Wikipedia : Photon | Photonics | Nanophotonics
Optics deal with light in a classical way (i.e, without quantum concepts) using one of two viewpoints:
By contrast, quantum optics (fundamental research) and photonics (applied science) are based on the explicit idea that light consists of packets of energy proportional to its frequency (the coefficient of proportionality being Planck's constant). This idea was formally put forth in 1905 by Albert Einstein to explain the photoelectric effect (in 1900, Max Planck had paved the way by showing that the blackbody spectrum could be explained by postulating that all energy exchanges between radiation and matter could only occur in quanta of energy proportional to the frequency).
So, the key difference between optics and photonics is that the latter deals primarily with the quantization of light which is ignored by the former.
Also, in optics we consider light to consist either of particles (explaining the light rays and sharp shadows on which geometrical optics is based) or waves (which explain diffraction using Huygens principle). In photonics, we integrate the quantum notion that the light quanta (photons) have properties characteristic of both waves and particles.
Wikipedia : Photonics vs. Geometrical optics.
The photoelectric effect was first observed in 1887, by Heinrich Hertz (1857-1894). He found that an illuminated metallic surface produced an electric current proportional to the intensity of the light (as could be reasonably expected) but only if the light frequency exceeded a certain threshold which depended on the metallic surface involved. That was a surprise begging for an explanation which Einstein would only provide in 1905 (he was awarded the 1921 Nobel prize mostly for that reason).
When the surface is highly polished the experimental value of the aforementioned threshold depends on the metal involved and its crystalline structure. Einstein conjectured that every electron was bound to the metallic structure by some binding energy W, dubbed work function.
Einstein further assumed that energy was carried by light carried in disrete packets proportional to the frequency n (for which Lewis coined the word photon, in 1926). Using the constant of proportionality h introduced by Planck in 1900. the kinetic energy of each released electron would then be:
½ m v2 = h n - W
That conjecture was verified experimentally in 1915 by Robert A. Millikan (1868-1953; Nobel 1923) who gave h to about 1% in the process...
Wikipedia :
Photoelectric effect
|
Work function
The photoelectric effect (22:54)
by Barton Zwiebach (MIT 8.04, L3.1, Spring 2016).
This imposes a lower limit on the noise of the image sensors used on modern digital cameras. Those are composed of a digital array consisting of millions of individual sensors of the type analyzed below: One per pixel for a black-and-white sensor, up to four per pixel for color photography.
The arrival of photons in a monochromatic light beam is essentially a Poisson process whose activity a is equal to the radiant power of the beam (in watts, W) divided into the energy of each photon (in joules, J).
For standard yellow-green light (540 THz) the luminous power in lumens (lm) is, by definition, 683 times the radiant power in watts (W). A surface area of S square meters receiving an illumination of L (expressed in lx, a lux being defined as a lumen per square meter) thus receives an average number of photons per second equal to the activity in becquerels (Bq) of the aforementioned Poisson process, namely:
a = S (L / 683) / (h 5.4 1014 Hz) = L S 4.092 1015
If we express a in Bq, L in lx and S in square microns, we have:
a = 4092 L S
In a Poisson process with an activity of a becquerels, the probability of observing exactly n arrivals in t seconds is given by:
Pn = exp(-lt) (at) n / n!
The average number of arrivals is at. Let N be the RMS of the noise:
N 2 + (at) 2 = S n Pn n 2
For the right-hand-side summation, we use the following remarks:
S n x n / n!
= exp (x)
S n n x n / n!
= x d/dx exp (x) = x exp (x)
S n n 2 x n / n!
= x d/dx [ x exp (x) ]
= x exp (x) + x 2 exp(x)
Applying this to the above with x = at yields:
N2 + (at) 2
=
(at) + (at) 2
So, the RMS value of the noise is
N = Ö(at).
and the signal to noise ratio is:
SNR = at / N = (at)½
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Wikipedia : Image noise | Shot noise
Gibbs (1902) and Einstein (1904) independently found the following expression for the mean-square energy fluctuations per unit of a constant volume V in thermal equilibrium with a bath at temperature T:
For blackbody radiation, the mean energy density [energy per unit volume] of the photons whose frequencies are between n and n+dn is given by Planck's radiation formula :
Introducing the spectral density of photons r we have r hn = un .
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Einstein noticed that the first term of that bracket corresponds to the shot noise discussed in the previous section, which would be the sole noise observed if light was purely corpuscular, while the second can be attributed to the wavelike nature also possessed by Plankian light radiation. He interpreted that as a direct clue to the dual nature of light. Both a wave and a flow of particles...
On
the present status of the radiation problem A. Einstein, Phys. Z. 10, 185-193 (1909).
On
the development of our views concerning the nature and constitution of radiation
by Albert Einstein,
Physikalische Zeitschrift, 10, 817-826 (1909).
Reappraising Einstein's 1909 application of fluctuation theory
to Planckian radiation
by F.E. Irons
American Journal of Physics,
72, 8, 1059-1067 (August 2004).
All ordinary light sensors are receptors of photons, which is to say that they absorb every photon they detect, thereby destroying it.
What Haroche discovered at the
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Serge Haroche (b. 1944)
The semi-classical model of interactions between light and matter is fairly adequate to descrive the photoelectric effect and the stimulated emission of radiation on which lasers are based, but it can't explain spontaneous emission or purely quantum effects like:
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56 videos
by Alain Aspect and Michel Brune (2017).
One-photon interference experiment (14:21)
by Alain Aspect (2017年11月07日).
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Soft particles by Andy Strominger (Lex Fridman 2023年02月15日).
