MASER's

A _ten_watt_ HeNe?? No wonder you had troubles. The biggest one I've ever seen was 50 mW or so, and that one was a meter long.

Cheers

Phil Honns

I would doubt you could get a sign shop (or any hobbyist) to build a 10 watt HeNe laser. Now if it was a CO2 laser, that would sound plausible.

Argh. You're right. It's been 45 years, I was half asleep, and I couldn't remember the type. It was a CO2 laser. The goal was 10 watts but in operation, it ran at much less power. I don't recall the numbers. I can't find any photos but the cavity length was about 1 meter long. At the time, 10 watts per meter tube length was considered good. Today, I believe it's up to 70 watts per meter.

It was mounted on a concrete block wall, with mirrors and plumbing ending in a microscope running backwards. Destroying the microscope objective lens with debris from the trimmer operation was a constant problem. We also had difficulties controlling the output, which tended to be either too much, or zero, with nothing in between. Despite using the wrong type of mirrors (silver), insufficiently baked glass, creative optics, and a genuinely dangerous high voltage power supply, the laser trimmer was in continuous operation for 2 to 3 years before it was replaced with a commercial product.

I have some of the hybrids buried somewhere in my mess. I need to clean up that area today anyway. A quick look didn't find any, but I did find a box of Chartpak and Brady PCB layout tape and donuts, which are going into the trash.

The company was Alpha Electronics in Stanton CA. I can't find any evidence that it ever existed with Google. Besides CTCSS tones, they also made hybrid LED digital watch modules which also used the same laser trimmer. My responsibility was Pacific Mobile Communications and was only involved in with the laser trimmer when something went wrong.

Yep, I goofed. Failing memory etc. It was a CO2 laser. See my reply to Phil Hobbs.

Wouldn't stimulated emission be the dividing line between an absorption cell and a maser?

-- john, KE5FX

Rubidium gas cells have optical loss, not gain. The 'a' in maser and laser are for 'amplification.'

The first demonstration of a visible LASER I saw was in about 1964, only a couple of year after its invention.

The tube with He, Ne and mirrors was fitted inside a helical flash light in side a white, plastic box. An inverter ran for about 10 seconds, emitting a n audible whine that rose in pitch. Then the box lit up white for an instan t and a small, red spot simultaneously appeared on a wall about 5 yards awa y.

Wow.

At that time, LASERs were being describe as " a solution looking for a pro blem ".

..... Phil

The first LASER (ruby rod) I saw was at an engineering open house (my father was an EE prof, advising several demonstration teams, so it was a personal play land each year). Must have been a few years before that.

Not as I recall. It was commonly known as a "death ray". ;-) Remember, it was during the Cold War. Also, ideas of using it as a cutting tool and other such obvious applications.

I know a guy who built a HeNe laser when he was an undergrad. It used electric discharge, like an old-fashioned neon sign. Since he knew it could be done, he did it.

Sure that wasn't a ruby rod laser? They were flashtube pumped.

a couple of year after its invention.

inside a white, plastic box. An inverter ran for about 10 seconds, emittin g an audible whine that rose in pitch. Then the box lit up white for an ins tant and a small, red spot simultaneously appeared on a wall about 5 yards away.

.... Phil

I remember seeing green laser holograms at Expo '67. Have not seen anything that impressive since. Probably a dangerously high-power laser. ;-)

The Soviet exhibit was a glittering showcase of space age technology, but I don't remember where the hologram display was. The US pavilion was contained in a Buckminster Fuller-designed geodesic dome.

And, of course, there was a monorail.. monorail.

--sp

OK if you like. To me it's a fuzzy line. Optical pumping is different because modulating an RF transition changes the optical absorption. The population inversion is in the RF states. I think in principle you could make an RF oscillator/ amplifier out of it. (In practice there is not enough pumping... optical light.)

George H.

Sure an Rb gas cell has absorption. In optical pumping (which is the physics behind an Rb clock) there is a population inversion and a huge amount of power gain. One RF "photon" causes the absorption of one optical photon. Rb clocks use the 6.8 GHz hyperfine transition. But I can see Zeeman transitions (between electronic states split by an applied B field) down to ~1 kHz (if the local B-field is stable and homogeneous enough.) The optical photon is ~3x10^14 Hz. So that's a power gain of 10^11!

I can't think of any single stage of gain that comes close.

George H.

Superregens. Johnson noise to headphones in a single stage.

Cheers

Phil Hobbs

Grin.. "smart ass" :^) I've never built a super-regen.

Tickling some system and seeing how the "tickle" changes the optical response can be a powerful technique. My favorite data as a post doc used ODCR (optical detected cyclotron resonance). You look at the change in florescence from a semiconductor sample as you blast it with FIR laser light (in a B-field) that is resonant with the electron or hole cyclotron resonance.

It's still taped to my wall.

George H.

Where's the gain? A lot of RF results in a really tiny change in optical attenuation.

The term "laser" was created to describe a pumped amplifier, a device with net gain.

Let's not get too side-tracked. (gain of a relay for instance.) I'm not saying there is any signal gain in optical pumping... like in a laser or maser. But there is power gain. Does an emitter follower have gain?

I'm pretty sure optical pumping can lead to a maser. Goggling optical pumping and masers there are lots. Here's two, the second one looks interesting...

George H.

Yeah, my bad; it's another kind of atomic clock, doesn't use the ion-beam and MASER tech at all. Probably that's why it's so portable. The experimental evidence for laser/maser action can be increased amplitude (due to coherent gain), or long coherence length, or even just fast pulses. For a free-electron laser, it's a sharp spectral peak in the (usually broadband) synchrotron radiation. The first FELs got about three orders of magnitude above the background; everyone was very excited (and I bought one of the commemorative tee shirts).

So, is the decay of the excited state (and therefore the number of available ground states available for excitation) artificially fast because of stimulated emission? That microwave excited state could be metastable, and the Rb atoms would approach inversion if 'twere so. Excited atoms wouldn't continue to absorb, so the absorption could fade to nil.

Wouldn't call it a laser, but the optical electronics is kinda... interrelated. MASER would result if there were a three-state situation, sometimes (like HeNe). Not my field; I shouldcurl up with a book and learn some more.