Help! Omnichrome Ar/Kr 643

[dhg6]

Hello,

I have an Omnichrome 643 Ar/Kr head that I can’t get aligned and lasing again. Here is what I’ve done

1. Removed HR and OC
2. Set up HeNe with white card and pinhole
3. Aligned bore of Ar/Kr until I have a perfect spot (no reflections)
4. Put HR back on and aligned dot back through pinhole. I can clearly see the dot again no reflections.
5. Installed OC and aligned its surface reflection back through the pin hole. I can clearly see its reflection not second order spot.
6. Fired up the tube and I still don’t have any laser output. The tube is healthy and was working before this. The mirror mounts are much too precise to do the screwdriver walk on the ouput coupler but I’ve used this technique on other lasers and it worked perfect.
Any ideas what to try as I have spent a lot of time and I know the initial alignment is close enough that lasing should occur?

[DZ]

Not sure where you're located but if you could get the laser to FLEM next weekend I'll get it aligned.

[turbohead]

How did it get out of alignment?

[dsli_jon]

..Any ideas what to try..

Yup, but +1 for what Sir DZ said.. If yer in / near where he'll be / is in FL, he can fix you right straight-up.. Otherwise, let us know where ya'r and we can (perhaps..) point you to someone 'in yer area' with the skillz.. I am also happy to 'take a call' / chat you thru a technique.. (too much to try and type, here..) Especially if yer on the West Coast / in PST..

Lettuce know!
j

[mixedgas]

Get one end really close using the HENE, then SLIGHTLY loosen (~0.010 to 0.020 Inch) the two OUTER screws on the circular mirror mount. Rock and scan the loosened mirror mount by hand against the end plate. Note where the laser flashes and adjust the mirror end plate as needed. This compensates for the index of refraction of the Brewster windows and the parallelism error of the mirrors.. Usually I start with the HR for this task.

The Omni optics have a slight wedge by design, this is what is mainly vexing you. This ensures the ghost beam is not collinear with the main beam.

The first time someone tries a short cavity aircooled, usually it takes them 2-4 hours to get it right.

Make sure the Brewsters are VERY clean.

Steve

[planters]

I am in no way going to disagree with the advise that has been posted. I would add however, that the threshold will be lower the better the laser is collimated. So, conversely , if the laser is run as high as possible, you might see a hint of lasing that can be dialed in as the alignment is perfected.

[mixedgas]

It's got krypton In a short tube with poor gas returns, perhaps best to run.at 3/4.power while aligning. The gas mix tends to seperate at full current in 643s. I''ve repumped that model.

[dhg6]

First off, thanks for all the quick responses. I live in Iowa, and on the second response this head was regassed by Evergreen with around 500hrs. on it. It had single line optics at 568nm. I had a set of full white light optics off of a RYB 643 in pristine condition. I acquired it very cheap as it's demise was due to gravity and the dreaded 1/2 G shock to the return and snapped the glass. Anyway I jumped the gun and swapped both optics at once and it hasn't had any output since. I did put the original optics back in and it did not work either. I know it is the alignment as I have moved the plates during the alignment procedure, I did make marks but it's a very fine line between ground state and excited state. I will retry the alignment again this weekend and stick close to Steve's suggestions as this is the first 643 I've ran into and need to learn it's behavior. I will let you know the outcome and thank you all so much!

[dhg6]

Well Steve, your trick worked. I realigned the 643 with the HeNe like before but this time I left the H.R. loose as you suggested and I jiggled it a little and it started flashing. I slowly brought the mirror mount screw in and kept moving the alignment nuts accordingly until I had it lasing. I tweaked both mirrors for maximum ouput. All lines are present with diffraction grating but after a while the red krypton line drops out. I have the matched squirrel cage blower box for the head and I also added a side draft fan to get more cool air in so it has plenty of cooling. Any Ideas what would cause the line to drop after five minutes of running 3/4 power?

[mixedgas]

When the red line fades does the yellow line ? : A. Get brighter, B. Stay the Same, C. Decrease in Intensity.

Does a slight misalignment of one mirror bring the red back?

The 568 yellow and the 647 red line share the same upper state. They compete with each other for lasing gain. Where it falls to a lower state and lases is dependent on gas pressure, magnetic field, and tube current, and slightly dependent on optics. You have no magnetic field, so that is not the issue here.

All lines air cooled lab lasers tend to be too red and too blue, so often the optics are tweeked to favor the yellow a bit.

Did you clean the Brewsters and Mirrors with UHP or Spectroscopic Grade methanol in a DRY environment? Dirty optics will favor the yellow and blue.

Steve