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Hanburry-Brown and Twiss (HBT), wave noise

Hi all, So another crazy idea of a project/ physics lab. I went looking on the web for a decent resource.. couldn't find one, so I made a little intro here,

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(I'm a little confused about some of the math, so hand-wavy) One could observe HBT in two ways. Either excess noise in a single detector (above shot noise) or correlations in the noise with two detectors. The idea is to use a laser diode run below threshold as the light source*. I did this measurement ~10 years ago, and at ~10% below threshold, I saw enough photo-current such that the wave noise would be about 10% of the shot noise. If I did all the numbers right!???

So that's the first thing to check. Get a laser diode and measure photo-current at proper distance away, and then measure BW (of diode).

If that looks OK then full speed ahead! I should be able to get something up and running in ~six months?

I've go a bunch of ideas I'd like to talk about.. But first a laser diode (750- 900 nm?) and a PD.

George H.

*I talked with this a bit with Phil H. He was concerned that a laser diode is not a thermal source... which very well might be right... (I need to do the experiment.) I tried to do this measurement (excess noise, single detector) with a Rb discharge lamp, small iris, and PD detector. There just wasn't enough light. (According to Bloom and Bell, (first guys to write about Rb lamps) when run at maximum light The intensity is such that each Rb atom within one optical path length of the surface emits one photon per Rb lifetime. So I'm hoping the laser diode with photons created all along it's length will have enough.
Reply to
George Herold
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If you plot a 2-D histogram (aka constellation plot for comms guys) of the probability of measurement vs I and Q amplitude components of laser light, the results are very different from thermal light.

In thermal light, I and Q are statistically independent, so you get a

2-D Gaussian peak centred around the origin in the constellation plot.

In laser light, the pumping rate constrains sqrt(I**2 + Q**2) to be nearly constant. Thus the constellation plot is a mildly funny annulus, essentially zero at the origin.

Goodman's "Statistical Optics" has a plot of this someplace. I'm currently coming to you from sunny Anna Maria, Florida, which is EOI South till the end of the month, and Amazon doesn't have a 'search inside' for the book.

(By the way, I take full credit for the warm winter in the NE--I booked this place back in July.) ;)

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

Enjoy the warmth. It's rainy, 35F and muddy here. (~freezing point of water and 100% humidity is my least favorite weather.) I've got an e-version of Goldman's book.. I'll give it a look see. Any hints on where or what to look for?

I'm mostly confused when it comes to photon statistics. So I and Q.. you are looking at 'noise' from the light source at one frequency and two (orthogonal) phases?... How hard is that to do? A picture of the set up would help a lot with my understanding. :^)

George H.

Reply to
George Herold

You aren't far from me or John Fields. :)

Reply to
Michael Terrell

You have to have a phase reference someplace, which is easy in RF but much harder at optical frequencies. It's possible using a delay line discriminator, where you interfere the beam against an old copy of itself. The delay has to be large compared with 1/linewidth in the simplest case. That's not super hard to do in fibre.

One could also use two lasers whose centre frequencies are offset by more than the sum of their line widths. That way you'd measure the convolution of the two phases, which would tend to fill in the centre of the annular distributions. It comes out as an RF beat that you can measure electronically.

Alternatively one could use three lasers and look at the closure phase. (I haven't done the math on that in 20 years or more, but with three lasers you get three unique pairs, so you get unique measurements of all the relative frequencies and phases except for the average of them all.

I've been thinking about some similar stuff today--I really need a wavefront measuring interferometer for sub-1mm beams. I'll start a cross-posted thread here and in sci.optics at some point, because there are points of interest for both groups.

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

OK so a semi crappy laser... nothing locked to some atomic line.

Ahh OK I did this with 'my' diode laser to measure the line width I locked one to an Rb line and let the other drift around ~100 MHz away, beat into fast PD. And into a fast DDS. (limited record length of 'scope set limit on measurement. :^(

Well with three you can beat them all against each other and find the BW of each...the two laser measurement I did measures some average.. You could have one really good one and not know it.

Hmm I know almost nothing about wave front interferometery... A big 'flat' piece of glass with mirror on surface.

We built an interferometer that did white light. Beautiful colors and shapes when working... The first one had horrible distortion in the beam-splitter. (due to how it was held.)

George H.

Reply to
George Herold

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