Photon counting for the masses

Doesn't that work mostly or completely in the IR range? The ones I worked with only detected IR, which you can't see. Early '70s in the US Army when they were being cold weather tested.

--
You can't have a sense of humor, if you have no sense.

Night-vision intensifiers can work in the visible and IR, and UV for that matter; depends on the photocathode material. I have a cheap ebay, probably Russian gen-1 unit, that does both. It does have an IR illuminator. When it's on, I can see stuff 50 feet below in our garden, like snakes and skunks and cats. Off, it amplifies scenes illuminated by moonlight or night lights. I was playing with it last night in a very dark room, with just a little street light leaking in through windows. Under a desk I spotted Comet, our black cat, who was invisible otherwise. (Our other cat is Ajax. Very clean cats, if somewhat abrasive.)

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

Mark Kahrs recently sent me this:

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John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

--
Of course it does, and the reason it does is because it supplies your
eyes with many more photons than it - the intensifier - receives.

The price paid is the graininess in the images supplied to your eyes.

Why would single photons be associated with "a high background rate"?

Well, I disagree. If you're trying to find your way around in the dark, I can't see how being blind is better than having a noisy single-photon-resolution image. There are animals with much better night vision than we have, probably single-photon. And image intensifiers can help one survive. Our rod cells apparently detect single photons but they are neurologically filtered out. I wonder why. There must be an evolutionary advantage or tradeoff somewhere, but I can't imagine what it is.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

--
A "high background rate" would represent noise, be it from phosphenes,
stray light, scintillation, or whatever, so in that sense
single-photon events would be associated with a high background rate
in that it would be more difficult to detect them than if the
background were quiet.

If the tiger can see me, and I can't see the tiger, I don't survive.

--

John Larkin         Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom laser drivers and controllers
Photonics and fiberoptic TTL data links
VME thermocouple, LVDT, synchro   acquisition and simulation

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George H.

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Another thing I like about San Francisco: there are practically no lawns.

--

John Larkin                  Highland Technology Inc
www.highlandtechnology.com   jlarkin at highlandtechnology dot com   

Precision electronic instrumentation
Picosecond-resolution Digital Delay and Pulse generators
Custom timing and laser controllers
Photonics and fiberoptic TTL data links
VME  analog, thermocouple, LVDT, synchro, tachometer
Multichannel arbitrary waveform generators

I'm not sure whether this is the case, but maybe it's because the nervous system itself sends the occasional spurious signal? IIRC, neurons can sometimes fire without being stimulated, just randomly. So the brain would do well to filter out the occasional flash, even if some of those flashes happened to be from actual photons. Something like the way digital cameras account for "hot" CCD elements and filter them out.

Just a thought.

--
Brain off-line, please wait.

Absolutely right. But if you're always seeing tigers when there aren't any, you still don't survive because you don't get to eat.

This is (apparently) Nature's way of saying it's better to miss the occasional tiger, than to see them all over the place.

--
When bad men combine, the good must associate; else they will fall one by 
one, an unpitied sacrifice in a contemptible struggle.
		-- Edmund Burke

Beer - because breakfast is your most important meal.

--
Slurm, n.:
	The slime that accumulates on the underside of a soap bar when
	it sits in the dish too long.
		-- Rich Hall, "Sniglets"

Like in engineering: It's probably a compromise of some kind, or may be we are stuck in a local optimum different from, say, nocturnal animals.

We are diurnal animals. It's a choice evolution has made for us at some point. Acute colour vision must have been a better choice than raw sensitivity. We survive in daylight. At night we can hide to survive.

Increasing the sensitivity of low-light vision certainly also causes more false triggers. There is no point in adding gain if it only gets you higher-amplitude noise. I also believe that light is not a stream of photons. A 'photon' is merely the amount of energy exchanged with an electromagnetic field by its interaction with matter. The interactions are discrete events, but the EM field isn't quantized.

Jeroen Belleman

--
Precisely the reason most folks don't go prowling around in the jungle
at night. ;)

On a sunny day (Wed, 02 May 2012 17:48:18 -0700) it happened John Larkin wrote in :

That is total bull. We have the ability to make tools, and live in houses where at night the tiger cannot enter.

The tiger may see me on TV too, and me not the tiger, and it would not worry me a bit, or through bullet proof glass, or sitting on top of a tree, or a tree house, or a car, or a plane or a balloon, use imagination for more cases...

On a sunny day (Thu, 03 May 2012 09:20:32 +0200) it happened Jeroen Belleman wrote in :

Exactly.

No. You would be swamped by the noise floor and a massive waste of bandwidth that could be better used for peripheral motion detection.

The molecules in individual rods are sensitive to a single photons once full dark adaptation is achieved and all the pigment is sensitive. The figure of merit quoted is something between 1 and 10 photons to fire an individual cell but to have the signal passed on to the brain takes several adjacent rods to trigger. The eye's dynamic range is quoted as

10^9 and in some individuals 10^10. That is pretty good! You can incidentally boost your eye sensitivity by breathing pure oxygen especially at altitude but it isn't a good idea to do it for long.

Our high resolution fovea where the cones are located is 10x less sensitive. All amateur astronomers know that to see the faintest objects in total darkness you look to one side of them and jiggle slightly. Averted vision will allow you to maximise vision in the dark.

But they pay for it in terms of resolution. Cats have asymmetric irises to close tighter in strong light and retro-reflective structures at the back of the eye so their retina gets two bites of the cherry.

The cats eye is about 6x more sensitive than a humans, but it is the enhanced lateral resolution and motion detecting tricks that allow it to home in on prey.

We already have that approximately once you become properly dark adapted

- which takes about an hour or so with no white light at all and minimal illumination of any kind. The quantum efficiency is a lot less than for modern CCDs though but quite good for mere chemistry.

You only really find out what your background noise floor looks like when you spend extended periods working in total darkness. These days most city dwellers have never seen the milky way or experienced anything even close to a dark night well away from light pollution.

--
Regards,
Martin Brown