Now with added Argon!

Hi All,

I thought I'd post some pics of my newly aquired Spectra Physics Argon. This was aquired for half a days work helping to clear a guys workshop. They are in the business of servicing repro-graphics machines and was in fact the very first place I tried to get parts to build lasers, (I originally came away with a 9mm, 780nm, 5mW diode. Not a successful first venture but I was just a noob then!)

The make of laser head, as mentioned; Spectra Physics
Model; 161B-1711
SN; L0253744
Manufactured; Feb 1997

PSU; Cyonics Uniphase
Model; 2101B-10SLSC
SN; 4152
Manufactured; May 1995

I saw it running at the workshop and ran it for an hour when I got it home and it has seemed to gain a little power which I'm pleased with. It stikes on the first click after about 20 seconds and my eyes are loving the colour.

In the shot of the spot you can see an artifact above the main spot. Is this an alignment issue or considered normal?

Although the fan is noisy I must get me more of these!

Can I join the gassy club now please? :bowdown:

Thanks for watching. Any comments, advice, observations welcome.

M

Welcome to the gassy side.

There is something extra cool about gas.

The extra dot is either alignment or something in the front of the laser housing. It is not "normal."

Peace,
dave

So you got this as payment for helping them, nice!

daguin said:

Welcome to the gassy side.

There is something extra cool about gas.

The extra dot is either alignment or something in the front of the laser housing. It is not "normal."

Peace,
dave

Click to expand...

The extra dot is the only downside so far. I guess the first approach would be to run it without the housing to see if it's anything physically in the way. If it is alignment I think it will have to wait until I consider this wonderful colour parse, and feel the need to mess with it. For the moment I am doing the, 'reach out and touch the light', thing. Thanks for the pointer. (Ahh, THAT'S why the site is called laser pointer forums? hehe)

Gryphon said:

So you got this as payment for helping them, nice!

Click to expand...

Yep, I asked to be paid in lasers! I thought it was a good trade myself. There are a few other, "dead", tubes too and more PSUs that I'd like to make a deal on. I am a happy bunny right now though!

M

The extra dot is known as a Ghost Beam.

They have two main causes, one fixable, one not.

Cause one. poorly installed/aligned light sensor beam pickoff. This can often be fixed. If you remove the light pickoff module, run the laser in constant current mode, and you still have a ghost, see cause #2

Cause two, and nothing you can do about it on a sealed mirror tube. Fresnel ghost reflection off the glass face of the output coupler. Amounts to roughly 4% of the beam power and results when the manufacturer did not want to apply a antireflction coating to the output side of the output coupler mirror. This often happens when the OEM the laser was made for had a application where the ghost was not a problem, and it saved the manufacturer about 30-50$ in the cost of the optic. To prevent back reflections the OC does NOT have parallel faces, so the ghost beam comes off at a angle. Your second spot is most likely caused by the designed in "wedge" that prevents Fresnel back reflections from getting amplified by the laser process, which would otherwise cause all sorts of noise and instability on the beam. No amount of mirror tweeking will get rid of a Fresnel ghost. It is physically impossible.

In a few rare cases with a largeframe ion laser you could get cavity misalignment ghosts. But not on a SP aircooled.

If you want to see a Fresnel reflection up close, aim the laser at a piece of window glass or microscope slide, the 4-6% reflection comes from the light having to "slow down" as it enters the glass, then a second reflection will come when it has to "speed up" as it re enters the air.

Steve

The extra dot is known as a Ghost Beam.

They have two main causes, one fixable, one not.

Cause one. poorly installed light sensor beam pickoff. This can often be fixed. If you remove the light pickoff and you still have a ghost, see cause #2 Make sure you power down the laser when cleaning the optic and removing the sensor pickoff for cleaning.
When you power back up the laser without the sensor, make sure your in current mode, or the laser power supply will think it is not producing light and rise to the upper current limit, which rapidly takes lifetime off the tube.

Cause two, and nothing you can do about it on a sealed mirror tube. Fresnel ghost reflection off the glass face of the output coupler. Amounts to roughtly 4% of the beam power and results when the manufacturer did not want to apply a antireflction coating to the output side of the output coupler mirror. This often happens when the OEM the laser was made for had a application where the ghost was not a problem, and it saved the manufacturer about 30-50$ in the cost of the optic. To prevent back reflections the OC does NOT have parallel faces, so the ghost beam comes off at a angle. Your second spot is most likely caused by the designed in "wedge" that prevents Fresnel back reflections from getting amplified by the laser process, which would otherwise cause all sorts of noise and instability on the beam. No amount of mirror tweeking will get rid of a Fresnel ghost.

In a few rare cases with a largeframe laser you could get cavity misalignment ghosts. But not on a SP aircooled.

If you want to see a Fresnel reflection up close, aim the laser at a piece of window glass or microscope slide, the 4-6% reflection comes from the light having to "slow down" as it enters the glass, then a second reflection will come when it has to "speed up" as it re enters the air. Watch your eyes when you insert a piece of glass into the beam, the results, if the glass is rough, or curved, are unpredictable sometimes.

Your second spot in the top of the picture is a Fresnel ghost and is unavoidable.

The garbage attached to the main spot is most probably a dirty OC face, although it could be some internal diffraction. If its internal diffraction you'll just have to live with it.


It looks like you have a dirty output optic. See the optics cleaning chapter in Sam's Laser Faq for the techniques used to clean it.

Steve

Thanks LSRFAQ that's very helpful.

As Argons are a whole new field to me your post leaves me with a couple of new questions.

The first is, how do I identify light sensor beam pickoff and how does it do it's job.

The second is regards a Fresnel reflection in a window pane. Is this observed when you see a beam-splitting effect at low incident angles? With double glazing you can get a whole series of staggered dots. (I will do a search on Fresnel reflections in the meantime)

The third is at a tangent; I've often wondered about your posting name. LRSFAQ. Are you associated with a certain Sam, of laser FAQs fame?

Thanking you again,

M

Morgan said:

The third is at a tangent; I've often wondered about your posting name. LRSFAQ. Are you associated with a certain Sam, of laser FAQs fame?

Thanking you again,

M

Click to expand...

He is Steve Roberts, he writes most ( if not all ) of the material on Sam's laser FAQ. I don't think anyone knows his/her way around an argon laser like Steve does.

[offtopic] you'll notice on my sale thread that there is a picture of my ALC60 with a ghost beam, I just called it a waste beam and now this part of this post is to save me having to edit that part. My internet is too slow for me to be bothered going back to it just now. [/offtopic]

Back on topic, nice little argon you have there. Well done

diachi said:

He is Steve Roberts, he writes most ( if not all ) of the material on Sam's laser FAQ. I don't think anyone knows his/her way around an argon laser like Steve does.

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I thought so. Good to put a name to a... well, another name!

diachi said:

[offtopic] you'll notice on my sale thread that there is a picture of my ALC60 with a ghost beam, I just called it a waste beam and now this part of this post is to save me having to edit that part. My internet is too slow for me to be bothered going back to it just now. [/offtopic]

Click to expand...

I shall go and have a look...

diachi said:

Back on topic, nice little argon you have there. Well done

Click to expand...

I have since opened up the case and taken a pic. Is the component in the centre of the attached photo the, "Light Sensor Beam Pickoff", that Steve mentioned? It looks like loosening a couple of allen bolts will allow removal but is there anything I should be careful of?

It also looks to me that the run time indicator is maxed out. No problem there but confirmation would be good.

Thanks,

M

Yeah that's the light sensor unit, it'll have a little bit of glass in it at a 45* angle which reflects some of the light into a photodiode.

From my experience with JDSU argons, your better just leaving that whole unit it on - it prevents dust getting on your OC mirror ... and trust me, with that fan sucking all the dust and smoke in - your OC is going to get dirty pretty fast. It's also a pain to get them back onto JDSU units without removing the front plate.

You could take it off and see if it has any effect, as well as give the glass window and OC mirror a clean to see if that has any effect on the quality of your dot, but I'd stick it back on once you're done.

As for the hour meter ... I can't even see the little pointer on the scale, so it looks like it's maxed out. But not to worry, if it was in a printer or copier then it was probably run at a low current (most likely it's idle current, usually 3.5-4A for a tube this size) for it's life in service so it should have plenty left on it. I've seen little argons like them with 15,000 hours or more on them still lase . Heck, my last 2211-20SLE had >10,000 hours on it IIRC and it was doing a cool 14mW above it's rated power at it's rated current.

Okay, thanks. I'll set that for next weekend's tinkering. I'll have to have another look for the needle. I thought it looked like a mercury line so wasn't even looking for a needle!

There is SOOO much dust on this thing it is untrue. Easy to write my name in it so it's no surprise the optics are dirty. (I'll follow your advice Steve and jump on to Sam's FAQs for help cleaning them).

I'll update when I have some news...

M

Morgan said:

Okay, thanks. I'll set that for next weekend's tinkering. I'll have to have another look for the needle. I thought it looked like a mercury line so wasn't even looking for a needle!

There is SOOO much dust on this thing it is untrue. Easy to write my name in it so it's no surprise the optics are dirty. (I'll follow your advice Steve and jump on to Sam's FAQs for help cleaning them).

I'll update when I have some news...

M

Click to expand...

It's not really a needle, it's like a little bright orange mark on the scale, it's easy to see. :yh:

Im jealous!...really jealous!

I feel like every time I post in an argon-related thread, I post 'do want' picture. I'm not one to break the streak, so...



Great piece of kit, I'll have to get one eventually.

-Trevor