writes:

On Tuesday, September 10, 2013 5:36:41 PM UTC-4, Roger wrote:
"Cydrome Leader" wrote in message ...



wrote:

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.

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



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
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.

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

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