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Method and apparatus for generating coherent radiation in the ultra-violet region and above by use of distributed feedback
| Details |
Inventors: Fletcher, James C. Administrator of the National Aeronautics and Space; Saffren, Melvin M.;
Assignee:
Primary Examiner: Sikes; William L.
Assistant Examiner:
Attorney, Agent or Firm: Mott; Monte F., McCaul; Paul F., Manning; John R.
Helium in the superfluid state has been found to emit copious amounts of radiation in the ultra-violet region when excited by an electron stream. Conventional laser action using mirrors is impossible in superfluid helium because there are no mirrors that will reflect VUV radiation. By utilizing the well known method of "distributed feedback" the superfluid helium can be made to lase. By setting up a standing wave in superfluid helium that has a wavelength equal to, or harmonically related to, half the wavelength of the photon radiation chosen to be emitted as laser radiation by the superfluid helium, the need for end mirrors to produce reflection of the laser radiation is eliminated and reflection occurs instead at the wavefronts of the standing wave. The photons leave the superfluid helium at right angles to the standing wave as coherent radiation having a very high intensity. The standing wave established in the superfluid helium may be an acoustical standing wave, a thermal standing wave (second sound), or an electric standing wave. |
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DETAILED DESCRIPTION An object of this invention is to provide high power coherent radiation in the vacuum ultra-violet region.
Another object of this invention is to provide coherent radiation from superfluid helium.
A further object of this invention is to provide coherent radiation in the vacuum ultra-violet region by use of distributed feedback.
Still another object of this invention is to provide coherent radiation in the ultra-violet region by setting up an acoustical standing wave in a liquid noble gas to provide the distributed feedback reflecting surfaces.
Yet another object of this invention is to provide coherent radiation in the vacuum ultra-violet region by setting up an acoustical standing wave in a superfluid bath of helium to provide the distributed feedback reflecting surfaces.
A further object of this invention is to provide coherent radiation in the ultra-violet region by setting up a "second sound" or thermal standing wave in a bath of superfluid helium to provide the distributed feedback reflecting surfaces.
Still a further object of this invention is to provide coherent radiation in the ultra-violet region by setting up an electric standing wave in a bath of superfluid helium to provide the distributed feedback reflecting surfaces.
These objects and the general purpose of this invention are accomplished by bombarding a liquid noble gas such as, superfluid helium with pumping energy such as, an electron stream, while maintaining a standing wave therein that has a wavelength that is harmonically related to half the wavelength of the photons emitted as a result of the bombardment.
Bombarding superfluid helium with an electron stream produces a copious amount of radition in the vacuum ultra-violet region.
By setting up a standing wave in the superfluid helium which has a wavelength that is harmonically related to half the wavelength of the photons emitted, the photons are distributively reflected by the wavefronts so that they are in phase.
The reflected photons cause other excited helium atoms to, in turn, emit photons of like frequency and phase
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