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Nov. 13, 1962 R. w. DAMON 3,064,201 PRESSURE TUNED THREE-LEVEL PARAMAGNETIC MASER Filed March 19, 1958 // $5: I SIG/VA L ' UTILIZATION SOUKCE CIRCUIT 37 X ' a; /7\_ 4/ 4-? 25' E: || ’ 27 [a 2” 29 Z? _ _ 2/ > 3/ I. ' ' I ll / 31'’ f” WI > In van 1.‘: 02-. F?/'char-ol W Damon, His Attorney. United grates 3,664,201 Patented Nov. 13, 1962 1 ' 2 In these maser systems, signals having only a narrow range of frequencies can be ampli?ed because if the external direct magnetic ?eld is changed in order to alter 3,064,201 PRESSURE TUNED TI-IREE-LEVEL PARA MAGNETHC MASER Richard W. Damon, Schenectady, N.Y., assignor to Gen the energy levels and thus the frequency that can be am~ eral Electric Company, a corporation of New York pli?ed, this ?eld varies from the magnitude of the internal magnetic ?eld produced by the orbit distortions. The Filed Mar. 19, 1958, Ser. No. 722,556 6 Claims. (Cl. 330-4) result is an adverse effect upon the transitions of the elec tron spins between energy'levels and consequently a de crease in ampli?cation. Thus, before amplifying a signal The present invention relates to a three-level para magnetic maser for amplifying microwave signals. An ampli?er has been recently developed in which the 10 of a certain frequency one must ?nd a paramagnetic ma terial having an internal ?eld comparable to the applied properties of paramagnetic materials are utilized. It is magnetic ?eld for this frequency. Obviously, it would be called a “maser,” which is an acronym derived from the advantageous if the system were adjustable so that many principle of operation: microwave ampli?cation by stimu frequencies could be ampli?ed through the utilization of lated emission of radiation. The operation is based upon electron spins, which produce an effect comparable to 15 a single paramagnetic crystal. Accordingly, an object of the present invention is to that obtained with a dipole magnet mounted on a gyro provide an improved three-level maser system. scope. Another object of the present invention is to provide a In the atoms of most materials the electron spins are three-level maser system that can be adjusted to amplify “paired” such that for every electron spinning in one signals over a range of frequencies. direction, another electron spins in the opposite direction. A further object of the present invention is to provide The magnetic dipole moments of each “pair” of electron a three-level maser system having a high gain over a spins cancel leaving no net magnetic effect. In certain greater range of frequencies than prior three-level maser solids, however, this pairing of electrons is incomplete systems. and elements in the crystal, usually ions, which are ?xed These and other objects are achieved in one embodi in location, can be found with unpaired electrons local 25 ment of my invention in which a crystal of paramagnetic ized in them. When one of these ions-called paramag material is subjected to an external pressure causing the‘ netic ions-is placed in a magnetic ?eld, it has an internal crystal electric ?eld to have di?ierent magnitudes orientational energy of a magnitude depending upon the at the paramagnetic ions along the three principal axes. angle between the magnetic dipole of the unpaired spins The novel features that I believe are characteristic of and the applied ?eld. When the dipoles are aligned with my invention are set forth in the appended claims. My the ?eld, the electrons have their lowest energy. They invention itself, together with further objects and ad have highest energy when the dipoles oppose the applied vantages thereof may best be understood by reference ?eld. The separation between these energy levels is a to the following description, taken in connection with the function of the applied magnetic ?eld. accompanying drawing, in which the single FIGURE According to the quantum theory, an electron moving illustrates a preferred maser ampli?er embodiment of from a level of energy WH to a lower energy level of my invention. WL emits radiation of frequency f=(WH~ WL)/h, where - In the ?gure those circuit elements which may in them maser ampli?es are approximately the same as the fre 49 selves be entirely conventional and whose details form no part of the present invention have been indicated in quency associated with two energy levels of the maser in h is Planck’s constant. The signal frequencies that a paramagnetic material. a simpli?ed block form with appropriate legends. I have illustrated a signal source 11 of the signals to be ampli ed, which source may be, for example, a radar‘ antenna _ In three-level masers, the ampli?cation process is re lated to three energy levels, two of which produce am receiving echo signals from an object in space. The sig pli?cation while the third supplies energy to the system. The orientational energies of the spins must be capable nals from source 11 are guided by a wave guide 13, a cir culator 15, and another wave guide 17 to a cavity resona of being changed directly from the lowest energy level tor 18 formed by irises 19. In the bottom of cavity of these three levels to the highest level Without assum resonator 18 a crystal of maser material 20, which has at ing the value of the intermediate level. Most maser ma least two unpaired electrons per paramagnetic ion, is re terials do not have this property but must be specially operated to obtain it. In one three-level maser system, 50 tained within some insulating material 21 such as poly styrene. Crystal 29 which preferably in an insulator so transitions from the lowest energy level to the highest are that microwaves will penetrate it deeply and which pref obtained directly through use of an applied direct mag erably has zero nuclear magnetic moment, can be formed netic ?eld which interacts with the electric ?eld created from: gadolinium ethyl sulfate diluted with lanthanum ethyl sulfate, potassium chromicyanide diluted with po tassium cobalticyanide, nickel silico?uoride diluted with by the ions and atoms in the immediate vicinity of the. paramagnetic ions. If the ions and the atoms immediately surrounding each paramagneticion produce a symmetrical electric ?eld, zinc silico?uroide or some other suitable paramagnetic material. At a side of cavity resonator 18 a threaded the shapes of the orbits of the electrons around the para screw 23‘ is positioned so that when turned it applies magnetic nuclei are not aifected by the presence of these pressure on the insulating material 21 which then distorts ions and atoms. But asymmetrical ?elds cause the orbits 60 the maser crystal 20. of the electrons around the paramagnetic nuclei to be Cavity resonator 18 is Within a cryostat 25 containing extended in the shapes of ellipses. The electrons mov a low temperature coolant 27, such as liquid helium, for ing in these elliptical orbits produce a magnetic ?eld cooling crystal 2% to a few degrees above absolute zero. affecting the dipole magnetic moment of the spinning elec trons. If a direct magnetic ?eld having a strength com parable to the magnetic ?eld produced by this distortion 65 A Variable strength D.C. (direct current) magnet having poles 29 and winding 31 submerges maser crystal 20 in a direct magnetic ?eld, the magnitude of which can be con trolled by a variable resistor 33 that controls the amount of the current ?owing through winding 31 from a source of the electron orbits is applied so that it has a compo nent at right angles to the axis of the electric ?eld in the material, transitions from the lowest energy level to the highest energy level are possible to permit efficient am 70 of direct voltage 35. By adjusting this ?eld, a separation in energy levels can be obtained within the paramagnetic pli?cation. > crystal 20 such thatit ampli?es-the signal from source 11. 3,064,201 3 For ampli?cation, crystal 2r’! must be energized by microwave energy at a frequency approximately equal to W3—W1/l1, wherein W3 and W1 are the highest and lowest energy levels respectively, of the three energy signal that is to be ampli?ed, amaser crystal including paramagnetic elements having at least two unpaired elec; tron spins pcr element establishing at least ?rst, second and third energy levels ‘in ascending order according to Of course, number, said crystal exhibiting interior electric and mag the spacing of the energy levels, Viva-W1, depends on the magnitude of the direct magnetic ?eld. In effect, crystal 20 “pumps” energy from the frequency of this microwave energy to the frequency of the applied signal, thereby am~ netic ?elds, means for conducting said signal to said levels utilized in the ampli?cation process. maser crystal at a ?rst frequency corresponding to the difference between the second and third levels, means for applying a higher frequency pump signal to said plifying the applied signal. For this reasonpthe micro 10 crystal corresponding to the energy difference between ?rst and third levels, mechanical means for phys wave energy is called the “pump energy" and its source ically compressing said crystal to a selectable degree, the the “pump source.” In the ?gure the micro‘, 'ave energy, compressing action distorting the crystal structure and which is provided by a pump source 37, is guided by a interior electric ?eld of said crystal which alters the mag wave guide 39 to a directional coupler comprising a hole netic ?eld interior to said crystal through altering the 41 in wave guide 17 and some absorbing material 43. electron orbits of said paramagnetic elements, means for The microwave energy passes through hole 41 to wave submerging said crystal in a direct magnetic ?eld having guide 17 and thence to cavity resonator 13. a magnetic ?eld strength of the same order of magnitude After ampli?cation, the signal re?ects out of cavity as the magnetic ?eld interior to said crystal and having resonator 18 up wave guide 17 to circulator 15, then to a component perpendicular to the internal electric ?eld, wave guide 45 which guides the signal to a utilization cir and means for conducting the ampli?ed output signal cuit 47 that, for example, in a radar application may be from said crystal for utilization purposes. an oscilloscope. A matched load 49 prevents energy 2. A three-level maser system comprising a- source of from the utilization circuit 47 from reaching the signal signal that is to be ampli?ed, a maser crystal including source 11 from where some of it might be re?ected into paramagnetic elements with at least four unpaired elec wave guide 17. trons per element, wherein each paramagnetic has at least To understand the operation of my maser system the three energy levels, W3, W2, and W1, wherein W2 is the electrical ?elds in the maser material must again be con intermediate energy level, mechanical means for phys sidered. If the electrical ?elds at the paramagnetic ions ically compressing said maser crystal acting to alter in are different in magnitude along the three principal di ternal crystal ?elds for permitting transitions between the rections, or in other words if the ?elds are asymmetrical, lowest energy level W1 to the highest energy level W3, direct transitions from the lowest energy level to the means for conducting the signal that is to be ampli?ed highest energy level of the three energy levels are per to said maser crystal, means for conducting a microwave mitted. Preferably the asymmetry is such that the crystal power signal to said crystal of a frequency approximately ?eld has a component of rhombic or lower symmetry. Most crystals do not have a signi?cant crystal ?eld of equal to W3—W1/h, wherein h is Planck’s constant, and means for conducting the output of said maser crystal to low symmetry in their natural form. However, I have discovered that such a ?eld component can be induced by applying to the crystal an external pressure that dis torts the unit cell of the crystal such that the desired transitions are permitted. This pressure not only permits the desired transitions but for those cells containing para magnetic ions with four or more unpaired spins per ion, three energy levels are obtained between which transitions are permitted even in the absence of a magnetic ?eld. Consequently, the DC. magnet with poles 29 may be dis pensed with. In such maser applications the energy level spacing, which determines the frequency that the crystal a utilization circuit. 3. A three-level maser system comprising maser ma terial containing paramagnetic elements having at least two unpaired electrons per element, said paramagnetic elements therefore exhibiting at least three energy levels, mechanical means for applying external physical pres sure to said maser material for compressing the same causing the maser material surrounding each paramag netic element to produce asymmetrical internal electric and magnetic ?elds at said element, means for applying an external magnetic ?eld thereto of substantially equiv alent strength to said internal magnetic ?eld at an angle 19 ampli?es, can be adjusted over a small range by pres to the electric ?eld whereby transitions from the lowest sure changes obtained by moving the screw 23. If a direct magnetic ?eld is used, the magnetic ?eld 50 of said three energy levels to the highest energy levels of three levels are permitted, means for subjecting said produced by the distortion of the orbits of the electrons around the paramagnetic ion nuclei can be adjusted by maser material to an electromagnetic power signal at a frequency corresponding to the difference in energy levels changing the pressure on crystal 20 to a value suitable to the applied magnetic ?eld. Consequently, the applied of two of said three energy levels, and means for ab magnetic ?eld can be adjusted to produce ampli?cation 55 stracting from said maser material electromagnetic energy of signals with many different frequencies. The correct having a frequency corresponding to a difference in energy crystal distortion can be maintained for wide variations levels of two or said three energy levels including the in the magnitude of the applied magnetic ?eld and thus highest energy level of said two energy levels and an maximum ampli?cation obtained at many frequencies. intermediate level. 4. The maser system as defined in claim 3 wherein There are, of course, ways of applying pressure to the 60 maser crystal 19 other than by using a screw 23. For said means for applying pressure is adjustable to produce example, a more permanent technique is the encapsula different amounts of external pressure on said maser ma tion of the paramagnetic salt by immersion in a liquid in terial whereby said maser system can be adjusted over sulating material such as water, and also some glasses that a wide range of frequencies of operation. subsequently expand upon solidifying, thereby exerting pressure on the crystal 20. While the invention has been described with respect to 5. In a three-level maser system, a crystal of paramag netic material containing paramagnetic elements having at least two unpaired electrons per element and charac certain speci?c embodiments, it will be appreciated that terized by a plurality of energy levels, an array of atoms many modi?cations and changes may be made by those arranged about each paramagnetic element in a predeter skilled in the art without departing from the spirit of the 70 mined crystalline order, said crystal being responsive to invention. I intend, therefore by the appended claims to physical pressure variation to alter the disposition of said cover all such modi?cations and changes as fall within atoms about each paramagnetic element from said prede the true spirit and scope of my invention. termined crystalline order to change the internal crystal What I claim is: electric and magnetic ?eld about a paramagnetic element, adjustable mechanical means for adjustably compressing 1. A three-level maser system comprising a source of 5 3,064,201 said crystal for causing atoms surrounding each para magnetic element to thus alter their positions from said predetermined crystalline order, and electrical means for raising the energies of said paramagnetic elements with an applied radio frequency wave corresponding in fre quency to the difference between a pair of said energy levels. 6. In a three-‘level maser system, a crystal of material containing paramagnetic elements having at least two un~ 6 ing in frequency to the difference between a pair of said energy levels. References Cited in the ?le of this patent UNITED STATES PATENTS 2,240,293 2,762,871 2,782,280 10 2,825,765 2,878,454 2,894,224 2,976,492 Goddard _____________ __ Apr. 29, Dicke _______________ __ Sept. 11, Bickford _____________ __ Feb. 19, Marie _______________ __ Mar. 4, Leming et al. ________ .. Mar. 17, Iversen _______________ __ July 7, Seidel ______________ _._ Mar. 21, 1941 1956 1957 1958 1959 1959 1961 paired electrons per element characterized by a plurality of energy levels, ions arranged about each paramagnetic element in a predetermined crystalline order, said crystal being responsive to an adjustable physical pressure to produce an assymmetrical disposition of said ions about OTHER REFERENCES each paramagnetic element di?ferent from said predeter 15 mined crystalline order to change the internal crystal Bloemberger: Physical Review, vol. 104, No. 2, Oct. electric and magnetic ?eld about a paramagnetic element, 15, 1956, pages 324-327. adjustable mechanical means for adjustably compressing said crystal to produce said asymmetrical disposition of Feher: Physical Review, vol. 105, No. 2, January ‘1957, elements to thereby cause the internal electric ?eld pro— 20 pages 760463. Braunstein: Physical Review, vol. 107, No. 4, Aug. 15, duced at the paramagnetic elements to have a component 1957, pages 1195-1196. of symmetry at least as low as rhombic symmetry, and “Introduction to Solid State Physics,” Kittel, 1956 (John means for raising the energies of said paramagnetic ele ments with an applied radio frequency wave correspond Wiley & Sons of New York), pages 229 and 230 relied on.