2.4 Radiation pressure in terms of photons.2.1 Radiation pressure from momentum of an electromagnetic wave.This transfer of momentum is the general explanation for what we term radiation pressure. Due to the law of conservation of momentum, any change in the total momentum of the waves or photons must involve an equal and opposite change in the momentum of the matter it interacted with ( Newton's third law of motion), as is illustrated in the accompanying figure for the case of light being perfectly reflected by a surface. The interaction of electromagnetic waves or photons with matter may involve an exchange of momentum. Radiation pressure can equally well be accounted for by considering the momentum of a classical electromagnetic field or in terms of the momenta of photons, particles of light. Direct applications of the radiation pressure force in these fields are, for example, laser cooling (the subject of the 1997 Nobel Prize in Physics), quantum control of macroscopic objects and atoms (2012 Nobel Prize in Physics), interferometry (2017 Nobel Prize in Physics) and optical tweezers (2018 Nobel Prize in Physics). That includes, but is not limited to, biomicroscopy (where light is used to irradiate and observe microbes, cells, and molecules), quantum optics, and optomechanics (where light is used to probe and control objects like atoms, qubits and macroscopic quantum objects). Radiation pressure forces are the bedrock of laser technology and the branches of science that rely heavily on lasers and other optical technologies. Furthermore, large lasers operating in space have been suggested as a means of propelling sail craft in beam-powered propulsion. The significance of radiation pressure increases rapidly at extremely high temperatures and can sometimes dwarf the usual gas pressure, for instance, in stellar interiors and thermonuclear weapons.
Radiation pressure from starlight is crucial in a number of astrophysical processes as well. For example, had the effects of the Sun's radiation pressure on the spacecraft of the Viking program been ignored, the spacecraft would have missed Mars' orbit by about 15,000 km (9,300 mi). This particularly includes objects in outer space, where it is usually the main force acting on objects besides gravity, and where the net effect of a tiny force may have a large cumulative effect over long periods of time. The forces generated by radiation pressure are generally too small to be noticed under everyday circumstances however, they are important in some physical processes and technologies. The associated force is called the radiation pressure force, or sometimes just the force of light. black-body radiation) by matter on any scale (from macroscopic objects to dust particles to gas molecules). This includes the momentum of light or electromagnetic radiation of any wavelength that is absorbed, reflected, or otherwise emitted (e.g. Radiation pressure is the mechanical pressure exerted upon any surface due to the exchange of momentum between the object and the electromagnetic field. Force on a reflector results from reflecting the photon flux
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