US2965795A

US2965795A - System for utilizing impact induced transitions in a microwave resonant medium

Info

Publication number: US2965795A
Application number: US525442A
Authority: US
Inventors: Lowell E Norton
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1955-08-01
Filing date: 1955-08-01
Publication date: 1960-12-20
Anticipated expiration: 1977-12-20

Description

Dec. 20, 1960 L. E. NORTON 2,965,795

SYSTEM FOR UTILIZING IMPACI` INDUCED TRANsI-IIoNs IN A MICROWAVE REsoNANI MEDIUM Filed Aug. 1, 1955 5, /f/l.. M Il1 a... m /a H Illu d A 1, w .i mz .w w+ I4/ll.| n@ u@ J in 4. M 52wk 7m Mw INVENTOR. LDWELI. E. Num DN BY g Z0 QZ Unite States Patent SYSTEM FOR UTILlZlNG IlVilACT INDUCED TRANSITINS IN A MICROWAVE RES()- NANT MEDEUM Lowell E. Norton, Princeton, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed Aug. 1, 1955, Ser. No. 525,442

31 Claims. (Cl. S15-5.35)

This application is a continuaton-in-part of my copending application Serial No. 497,762, filed March 29, 1955, now abandoned.

This invention relates generally to systems employing microwave resonant media and particularly to improved methods of and means for increasing the intensity of a spectral line exhibited by a microwave resonant medium by an impact phenomenon which produces a preferred nuclear orientation of particles in certain energy levels` According to the invention the particles having the preferred orientation may be used in microwave spectroscopy and frequency stabilization systems, or for microwave energy generation or amplification.

Spectral lines in the microwave region of the radiofrequency spectrum are relatively weak in intensity primarily because of the small population differences of atoms or molecules in the various quantum energy levels of interest. At 25,000 megacycles per second, for example, where ammonia is the resonant medium employed,

the ratio of the two energy levels involved differs from unity by only about 4 10*3. The ratio of the populations of the molecules in these energy levels in then [l-i-(4X10-3N. For transitions where the nuclear spin of Na23 is involved, a spectral line is exhibited at about 1,771 megacycles per second, and the per unit population difference of the energy levels concerned is approximately 2.8Xl-4. The corresponding ratio of the populations of the sodium atoms is [1+(2.8 10*4)]. For other resonant media and frequencies the per unit population diiferences of energy levels of interest is even less desirable.

An object of the invention is to provide an improved method of and means for utilizing a microwave resonant medium.

Another object of the invention is to increase the intensity of a spectral line of a microwave resonant medium by a particle impact phenomenon.

Another object of the invention is to provide an improved method of and means for utilizing a microwave resonant medium for microwave spectroscopy and/or frequency stabilization.

Another object of the invention is to provide an improved method of and means for utilizing a microwave resonant medium for generating electrical energy.

A further object of the invention is to provide an irnproved method of and means for utilizing a microwave resonant medium for amplifying electrical energy.

A further object of the invention is to improve the signal-to-noise ratio of systems in which microwave resonant media are employed.

A still further object of the inventionv is to produce a spectral line of increased intensity and reduced bandwidth.

The foregoing objects and advantages are achieved in accordance with the invention by enhancing the small population difference heretofore mentioned which is due to the initial thermal equilibrium condition of particles of a microwave resonant medium. The small population difference is improved by selecting as preferred at least one allowed energy and angular momentum state of the atom or molecule. Preferential population of the preferred quantum state or states results in intensification of the selected spectral line.

Briefly, the preferential energy state population referred to above is achieved by subjecting a microwave resonant medium such as a gas, a vapor, or a solid to a particle beam which moves at a selected and controlled velocity. The beam particles collide with the atoms of the resonant medium and, with the beam velocity properly controlled, cause certain permitted energy level transitions to occur between magnetic substates of at least a pair of quantum energy states. The magnetic substates are made definite by applying a weak magnetic eld of definite direction to the resonant medium. These impact induced transitions are followed by spontaneous drop-down transitions from magnetic substates of the higher energy state to magnetic substates of the lower energy state. The net result of the impact induced and drop-down transitions is that the populations of certain magnetic substates of the lower energy quantum state are enhanced at the expense of the populations of other magnetic substates of the same lower energy level. The enhancing of the population of one magnetic substate at the expense of another magnetic substate to a large extent improves the initial thermal equilibrium condition mentioned previously, and enables the microwave resonant medium to be used more efficiently for microwave spectroscopy, frequency stabilization, or for the generation or amplification of microwave energy.

Since the intensity of the spectral line of interest is greatly enhanced by means of the impact phenomenon briefly described above, in some instances it may be desirable to sacrifice a portion of the increased line intensity for a reduction in the spectral line bandwidth. Therefore, in situations where the microwave resonant medium is a gas or a vapor, the Doppler-breadth of the spectral line may be reduced, in accordance with a further feature of the invention, by mixing a buffer gas with the microwave resonant gas or vapor. However, the Dopplerreduced bandwidth line intensity still is considerably greater than would be the case if impact induced transitions were not caused to occur.

The invention will be described in detail with reference to the accompanying drawing in which:

Figure 1 is a schematic sectional diagram of apparatus for producing preferential populations of certain quantum energy states, according to the invention; and

Figure 2 is an energy level diagram of transitions which are permitted to occur between various quantum energy states in accordance with the invention.

Structure Referring to Figure 1, a typical embodiment of the invention includes a non-magnetic envelope 11, for example, a glass envelope, containing therein a microwave resonant medium. The resonant medium, further by way of example, may comprise a gas such as ammonia, vapors such as sodium 23 or cesium 133 (uids), or materials such as CHI'CHI (methyl iodide) or I2 (iodine) which are solids at room temperature and pressure.

In the present example it is assumed that the microwave resonant medium chosen is sodium (Na23) at a vapor pressure not greater than 102 millimeters of mercury. Preferably the vapor pressure is between l04 and 10-6 millimeters of mercury. The sodium vapor is provided by a reservoir or source 13 which is connected to the envelope 1l via a conduit 15. A heater 17, supplied with current from a source (not shown), is provided for controlling the temperature and thereby the pressure of the sodium vapor in the reservoir or source 13.

The envelope 11 also contains means for generating a particle beam wherein the particles move in a predetermined direction at closely controlled velocities. In the embodiment illustrated a cathode 19 emits electrons at thermal velocities. An apertured accelerating and beam forming electrode 21 is spaced from the cathode 19 and is maintained, by a battery 23 or other D.C. source, at a potential which is positive with respect to the cathode potential, for example, +100 volts. A reasonably intense electron beam is thereby produced. This electron beam then is subjected to a decelerating field and enters an electron permeable cavity resonator Z5. The dccelerating field is produced by means of a battery 27 or equivalent source connected between the accelerating electrode 21 and the resonator 25. The decelerating field in the present example may be 97.9 volts. A relatively intense |-2.l volt electron beam thus is produced and caused to enter the resonator 2S.

In the event that it is necessary to focus the electron beam conventional electrostatic or magnetic focusing structure, per se well known, may be employed.

The electron permeable resonator 25 may be a wire mesh cage formed from a non-magnetic material such as copper or aluminum. The resonator preferably is cylindrical in shape and preferably is operated in the TEM mode at a frequency which is determined by the difference in energy levels of two selected magnetic nuclear substates. The only requirement imposed on the cage mesh size is that the mesh must be transparent to impacting electrons yet be opaque to electromagnetic fields set up therein. For Na23 the frequency to which the resonator 25 may be tuned is 1771 megacycles per second, whereas for Cs133 the operating frequency may be 9192.6 megacycles per second. Input and output couplings to the resonator 25 are afforded by coupling loops 29 and 31, respectively.

A weak D.C. magnetic field, approximately 0.1 gauss, for example, is impressed on the vapor by means of current through a coil 33 located outside the envelope. The magnetic lines of force H extend in the direction of motion of the electron beam.

Theory of operation The operation of the structure described in the foregoing paragraphs is believed to be as follows. The sodium vapor atoms initially are in a 381/2 ground state. Considering that the nuclear spin I is 3/5, the permitted magnetic substates MF of the F=l energy level of the ground state and the F :2 level of the 3P1/11 excited state are as shown in Figure 2. For the case where eV, the impacting energy of the electron beam, is just equal to the energy difference between the 3P and 3S states, the electrons, after collisions with sodium vapor atoms, have zero velocity and energy. The angular momentum transferred from the impacting electrons to the sodium atoms is at right angles to the motion of the electron stream, and the Weak magnetic field H produced by the coil 33 resolves the degeneracy of the magnetic substates. Thus, the transferred angular momentum also is normal to the magnetic field H. The important conclusion which follows is that only transitions which follow the interval rule can be induced by the impact of electrons moving in the direction of the magnetic field H.

With the electron energy eV=2.l volts, the electrons entering the resonator 25 cause impact induced transitions to occur between the F=l level of the 381/2 ground state and the F=2 level of the 3P1/2 state. The SP1/2 yand SP3/1 states are the excited states which give rise to the well known sodium D lines.

Using the interval rule Am=0, only the transitions shown in Figure 2 are permitted. Electron impact induced transitions from the magnetic substate M F=-l of the F=l level of the 381/2 ground state to the magnetic substate MF=1 of the F=2 level of the SP1/2 excited state are followed by drop-down" transitions to the MF=l or MF=0 substates of the F=l level of the 381/2 state. Similarly, impact induced transitions from the MF=11 substate of the F=l level of the 381/2 ground state to the MF=+1 substate of the F=2 level of the SP1/2 excited state are followed by drop-down transitions to the MF=+1 and MF=0 substates of the F =l level of the 381 /2 state. Also, impact induced transitions from the MF=0 magnetic substate of the F=l level of the 381/2 ground state to the MF=O substate of the F=2 level of the SP1/2 excited states are followed by drop-down transitions to any of the MF=1, MF=0, MF=+1 substates of the F =1 level of the 381/2 ground state.

As a result of the above-described impact induced transitions and the ensuing drop-down transitions, the number of sodium atoms in the MF=0 magnetic substate of the F=l level of the 381/2 state is enhanced at the expense of the MF=1 and MF=+1 magnetic substates of the F =l level of the 381 /2 state. The new population distribution comprises a preferred nuclear orientation in which the original population difference of the MF=0 substates of the F=l, F=2 levels of the 381/2 state is enhanced by several orders of magnitude. The MF==0 substate of the F=2 level of the 381 /2 ground state is less densely populated than the MF=0 substate of the F=l level of the ground state both before and after the impact or collision process is caused to occur. However, as a result of the impact phenomena the population difference between these substates is enhanced by a factor of about 103 which results in a spectral line of greatly increased intensity.

Since the intensity of the spectral line is increased in accordance with the method described above, the signalto-noise ratio of the system in which the apparatus of Figure l is employed is considerably improved. In systems for providing microwave spectroscopy or frequency stabilization the apparatus may be connected into such systems by means of the resonator input and output coupling loops 29 and 31, respectively. The frequency of the monochromatic excitation applied to the resonator 25 via the input coupling loop 29 is determined by the e11- ergy levels of the M1=-=0 substates of the F=l and F=2 levels of the 381/2 state. As indicated previously, for Na23 this frequency is 1,771 megacycles per second. For other spectral lines or resonant media the resonator tuning and the frequency of excitation energy are different.

In situations where microwave amplification or oscillation generation are desired, rather than microwave spectroscopy or frequency stabilization, it is necessary only to select other magnetic substates for utilization. In both cases, i.e., amplification and oscillation generation, it is necessary that the selected magnetic substate of the upper energy level of the ground state be more densely populated than the selected magnetic substate of the lower energy level of the ground state. Preferably, the population inequality of these two substates should be as great as possible.

It is important to note at this point that the population condition for amplification or oscillation generation is the reverse of the population condition for microwave spectroscopy or for ordinary absorption spectral line frequency stabilization. In those cases i.e., spectroscopy or frequency stabilization, the upper energy level of the ground state is less densely populated than the lower energy level of the ground state.

In general the greatest population increase in the upper energy level of the ground state occurs for (or near) the magnetic substate where I is the angular momentum of the particle (a sodium atom in the present example) and I is the nuclear spin of the atom.

The greatest population decrease in the lower energy level of the ground state occurs, for (or near). the mag,- netic substates Therefore, by selecting the magnetic substates so that the population of the upper energy level of the ground state is greater than the population of the lower energy level of the ground state, the resonant medium coherently radiates or emits rather than absorbs energy at a frequency at which the medium is resonant. When the medium is in this radiative or emissive condition it may be said to have negative attenuation.

With the intensity of the coherent radiation sufficient to exceed the usual cavity resonator losses, the overall attenuation of the structure is negative and the structure ampliiies microwave energy applied to the medium at a frequency at which the medium is resonant. Amplified output energy is. derived from the resonant medium at a rate equal to the sum of (l) the rate at which energy is applied to the resonator and (2) the rate at which electromagnetic energy is generated within the resonator by the quantum transition process. Inasmuch as the magnetic substates selected for amplification purposes are different from the magnetic substates selected for spectroscopy or frequency stabilization, the frequency of the input energy applied to the medium (the sodium) vapor) for amplification is close to, but not the same as, the 1,771 megacycles per second frequency referred to previously. This is because the excitation frequency is determined by the energy levels of the selected magnetic substates. The frequency of the input energy applied to the vapor via the coupling loop 29 may differ from the 1,771 megacycles per second frequency by one to several megacycles, depending on the particular substates chosen.

In the event that oscillation generation rather than amplification is desired, the input coupling loop 29 may be omitted and the cavity resonator 25 strongly decoupled with respect to its association load circuit (not shown). The magnetic substates selected for oscillation generation may be the same as those selected for amplification purposes. In such case a spontaneous build-up of electromagnetic oscillations occurs within the resonator 2S at a frequency at which the sodium atoms are resonant. With the electromagnetic energy withdrawn from the resonator at a rate which is slower than the rate of build-up of the oscillations, the device generates microwave energy which may be coupled therefrom by the output coupling loop 3l. In some instances it may be desirable to improve the oscillation generation capabilities of the device by operating the device at a reduced temperatuer to increase its Q.

While the embodiment of the invention described above teaches the use of electrons as the impacting particles, it is emphasized that other particles also may be employed, for example, ions, a molecular beam, or neutrons.

Doppler breadth reduction In view of the fact that the impact phenomenon affords a spectral line of greatly increased intensity, in some instances it may be desirable to trade some of the increased line intensity for a line of effectively narrower bandwidth. In these instances, and in accordance with a further feature of the invention, a small quantity of buffer gas, for example, a noble gas such as helium or argon, is introduced into the envelope 1l and mixed with the resonant gas or vapor. The partial pressure of tne resonant medium preferably is less than 10c-2 millimeters of mercury, as described previously, whereas the partial pressure of the noble gas preferably is several orders of magnitude greater. The particles of the noble gas effectively provide a long diffusion time for the particles or molecules of the microwave resonant medium before they strike the resonator walls. This is because the resonant particles or molecules collide with the noble gas particlesbefore they strike the resonator walls. Internas of the wavelength associated with magnetic dipole transitions of the particles or molecules of the resonant medium the mean free path is small.

In considering the overall effect of inter-particle collisions it is necessary to average overall particles in all velocity classes. In general the resonant atoms or molecules of all classes contribute to spectral line components at discrete frequencies. However, the resonant atoms or molecules of all classes also contribute to one common spectral line component at the non-Doppler shifted frequency. The result is a spectral line of essentially normal Doppler breadth with a sharp, narrow bandwidth line superimposed thereon which is free from Doppler broadening.

What is claimed is:

l. Microwave apparatus comprising, a microwave resonant medium capable of exhibiting discrete energy level transitions between quantum energy rotational states with resultant signal translation at at least one resonant transitional frequency distinctively characteristie of said medium, means for producing a beam of particles having energies sufficient to induce said rotational transitions but insufficient to ionize said medium, means for applying a magnetic field to said microwave resonant medium to resolve the degeneracy of said rotational states, means for causing said beam particles to collide with said microwave resonant medium to induce said transitions with said resultant translation, and means for providing electrical coupling to said signal translation from said microwave resonant medium.

2. Microwave apparatus comprising, a microwave resonant medium capable of exhibiting discrete energy level transitions between quantum energy rotational states with resultant signal translation at at least one resonant transitional frequency distinctively characteristic of said medium, means for producing a beam of particles having energies sufficient to induce said rotational transitions but insufficient to ionize said medium, means for applying a magnetic field to said microwave resonant medium with the magnetic lines of said field parallel to the path of said beam to resolve the degeneracy of said rotational states, means for causing said beam particles to move at predetermined uniform velocities whereby said uniform velocity particles collide with said microwave resonant medium to induce said transitions with said resultant translation, and means for applying microwave input energy to and coupling microwave output energy from said medium at a frequency for which said medium is resonant to utilize said translation.

3. Microwave apparatus for producing an intensified spectral line comprising, a microwave resonant medium capable of exhibiting energy level transitions between quantum energy rotational states with resultant spectral line intensification at at least one resonant transitional frequency distinctively characteristic of said medium, means for producing a beam of particles having energies suflicient to induce said rotational transitions but insumcient to ionize said medium, means for applying a magnetic field to said microwave resonant medium with the magnetic lines of said field parallel to the path of said beam to resolve the degeneracy of said rotational states, means for causing said beam particles to move at predetermined uniform velocities whereby said uniform velocity particles collide with said microwave resonant medium to induce transitions with said resultant line intensification, means for applying microwave input energy to said medium at a frequency for which said medium is resonant, and means responsive to said intensitied spectral line for deriving from said medium output microwave energy at said resonant frequency.

4. Microwave apparatus comprising, a microwave resonant medium, a noble gas mixed with said microwave resonant medium, means for producing a beam of par' ticles, means for causing said beam particles to collide with said microwave resonant medium, means for applying a magnetic eld to said microwave resonant medium with the magnetic lines of said field parallel to the path of said beam, means for applying microwave input energy to said medium at a frequency for which said medium iS resonant, and means for deriving from said medium output microwave energy at said resonant frequency.

5. Microwave apparatus comprising, a microwave resonant medium capable of exhibiting discrete energy level transition between quantum energy rotational states with resultant signal translation at at least one resonant transitional frequency distinctively characteristic of said medium, means for producing particles having energies sufficient to induce said rotational transitions but insufcient to ionize said medium, means for applying a magnetic field to said microwave resonant medium with the magnetic lines of said field parallel to the path of said beam to resolve the degeneracy of said rotational states, means for successively accelerating and decelerating said particles to form an intense low velocity particle beam whereby said beam particles collide with said microwave resonant medium to induce said transitions with said resultant translation, means for applying microwave input energy to said medium at a frequency for which said medium is resonant, and means responsive to said translation for deriving from said medium output microwave energy at said resonant frequency.

6. Microwave apparatus comprising, a microwave resonant gas capable of exhibiting energy level transitions between quantum energy rotational states with resultant spectral line intensification at at least one resonant transitional frequency distinctively characteristic of said gas, means for producing a beam of particles having energies sufficient to induce said rotational transitions but insufflcient to ionize said medium, means for applying a magnetic field to said microwave resonant gas with the magnetic lines of said field parallel to the path of said beam to resolve the degeneracy of said rotational states, means for causing said beam particles to move at predetermined uniform velocities whereby said uniform velocity particles collide with said microwave resonant gas to induce transitions with said resultant line intensifcation, means for applying microwave input energy to said gas at a frequency for which said gas is resonant, and means responsive to said intensified spectral line for deriving from said gas output microwave energy at said resonant frequency.

7. Microwave apparatus comprising, a microwave resonant vapor capable of exhibiting energy level transitions between quantum energy rotational states with resultant spectral line intensification at at least one resonant transitional frequency distinctively characteristic of said vapor, means for producing a beam of particles having energies sufficient to induce said rotational transitions but insufiicient to ionize said medium, means for applying a magnetic field to said microwave resonant vapor with the magnetic lines of said field parallel to the path of said beam to resolve the degeneracy of said rotational states, means for causing said beam particles to move at predetermined uniform velocities whereby said uniform velocity particles collide with said microwave resonant vapor to induce transitions with said resultant line intensification, means for applying microwave input energy to said vapor at a frequency for which said vapor 1s resonant, and means responsive to said intensified spectral line for deriving from said vapor output microwave energy at said resonant frequency.

8. Apparatus as claimed in claim 7 wherein said vapor 1s sodium and said particles are electrons.

9. Microwave apparatus comprising a microwave resonant material capable of exhibiting energy level transitions between quantum energy rotational states with resultant spectral line intensification at at least one resonant transitional frequency distinctively characteristic of said material which is solid at room temperature and pressure, means for producing a beam of particles having energies sufficient to induce said rotational transitions but insufficient to ionize said medium, means for applying a magnetic field to said microwave resonant material with the magnetic lines of said field parallel to the path of said beam to resolve the degeneracy of said rotational states, means for causing said beam particles to move at predetermined uniform velocities whereby said uniform velocity particles collide with said microwave resonant material to induce said transitions with said resultant translation, means for applying microwave input energy to said material at a frequency for which said material is resonant, and means responsive to said translation for deriving from said material output microwave energy at said resonant frequency.

l0. Apparatus according to claim 2 wherein said medium has a pressure not greater than 10-2 millimeters of mercury.

1l. Apparatus as claimed in claim 12 wherein said particles are electrons.

12. Microwave apparatus comprising, an envelope containing a microwave resonant medium capable of exhibiting discrete energy level transitions between quantum energy rotational states with resultant signal translation at at least one resonant transitional frequency distinctively characteristic of said medium at a pressure not greater than 10-2 millimeters of mercury, means within said envelope for producing a beam of particles having energies suicient to induce said rotational transitions but insufficient to ionize said medium, means located outside said envelope for applying a magnetic field to said microwave resonant medium with the lines of said magnetic field parallel to the path of said beam to resolve the degeneracy of said rotational states, a cavity resonator within said envelope permeable to said particles and opaque to electromagnetic fields set up in said resonator, means for forming said particles into a beam of particles which enter said resonator and collide with the microwave resonant medium contained therein to induce said transitions with said resultant translation, means for coupling microwave input energy into said resonator at a frequency for which said medium is resonant, and means responsive to said translation for coupling microwave output energy from said resonator at said resonant frequency.

13. Apparatus as claimed in claim 12, including means for controlling the pressure of said microwave resonant medium.

14. Microwave apparatus comprising, an envelope containing a microwave resonant medium at a pressure not greater than 10-2 millimeters of mercury, a noble gas mixed with said microwave resonant medium, said noble gas being at a pressure at least two orders of magnitude greater than the pressure of said resonant medium, means within said envelope for producing a vapor of particles, a cavity resonator within said envelope permeable to said particles and opaque to electromagnetic fields set up in said resonator, means for forming said particles into a beam which enters said resonator and collides with the microwave resonant medium contained therein, means located outside said envelope for applying a magnetic field to said microwave resonant medium with the lines of said magnetic field parallel to the path of said beam, means for coupling microwave input energy into said resonator at a frequency for which said medium is resonant, and means for coupling microwave output energy from said resonator at said resonant frequency.

15. A microwave amplifier comprising, a microwave resonant medium capable of exhibiting energy level transitions between quantum energy rotational states with resultant signal generation at at least one resonant transitional frequency distinctively characteristic of said medium, means for producing a beam of particles having energies sufficient to induce said rotational transitions but insuicient to ionize said medium, means for applying a magnetic field to said resonant medium to resolve the degeneracy of said rotational states, means for causing said beam particles to collide with said microwave resonant medium to induce transitions with said resultant generation, means for applying microwave input energy to said medium at a frequency at which said medium is resonant and means for withdrawing microwave energy from said medium at a rate not exceeding the sum of the rates at which energy is applied to and generated by said medium.

16. A microwave oscillation generator comprising, a microwave resonant medium capable of exhibiting energy level transitions between quantum energy rotational states with resultant signal generation at at least one resonant transitional frequency distinctively characteristic of said medium, means for producing a beam of particles having energies sufiicient to induce said rotational transitions but insufficient to ionize said medium, means for applying a magnetic field to said resonant medium to resolve the degeneracy of said rotational states, means for causing said beam particles to collide with said microwave resonant medium to initiate the build-up of electromagnetic oscillations at a frequency at which said medium is resonant, and means for withdrawing electromagnetic energy from said medium at said frequency at a rate which is slower than the rate of build-up of said electromagnetic oscillations.

17. Apparatus as claimed in claim resonant medium comprising a fluid.

18. Apparatus as claimed in claim resonant medium comprising a gas.

19. Apparatus as claimed in claim resonant medium comprising a vapor.

20. Apparatus as claimed in claim 1, said microwave resonant medium comprising a solid at room temperature and pressure.

2l. Microwave apparatus comprising, a microwave resonant medium normally presenting positive attenuation to electrical energy at frequencies for which said medium is resonant, means for introducing energetic particles into said microwave resonant medium having energies sufiicient to induce quantum energy rotational transitions in but insuicient to ionize said medium to cause said medium to present negative attenuation to microwave energy at a frequency for which said medium is resonant, and means for providing electrical coupling to said medium.

22. Microwave apparatus comprising, a microwave resonant medium normally presenting positive attenuation to electrical energy at frequencies for which said medium is resonant, means for introducing electrons into said microwave resonant medium having energies suficient to induce quantum energy rotational transitions in but insuicient to ionize said medium to cause said medium to present negative attenuation to microwave energy at a frequency for which said medium is resonant, means for providing electrical coupling to said medium.

23. Microwave apparatus comprising, a microwave resonant medium normally in a condition of thermal equilibrium, means for introducing energetic particles into said microwave resonant medium having energies suficient to effect energy level transitions between quantum energy rotational states of, but insufcient to ionize, said medium thereby disturbing said thermal equilibrium condition, and means for providing electrical coupling to said medium.

24. Microwave apparatus comprising, a microwave resonant medium normally in a condition of thermal equilibrium, means for introducing electrons into said microwave resonant medium having energies sufficient to eect energy level transitions between quantum er1- ergy rotational states of, but insufiicient to ionize, said medium thereby disturbing said thermal equilibrium con- 1, said microwave 1, said microwave 1, said microwave l@ dition, and' means for providing electrical coupling to said medium.

25. A microwave amplifier comprising, a microwave resonant medium normally presenting positive attenuation to electrical energy at frequencies for which said medium is resonant, means for introducing charge carriers into said microwave resonant medium having energies suficient to induce quantum energy rotational transitions in but insufficient to ionize said medium to cause said medium to present negative attenuation to microwave energy at a frequency for which said medium is resonant, and means for applying microwave input energy to said medium at a frequency for which said medium presents negative attenuation and for deriving amplified microwave input energy from said medium.

26. A microwave amplifier comprising, a microwave resonant medium normally presenting positive attenuation to electrical energy at frequencies for which said medium is resonant, means for introducing charge carriers into said microwave resonant medium having energies sufiicient to induce quantum energy rotational transitions in but insufficient to ionize said medium to cause said medium to present negative attenuation to microwave energy at a frequency for which said medium is resonant, means for applying microwave input energy to said medium at a frequency for which said medium presents negative attenuation, and means for deriving amplified microwave input energy from said medium.

27. A microwave generator comprising, a microwave resonant medium normally presenting positive attenuation to electrical energy at frequencies for which said medium is resonant, means for introducing energetic particles into said microwave resonant medium having energies sufficient to induce quantum energy rotational transitions in but insuficient to ionize said medium to cause said medium to present negative attenuation to microwave energy at a frequency for which Isaid medium is resonant, and means for deriving microwave energy from said medium at a frequency for which said medium is resonant while said medium presents negative attennation.

28. A microwave generator comprising, a microwave resonant medium normally in a condition of thermal equilibrium, means for introducing energetic particles into said microwave resonant medium having energies sucient to eiect energy level transitions between quantum energy rotational states of, but insufficient to ionize, said medium thereby disturbing said thermal equilibrium condition, and means for deriving microwave energy from said medium while said thermal equilibrium condition is disturbed.

29. A microwave resonant medium atoms of which are in thermal equilibrium in magnetic substates of a ground state; and means for inducing energy level transitions between quantum energy rotational states in said medium for increasing the population of atoms in one of said magnetic substates of the ground state at the expense of those in another, said means including means for applying energetic particles to the medium having energies sufficient to induce said rotational transitions but insufiicient to ionize said medium.

3G. A microwave resonant medium atoms of which are in thermal equilibrium in magnetic substates of a ground state; and means for inducing energy level transitions between quantum energy rotational states in said medium, said means including means for applying a beam of energetic particles to the medium having energies sufiicient to induce said rotational transitions but insucient to ionize said medium for increasing the population of atoms in one of said magnetic substates of the ground state at the expense of those in another.

3l. Apparatus as claimed in claim 1 wherein said particles have energies substantially equal to the difference in energies between said rotational states.

(References on following page) References Cited in the file of this patent UNITED STATES PATENTS Pratt June 9, 1936 Pierce et al. Jan. 16, 1951 Hershberger Apr. 24, 1956 Norton May 6, 1956 Dicke et al. June 5, 1956 Dicke Sept. 11, 1956 12 2,837,693 Norton June 3, 1958 2,848,649 Bryant Aug. 19, 1958 2,879,439 Townes Mar. 24, 1959 OTHER REFERENCES Weber: Reprint from I. R. E. Transactions, Professional Group on Electron Devices, published June 1953.

Gordon, Zeiger and Townes: Physical Review, v01. 95, page 282 (1954).