LED on Photodiode step response

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Thanks for the link John D, There's so many kinds of solid state light emitting devices it's hard to keep track of them all. (I think I know 3/4's of the acronyms, and maybe 1/4 of the under-lying physics.) FP laser diodes?

Where did you find the prices?

George H.

Reply to
George Herold
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Better than Skoal on your screen!

Jamie

Reply to
Jamie

Mechanical streak cameras are surprisingly fast--you spin a polygon on an air bearing (or a magnetic bearing in a vacuum) and look at the scanned beam from some distance. You can do 12 facets x 100k rpm x 10m ~ 2500 km/s. (*) Nanoseconds are _easy_. They did stuff like that back in the 40s and 50s for bomb development.

Cheers

Phil Hobbs

(*) There's an additional factor of 4 pi in there--2 pi for the angular velocity and another 2 for the law of reflection (the beam scans twice as fast as the polygon turns).

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Dr Philip C D Hobbs
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Reply to
Phil Hobbs

They may have a really thick N+ diffusion on the back. That's one common method of making ohmic contacts--you dope the Si so heavily that it becomes a metal (i.e. lots of electrons sloshing round in the conduction band). Better diodes keep that layer as thin as possible, because it hurts the PD performance.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

So true. I'm glad I gave up tobacco years ago. Life is much easier, screen wise anyway.

John

Reply to
John KD5YI

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I was wondering if you can wiggle something faster than you can rotate it?

Well maybe just easier to wiggle.

I think I've seen the optical lever trick done multiple times... 'no smoke but lots of mirrors'

George H.

Reply to
George Herold

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Streak tubes can do 1 ps/div--Hamamatsu still makes them, I think, but they seem to have discontinued their streak cameras. You need a microchannel plate to get enough photons to see at that rate.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

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Ohh, the back side. I was thinking about the front p layer. Well then shorter wavelengths should be 'better'.

Dang! I hope it's not the PD. It'd be a lot easier to replace the opamp!

Did I mention I really like the metal to-5? package the PD comes in. About the same diameter as a 5mm LED and T1-3/4 light bulb.

George H.

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Reply to
George Herold

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They did an optical-input equivalent-time sampling oscilloscope. It had a photocathode, deflection plates, and a PMT, all in the same jug. Vaguely like an image dissector tube. They tried to demo it for me in Hamamatsu, but they couldn't get it to trigger. I don't think it ever went commercial.

Which reminds me of a very strange idea I had for detecting you-know-whats.

John

Reply to
John Larkin

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I put in a requisition for one of those things for my antenna-coupled tunnel junction project, but never got the money.

Cheers

Phil Hobbs

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Reply to
Phil Hobbs

Yes nanoseconds are tough. I come from the optics side but, I also know about the electrical stuff. With the proper analysis of the apertures. the risetime can be calculated even with a curved chopper, the difference is the photodiode/photoconductor response, that depend on temperature, pressure, and the odor of your farts. That does not make the photothingies useless.

Reply to
Will Janoschka
[snip]

Yep. My first job as a technician in MIT Building 20 was designing and building a dual 400W amplifier to drive a two-phase motor for a smear camera at 30K RPM ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
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Reply to
Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

That would have been no small task back then. Now they are less than $100.

tm

Reply to
tm

What is it that you want to measure? Please note 'that that' measurement will have nothing to do with other photodiodes!

Reply to
Will Janoschka

The trick would be to make a clean step, namely a fast rise and a long, flat top.

I suppose you could measure the impulse response of a pd and math that to the step response, making some assumptions.

John

Reply to
John Larkin

Oh. In that case, equalize it out.

John

Reply to
John Larkin

We buy VCSELS from Lasermate and Appointech. The connectorized, aligned fiber-coupled ones are around $30, so I'd imagine the TO18s would be a lot cheaper. We buy 850, 1310, and 1500 nm [1], and they typically put a couple of milliwatts into a fiber. Risetimes are brutal, like 100 ps.

The Optek VCSELS have been, well, disappointing. Their photodiodes are OK.

John

[1] the 850s are VCSELS for sure; not positive about the longer wavelengths.
Reply to
John Larkin

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Not sure what you mean but never had any hassle with anything like that. Then again I never tried to buy the $42000 15kW laser diode either.

I'd probably blow it up :)

Shipping is normally a few days (from them in Austria to me in the UK). They do seem to stock the things I have bought. Shipping and other charges can be a bit expensive for "hobbyist" uses IME.

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John Devereux
Reply to
John Devereux

Fabry-Perot. "Something to do with the mirrors I expect" :)

Hey, googles first link is that britney spears semiconductor physics site. I remember that from 10 years ago!

Top left link on home page - you get a PDF price list of most of their range then you have to search through it. Their website is a bit primitive I'm afraid, but unmatched as far as range of available opto devices is concerned IMO. UV lasers! VCSELS, Resonant Cavity LEDs. "Superluminescent Diodes". "Quantum Cascade Lasers" - sounds like something off the Starship Enterprise.

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John Devereux
Reply to
John Devereux

On a sunny day (Tue, 12 Apr 2011 18:19:57 -0700) it happened John Larkin wrote in :

And that is?

Reply to
Jan Panteltje

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