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lite leak

cheech226

cheech226

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i expect it's normal, but my bare greeNe emits weak coherent light from the HR on the anode end. in reading sam's and other basic laser data/theory i thought that the HR was 100% reflective. why does this happen?
 





Ideally you'd want 100%. But it's a dichro mirror - not a regular one. This is to be sure lasing happens at the line you want. Even the best dicros are not 100% efficient (or are they?), and the circulating power is much much higher than the output. You will inevitably get some leaking. If it's bothering you, you can paint the end black and that's about it.
 
thanks, no it isn't a bother. seems a contradiction. i just wanted to see if it's normal
 
Yeah it's normal...
I've seen this on all HeNe tubes Red and Green..

Jerry
 
Cyparagon said:
Ideally you'd want 100%. But it's a dichro mirror - not a regular one. This is to be sure lasing happens at the line you want. Even the best dicros are not 100% efficient (or are they?), and the circulating power is much much higher than the output. You will inevitably get some leaking. If it's bothering you, you can paint the end black and that's about it.
Click to expand...

Normal silver or aluminum mirrors reflect up to something like 98% and absorb the rest. The dielectric mirrors in a green HeNe reflect something like 99.995%, still enough for the circulating power to pass something, cosidering the OC is also over 99%. You'd have to look up the actual numbers at sams laser faq though.
Stabilized HeNe's use that beam out of the HR to lock the frequency of the lasers, adjacent modes are orthogonally polarized.
 
lasersbee said:
Yeah it's normal...
I've seen this on all HeNe tubes Red and Green..

Jerry
Click to expand...

You'll see it on most lasers unless they have something covering the HR. The beam from the HR on some larger systems is fairly powerful. Not as powerful as whats coming out the OC, but often still enough to cause eye damage.

I imagine you already know this, just putting it out there for other folks. :)
 
diachi said:
You'll see it on most lasers unless they have something covering the HR. The beam from the HR on some larger systems is fairly powerful. Not as powerful as whats coming out the OC, but often still enough to cause eye damage.

I imagine you already know this, just putting it out there for other folks. :)
Click to expand...

More info is always better than not enough info....;)

Jerry
 
Back in school we did an experiment where we built a HeNe cavity with external optics and special laser tubes that had AR-coated windows instead of mirrors. One guy accidentally used two OC mirrors, and had equal power coming out both ends! We were surprised it even worked.

Because of that mistake I ended up with two HR mirrors. No matter how hard I tried I could barely get any output (and I tried for HOURS). Not cool....
 
My argon does this too if the cover is off. I shouldn't have the cover off. It doesnt like being run without the hurricane of air from the fan :)

If you look at an angle from the beam axis (with the tube off of course) you can see straight through most HeNe mirrors :)
 
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