Variable frequency laser using shaken ball bearings

[dnar]

I found this interesting article on Hackaday and thought you guys would be interested also.

http://hackaday.com/2012/09/19/varia...-ball-berings/

[Meatball]

Amazing. I hope more details come around. Perhaps yellow is wavelength better off done yourself.

[Meatball]

I think this setup constitutes what qualifies as a random laser, where the monochromatic light is emitted in nearly all the directions since the granular particles are each a spherical mirror. The mirrors are sort of built in the oscillator. The vibration frequency is what determines the most probable "cavity size" which exists between any two grains.

So while the emission is not realized with a coherent beam, the light is still very useful is it not?

[dsli_jon]

I think this setup constitutes what qualifies as a random laser, where the monochromatic light is emitted in nearly all the directions since the granular particles are each a spherical mirror. The mirrors are sort of built in the oscillator. The vibration frequency is what determines the most probable "cavity size" which exists between any two grains.

Ok, read all the connecting-articles possible, and while I'll concede a 'paradigm-shift', from the previous-post, a) I'm not seeing that these bearings - as-shown - are anywhere's near 'reflective' enough to be 'gain-mirrors', and I don't believe that 'vibration alone', somehow makes them more-so, b) I still don't believe this set-up is *anywhere-close* to lasing-threshold for Rhodamine.. I've personally pumped very-freshly mixed / well-saturated R6G and SR 640, focused in a properly-flowing cell -
with 32 Watts of CW 532 - and did-not achieve threshold.. Only-when Q-switching - at 12 Watts 'average-power' (..where there are kW 'peaks' in the pulse-train..) and up, is the lasing-process sustainable...

...Are the 'vibrations', alone, enough to make this whole-process *so* efficient, that threshold is reduced to 30mW of CW Green?? I assert: no-way, but... .Steve, Eric, help?

So while the emission is not realized with a coherent beam, the light is still very useful is it not?

Yes, but at-best, imo, all he's created is a 'vibrating glo-stick'.. "Light Amplification by Stimulated Emission of Radiation", it is-not, nor can I see it ever being, in his configuration.. it's just stimulated fluorescence, imho.. I'll have to see about the cost of Conti's paper, there, to see what kind of pump they were using, etc.. Or, maybe I should ring up my old Client, F.J. Duarte.. I'm sure he'll be 'up to speed'..

j

[mixedgas]

Long ago and far away, I was using a Lexel 88 argon to illuminate polymer nanofibers as they were being made. I focused the laser down the nozzle so as to illuminate the inside of the fiber where it was at a few hundred microns diameter. Gravity and electrostatic force was pulling the fluid out of the nozzle, which was a vertical cone. We had a high speed camera aimed at the nozzle, and picture results were not good at the time. My fellow technician said, "Why dont you mix some Rhodamine into that?". This was a water based , foggy looking, polymer solution, so what the heck... We did.


After some tedius aligning, my partner in crime, said, "Look at the ceiling Steve...." . Now a 88 would barely threshold a classic dye jet laser in overdrive. However, I had coherent, stimulated, emission with a narrow spectrum on the ceiling. A fat, moving, lumina like splotch, but clearly lasing at a watt and change of pump. Shocked, giggling with glee, I rushed for a patent form and started Googling. The other guy beat me by about three months.

Congrats Dr Lawandy.....

The Lawandy effect. Dense scattering media can sustain a laser. It follows different rules. It does produce coherence, but it is a noisy coherence. What your looking for is per pass gain and some spectral narrowing. If you have gain and narrowing you probably have a laser.

See:

http://www.google.com/url?sa=t&rct=j...myFpTBHU56TsYQ

Talk about a heartbreak.... I was Oh so close to a new type of laser...

However, no matter how low the Lawandy threshold is, 30 mW of CW and a few reflectors is not it. He can have a chain of unstable resonators, but I would be very suprised if that short device does it. I don't know what is going on in the fellow's device, I'd need to see the spectrum vs time. I'm well aware the lowest CW dye laser threshold recorded is 5 mW of pump using a hene to pump a IR dye. I'm well aware that a few mW of average power from a N2 laser can cause a dye to lase. Qswitched 532, yes, at some point you'll get lasing from super-radience. Peak power is what does the trick at low excitation rates.


But if that was going to go at 30 mW CW of 532 pump, I would have probably seen it a long time ago when goofing around.

There are others with great big pump lasers who have done grain array lasers.

Never say never, but I suspect this is something else going on.. Without a spectrum shot, I can't say its lasing. From the pics I see, my bet is he's just changing the adsorption length in the dye, which can change the color a little. Lasing, 99.95% chance of NO, not with that short path and such large balls.

So I let my fingers do the walking and read the paper he's working out of. It is what I expected, lots of pump power. It shows spectral narrowing in repeatable narrow bands when shaker amplitude is increased. However their pump is Quote: "532 nm Nd:YAG, 10 Hz repetition rate and 7 ns pulse duration " at 3.5 millijoule per pulse. Its simply a study of reflected light showing spectral narrowing at 620 nm and a few other wavelengths when the shaker is on.

Steve

[dsli_jon]

From the pics I see, my bet is he's just changing the adsorption length in the dye, which can change the color a little.

Ya, I'd say the claimed '30nm spread' is merely a visual-anomaly, a perceived 'color-shift' from the yellow being reflected off the spheres.. (?) 'course, that's just 'speculation', but.. he's certainly not 'tuning any lasing', here..

Kudos to his 'spirit of exploration', but the 'rub' is the subsequent-oversimplification behind the science, (ie: this http://www.newscientist.com/article/...ble-laser.html ..sounds like 'tunable shake-lasers' will be on the shelves at Safeway, in 2 weeks..) ..and other fundamental-facts, not-straight... ie:

..read the paper..It is what I expected, lots of pump power..their pump is Quote: "532 nm Nd:YAG, 10 Hz repetition rate and 7 ns pulse duration " at 3.5 millijoule per pulse.

..Yup, makes far-more sense... still, it seems an awful big-stretch to call it a 'tunable dye laser'... but, Kevin did-made a nice glo-stick...

Nonetheless, the 'theory' is fascinating, and I'd imagine with further-inspired experiments, ie: imagine using tiny, micromachined cubes or 'diamonds' of galena or silver or gold (..since, apparently, having a 'bit of mass' is helpful, vs the formerly-popular 'nanoparticles'..) - far-more efficient a 'reflector-array', than sphere-surfaces...

So.. who's gonna be the first to stick a 445 on the end of a vibrator to see if they can 'shake it up' to 460??

j

[mixedgas]

Silver nanoparticles are easy to make from silver chloride. But there is a trick to it. You need to cap the un attached ions on the silver particles with a sugar or similar molecule, or you get "Clumps" of nanostuff in the bottom of the reaction tank. Further details will NOT be available from me. Too close to what I do at work.

Steve

[Ragdoll]

Im not bound by any NDAs on that, lol

Mario

[planters]

There is not too much that I can add to Steve's discussion. I also agree with his speculations. It is telling that the the fluorescence tuning range described in the post is well within the fluorescence envelope of Rhodamine 6 dye. I suspect that the perceived color shift seen by Keven is largely due to the greater spacing between the bearings as the frequency is altered. This will increase the penetration depth of the pump but, also as the fluorescence originates from deeper within the vial there will be increased filtering of this emitted light as it passes out. The absorption and florescence curves for Rhodamine DO overlap.

All that aside and despite Keven's claims, granular lasers exist and I think there is a fair body of work published on quantum dot solutions tuning output by adjusting the size of the silver particle ( on the order of 10 to 30 nm diameter). There was a blurb about this in Photonics Spectra a couple of months ago. Aside from the tuning effect, the principal that lowers the threshold is the generation of plasmons. At the interface between a metal surface and a nonmetallic medium there is a huge increase in the electric field (orders of magnitude). In addition, this field is constrained to follow the surface contour around the particle. I don't think the output of these lasers is low order and useful for projection, but I may be wrong.