Coherent light generators – Particular resonant cavity
Patent
1987-04-17
1989-02-28
Scott, Jr., Leon
Coherent light generators
Particular resonant cavity
372 69, 372109, H01S 308
Patent
active
048092924
DESCRIPTION:
BRIEF SUMMARY
The invention refers to a method and a device to transform electromagnetic waves, in particular light, into monochromatic coherent electromagnetic radiation of a predeterminable frequency and heat radiation, where the predeterminable frequency is the lowest frequency of the Planck-distributed frequency spectrum of the heat radiation. It is an object of the invention to concentrate electromagnetic radiation in a cavity with reflecting walls to such a degree that the mean density of the radiation in the cavity exeeds a critical value, and that the portion of the radiation exceeding this value occupies the lowest electromagnetic energy mode of the cavity.
For cavities with reflecting walls one faces the following two problems: electro-magnetic radiation?
Focussing light, for example, and "filling" it through an opening (or a window) into a cavity with reflecting walls the prior-art expectation is a stationary equilibrium established at the opening between in-going directed, and out-going light, such that the intensity of light cannot exceed an amount given by the degree of focussing. When the supply of light is interrupted and the cavity is closed, due to the reflectivity losses, a "black radiation" ("Hohlraumstrahlung", "black body radiation") determined by the temperature of the walls, will be established in a very short time so that a storing of energy is not possible.
In the case of superconducting microwave cavities (D. G. Blair, S. K. Jones: High Q sapphire loaded superconducting cavities and applications to ultrastable clocks, IEEE Trans. Magn. Mag 21 (1985) 142-145; contains further references) the enclosure of electromagnetic energy is extended to a duration in the order of magnitude of seconds; owing to the small energy of the involved radiation, the still very short storage time, and the disproportionate cooling requirements, again, a practical application to convert and to store energy cannot be considered.
By means of the invention described below it is possible to concentrate electromagnetic radiation energy to such an extent, and simultaneously to reduce the relative losses during the enclosing so greatly that, among other things, it can be used to store energy. The invention thereby applies Bose-Einstein condensation of electromagnetic radiation.
For the quantum-statistical description of an ideal gas of indistinguishable particles of non-zero rest mass, subject to Bose statistics, Einstein found (A. Einstein: Quantentheorie des einatomigen idealen Gases, zweite Abhandlung, Sitzungsberichte der preussischen Akademie der Wissenschaften, physikalisch-mathematische Klasse, 1925, I), that there is a critical particle density so that, when it is exceeded, the excess particles go over spontaneously into the state of lowest energy, where their kinetic energy is zero and their contribution to the pressure of the boson gas vanishes; hence, for the critical particle density, there exists a critical pressure which cannot be exceeded. This "Bose-Einstein condensation" is used to explain the superfluidity of Helium.
Photons, the basis for the quantum-field-theoretical discussion of electromagnetic radiation, are subject to Bose statistics. However their rest mass is zero. Therefore the question of a Bose-Einstein condensation in a gas of free photons presents a problem, since particles, whose rest mass and kinetic energy are simultaneously zero, cannot exist. Hence, in physical literature, up to now, a Bose-Einstein condensation of free photons has not been considered to be physically relevant; the discussion of the photon gas excludes a photon condensation either from the very ansatz, by proceeding on the assumption of a canonical ensemble of indefinite particle number (e.g. R. Jost: Quantenmechanik II, Verlag der Fachvereine an der ETH-Zurich, 1973) or the mathematical deduction is incorrect (e.g. L. D. Landau, E. M. Lifschitz: Lehrbuch der theoretischen Physik, Bank V, Akademie-Verlag, Berlin, 1975; an error which excludes Bose-Einstein condensation in an ideal Bose gas for Dirichlet boundary conditions
Hinds William R.
Jr. Leon Scott
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