Ito, Taro

Yamamoto, Motokazu

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RIGHT:URL:CITATION:AUTHOR(S):ISSUE DATE:TITLE:An Ammonia Beam Maser on the2,2 LineIto, Taro; Yamamoto, MotokazuIto, Taro ...[et al]. An Ammonia Beam Maser on the 2,2 Line. Memoirs ofthe College of Science, University of Kyoto. Series A 1964, 30(3): 353-3581964-03http://hdl.handle.net/2433/257468           Memoirs of the College of Science, University of Kyoto, Series A,                       Vol. XXX, No. 3, Artic!e 4, 1964.       AN AMMONIA BEAM MASER ON THE 2,2 LINE                                  BY                  Tar5 ITO aRd Motokazu YA]Y[AMOTO                          (Received May 23, 1963)                               ABSTRACT       An Ni4H3 beam maser on the 2, 2 line (f=!K==2) was operated, using the same    cavity, at different tunings, with the 3, 3 line. The oscillation Åëharacters of the 2, 2    line maser were compared with those of the 3, 3 line maser which had been obtained    in our laboratory (1). The characters of both agreed with the same theory.       The center frequency of the 2, 2 line ma$er was rneasured on the basis of the 3,    3!ine maser asastandard. •1. Intreduetioli   The ammonia beam maser is the amplifier or oscillator in a microwaveregion operating on the quantum-mechanical principle. The bearn is coupled toa microwave cavity in which there occurs a process of induced emission coherentwith tlae fields in the cavity. The maser system breaks into spontaneousoscillation, when the beam flux exceeds a certain value, called starting fiux.As is well known, the iinaser oscillator kas a suMclent frequency stability andreproducibility to be used as a primary frequency standard. The 3, 3 line maserhad been operated in our laboratory and the shift of the center frequency wasinvestigated in detail (2). In the neighbourhood of the 3,3 line, there existrr}any inversion lines based on the different rotational states. The• comparisonbetween the masers is favourable for the investigation of the oscillationbehaviours. The maser oscillation on the 2, 2 line was tried, since this line istke nearest to the 3,3 line, and it was possible to operate the maser on eachline using the same cavity at' different tunings. The so-called threshold voltage,Vo(L K), which menas the focuser voltage giving the starting fiux, was measuredversus tl}e source pressure. We took the ratio of the threshold voltages on bothlines for a convenient comparison with the theory, and found a good agreemeiat.In the region above the threskold voltage, the oscillation amplitude versus focuservoltage ckaracteristic of the 2, 2 lirae maser was compared with that of the 3, 3line maser, and was found to be consistent with the theory, as the latter hadbeen (1). '   The measurement of the center frequency of the 2,2 line maser was made,354 T. ITO and M. YAMAMOTOthrough a 100Kc quartz oscillator, on the basis of the center frequency of the3, 3 Iine maser. The resulting value was compared with the values which hadbeen obtained by the absorption method.2. Experimental apparatus   The experimental apparatus is similar to that reported in (1). The blockdiagram of the detecting system is shown in Fig. 1. The eight-pole focuser is355mm in length. The cylindrical cavity consists of a copper pipe section 120mm in length, 10 mm in inner diameter and 3 mm in thickness, which, however,has been electroplated with copper in order to finely adjust the inner diameter.This cavity is operated in TMoio mode and has the loaded Q value of 7000.Furtker, it is cooled by the liquid air trap in order to increase the Q value andis provided with an a!most ful!-length slot to al!ow the tuning over a range ofabout 200Mc by a movable fin. And so, it has become possible to operate themasers on the 3,3line (23870Mc) and the 2,2line (23722Mc) w2th the same3,3 lineMaser2,2 1ineMaser1oo KcQuartzoscillatorUniguideKlystron 2K 33Mixer1N26SawtoothgeneratorLF. Arnplifier 20.5 McDetectorAudioamplifierÅ~ 2880Frequencymultiplyingchain .8.2882394 Mc  Quartzosci}laterFrequencycounters.Å~12Freqllencymuitipliet                        12,2910 Mc         tOscilloscope .                        OscillatorFig. 1. Block diagram of detecting system.                         AMMONIA 2,2LINE MASER 355cavity. Consequently, we can avoid the experimental ambiguities such as thecltanges in the cavity loaded Q, the coupling Q to the waveguide, the sourcepressure and the tank pressure, which would result, if we change from one lineto the other.    The present detecting system is a super-heterodyne type using a crystalmixer IN26 and a klystron 2K33 as local oscillator.3. ExperimeRtal results  (A) Threshold of oscillation    From the theory which takes into account the velocity distribution ofmolecules (1,3,4,5), the focuser voltage near the threshold can be expressedas follows :                 v2 -= 6veL.'2,Y,o,R,,,2Qai(i " ln j2//)umi ii[/i{fli,i-)2 Ni,,,, (i)where V is the focuser voltage, m the mass of molecule, h Planck's constant, vothe center frequency, pa the permanent molecular dipole moment, R the focuserradius, l the focuser length, L the cavity length, J, K, M quantum numbers, athe most probable velocity, Q the cavity loaded e, pt a transition matrix elementof moleÅëular dipo!e moment, and N the density of molecules in a particularenergy state. N is considered proportional to the fract2onal population f(f, K)(6). pt2 and f(L K) are given respectively by                                    K2pt2                                                                   (2)          pt2 ..                                   31<f+ 1) 'and                       f(f, K) == gi(2J+i)(.B(ifC41,) '/2, (3)                                           'where B, C are the rotatioiial constants, and gi the statistical weight factor.Then, the theoretical value of the ratio of the thresho!d voltage of the 2, 2 Iinemaser to that of the 3, 3 line maser can be obtained using (1), (2) and (3) as:                            (ll[231 Z])theor "x i'9' (`)From the experimental result shown in Fig, 2, the correspond2ng experimentalratio becomes                         (}l:((Z; 23i)... == i•g ! o•o2, (s)and it will be seen that the agreement between theoretical and experimentalvalues is satisfactory.3564121e1g-83,64"/k2o •2,2 lineo   3,3 lineoo.Å~T. IT6 and M. YAMAMOTOooTank pressure       31ig         4 6 8 10 12 14 16 18                          Source pressure (rnm Hg)       Fig. 2. Experimental threshold voltage versus source pressure of 2, 2 and 3,             line masers.  (B) AmPlitude characteristic   The oscillation amplitude versus focaser voltage characteristic of each maseris shown in Fig. 3, where the curve and experimental points for the 3,3 lineare reproduced from the previous report (1). The curve for the 2,2 line hasbeen plotted relative to that for the 3,3 Iine, since in the present case theoscillation amplitude has been measured only relatively. Thus, the experimentalpoints for the 2,2 line well Iie on the curve, showing the agreement betweenthe experiment and the theory for the present case.  (C) Frequency measurement   The center frequency of the 3, 3 line maser had been measured, using two3,3 line masers in our laboratory, to be 23870. 12953 Mc (2) to an accuracy ofÅ}2Å~10-g. We could in this case produce the above frequency only to anaccuracy of Å}1Å~10-8, at the cavity tuning giving the maximum oscMation           le           9        vo        gs        k"n        g7           6        gs        be.-as        =4        8        o           3        .0 2       Lts"       di 1         Fig.amplitude, '    Theoscillator,.mg way.the8.2882394 Mc,frequency ofThen, thetuning givingmaser, asfrequency toharmonic ofoscillator12.2910 Mc.by theoAMMONIA 2, 2li  ."j3,3DLINE MASERooo   2,2 lineo6357                       i        3 4 5 6 7 8 9 10 11 12 13 14 15         3. Relative oscillation amplitude versus focuser voltage of 2, 2 and            3, 3 ]ine masers at the source pressure of 18mmHg : small circles            show the experimental points.      since a single maser was used.    frequency counter had the time scale determined by tke 100 Kc quartz      which was calibrated to have an accuracy of Å}1Å~10-S, in the follow-      The process of determination and calibration was done by countingfundamental frequency of another quartz oscillator which is variable about         when its 2880th harmonic makes the zero beat with the center         the 3, 3 line maser, which is observed on the oscilloscope screen.     center frequency of the 2, 2 line maser was measured at the cavity          the maximum oscillation amplitude, just as that of the 3,3 line     follows. We observed on th6 oscilloscope screen the zero beat of the         be measured with the difference frequency between the 2880th        the 8.2882394 Mc oscillator and the 12 th harmonic of the 12.2910 Mc     which was varied, and counted both frequencies of 8.2882394Mc and       The result is shown in Table 1 together with the results obtained   absorption method.                             Table Z.W. Goedet al. (7)23,722.63 thOD2 McM. Strandberg et al. (8)23 722.59+O.05 Mc J-I. Takahashi et al. (9)23,722.62Å}O.024 McPresent authors23 722.636"O.O05 Mc lve358 T. ITd and M. YAMAMOTO                                                 '   The direct comparison of the 2, 2 Iine maser with the 3, 3 Iine maser is nowm progress.Aeknowleagement   The authors would like to thank Prof. I. Takahashi for his guidance, andDrs. T. Hashi and A. Hirai for their discussions, and Mr. K. Nlshida for hisassistance in the experiment.                             REFERENCES1. M• Yamamoto, Mem. Coll. Sci., Univ. of Kyoto, Series A, 30 (1962), 69.2. M. Yamamoto, Mem. Celi. Sci., Univ. of Kyeto, Series A, 30 (1962), 75.3. K. Shimoda, T. C. Wang and C. H. Townes, Phys. Rev., 102 (1956), 1308.4. K. Sh2moda, J. Phys. Soc. Japan, 16 (1961), 1728.5. I<. Shimoda, J. Phys, Soc. Japan, 12 (1957), 1006.6. C. K. Tewnes and A. L. Shawlow, Microzvave SPectroscoPy (McGraw-Hill, New York, 1955).Z W. E. Good et aL, Phys. Rev., 71 (1947), 383.8. M. W. P. Strandberg et al. Phys. Rev., 71 (1947), 326.9. I. Takahashi et al., Journal of the Institute oÅí Electrical Communication Engineer$ ef Japan,   35 (1952), 462 (in Japanese),

An Ammonia Beam Maser on the 2,2 Line

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An Ammonia Beam Maser on the 2,2 Line

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