Physical world and mathematics

Photodissociation mass spectrometry

Photodissociation mass spectrometry fragments gas-phase ions with laser light, typically ultraviolet, and detects the product ions, yielding rich fragmentation patterns and selective bond cleavage for structural analysis.

Photodissociation region

A photodissociation region, also called a photon-dominated region, is neutral interstellar gas whose heating and chemistry are controlled by far-ultraviolet photons from massive stars at cloud boundaries.

Photoelasticity

Photoelasticity, or the photoelastic effect, is a non-destructive experimental optical method that visualizes stress in transparent materials as fringes via stress-induced birefringence under polarized light.

Photoelectric effect

The photoelectric effect, also called photoelectric emission or the Hertz effect, is the emission of electrons from a material under high-frequency light; Einstein's 1905 explanation helped found quantum theory.

Photoelectrocatalytic oxidation

Photoelectrocatalytic oxidation (PECO) is an electrochemical method that oxidizes organic compounds at a light-activated semiconductor photoanode under applied bias, used to mineralize water pollutants and to synthesize value-added chemicals.

Photoelectrocatalytic reduction

Photoelectrocatalytic reduction drives reactions such as CO2 conversion, nitrate reduction, and hydrogen evolution at a light-activated semiconductor photocathode, with light and applied bias sharing the driving force.

Photoelectrochemical C–H functionalization

Photoelectrochemical C–H functionalization, known as electrophotocatalysis (EPC), is a synthetic method that activates inert carbon–hydrogen bonds using combined light and electric current, avoiding chemical oxidants.

Photoelectrochemical CO2 reduction

Photoelectrochemical CO2 reduction is a catalytic method using light-absorbing semiconductor electrodes, often with an electrical bias, to convert carbon dioxide into fuels and chemicals such as methanol.

Photoelectrochemical detection

Photoelectrochemical detection is an analytical method measuring photocurrent at a photoactive electrode; light excitation and electrical readout keep background low, enabling DNA, immunoassay, and cell biosensing.

Photoelectrochemical sensing

Photoelectrochemical (PEC) sensing is an analytical technique combining optical excitation with electrochemical detection, measuring a target analyte through the photocurrent a photoactive electrode produces under illumination.

Photoelectrochemical water oxidation

Photoelectrochemical water oxidation is the light-driven oxidation of water to oxygen at a semiconductor photoanode, the half-reaction that, paired with hydrogen evolution, converts sunlight and water into hydrogen fuel.

Photoelectron circular dichroism

Photoelectron circular dichroism (PECD) is a chiroptical effect where chiral molecules ionized by circularly polarized light emit electrons with a forward–backward asymmetry, predicted in 1976.

Photoelectron diffraction

Photoelectron diffraction, also called X-ray photoelectron diffraction, is a surface science technique that determines local atomic structure and adsorption geometry from the angular and energy dependence of photoelectron emission.

Photoelectron holography

Photoelectron holography is an imaging technique that reconstructs atomic positions from the interference of direct and scattered photoelectron waves, extended to femtosecond molecular imaging with x-ray free-electron lasers.

Photoelectron spectroscopy

Photoelectron spectroscopy (PES) measures the kinetic energies of electrons ejected from matter by photons, converting them into binding energies, electronic-structure information, and elemental and chemical-state composition. Its main branches include XPS, UPS, and ARPES.

Photoemission electron microscopy

Photoemission electron microscopy (PEEM) images a surface by illuminating it with ultraviolet or X-ray light and forming a magnified image from the ejected electrons, revealing topography, composition, and magnetic domains.

Photoenzymatic radical catalysis

Photoenzymatic radical catalysis is a field growing rapidly since 2016 in which visible light excites an enzyme's cofactor to generate radical intermediates, enabling new-to-nature enantioselective reactions.

Photoevaporation

Photoevaporation is the loss of a planet's atmosphere driven by extreme ultraviolet and X-ray radiation from its host star, and one of two leading explanations for the exoplanet radius valley.

Photofission

Photofission is nuclear fission of a heavy nucleus induced by absorbing a high-energy photon, written (γ, f), with a threshold of about 5 to 6 MeV.

Photofragment-ion imaging

Photofragment-ion imaging, also called ion imaging, is a chemical dynamics technique introduced in 1987 that images fragment recoil velocities from photodissociation; a 1997 refinement, velocity map imaging, improved its resolution.

Photogating effect

The photogating effect is a photodetection mechanism in which photo-induced charges trapped in or near a semiconductor act as an internal gate, modulating a transistor's channel conductance instead of generating photocurrent directly.

Photogeology

Photogeology is the study and interpretation of aerial photographs, normally vertical, to obtain geologic information and present it as mosaics, geologic maps, and cross sections.

Photografting

Photografting is a surface-modification method in which ultraviolet or visible light drives the covalent attachment of polymer chains or functional groups onto polymers, metals, carbons, and oxides.

Photographic film

Photographic film is a light-sensitive material of silver halide crystals in gelatin on a plastic base, on which light exposure creates a latent image developed into a visible picture.

Photoinduced electron transfer

Photoinduced electron transfer (PET) is an electron transfer reaction driven by light, where excitation makes a molecule a stronger reductant or oxidant, underlying photosynthesis and photoredox catalysis.

Photoinduced ferroelectricity

Photoinduced ferroelectricity is the emergence or modification of switchable electric polarization driven by light rather than cooling or electric fields, first shown in strontium titanate in 2019.

Photoinduced force microscopy

Photoinduced force microscopy (PiFM) is a scanning probe technique that maps chemical composition at nanometer resolution by detecting the force light induces between an AFM tip and a sample.

Photoinduced phase transition

A photoinduced phase transition is an ultrafast, light-triggered change in a solid's electronic, spin, or lattice order, studied most intensively in 1T-TaS2 and explored for ultrafast memory and photodetection.

Photoinduced self-healing in perovskite films

Photoinduced self-healing in perovskite films is the autonomous recovery of photoluminescence and solar-cell efficiency after light-induced damage, first reported in 2015, requiring no external material and working over seconds to days.