Fotonok

Fotonok, also known as photons, are elementary particles and quanta of the electromagnetic field. They are massless, carry no electric charge, have spin 1, and propagate at the speed of light in vacuum.

Their energy and momentum are given by E = h f = h c / λ and p = h / λ, with the relation E^2 = (pc)^2 + (mc^2)^2; for m = 0 this reduces to E = pc.

Fotonok exhibit wave-particle duality and polarization. They are described by quantum electrodynamics; produced and absorbed in atomic transitions, chemical reactions, and thermal emission; lasers emit coherent photon streams.

Propagation: in vacuum they travel at c; in media, speed is reduced by the refractive index; their behavior is described by group velocity and phase velocity; dispersion and scattering affect their propagation; many interactions involve absorption or scattering by matter.

Detection and generation: photon detection relies on photoelectric effect, photomultiplier tubes, avalanche photodiodes, or superconducting detectors; creation occurs in atomic and molecular transitions, blackbody radiation, radiative decay processes, and nonlinear optical processes such as parametric down-conversion.

Applications and significance: photons are central to optical communication, imaging, spectroscopy, and quantum information science; cosmic microwave background photons carry information about the early universe; in astrophysics, photons across the spectrum reveal physical conditions of celestial objects.

History: the concept originated with Planck's quantum hypothesis (1900) and Einstein's explanation of the photoelectric effect (1905). The photon concept became central to quantum electrodynamics in the mid-20th century, earning Nobel recognition.