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Low pressure, transversely excited nitrogen lasers, utilizing sliding discharges.
Twin Vertical Sliding Discharges
The tube: two strips of acrylate/PMMA ("Plexiglas") sheet are epoxied between two aluminum "L"-shaped pieces. The discharges should slide down the acrylate pieces. This also is supposed to provide preionization.
A hole drilled for the valve stem. The aluminum L-stock I found for the tube is narrower than the peaking capacitors. The tube is not screwed to the capacitor mounts because screw holes in the tube will introduce more problems. The tube is 20 mm square, and 45 cm long.
The windows are Corning Vycor 7913.
Electrical tape on the spark gap is to prevent the HV from sparking between the spark gap's electrodes on the outside of the gap body. This is not yet the full compliment of capacitors.
First light. The mirror isn't being used; it's superradiant here. I was expecting a beam from both sides of the tube, but it wasn't carefully enough tuned at this point. Because of the too narrow tube, shims to ensure electrical contact are part of the tuning formula.
The inside of the tube using a lens that passes near-UV: the sliding discharge lasing areas (purple) aren't covering the entire wall of the tube. This seems to be due to poor electrical contact between the tube and the capacitors. The dark blobs are excess epoxy. The tube was producing a beam at the time, but the camera was angled so as not to receive it.
With the shims adjusted there are now beams from both dielectric walls in the tube. It is also dependent on the tube pressure; with lower pressure there is only a beam from the ground side of the tube. With higher pressure, just one beam, but on the hot side. I had to reduce the charging voltage because of the sparking problem around the outside of the gap body, so the beams are not as bright as in the "first light" image.
Twin sliding discharges. Some of the epoxy holding the window onto this end sticks out into the beam from what is the hot side of the tube in this picture.
Two more peaking capacitors were added subsequent to the above testing. The inductors are an attempt to protect the power supplies from surges.
Single Horizontal Sliding Discharge
The sides of these tubes are made from an aluminum edge protector for plywood sheets. They are separated by a strip of acrylate (PMMA) glued inside. A second strip is glued to the top. The discharge slides on the underside of the top strip. A third, narrow strip of acrylate will be put on the bottom for electrical insulation to prevent a discharge there.
A window mount with tubing for the gas. The mount is double thick to separate the window from the discharge, to avoid deposition of crud. The Vycor windows also get deposits, like the acrylate.
Experimenting with resonator optics. The HR brightens the beam a lot, the OC not so much.
The HeNe in the background was used for alignment.
The circuit is being powered by an FBT and ZVS driver.
Beam profile
Surface plot of the beam profile image above.
The tube rapidly looses power, within a half a minute. I think because of contamination from the PMMA when it's heated by the discharge.This picture shows deposits (or something) on the acrylate, caused by the discharge.<=========
I've tried two other materials for the discharge surface: 1) polycarbonate (don't bother), and 2) a strip of Kapton (polyimide) taped onto the discharge side of the acrylate piece.
The Kapton tape lines the underside of the PMMA to serve as the dielectric surface for the discharge.
The two tubes: with and without Kapton.
With the Kapton, the beam is strong for a couple of minutes instead of disappearing in 30 seconds as with the tube without the Kapton; it takes over 10 minutes before it's almost invisible.
The problem remains that it doesn't recover after a cooling off period; I have to replace the N2. So, I think there is still contamination coming from one of the materials.
Pumping Coumarin 1 with the single sliding discharge N2.
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