> >>> So to see this correlation/ overlap between photons, I need to meet
>>> two criteria.
>>> 1.) photon flux, to have intensity (wave) noise equal to shot noise
>>
>> You're shooting for a fairly dramatic effect there. HB's Narrabri
>> observatory worked down at the 1% level IIRC. Of course you want
>> students to actually see it, but getting an effect that large is asking
>> a lot. Shot noise is nearly always the ultimate limit in optical
>> measurements.
> Oh the equivalent to shot noise is just a measure. I'm getting
> a numbers of a few percent... which looks hard.
>>
>>> I need I_dc = e * opt_BW,* which I guesstimate to be about 1 uA.
>>> 2.) spacial 'uncertainty' I need the quantity,
>>>
>>> D*d/(lamda*L) >
>> Source needs to be unresolved at the detector, check.
>>
>>>
>>> Where D is detector diameter, d is source diameter,
>>> L is distance from source to detector and lamda is the
>>> wavelength of the light.
>>>
>>> So I don't know the optical BW nor the source size.
>>> I can measure the Laser diode.. ~0.015" ~350 um
>>> (the source size might be a lot less than this?)
>>
>> A single transverse mode has an etendue of lambda**2/2 in each
>> polarization. With lenses you can have any tradeoff of solid angle vs
>> area you like.
> Yeah, but if I stick a lens in front of my detector I'm changing the
> detector area.. so I don't really gain anything.. (maybe that is what you
> are saying. I get confused when etendue is mentioned. )
Etendue is the product of area and projected solid angle. It's related to the thermodynamic idea of phase space volume.
>
>>>
>>> When I dial this all up in the lab I see about 10 nA
>>> of photocurrent. (1%) The number one problem with this
>>> measurement is knowing when the LD starts to lase.
>>
>> Stimulated emission effects start showing up well below threshold,
>> unfortunately.
> Hmm.. Yeah that will be a problem. The wave noise will be a function
> of the det. source geometry.. so maybe can be disentangled.
>>
>>> (I'm thinking some real-time optical spectrum measurement
>>> would help...)
>>> I also dream of scraping the back reflective bit off the laser diode
>>> There's a gold wire bond there and I need some good optics!
>>
>> You can make superluminescent diodes (SLDs) in the lab by gouging the
>> back facet of a laser diode with a scriber. Of course this destroys any
>> passivation back there, which doesn't help reliability. Also there are
>> still important feedback effects even from a damaged back facet.
> OK this is what I was thinking of. These two wavelength laser diodes have
> their active element exposed.
> (I can break the gold wire bonds with my finger.. or finger nail.)
> Any idea How much scratching I need? Will some hunk of metal work?
> Or by scribber do you mean a diamond tipped thingie?
I'd certainly use a diamond or carbide scriber to reduce the amount of force required.
Cheers
Phil Hobbs