Contains a report on a research project.Lincoln Laboratory (Purchase Order DDL BB-107)United States Air Force (Contract AF19(628)-500

Kukolich, S. G.

Contains report on one research project.Joint Services Electronics Program (Contract DA36-039-AMC-03200(E

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GENERAL PHYSICSI. MOLECULAR BEAMS*Prof. J. R. Zacharias R. S. Badessa S. G. KukolichProf. J. G. King J. F. Brenner F. J. O'BrienProf. C. L. Searle R. Golub R. D. PosnerProf. K. W. Billman G. L. Guttrich C. O. Thornburg, Jr.Prof. E. F. Taylor W. D. Johnston, Jr. L. H. VeneklasenA. HIGH-RESOLUTION MEASUREMENTS WITH A TWO-CAVITY MASER - ANALYSISOF UNRESOLVED SPECTRAThe resonance pattern produced by the two-cavity maser spectrometer 1 for a singlemolecular resonance line is the typical "Ramsey" line shape shown in Fig. I-1, and itmay be easily analyzed to determine the resonance frequency. There are many casesin the ammonia inversion spectrum, however,in which the resonance lines are so close thatthese patterns overlap and the lines are notcompletely resolved. In order to analyzesuch cases a computer program was writtenito perform a least-squares fit to the exper-I: imental spectrum by using a superpositionof the known single-line resonance patterns.Fig. I-1. Single line Ramsey function This program was used successfully to deter-with 0. mine the amplitudes and frequencies of threeoverlapping lines.One case that was analyzed successfully is the main line (AF = AF 1 = 0) of the J = 3,K = 3 inversion transition. The signal-to-noise ratio is very good in this case (1000/1).The resonance pattern for a single line can be accurately represented by the functionA exp(-b(f-f )2) sin (w(f-fo)/Af- ). This spectrum contains three overlapping functionsof this form. We have assumed that these functions are linearly superposed, since themicrowave receiver response is linear and the microwave power from the molecules isconsiderably less (20 db less in the second cavity) than the stimulating signal. Theexperimental spectrum (circled points in Fig. I-2) is divided into two parts, and the partcontaining the line that is least influenced by the others is used to determine values forthe phase t1, the frequency fl, and the amplitude Al which give the best fit to that partof the spectrum. We assume that the phase 1 will be the same for all three components,so we use the value of 01 for the phase of the other components. The second part of thespectrum is then used to determine the frequencies and amplitudes of the second andthird components, while the amplitude and frequency of the first component are heldconstant. Then the first part is corrected for the influence of the second and third*This work was supported principally by the Joint Services Electronics Program(Contract DA36-039-AMC-03200(E).QPR No. 79MAIN-LINE FIT OUTPUT 7-3- a .W414 --i tit#-', ---- 4 1j, ..7ri127.842 129.608 130.228o THEORY- EXPERIMENTFREQUENCY IN KC=23,870,000+PANd~i 4ffai1Fig. I-2. Results of the fit procedure for one set of data. Circles representexperimental points, line is theoretical curve which gives best fit.Table I-1. Results of the fit procedure for three sets of data.MAIN LINF FIT PFSULTSFREQUENCIESFIT RESULT,870,1270842,870,127,8951870,127,9089870,129.6089870,1290608,870,129.6353 - 3 LIN.FIN KC23,8709130.22823,870,130.20423,870,130.230STANDARD DFVTATTON =AVERAGE23,870,127.8816723,870,127.8816723,870,127.8816729,870,129.6170023,870,129.6170023,870,129.6170023,870,130.2236723,870,130.22367239870,130.22367.01992QPR No. 79a lr_ ~ _ _3-3 LINEI IFUN al(I. MOLECULAR BEAMS)components and a better value of 1 is obtained. This procedure is repeated many timesto minimize effects of interdependence of the variables.This whole fit is then carried out for various values of b and Af, and then the fitgiving the smallest standard deviation over the whole pattern is chosen. , Af, and bare assumed to be the same for all three components in one experimental curve. Theseparameters may be varied experimentally, 0 may have any value from 0 to ZTr, but Afand b may only be varied by ±20 per cent. The typical molecular resonance linewidth,Af, for the present device is 350 cps and 1/b ~ (ZAf). The result of one of the fits isshown in Fig. I-2. Table I-1 shows the results of fits to three different sets of experi-mental data which had different values of c, Af and b. The standard deviation of thefrequencies of the component lines in these fits was 20 cps.I wish to thank my wife, Joan Kukolich, for programming help and the ComputationCenter, M. I. T., for supplying the computer time.S. G. KukolichQPR No. 79

Molecular Beams

RADIO PHYSICSI. MOLECULAR BEAMS*Prof. J. R. Zacharias R. S. Badessa W. D. Johnston, Jr.Prof. J. G. King V. J. Bates S. G. KukolichProf. C. L. Searle J. F. Brenner F. J. O'BrienProf. K. W. Billman R. Golub C. O. Thornburg, Jr.G. L. GuttrichA. AMMONIA MASER WITH SEPARATED CAVITIESSome improvements have been made in the ammonia maser with separated micro-wave cavities discussed in Quarterly Progress Report No. 72 (pages 8-11). The sepa-ration of the microwave cavities has been increased from 36 cm to 105 cm. Thisresults in a molecular resonance linewidth of 350 cps.Previously, a crinkle-foill molecular beam source was used. The holes in thissource were approximately 0. 002 in. in diameter and 0. 125 in. in length, and the totalsource diameter was 0. 25 in. A new source consisting of a "glass capillary array" wasobtained from Permeonics Corporation, Southbridge, Mass. This source containsholes 0. 00012 in. in diameter and 0. 01 in. in length, and the total source diameteris also 0. 25 in. This new source resulted in approximately twice the beam intensity(molecules/steradian second) with only one-half as much total flux through the source.Also, the resonance linewidth for 105-cm cavity separation was reduced from 400 cpswith the crinkle-foil source to 350 cps with the new source. The molecular resonanceobserved with the new source and 105-cm cavity separation is shown in Fig. I-i.Figure I-2 shows a plot of intensity of the resonance signal as a function of focusservoltage. This voltage determines the focal length of the "quadrupole lens" focusser.I -v~ 4-i.- -4II Ir { IL:Fig. I-1. First derivative of molecular resonancewith 105-cm cavity separation. (Mole-cular resonance linewidth is 350 cps.)This work was supported in part by Purchase Order DDL BB- 107 with LincolnLaboratory, a center for research operated by Massachusetts Institute of Technology,with the support of the U. S. Air Force under Contract AF 19(628)-500.QPR No. 73(I. MOLECULAR BEAMS)10 15 20 25FOCUSSER VOLTAGE (KV)Fig. I-2. Molecular resonance amplitude as a function of focusser voltage.The maximum in this function indicates the condition for the most probable velocitymolecules to be focussed into the second cavity. The center frequency of the molec-ular resonance was also measured for focusser voltages from 6 kv to 24 kv. Thislarge range of focusser voltages produced a variation in the center of the resonancesignal by less than 1 part in 109.S. G. KukolichReferences1. J. G. King and J. R. Zacharias, Technology in molecular beams, Advancesin Electronics and Electron Physics, Vol. 8 (Academic Press, Inc., New York, 1956),pp. 19-20.QPR No. 73

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Molecular Beams

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