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optical super-regen

used.)

ser. But the spontaneous emission is so noisy that there isn't much point u nless the system is super simple.

Lithium niobate.

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That's the x-tal I was thinking of.. I've only used this cut is some direction I'd have to look up... X-cut? Anyway you apply a DC E-Field and that rotates counter propagating beams in different directions. (I think it's the only 'sample' we have for a Sagnac interferometer with overlapping beams*....

For JL's thing, I was picturing leaking some 'start-up' light into the diode, so when he slammed on the gain it was ready to go!

John, is there any way to leak a bit of light back in? Fiber coupling?

I know one laser diode very well, no longer made, LTS, as long as I don't live too long. It's got some weird 'birdies', I could talk about.. but I don't understand in detail. Gain 'relaxation oscillations' which for this DL has one peak near 6 GHz. I know nothing beyond what I can measure. :^)

George H.

*In principle we could spin it real fast and measure absolute rotation... but the numbers suck and you are better with a spool of fiber. There's a turns*area number.. for some angular velocity**.

*Oh or Fizeau drag... which involves flowing water, (which I like to watch, but not sure I want to measure.)

**'angular velocity' is a crappy term, 'angular rate of change' would be more accurate, but longer.

GH

Reply to
George Herold
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s used.)

laser. But the spontaneous emission is so noisy that there isn't much point unless the system is super simple.

With some chirp on the start-up light? I think you want to 'cover' the FSR (free spectral range)of the laser cavity.

GH

Reply to
George Herold

You can use niobate or KTP or KDP or KD*P or BBO or whathaveyou for Pockels cells. I have a couple on the shelf, one niobate and one KTP.

Still, when there's a big population inversion on the laser transition, you get a lot of spontaneous emission noise even if you spoil the gain.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC / Hobbs ElectroOptics 
Optics, Electro-optics, Photonics, Analog Electronics 
Briarcliff Manor NY 10510 

http://electrooptical.net 
http://hobbs-eo.com
Reply to
Phil Hobbs

There are SOAs, basically laser diodes without mirrors, used as once-through amplifiers.

But the cool thing about gain switching is that a laser diode can make sub-100 ps light pulses with relatively slow electrical drive. A lot of CW startup light would (maybe) trash the gain switching mechanism. And I wouldn't know where to get a sub 100 ps seed pulse.

I guess the gain-switched laser makes some random LED-mode photons to seed itself when the gain finally gets high enough. There are similarities to detonating a plutonium bomb.

--

John Larkin         Highland Technology, Inc 
picosecond timing   precision measurement  

jlarkin att highlandtechnology dott com 
http://www.highlandtechnology.com
Reply to
John Larkin

:

is used.)

laser. But the spontaneous emission is so noisy that there isn't much poin t unless the system is super simple.

OK I thought you were trying to get it to turn on faster, (like a super regen.) So my picture of how a laser starts up may be wrong. (hopefully Phil will slap my wrist if I make a blunder.) I figure it's much the same as an oscillator, there's some noise (light) at the right frequency, this get's gained up bouncing back and forth (sloshing from C to L in oscillator ) There's one dominate 'mode/phase' that eventually sucks up all the gain.. (killing other modes/phases.) Viola, a laser. If you had a little CW light that was below threshold, but above the noise it might get the laser started faster. (Or not... i'm half talking out my arse.)

Not sure of the bomb analogy, but if you look at a laser below threshold you see 'LED' type light... much broader (spectrum) than the laser.

George H.

Reply to
George Herold

Hi John, One way to amplify light is with a fiber laser. A glass fiber is doped with erbium and that amplifies light.

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That boosts the signals on long fibers for many kilometers of erbium glass. Maybe you can adapt that phenomenon to your application. Al

Reply to
Alan Folmsbee

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t is used.)

de laser. But the spontaneous emission is so noisy that there isn't much po int unless the system is super simple.

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Walking around, thinking 'how to leak light in'. I realized the best ways is some DC bias current (below threshold) while you blast it. You are probably already doing that. So never mind,

George H.

Reply to
George Herold

Very short seed pulses are easy enough to generate. Google "mode locking". You can also use an incredibly short cavity with an EO switch and only a single transverse mode lazing.

I've worked on mode locked lasers. Before I worked on them I thought they'd be a nightmare. In reality they are quite easy to get going, if your willing to sync the rest of your gear to the mode locked laser.

If you can generate your timing from the mode locked laser, then pulse picking is easy. If you have to try to sync the mode locked laser to an external clock, life can a nightmare.

Steve

Reply to
sroberts6328

In fact, if you don't mind restricting your work to the 1064 nm region, you can try a microchip laser as a seed pulse.

Basically a really thin plate of laser crystal is made with the cavity mirrors coated on the plate. The pump diode is held with a DC bias current just below the lasing crystal's threshold and a pulse is dumped Into the pump diode to take it above threshold but be low saturation. The crystal my or may not have a thin passive adsorptive q-switch crystal bonded to it.

Steve

Reply to
sroberts6328

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