another mirror in front or in back of the laser (if accessible) and get 1 or more of the other HeNe wavelengths.

I can go on and on..... :)

Contact me directly via repairfaq.org if you'd like.

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Reply to
Samuel M. Goldwasser

It's a crap shoot. Some diodes have exception coherence length but many/most are very short.

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Reply to
Samuel M. Goldwasser

IF they are soft-seal. If newer than around 30 years of age, they will be hard-seal with an essentially infinite shelf life.

Running a soft seal tube that has a decently bright discharge may get it to come back to life after anywhere from a few hours to months.

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Reply to
Samuel M. Goldwasser

I worked for a company in the mid 80s that sold Pioneer Laser Disc players. A high school kid came in one day who experimented with the laser tubes from these players. He had holes burnt into the iris of one of his eyes. Chuck

------------------------------------------------------------------------------------------------ Bullshit!

A read laser does not have that much power. If it was a CD Burner - then that could happen. With a regular CD player, the laser might damage the Retina which is at the back inside of the eye ball, it converts what we see into a signal that our brain decodes as an image.

I would still like to know why it is allowed that anyone can buy a handheld diode laser under 5 milliwatts without any safeties or adult supervision. They can do lots of damage!

Roger

Reply to
Shaun

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