Lexel 65 help

Hi all, well I conquered the 643 and it's been running great (see my other post). This inspired me to pull out an old Lexel 65 I purchased a while back with its matching boat anchor power supply. It has never had output since I've acquired it. So, forging ahead I went with a full cleaning and alignment. After a couple of hours of alignment with my HeNe setup I still can't get this thing to lase. It has much larger optical mounts then the 643 so I tried the screwdriver rock trick and not a hint of a flash. Before alignment I cleaned the optics and Brewster windows. The high reflector has an interesting configuration with a threaded plug and a top hatch bolted down. Now for my main question:

The tube fires right up, no hard starting or anything like that. Is it possible for a tube to ionize but not be able to produce a beam? I know pictures are worth a thousand words so I've included some. I was able to get two decent lit bore pictures as well. I hope to hear some ideas. :)

Quote:

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Originally Posted by dhg6

Is it possible for a tube to ionize but not be able to produce a beam?

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Yes. However, it's far more likely that you simply have an alignment problem.

If your tube voltage is good, then you should be able to get a beam out. Have you tried pulling the OC and aligning the plasma spot on an index card yet?

Where are you located? There may be someone close to you who can help you out in person.

Adam

Do you have access to a lathe? On Lexels I often use an alignment aid consisting of a 15 mm brass "pig" that goes in the optics holder and has a 0.65 mm hole centered in it for the HENE beam. This forces the alignment to the high gain, central region of the bore and greatly aids in lasing.

How many amps do you have in the plasma?

Was the Buna-N O-ring in the back of the threaded optics mount against the mirror?

Steve

No Steve I do not have access to a lathe at home and I wouldn't be able to haul it into work. The o-ring is in the HR as I discovered looking at it. It also contains a prism (see new photos). it's odd as the H.R. side with the prism cover removed looks as it's almost lasing, however on the output coupler side it looks more like the pinkish glow of a hene. I'm not sure of the current other than the selector on the power supply. I started on the lowest position and walked it up to the full fifteen amp setting and 350mw. position. The optics aren't fun to remove as they have a simple rectangle block with a screw for retention and trying to center and lock them down is a treat. Take a look at the three new photos.

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Quote:

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Originally Posted by mixedgas

Do you have access to a lathe? On Lexels I often use an alignment aid consisting of a 15 mm brass "pig" that goes in the optics holder and has a 0.65 mm hole centered in it for the HENE beam.
Steve

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I have a lathe. If you provide or verify the 15mm dimension of the hole for the optics holder, I can make the "brass pig" with 0.65 mm hole in the center.

Willie

You can make the alignment guide out of a business card too. It doesn't need to be made of metal, or be very accurate to work.

Is your alignment beam passing thru the Littrow prism? In which case your HENE just tuned the laser for a red line it does not produce!
You have a tunable laser. It will only lase on one line at a time. So the wrench in the works, so to speak, is that you need to sweep the prism thru the vertical to find lasing. It adds two more steps to the alignment process.

One: the prism holder needs to rotate about the laser beam axis to make the Brewster angle on the prism face match the angle on the Brewster Windows on the tube. Otherwise the losses are huge and it will not lase. This is why the optics holder is held in with three clamps. Think of this as a "twist" in the beam path. You want ZERO twist. When you have zero twist, the prism's sharp edges are perfectly parallel to the base plate. Often a eyeball alignment is close enough, followed by examining the reflected plasma glow from the prism on the ceiling(or bottom of the laser) with a business card. Watch for the ghost beam coming out of the top of the prism holder when the cover is off.

Two, The prism selects one lasing line. So if the prism angle, tuned by the vertical adjustment screw, does not match up with a laser line, you get no lasing whatsoever. So once the prism is close, you need to sweep the vertical axis to select a line and peak it once it flashes.

The prism is what is causing you pain, but in time you can align it close enough with the hene for it to flash.

Watch the Brewster Stem covers, they can bend the rear Brewster Stem enough to break it during course alignment. There should be a way to ever so carefully slide them back, you may need to remove the optics holder to do so.

The easy way out is to get your hands on a High Reflector Holder for alignment and then, if desired, put the prism holder in. I'll see what I have in the 20 pound box of Lexel parts. There are a few different HR holders.

I have a drawing of the "PIG" at home. I'll try and post it tomorrow.

SEE ATTACHED PIC!


Steve

This project is becoming more fun. I will have to give it a go this weekend as I'm running out of time. But THANK YOU SO MUCH!!! Your optics should arrive today and I hope they work for you. On a side note I was playing a little with my coherent Enterprise II Ar/Kr. I revamped the heat exchanger with a filter for closed loop cooling and I also have a photo with the Pheonix lights explained. :) God bless buddy! And I will let you know my progress. :)

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OK, Alignment Piglet dimensions for SP/Lexel Lasers with 15 mm Optics:

14.95 mm aka 0.588 Inch Diameter + 0.0/ -0.02 mm. (Loose Sliding fit in a holder for a 15 mm Optic)

15.26 mm aka 0.60 Inch Length

1.2 mm Diameter aka 0.050" Central hole along axis.

Slightly Bevel Edges for easy entry into mount.

Lathe ends perpendicular to axis as ends bump up against a 3 point rest made of steel balls on the inner face of the optics mount.

Material, Marine or Free Machining Brass, Natural Matt Finish. Do not use Aluminum.

Steve

Hi Steve,
First off I tried the alignment with paying particular attention to the twist on the H.R. prism as you noted. I had it dead on as you could see the reflection on the ceiling inline with the Brewster reflection. The return beam actually started to cancel and sputter the HeNe so I thought Yes it's going to work. I finished with the O.C. and it to went directly back into the HeNe but didn't cancel the beam due to being a partial reflector. I then fired it up and slowly walked it vertically and still nothing. :( So, we will go with baby steps and see the rest of the post for details.

William (turbohead) was kind enough to make me an alignment jig and he is shipping it tomorrow. He only charged me for the brass and shipping and that was very little, what an awesome member. 
I sent him your specs this is what he came back with and I have pictures. The hole is supposed to hold the high reflector correct? I can modify it if I have to but the main body should be right on.

Hi Dave,

Thank you for sending the funds.

Attached is a picture of the alignment tool I just made.

I made a small mistake in that I started to drill the center hole with a #50 drill which is .070" diameter. I realized my mistake after drilling about 30% into the brass. After I realized my mistake, I used the closest number drill available which is .052" diameter. Based on my experience aligning gas laser mirrors, I don't think the partially drilled .070" hole will affect your alignment process since the majority of the hole is per Steve's specification of .050".

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Once you have the alignment jig you'll be able to set the prism's vertical tracking by eye with the hene. You put the jig it at the HR.

Otherwise we need to get/find/make you a mount for the OC.


Keep trying, first prism alignemnts usually take enthusiastic beginners about 8 hours.

I know, I've trained enough grad students to do it!.

Steve

Hi Steve,

I received the alignment jig today (thanks so much turbohead). Is it supposed to go in front of the prism between the Brewster stem and the prism, because it doesn't fit and it will require a little love to get it to that point which I can do?

Can you provide a picture? Is the alignment tool diameter larger than the hole it is suppose to fit into? If the diameter is too large, do you have a digital caliper to measure the actual hole size?

The pig goes at the other end of the laser during alignment. It is NOT at the Prism end.

Please see the attached PDF with cutaway drawing for correct use of the pig. It goes in place of the output coupler mirror.

The HENE is placed at least half a tube length away from the laser head. It is aligned down the bore.

Then the OC mirror is replaced by the pig in the oc mount.

Beam should exit hene then pass thru the centering pig, down the tube bore, thru the prism, and hit the HR mirror.
The beam reflected from the HR mirror should pass back thru the prism, back down the tube and out the pig into the hene.

As you tilt the prism using the vertical control, the beam should track perfectly vertically up and down the rear Brewster window. The portion that passes back thru the plasma tube should track vertically on the rear of the pig. If it does not track perfectly vertically you have twist in the mount.

Once that is done, the beam is centered in the pig's hole and the PIG is replaced by the OC in the OC mount.

Then the ghost from the REFLECTIVE side of the OC is aligned to reflect back into the HENE, which has NOT been moved at all.

The plasma is started.

Searching for lasing:

The prism is then swept vertically by tilting the rear plate using the Vert knob until a flash of lasing is found. Remember the prism is tuned for red by the HENE and you have NO red lines. So you have to find a green or blue line with lots of gain, ie 514.5 or 488.1 nm. Leave the HENE in place.

If you cannot find lasing, note the position of the rear mirror horizontal control using a pencil mark on the knob. Then turn it a TINY fraction of a turn in one direction and search again. If that does not work, go the other direction on the horizontal and search again.

If that does not work, rock the prism like you rocked the Omni rear mount while its loose. If that still does not work, realign the OC again and repeat all search steps.




Prisms require extreme patience. It would help a lot if you had a green alignment laser....


The easy way is to find/buy / make / lathe a proper HR mount without a prism to obtain lasing. Then install the prism. This way you know the OC is right on.





Steve

Hi turbohead and Steve,

Thanks so much Steve for the picture now I understand. Turbohead I will remove the lock ring on the O.C. and see if it fits, I bet it will fit there Thank you both so much and I will update. God bless! :)

See edit of my post #14 .!!

Steve

Thanks Steve,

I will have a chance to work on it Sunday evening and I will take pictures through the steps. I do have a green solid state laser I can also try if the HeNe doesn't get me there. :)

Hi Turbo head and Steve,
I went ahead and removed the O.C. and did a measurement for Turbo head and the jig fits as it should in place of the O.C. with the .070” side facing out. This minor size difference should be negligible as the optimal .050” is facing into the Brewster stem along the axial path. I removed the assy. for pictures and I won’t be able to go for the alignment today as work is calling. Have a great evening all and God bless! 
*nyancat