Observations of Nonlinear Maser PhenomenaWalter H. Higa Citation: Review of Scientific Instruments 28, 726 (1957); doi: 10.1063/1.1715993 View online: http://dx.doi.org/10.1063/1.1715993 View Table of Contents: http://scitation.aip.org/content/aip/journal/rsi/28/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Nonlinear and collective phenomena observed in plasma wakefield acceleration driven by multiplebunches AIP Conf. Proc. 395, 343 (1997); 10.1063/1.52939 Nonlinear analysis of the Cerenkov maser Phys. Fluids B 2, 2506 (1990); 10.1063/1.859515 The nonlinear description of a plasma maser J. Appl. Phys. 68, 2051 (1990); 10.1063/1.346556 Observation of nonlinear optical transmission and switching phenomena in polydiacetylenebaseddirectional couplers Appl. Phys. Lett. 55, 1829 (1989); 10.1063/1.102179 Nonlinear phenomena as observed in the ear canal and at the auditory nerve J. Acoust. Soc. Am. 77, 599 (1985); 10.1121/1.391878

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726 LETTERS TO THE EDITOR

to be lowered somewhat, but is not necessary for the immediate applications envisaged for this simple method.

We thank the Chemical Society for a grant from the Research Fund, and the Royal Society for the loan of apparatus purchased from the Government Grant.

1 E. Matsukawa and C. Eaborn, Research Correspondence 9, S 37 (1956).

Step-Type Demountable Metal Vacuum J oint*

W. J. LANGE AND D. ALPERT

Westinghouse Research Laboratories, Pittsburgh 35, Pennsylvania

(Received June 21, 1957)

D EMOUNTABLE all-metal vacuum joints have been reportedl- 4 which employ OFHC copper as

the gasket material between steel flanges. In using this type of seal, we have become aware of certain dis­advantages which have been avoided or reduced in the design shown in Fig. 1. Flanges are machined from stain­less steel and are heliarc welded to vacuum system components. The gasket is a washer-shaped ring of OFHC copper about 0.040 in. thick. It is hydrogen annealed at 950°C after cutting. The seal is made by pulling up on the bolts (twelve are used in a 6-in. flange, i in. thick) until the copper gasket is roughly one-half of its original thickness between the sealing edges (see detail in Fig. 1).

This flange assembly has the advantages over knife­edge-type sealsl- 3 that the steps are much more easily machined and the tolerances are less stringent. Further, if a step flange is damaged, for example, by marring the sealing edge, it can be repaired very easily in com­pairson to a knife-edge flange which must be completely remachined. Advantages are also offered over gold gasket or copper wire gasket4 seals since the washer­shaped copper gasket is rigid enough to enable one to make vertical seals easily even in the case of sealing to larger systems. To facilitate assembling the seals, it will

FIG. 1.

be noted that the steps in the female flange serve to position and hold the gasket.

Variations of the design shown in Fig. 1 have been tested and also shown to be satisfactory. These include negative as well as positive overlap of the mating seal edges and a 45° bevel, 0.005 in. across on the sealing edges.

The seals were tested on an ultrahigh vacuum glass system and subjected to repeated heat cycling to 450°C. The rate of rise of pressure was found to be as low as the rate of rise due to helium permeation through Pyrex.6

Such flange assemblies are still under life test with­standing as many as 70 bakeout cycles without failure.

* This work was supported in part by U. S. Atomic Energy Commission Contract AT-1l-1 gen-14.

1 J. B. Mann, Rev. Sci. lnstr. 27, 1083 (1956). 2 P. J. van Heerden, Rev. Sci. lnstr. 26, 1130 (1955). 3 H. H. Pattee, Jr., Rev. Sci. lnstr. 25, 1132 (1954). 4 R. L. Sproull, Rev. Sci. lnstr. 22, 410 (1951). 6 Rogers, Buritz, and Alpert, J. Appl. Phys. 25, 868 (1954).

Letters to the Editor

Prompt publication of brief reports of NEW ideas in measurement and instrumentation or comments on papers appearing in this Journal may be secured by addressing them to this department. No proof will be sent to the authors. Communications should not exceed 500 words in length. The Board of Editors does not hold itself responsible for the opinions expressed by the correspondents.

Observations of Nonlinear Maser Phenomena *

WALTER H. HIGA

Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California

(Received June 19, 1957)

T WO experimental observations have been made in working with a double cavity maserl which

appear to be quite interesting. Two TEoll cavities reso­nant at the 3,3 line of NHa were cascaded and provided with separate wave guides so that signals from each could be observed independently. The same beam was allowed to enter first cavity No.1, then cavity No.2, and the following results were obtained:

(a) Initially both cavities are tuned to the center frequency and a strong signal is obtained from cavity No.1 and a reduced signal from No.2. Now as No.1 is detuned it is observed that the signals in both cavities are reduced. If the detuning is large enough it is found that the second cavity will suddenly break out into oscillations at the center frequency. The two cascaded

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LETTERS TO THE EDITOR 727

cavities thus oscillate individually, and by heterodyning the two signals a beat of the difference frequency is obtained. Difference frequencies of 2 to 5 kc (increasing with beam intensity) have been measured. Qualita­tively, this phenomenon can be explained as follows: As the No.1 cavity is detuned, more and more molecules entering cavity No.2 do so with diminishing probability for induced emission; at the critical point the thermo­electric field in cavity No.2 starts oscillations at the optimum frequency.

(b) The beat phenomenon of part (a) can be observed directly by rectifying the signal from cavity No.2. That is to say, the molecules ringing at the frequency deter­mined by cavity No.1 cause the oscillations in No.2 to

be amplitude modulated. Invariably, such modulation must find its origin in certain nonlinear properties2 of the maser. More specifically this experiment shows that the maser can continue to amplify signals even in the oscillating state. This property can be useful for many applications, since the maser can be used simultaneously as a reference frequency standard and signal amplifier. The signal frequency must, of course, be within the band width of the molecular amplifier.

* This paper presents one phase of research carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract No. DA-04-495-0rd 18, sponsored by the Depart­ment of the Army, Ordnance Corps.

1 Gordon, Zeiger, and Townes, Phys. Rev. 99, 1264 (1955). 2 Shimoda, Wang, and Townes, Phys. Rev. 102, 1308 (1956).

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