Some Brewster shots for the Gassy side of LPF

[ultimatekaiser]

I don't have a mirror mount yet, but I decided to play around with my brewster tube today and hand aligned (with the assistance of some soft moldable rubber) my brewster tube for some high power intracavity HeNe goodness. With this crappy makeshift alignment, not calculating optimum distance, not using the center of the mirror, the mirror's semi-crappy condition and other factors, its not even doing a fraction of what it can, but that doesn't stop the intracavity power from being what is probably at least a watt of 632.8nm at about a mm in diameter.

Some gassy exotic intracavity beamshots ahoy! they just begged for some quick camera action.

Cheers! Hope you like! :beer:

 

[Escher]

Very cool - although I'll admit I only understand the physics behind about 50-70% of what your doing here...

I wish you lived closer so we could meet up and have a detailed discussion - I'm very interested in what your doing as well as what Bloom has done to get additional lines out of his HeNe tube..

 

[ultimatekaiser]

Very cool - although I'll admit I only understand the physics behind about 50-70% of what your doing here...

I wish you lived closer so we could meet up and have a detailed discussion - I'm very interested in what your doing as well as what Bloom has done to get additional lines out of his HeNe tube..

This is what technology is for my friend skype is my best friend with some people. Bloom is a bit more of the go to guy, as I'm still learning in some ways, but I quite enjoy working on gas, there's so much more to play with and the lasers are generally higher quality, though that isn't always the case. Glad you enjoyed.

 

[bloompyle]

It's moments like these that really get me going as far as gas goes.

I love seeing others really get into the in-depth parts of gas beyond the pretty lights and cool plasma

Well done with the shady alignment Probably better than what I could do by hand, I've sort of been spoiled with the mounts, holders, and mirrors available.

If I may, I will try to explain what's happening here in a "nutshell" format.

SO!

To begin, a standard HeNe has involves a gas tube, vacuum sealed, two electrodes, and two mirrors. When a power is applied to these electrodes, and a discharge forms between the tube, you get excited atoms as a result.

Initially, you have excited He atoms, as well as Ne atoms. Both of which have high energy electrons. To get this light that you see, the He atoms collide with the Ne, increasing the energy. After this, the electrons fall back to ground, falling through many other levels, and releasing photons in the process.

However, at any one point, there's not enough light being produced to be visible. You use these mirrors to thus trap the light, allowing it to build with every passing second, until the cavity is saturated with enough light as possible. This "amount" is determined by cavity length, bore width, mirror reflectivity, etc, etc. Though that's not really worth getting in to.

However, that's a TON of light being trapped inside the tube. Also, keep in mind that one mirror is ~99.9%+ reflective (high reflector) and the other is about 98.5% (the output coupler). This is a roughly standard figure set for the 632.8nm line.

However! With this tube, only one side has a mirror, generally the HR. The other side is a window that is nearly 100% transparent to light one one polarization (resulting in a polarized output). When one places an external HR with the same radius of center (ROC) then you can get a stable resonator with dozens of watts intracavity power.

The ROC is very important, and difficult to explain in words. Similarly to how we use lenses to focus our lasers to a point, the mirrors do the same thing. Though the mirror is concaved, so the light hits it, and reflects back and at one point, will focus.

In order for a resonator to be stable, the diameter of the beam inside these two mirrors must never exceed the diameter of the mirror itself. I.E. no light is lost. Thus the light will continuously expand, then focus, and expand, and focus. Think of it in slow motion with a rod of light shining at one mirror, reflecting, focusing to a point, unfocusing, then getting to the same diameter again, hitting the other mirror, and doing the same. Like a tennis ball. In this case, the ball gets smaller, and then smallest while over the net, then largest when it hits the racket, no larger than the racket, and then back again.

That was a pair of awful run-on sentences, but I think I made my point

Basically. Good mirrors = lots of light. Bad mirrors = little to no light.

All about math!



Also, PM me if you need my skype name. I can definitely explain this two you verbally if you want.

 

[Sigurthr]

Hey Bloom,
I've been wondering, to what extent would intracavity power increase if the OC was replaced with a HR? Would the total gain in power equal what would normally be transmitted or would it enter a quasi-runaway condition similar to what would happen for a resonant circuit? I ask because I know that particle counting systems used only the intracavity beam and had no real use for the traditional output. Would it not make sense then for these systems to have two HRs?

 

[bloompyle]

The rated power of these Brewster lasers is done using 2 HRs. Generally, there's no need for a Brewster laser if you're just going to use a partially transmissive OC.

Otherwise you would have bought a regular HeNe instead

Generally Brewster lasers are put in use for the intracavity power. So the instruments being used require the high power of the intracavity made available via the use of a second HR.

Some used include particle counting, cavity dumping, boring grad students, tunable lasers, and some others that I can't currently think of.

Though to caviate on the tunable lasers, their design is different from a typical Brewster laser. Yes, there is a Brewster window. However, on the mirrored end, there's an OC instead. With HeNes, there's a littrow prism on the other. This is a combo of a prism with an HR coated face. Basically, it utilizes the diffraction capabilities of a prism, with the HR/resonator capabilities of the HR. I have NO IDEA how ROC comes into play here....

Tunable ions just use a regular prism, and an HR beyond that.

Turning either prism, changes the line in resonation, thus tuning the laser

 

[ultimatekaiser]

Bloom nailed it right on the head. +1 and I believe tunable HeNes use a almost planar broadband OC and a littrow broadband HR variable coated prism. And I don't think they use a brewster, I think they use zero degree windows to maximize throughput, as the brewsters cause light loss. But I could be wrong, I'd have to look it up.

 

[bloompyle]

A planar - planar resonator is damn-near impossible. Pardon the French.

Though it would not surprise me if the coated face of the prism is slightly concaved relative to the input light. However, once you start getting just slightly planar - planar (confonical resonator?) things get a bit more .... Mathy.

There wouldn't be much loss if the angle is cut specifically to a certain wavelength. Though having a range of 543 - 632, 89nm, there'd be no safe b-angle.

I do agree with that speculation.

Also, I'd like to make a correction to my spelling out of RoC. It actually stands for "radius of curvature". My apologies.

Also, care give me a quick explanation of a zero degree window? I haven't spent really any time reading about them, nor have I heard of a use until now.

I can't imagine a safe method of place a window perpendicular, or a non-b-angle. Currently I can't imagine another way to place a window without losses.

 

[ultimatekaiser]

A planar - planar resonator is damn-near impossible. Pardon the French.

Though it would not surprise me if the coated face of the prism is slightly concaved relative to the input light. However, once you start getting just slightly planar - planar (confonical resonator?) things get a bit more .... Mathy.

There wouldn't be much loss if the angle is cut specifically to a certain wavelength. Though having a range of 543 - 632, 89nm, there'd be no safe b-angle.

I do agree with that speculation.

Also, I'd like to make a correction to my spelling out of RoC. It actually stands for "radius of curvature". My apologies.

Also, care give me a quick explanation of a zero degree window? I haven't spent really any time reading about them, nor have I heard of a use until now.

I can't imagine a safe method of place a window perpendicular, or a non-b-angle. Currently I can't imagine another way to place a window without losses.

Brewster windows are not 100% transmissive (ane they are used in tunables, i looked). They still induce reflection and refraction, I could show you in a video. They have 100% transmissiveness only for linearly polarized light that is parallel to the angle of incidence of the photons striking the window. All other forms of light are forced into this linear polarization, or lost. the result is linearly polarized light only, and once it is polarized linearly, it cannot be changed to another polarization, lets say for this example, we need circular polarization, or something else. then that rules out all brewster tubes, or lasers with a brewster plate in them. (usually anode end so the reflections don't interfere with output, and are lost to traps in the enclosure) you would need something non-polarizing. so this is where 0 degree tubes come into play. they are very uncommon, much like B-tubes, as their uses are few, and the cost of making them is tremendously higher, much like b-window tubes. so, like their counterparts, they typically are only made by request. they allow random output outside the cavity, as opposed to forcing it to be linear, leaving the user to determine the particular polarization needed for the application. Also, like most B-tubes, they tend to have a wide bore, and operate in multimode unless you align them a special way to limit gain, this also has some plusses, such as reduced power consumption, and higher power output, since beam quality is usually not something you have to care about. Essentially its just a tube with high quality optical flats at each end. they do suffer from loss, slimilar to the b-windows, but for different reasons. Much like the coaxial tubes come random and linearly polarized, think of them as the random polarized version of a brewster window tube.

as for the subject of the tunables. yes i'm almost positive they use a low RoC. not totally planar, but close...and the littrow prism that is used, generally is rotated only to a certain degree, and the side that is used for selection is not perfectly flat, the coatings thicken as you rotate it I believe to help with the gain of the lower wavelengths, since HeNes have low output, otherwise you'd have a huge tube. and the more-planar mirrors would help to reduce angle change within the construct. which is why it is so critical that the prism not be damaged or corrupted.

 

[Sigurthr]

The rated power of these Brewster lasers is done using 2 HRs. Generally, there's no need for a Brewster laser if you're just going to use a partially transmissive OC.

Otherwise you would have bought a regular HeNe instead

One of the reasons I asked was if I ever got my hands on a Brewster tube I'd want to try cavity dumping. I didn't know B tubes were rated by the intracavity power.

 

[ultimatekaiser]

One of the reasons I asked was if I ever got my hands on a Brewster tube I'd want to try cavity dumping. I didn't know B tubes were rated by the intracavity power.

They sure are, and the differences can be quite astounding. A 98.5% mirror gives me at most 5W intracavity with 5+mW or so out, where two HRs its rated at a whopping 60W! Monstrous amounts of power here, at relatively low cost, and safely tucked away between the mirrors. RoC and cleanliness, even the part of the mirror you use factor in heavily when using one of these. :tinfoil:

 

[bloompyle]

Plus that's from what, a 10" cavity?

Imagine what I could do with an SP 127/107 with 2 HR's This is exactly the surrogate host I plan to use for cavity dumping. Finding a mirror with an RoC that far will be ... difficult. I have some 5m RoC mirrors though.

It should be noted that cavity dumping isn't a game. It's not like just lining up a couple mirrors in an hour, and boom, QCW 65W HeNe.

You're fighting with the speed of light to pull this off. It's been done with a PCAOM for a couple mW from a B tube. I have a plan in mind, but it takes parts harder to find than the lasers I'm using them with.

I'll do it one of these days, if I have any say in it. Sam can continue to call me crazy, but he knows that's never stopped me yet........

 

[ultimatekaiser]

Just depends on how much money you wish to spend my friend...and if you wish to share the project....

 

[bloompyle]

Spending $700 on a single component, without the driver, is unsettling.

It's mostly just waiting for the right parts. I've got to bounce some ideas off of Sam, we are more or less sharing the project. Though it'll likely be funded by me as I think I'm the only one very interested in it (between the two of us).

I have everything I want to do down from start to finish. I just need to source the parts. He's definitely done more networking than I, perhaps he knows a source.

 

[ultimatekaiser]

indeed. my current project lies more in solid state. I'm looking for a Ruby rod. not exactly common nor cheap. (not talking about a little teeny one ) Ruby has a wonderful output, despite its high threshold due to its light decay. Tho using a YAG to pump a dye laser is fun I must say.

 

[bloompyle]

Fun fact. The first "SHG" was someone pumping a quartz sample with a ruby laser. While imaging the spot through a grating, the gentleman noticed an artifact by the main spot.

Apparently the quartz sample doubled the 694 for 347