> With CUP, the photons necessary to take an image are blasted through a beam splitter and then through a tube that has several tiny mirrors. These photons are converted into electrons, which encode the data you want captured—namely the time and space data necessary to create an image.
Can photons actually be converted to electrons? I've never heard of anything like this. Very interesting.
I'm a Nature subscriber; here's some information from the paper:
> To record events occurring at subnanosecond scale, currently the most effective approach is to use a streak camera, that is, an ultrafast photodetection system that transforms the temporal profile of a light signal into a spatial profile by shearing photoelectrons perpendicularly to their direction of travel with a time-varying voltage.
It references:
Guide. to Streak Cameras http://www.hamamatsu.com/resources/pdf/sys/e_streakh.pdf (Hamamatsu Corp., Hamamatsu City, Japan, 2002)
From that PDF:
> The incident light on the photocathode is converted into a number of electrons proportional to the intensity of the light, so that these four optical pulses are converted sequentially into electrons. They then pass through a pair of accelerating electrodes, where they are accelerated and bombarded against a phosphor screen.
The paper does present a new method, but they are still using a streak camera:
> To overcome this limitation, here we present CUP (Fig. 1), which can provide 2D dynamic imaging using a streak camera without employing any mechanical or optical scanning mechanism with a single exposure.
---
I do not know anything about the topic, so I can't answer any questions. I was fascinated by the paper back in December when it was published---I'm curious to see eventual applications.
More accurately, these photons then excite electrons to a higher valence band and when those electrons fall back they give off a tiny electric current.
They can, but that's not what they actually mean here.
In this case, it would be more accurate to say that the energy of the photon is being used to excite an already existing electron.
As for creating electrons from photons: if you collide two photons at the correct energy level, you can get an electron-positron pair. This is a very high-energy process, and not how cameras work.
They can ( or more precisely into positron electron pairs), but only at much higher energies ( so for example gamma rays). Most likely here some effect, for example photo-electric effect, where you can reconstruct the original photon from the electron, so that you only transfer the information of the photon.
One way is via Photomultiplier http://en.wikipedia.org/wiki/Photomultiplier
essentially the photoelectric effect is used to create a cascade of electrons, the created current can be measured and related to the energy of the original photon (which is h * f, where h is Planck's constant and f = c/lambda is the light frequency.)
I've possibly missed the point of what you're asking, but... surely it's obvious that photons can be converted to electrons, given that's what a photodiode does and that's how digital cameras work?
>surely it's obvious that photons can be converted to electrons, given that's what a photodiode does and that's how digital cameras work?
This is a common misconception. Both of those use light to facilitate electron excitation, but neither of them actually convert photons into electrons. The electrons are already there.
Can photons actually be converted to electrons? I've never heard of anything like this. Very interesting.