Why is my Stabilite 2017 AR giving me the blue line when it's set to the green?

[optonano]

Here is the manual for it, we have the Argon version:

http://www.spectra-physics.com/docum...r%20Manual.pdf

In the back, there's a knob to let you select the 488nm blue line, or the 514nm green line.

So, we had it set to the green one, it was lasing, and we were trying to align it so we could decrease the aperture as much as possible. We got it aligned enough so we had a beam going through aperture 5 or so (smaller numbers here mean a smaller aperture), but it seemed like we couldn't get it to align enough to make it through aperture 4.

So we thought that maybe it was way off -- and turned the alignment knobs through their full range to see if there was another position that would be more adjustable. This was a bad idea, and we couldn't get it back to the original position.

So I read a few threads on this forum and someone suggested "rocking the back plate", so we slowly stepped through the horizontal dimension, and at each position, rocked the back plate in the vertical direction.

And this worked! Well, kind of -- we got a beam, but now it's the blue one! And it's still set to the green setting (all the way clockwise).

Now, at one point, my coworker took out the prism that's being aligned. So maybe it's possible he put it in upside-down, and so even though it's set to the "green position", it's backwards so it's blue. I'm going to go check on that now.

But my question is, is it possible to see the blue beam when it's set to the green position, and vice versa?

thank you!

[mixedgas]

There is only a narrow range angular where the prism works. It does not have repeated tuning ranges like a grating. It either is in the narrow range or it is not. It does not reverse as its moved, either.
Since on a Stab-lite you cannot install the prism upside down, that is not it.

As you turn the vertical knob, Does it still tune the whole "rainbow" of violets, blues, greens? If not, your prism is not tracking correctly, or the iris is not open wide enough and you need to repeat some of the alignment steps.

How much tube current are you running? If the plasma current is down low, you may not see 514.


I read your manual, the 2017 is the economy version and apparently Does NOT have Spectra's traditional rotary wavelength scale that moves on the vertical knob.. If you did, the dial rotates on the v adjust with a set screw and you could recalibrate it.

Did you accidentally unlock the course adjustment screws, which are factory set?

That leaves the wavelength calibration switch, which has nothing to do with the mechanical intra-cavity prism wavelength selection. If your referring to the sensor calibration thumb switch still reading 514 when lasing 488, that is not connected to the prism at all, it just sets the wavelength correction factor for the built in power meter. Your supposed to manually set the switch when you change wavelengths. It will not hurt anything, just be a 5-10% reading error on the meter dial.

Steve

[optonano]

Hey, thanks for the response. I'll try to answer everything I know how to... This isn't my area of expertise (yet) so please be gentle with me if I say something really dumb.

When you talk about turning the vertical knob and seeing the rainbow, you mean that it would (for a fixed prism position) change the beam through that range of colors? I'm not sure at the moment because I was looking at it through goggles before that made the beam just a little yellow speck, so I couldn't see the actual color of the beam (except to verify that it was now blue). I'll try that though, if that's what you mean.

I'll check how much current we are running. We were running it in "current" mode, and turning the current knob up to the line I've drawn in this picture:



I'm honestly not totally sure how to read the meter there -- if I had to guess, the top two scales are watts, out of 10 and 2W, then the 2nd lowest is Volts (out of 300), and the bottom is Amps? So we made it so the needle went there, I guess 15A?

I don't think we touched the coarse adjustment screws... This is the extent of what we did: took off the hood, messed with the horiz and vert knobs a ton, took the prism out, put it back in, messed with the aperture. Just to be totally clear, at the beginning of today we had the green line lasing fine and now we currently have the blue one lasing. So we can definitely get both.

Something I didn't understand from the manual was where they're explaining the Wavelength Switch on the back, it says:

WAVELENGTH (nm) switch — calibrates the light pick-off assembly so that the power meter reading remains accurate at different wavelengths (refer to Figure 4-2).

What is the "light pick-off assembly"? I can't find another reference to it in the manual. It sounds like some sort of filter, is the idea that it's filtering everything besides the wavelength you set it to or something?

Thanks for the help!

[mixedgas]

The Bottom scale is the current range. You are showing 17 amps which is not much current for that laser. The tube current scale is the bottom scale. The power scale is the upper scale.. The meter has a three position switch, make sure its set to current when first aligning optics. Do not exceed 25 amps during alignment. Once its lasing you can set the meter switch back to WATTs to manually peak the mirrors for best power. Make sure the mode switch is set to CUR when aligning optics

As you tune the vertical adjust knob it rotates the prism. The prism only permits one line to lase at a time.This is called intracavity line selection, the laser can lase on the following lines:

514.5
501.7
496.5
488.0
476.5
472.7
465.8
457.9
454.5

As you tune the vertical control, the prism will select out one of the above lines for lasing, one at a time. In between each line will be darkness. If the tube current is low or the mirrors are poorly aligned, you will only get 488 and maybe 514.5. Make sure the iris is open when first finding lasing.

I'm jammed up working on my Masters tonight. Come back tomorrow and we will finish the tuning discussion. Don't move the front output coupler mirror if you have not moved it up till now.

Steve



Generally the laser will lase at 55-60% of the specified all lines power when the prism is installed.

The light pickoff is a well enclosed beam splitter at the output end of the laser , it picks off ~ 1% of the laser beam and routes it into a photodiode to drive the Wattmeter and constant light output functions of the laser.

Put the laser in constant power mode (constant light output) and set the power down to ~ 100 mW. Aim the laser at a cinder block wall or other diffuse, fireproof, surface. Make sure your eyes are one and a half meters from this diffuse surface and gently lift the goggles. You should see the true color of the beam. But keep the power below 50-100 mW until your LSO helps you determine if you have safe viewing.

[lasertom1964]

You could remove prism and put in full reflective mirror and get all lines. I have seen the Brewster windows get cloudy and cause power loss. You can adjust these lasers at full current, best way to get back in alignment then decrease to tune fine. Clean all optics with reagent grade acetone to get off oils the clean with alcohol 90% or better 5 or 6 times to remove water solubles. Go back over optic with clean dry q tip wooden handle type, plastic ones melt in acetone an ruin optics. I have seen a laser go from 1 Watt to almost 5 Watts with this method. Takes extreme patients.

[mixedgas]

Don't run the 2017 at full current. Spectra sets the limits way too high. I'm responsible for five of the next model up in a lab.

Steve

[lasertom1964]

You could remove prism and put in full reflective mirror and get all lines. I have seen the Brewster windows get cloudy and cause power loss. You can adjust these lasers at full current, best way to get back in alignment then decrease to tune fine. Clean all optics with reagent grade acetone to get off oils the clean with alcohol 90% or better 5 or 6 times to remove water solubles. Go back over optic with clean dry q tip wooden handle type, plastic ones melt in acetone an ruin optics. I have seen a laser go from 1 Watt to almost 5 Watts with this method. Takes extreme patients. I also walk front and rear reflectors cw and then ccw with both hands to get peak output but dont go to the point of loosing beam. I have spent hours after changing optics getting a beam back, if its real bad I use a red laser to align front mirror, then rock vertical on rear mirror while cw and ccw to get laser to flicker.

- - - Updated - - -

Run at 75 to 80%

[lasertom1964]

I think the laser will limit current to safe value if you go too high.

[catalanjo]

Hi, me again jumping in where angels fear to tread.

This is just to boost your morale and inject a bit of humor really, since you are already in good hands.

When Steve says "As you tune the vertical adjust knob it rotates the prism."
and when you say "(for a fixed prism position)" you must bare in mind that despite appearances both statements are simultaneously true.

The prism is fixed RELATIVE to the mirror (unless someone has been screwing with its mount),
so vertical mirror adjust and prism rotate are the same thing.

When you say "took the prism out, put it back in", I get the feeling (and sincerely hope) you mean the prism AND mirror assembly.
Very rarely can you do this and get a beam again without "tweaking" the vertical at the very least.

If you follow Steve's instructions to the letter you will end up having it lasing with the color you want AND with both eyes intact !

Be careful and best of luck !

Cheers

[mixedgas]

Not for that model. They are not set up like a traditional Argon. The factory locks the course adjustments on both ends. The front mirror radius is picked to be stable with a great deal of misalignment.

It's locked down to the point that the regular concept of walking the cavity is rare with these.

Unless the user has popped the locks, all he needs for now is to find the right aperture setting and peak the rear.

While the concepts are the same, trust me on this, he is very close to where he needs to be.

The whole front mirror assembly is plasma cleaned at the factory, this laser was set up to require minimal maintenance in use. The front end is Teflon enclosed and has a catalyst to reduce the need for cleaning.

Depending on factory option, the rear optics mounts are designed to have their own internal adjustments for tracking. So the prism matches the rear mirror. They are set to match each other by the installing FSE. Major changes to the rear end adjustments. are thus not needed.

If he has the UV option, the current limit is set way higher then you'd.expect.

It is wise to wait and see what is really wrong before advocating traditional style operator work on this unit. It's not a 164.


Steve