ISSN:0031-9228    

DOI:10.1063/1.3070758

出版商:AIP    

年代:1972

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.3070759

出版商:AIP    

年代:1972

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.3070763

出版商:AIP    

年代:1972

数据来源: AIP

ISSN:0031-9228    

DOI:10.1063/1.3070765

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

Two questions confront those who would interpret recent measurements of the far‐infrared background radiation in the night sky. The first is: Are the data compatible with what would be expected from a blackbody cosmic background, left over from a “big‐bang” origin of the universe? And if so, what is the equivalent temperature of the blackbody? The second problem is: What is going on down at much shorter wavelengths—around 100 microns—where the blackbody envelope has fallen essentially to zero, but radiation has been detected with an apparent diurnal variation? Late last year two groups, one at the Los Alamos Scientific Laboratory, the other at the Naval Research Laboratory in Washington D.C., reported new far‐infrared measurements. The Los Alamos work at millimeter wavelengths supports “big‐bang” cosmology with a 3.1‐K equivalent blackbody temperature, and the new 100‐micron data from both groups suggest that discrepancies already noted in earlier work may besigns of real variation in the flux.

ISSN:0031-9228    

DOI:10.1063/1.3070767

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

During the past year many problems connected with development of the superconducting linear accelerator at Stanford have been resolved, according to Alan Schwettman and William Fairbank of Stanford's High‐Energy Physics Laboratory. When we recently visited the laboratory, the two men told us that in the past year they had demonstrated that an intense continuous electron beam can be produced in a superconducting accelerator with exceptional stability and energy resolution. But a critical problem remains—achieving the high energy gradients of 4 MeV/ft hoped for in the superconducting structures.

ISSN:0031-9228    

DOI:10.1063/1.3070768

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

At the Esfahan Symposium on Fundamental and Applied Laser Physics, which took place 29 August–5 September 1971, the world's laser specialists gathered to exchange notes on the state of the field and its probable future. The symposium was held on the campus of Esfahan University in Esfahan, the second largest city of Iran, under the auspices of Arya‐Mehr University of Technology and with the support and cooperation of Esfahan University and the Massachusetts Institute of Technology. Ali Javan (MIT) was director of the symposium, which was sponsored by the International Union of Pure and Applied Physics.

ISSN:0031-9228    

DOI:10.1063/1.3070769

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

With the award of the 1971 Nobel prize in physics to Dennis Gabor, holography has reached a new pinnacle of prestige. Gabor won his prize for the invention of holography, a form of wavefront reconstruction in which a coherent reference wave appears to unlock a three‐dimensional replica of an object from a two‐dimensional standing‐wave pattern.

ISSN:0031-9228    

DOI:10.1063/1.3070770

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

The idea of the photon has stirred the imaginations of physicists ever since 1905 when Einstein originally proposed the use of light quanta to explain the photoelectric effect. This concept is formalized in the quantum theory of radiation, which has had unfailing success in explaining the interaction of electromagnetic radiation with matter, seemingly limited only by the ability of physicists to perform the indicated calculations. Nevertheless, it has its conceptual problems—various infinities and frequent misinterpretations. Consequently an increasing number of workers are asking, “to what extent is the quantized field really necessary and useful?” In fact the experimental results of the photoelectric effect were explained by G. Wentzel in 1927 without the quantum theory of radiation. Similarly most electro‐optic phenomena such as stimulated emission, reaction of the emitted field on the emitting atom, resonance fluorescence, and so on, do not require the quantization of the field for their explanation. As we will see, these processes can all be quantitatively explained and physically understood in terms of the semiclassical theory of the matter–field interaction in which the electric field is treated classically while the atoms obey the laws of quantum mechanics. The quantized field is fundamentally required for accurate descriptions of certain processes involving fluctuations in the electromagnetic field: for example, spontaneous emission, the Lamb shift, the anomalous magnetic moment of the electron, and certain aspects of blackbody radiation. (The Compton effect also fits here, but see later under references 8b and c.) Here we will outline how the photon concept originated and developed, where it is not required and is often misused, and finally where it plays an essential role in the understanding of physical phenomena. In our discussion we will attempt to give a logically consistent definition of the word “photon”—a statement far more necessary than one might think, for so many contradictory uses exist of this elusive beast. In particular consider the original coining of the word by G. N. Lewis:“[because it appears to spend] only a minute fraction of its existence as a carrier of radiant energy, while the rest of the time it remains an important structural element within the atom…, I therefore take the liberty of proposing for this hypothetical new atom which is not light but plays an essential part in every process of radiation, the name photon!”(our exclamation point). Clearly the present usage of the word is very different.

ISSN:0031-9228    

DOI:10.1063/1.3070771

出版商:AIP    

年代:1972

数据来源: AIP

摘要:

In the best of all possible worlds, we would have the ideal photon detector, a device that caught a photon, gave an unambiguous meter reading and kept count of the number of events. In the real world, these ideal devices do not exist; competing events both outside and inside the detector confuse the true measure of the photons that we are trying to monitor. Phenomena such as quantum noise, “dark” current and background radiation interfere to a degree that depends on the intensity of the signal being measured and on the photon frequency, to mention only a few of the experimental parameters.

ISSN:0031-9228    

DOI:10.1063/1.3070772

出版商:AIP    

年代:1972

数据来源: AIP