US2909654A - Uninterrupted amplification key stimulated emission of radiation from a substance having three energy states - Google Patents

Uninterrupted amplification key stimulated emission of radiation from a substance having three energy states Download PDF

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US2909654A
US2909654A US616004A US61600456A US2909654A US 2909654 A US2909654 A US 2909654A US 616004 A US616004 A US 616004A US 61600456 A US61600456 A US 61600456A US 2909654 A US2909654 A US 2909654A
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energy
levels
frequency
cavity
maser
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Bloembergen Nicolaas
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Priority to NL221512D priority Critical patent/NL221512A/xx
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Priority to US616004A priority patent/US2909654A/en
Priority to DEB46369A priority patent/DE1095326B/de
Priority to GB31853/57A priority patent/GB880478A/en
Priority to CH1157361A priority patent/CH378378A/de
Priority to DK191961AA priority patent/DK106678C/da
Priority to CH359757D priority patent/CH359757A/de
Priority to DK348157AA priority patent/DK114073B/da
Priority to FR749407A priority patent/FR1267115A/fr
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Publication of US2909654A publication Critical patent/US2909654A/en
Priority to NL6605677A priority patent/NL6605677A/xx
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
    • H03H2/00—Networks using elements or techniques not provided for in groups H03H3/00 - H03H21/00
    • H03H2/005—Coupling circuits between transmission lines or antennas and transmitters, receivers or amplifiers
    • H03H2/006—Transmitter or amplifier output circuits
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S1/00—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range
    • H01S1/02—Masers, i.e. devices using stimulated emission of electromagnetic radiation in the microwave range solid
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03F—AMPLIFIERS
    • H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
    • H03F3/60—Amplifiers in which coupling networks have distributed constants, e.g. with waveguide resonators
    • H03F3/608—Reflection amplifiers, i.e. amplifiers using a one-port amplifying element and a multiport coupler

Definitions

  • Thisinvention relates to microwave amplification by stimulated emission of radiation. Apparatus for achieving such amplification is now generally described as a maser, a term which is an acronym for microwave amplification by stimulated emission of radiation.
  • the population distribution among the possible energy levels in a medium is governed by Boltzmanns equation and, accordingly, in the system higher energy levels are less populated than lower energy levels.
  • electromagnetic Wave energy of the frequency proper to the, energy difierence between two particular levels in accordance with Plancks equation where h is Plancks constant is applied to the medium, there will be an exchange between the populations of these levels; acertain fraction of the population in the lower level will absorb radiation and be raised to the higher levelj an equal fraction of the population in the higher level will be stimulated to emit radiation and will drop to the lower level.
  • the result will be a net absorption of energy.
  • a medium in which the population of an upper energy level is greater than that of a lower energy value is not in thermal equilibrium. It will be convenient'to describe a medium which is in this condition as exhibiting a negative temperature. It is a characteristic of masers that ideally they have a noise figure considerably lower than the noise figure of other known forms of microwave amplifiers. Such lower noise figure can be utilized to provide a much higher sensitivity.
  • the desired nonequilibrium energy state may be provided by flowing ammonia gas through a region where an electric field is applied in which the Stark effect known to workers in the art is linear and which is characterized by an abrupt reversal in direction. In passing through the region of field reversal, the ammonia molecules should experience a change in rotational energy state which should result in a nonequilibrium distribution of rotational energy states.
  • a molecular beam of ammonia which is made to traverse a region in which a. nonuniform electrostatic field is used to select for passage into a cavity substantially only those molecules which are in upper inversion energy states.
  • a gaseous medium in which the population of molecules in the upper inversion energy states exceeds that in the lower energy states. This corresponds to a medium which is at a negative temperature.
  • a radio signal of frequency corresponding to the energy difference betwen the upper and lower inversion energy states, amplification of the radio signal is realized.
  • a molecular beam may be provided in which the population of molecules in an upper state exceeds the population of molecules in a lower state by preexposure of the molecular beam to auxiliary high frequency fields which induce resonance transitions between two levels which straddle an intermediate level.
  • the desired nonequilibriurn distribution of energy levels which can be used to provide radiation at the frequency corresponding to the diiference between the two appropriate energy levels.
  • silicon crystal doped with phosphorus is positioned in a cavity and thereafter subjected to a magnetic field which acts to line up parallel to it the spin magnetic moments of the conduction electrons. Thereafter, the magnitude of the applied magnetic field is varied to pass through the value corresponding to the electron spin resonance line in the manner similar to the adiabatic rapid passage technique used in nuclear magnetic resonance experiments known to workers in the art.
  • the negative temperature effect is discontinuous, existing only for the time it takes the spins to relax to equilibrium. After such time, another inversion is necessary if the negative temperature is to be reestablished.
  • the medium is a gas confined to a closed chamber within which there is also included a Stark electrode.
  • the Stark effect it is made possible to provide a difference in frequency between the microwave energy applied to effect the inversion in population states and the signal to be amplified.
  • continuous operation is made possible, energy of one frequency being applied continuously to maintain the gas at a negative temperature, and incident signal energy of a different frequency being applied continuously to stimulate emission of radiation for its amplification.
  • the primary object of the present invention is to provide a solid state maser which is inherently capable of continuous operation. Additionally, it is advantageous that the maser have a relatively wide frequency band of operation, be readily tuned to the desired band of operation, be capable of handling relatively high powers, and have an inherently low noise level.
  • a feature of the present invention is a solid state medium in which a negative temperature exists continuously during'operation.
  • a medium comprises a paramagnetic solid which is characterized by a multiple energy level system with the separations of the energy levels fall ing within desired operating frequency ranges.
  • To this solid there is supplied continuously energy which effects transitions from a low energy level to a nonadjacent high energy level, bypassing an intermediate energy level.
  • By power saturation of the high energy level there can be established in the solid a nonequilibrium energy distribution with respect to the intermediate level, which can be used for the amplification of a signal of appropriate frequency.
  • Fig. l is an energy diagram which will be helpful in explaining the principles of the invention.
  • Fig. 2 shows partly in schematic form and partly as a cross sectional view apparatus utilizing a solid as a negative temperature medium in accordance with the invention
  • FIG. 3 illustrates in schematic form a typical arrangement embodying a maser in accordance with the invention.
  • the population of intermediate level E Will either be greater or smaller than the equalized populations of levels E and E
  • maser action is possible at the frequency corresponding to the difference in energy levels E and E
  • maser action is possible at the frequency corresponding to the difference in energy levels E and E
  • ergy level E is .closer to energy level E in practice this is immaterial, the energy level i jrnay fall anywhere intermediate between the nonadj'acent energy levels E I It should be evident that, itflis'possible tojemploy the techniques .described'in an analogous manner'to achieve a negative temperature. in asolid having more than three energylevels, by making use'of transitionsof the kind described between any chosen three of such levels.
  • paramagnetic salts ionically'bound paramagnetic salts.
  • the choice of a particular paramagnetic salt is largely dependent on the existence of suitable energy levels and the existence of matrix elements of the magnetic moment operator between the various spin levels. The absorption and stimulated emission process depend directly on this operator, butthe relaxation times also dependon the spin angular 'mom'entumoperator via spin-orbitcoupling terms. It is importantthat-all offdiagonal elements between the three spin levelsunder consideration be nonvanishin'g. This is achieved by putting the paramagnetic salt with'a'crystalline fieldsplitting parameter 5 in a magnetic field which makes an angle with the crystalline field axis.
  • the magnitude of this field is chosen such that the Zeeman energy is comparable to the crystalline field splitting.
  • the. stateswith magnetic quantum numbers'm are all scrambled. 'Ihe mixing of the spin states by Zeemanand crystalline field interactions of comparable magnitude is important.
  • Paramagnetic salts which have previously been reported in. detail in the literature and which exhibit the properties desired include nickel fluosilicate' and gadolinium ethyl sulphate. Variousother ionically bound paramagnetic salts of the transition groups, such as iron and rare earth groups, exhibit similar properties.
  • a single crystal which is 95 percent ZnSiE -6H O and 5 percent the isomorphous nickel salt has a line width of 50 oersteds and an average crystalline field splitting 6 equal to .12 cm.- -for the nickel ions. 1
  • spin lattice relaxation time has been measured to, be about 10* seconds at .2" K. Relevantproperties of this salt are described in a paper published inthe Proceedings of the Physical Society A63,29 (1949").
  • a' crystalline field splitting 6 of .113 cmr j, .083 cmr and .046 cm. measured at 20 K. These splittings are substantially independent of temperature.
  • the line width is seven oerstedsi This width may be reduced by a factor of three by using the deuterated salts.
  • the relaxation time at 2 K. is about 10- seconds. Relevant properties of this salt are described. in a paper in the l?roceedings of the Royal Society A223, 15 (1954).
  • the combination 10 includes a coaxial cavity 11 which is of a kind known to workers in the microwave art and has a fundamental mode resonating at the signal frequency and a higher mode resonating at the frequency of the driving microwave energy to be used to efiect the transitions from the low level E to the high level E In this embodiment, this frequency corresponds to 10,000 megacycles.
  • the coaxial cavity is provided with a dielectric element 12, advantageously a piece of rutile whose configuration resembles a sector of a circle 'and whose position is adjusted to tune the cavity at the higher of the two frequencies of interest. Because the element is positioned near a node in the electric field of the lower of the two frequencies of interest, its presence will little affect the tuning of the cavity at the lower fre quency. Additionally, for tuning the cavity to the lower frequency, there is provided a tuning screw 13 of the kind known to workers in the art.
  • a single crystal 14 ofthe diluted nickel fluosilicate salt there is included within the cavity a single crystal 14 ofthe diluted nickel fluosilicate salt.
  • a Q of 10 and an effective volume of 60 cm. it is calculated that the condition for amplification is satisfied if the total number of electron spins in the crystal exceeds 3x10
  • the required minimum number of nickel ions is contained in approximately .02 cm. of the nickel fluosilicate salt diluted as described. ,However, as may be expected, itwill generally be advisable to employ crystals largerthan the minimum size required.
  • apparatus 15 which provides a static magnetic field having a prescribed orientation with respect to the'crystalline axis as previously described.
  • the separations between the discrete energy levels, and hence the useful operating frequency ranges will be controlled by the. strength of the static magnetic field applied.
  • a field of approximately a thousand gauss is applied initially.
  • the orientation of the crystalline axis of the paramagnetic salt with respect to the radio frequency magnetic field is adjusted experimentally to give optimum values for the relevant matrix elements.
  • Microwave energy of the desired driving frequency is supplied by an excitation oscillator 16 and introduced into the cavity by a coupling probe 17 in the manner familiar to workers in the art. Enough poweris supplied to obtain saturation between energy levels E and Typically, saturation is obtained when the magnetic field of the driving energy has an intensity in the crystal of approximately 0.2 oersted.
  • the width of the band in which m-aser action is feasible is controlled by the strength of the driving magnetic field, because the line width is due to inhomogeneities in the internal fields of the paramagnetic salt.
  • a field strength as described results in a useful band of about one-half a megacycle. Stronger fields result in a proportionate increase in the width of the useful band up to a maximum determined by the power handling ca 'pacity ofthe system.
  • the input signal supplied from a suitable source is introduced into the-cavity by means of an input signal coupling probe 18.
  • the amplified signal is abstracted for utilization by a suitable load by way of an output coupling probe 19.
  • an output coupling probe 19 it is advantageous to employ the same coupling probe both to introduce and to abstract the signal energy as will be described in more detail hereinafter.
  • the cavity resonator is maintained at a temperature of about 2 K.
  • the broken line 20 is used to .indicate that the cavity and its contents are confined within Suitable refrigerating apparatus.
  • a straight-through wave path such as a hollow wave guide, a portion of which houses the medium exhibiting negative temperature.
  • signal energy in traveling along the wave path is made to pass through the portion housing the medium which is at a negative temperature.
  • Directional couplers advantageously may be used to couple the driving energy into the wave path from an auxiliary path.
  • Various other arrangements of directional couplers and wave guides will be apparent to workers in the art for applying to the negative temperature medium both signal power and driving power.
  • a maser in accordance with the invention is capable of a variety of applications, as is characteristic generally of amplifiers. For example, if operated at a high enough gain, it can be made to oscillate, the noise inherent in the walls enclosing the medium acting initially tostimulate emission.
  • the arrangement shown in Fig. 2 accordingly may be made to serve as an oscillator. In such a case, the input connection becomes superfluous and is advantageously omitted.
  • the maser has primary importance as a highly sensitive amplifier because of its low inherent noise level. It is characteristic that a maser has a linear gain response over a wide range of input levels. If the level of the input signal is suificient to cause saturation of the relevant transitions, the gain will automatically decrease. This reduces the need for any bum-out protection for the maser.
  • a maser can readily be introduced to provide amplification at any point of an extended wave transmission system. Typically, however, a maser will find application as an amplifier in an arrangement of the kind shown in Fig. 3.
  • an antenna 21 is used to pick up transmitted signals and these signals are then supplied to arm a of a circulator 22.
  • a circulator as the term is understood in the microwave art, is a one way transmis sion element.
  • Arm b of the circulator is used to supply input signal energy to the maser 23, which advantageously is of the kind shown in Fig. 2 with the exception that there is not included the coupling connection whichhas been described as the output coupling connection in the accompanying description.
  • the output signal power is abstracted from the cavity by the same coupling loop which serves to introduce the signal power into the cavity.
  • the out put power supplied to arm b from the cavity is-transmitted selectively through the circulator only in the direction .toward afm c.
  • the maser is supplied with driving power from the local oscillator 24.
  • Arm c of the-circulator in turn supplies 10511.25 which typically may be-a'receiver or the cavity of a second maser stage in instances wheremoregain is desired than it is convenient to realize in'a single maser stage.
  • Any power reflected back by the load asa result of mismatches is transmitted through the circulator selectively only in the direction towards arm d.
  • Arm d in turn-supplies a dummy load 26 which typically is .a matched termination designed to minimize reflections therefrom. 1 I
  • the broken line 28 is used to denote that the elements enclosed thereby are kept within suitable refrigerating apparatus.
  • a maser in accordance with the invention may be made which uses changes in the nuclear quantum number.
  • the negative temperature medium there may be employed as the negative temperature medium a paramagnetic salt or an organic free radical with hyperfine structure, such that a hyperfine splitting is superimposed upon the electronic Zeeman splitting whereby multiple levels are provided. Transitions may then be induced between levels separated by one or more intermediate levels for achieving a nonequilibrium distribution in the medium which may be used for the emission of radiation.
  • a maser of the kind described may find application in a variety of modulation arrangements. As has been described, in a maser in accordance with the invention, various parameters exist whose variation may be used to vary either the amplitude level of the output or the frequency response.
  • a solid which is characterized by a multiple energy level system, means supplying driving energy to said solid for inducing enough transitions from one energy level to a non-adjacent, higher energy level of the system whereby the solid exhibits a negative temperature at a particular frequency, and means supplying to and abstracting from said solid energy of the particular frequency diiferent from the frequency of said driving energy and corresponding to the separation between a different pair of energy levels.
  • an ionically bound paramagnetic solid which is characterized by a multiple energy level system including at least three energy levels out of which a lowest, an intermediate and a highest are chosen, means supplying driving energy to said solid for inducing enough transistions from said lowest energy level to said highest energy level whereby the solid exhibits a nonequilibrium thermal distribution of energy states between said intermediate energy level and one of said lowest and highest energy levels, and means supplying to and abstracting from said solid energy of a frequency corresponding to the energy difference between said intermediate level and one of said other two levels whereby amplification results.
  • a cavity having at least two resonant modes a solid which is characterized by a multiple energy level system positioned within said cavity, means supplying to the cavity driving energy at a frequency corresponding to one of the resonant modes of said cavity for inducing transitions between non-adjacent levels in said solid and establishing a negative temperature in modes of the cavity, .and means supplying to the solid energy at the last mentioned frequency for utilizingthe negative temperature of the solid for amplification,
  • a cavity having at least two resonant modes an ionically bound paramagnetic salt which ispositioned in the cavity and which is characterized by a multiple energy level system including at least energy levels
  • a cavity which has at least two resonant modes of different frequencies, an ionically bound paramagnetic crystal positioned in said cavity and characterized by a multiple energy level system including at least three levels, means for impressing a static magnetic field on said crystal of strength that the difference in energy levels between the lowest and highest levels of said three corresponds to a higher of the resonant frequencies of the cavity and the difference in energy level between the intermediate level of said three and one of said highest and lowest levels corresponds to -a lower of the resonant frequenciesof the cavity, means for supplying to the cavity driving energy of said higher frequency for establishing a negative temperature in V the cavity for energy of said lower frequency.
  • said means in energy exchange relation comprises means for supplying signal energy for amplification and for abstracting amplified signal energy for utilization.
  • Receiving apparatus comprising amplifying apparatus including a solid which is characterized by a multiple energy level system and to which is supplied driving energy of a frequency corresponding to the difference in energy levels between two non-adjacent levels whereby the solid is made to exhibit a negative temperature with respect to a difierent pair of energy levels of the multiple energy system, a source of signals, a load, and a circulator having a plurality of arms of which one is supplied by a source of signals with signal energy of a frequency suitable for amplification by the amplifying apparatus, an-
  • the solid at the frequency of another of the resonant other of which supplies signal energy to the amplifying Iap ia a'ms'and abstracts amplified signal povver merira of adjacent energy levels and one pair of nonadjacent energy levels of said four energy level systefn whereby a negative temperature with respect to another 'pair of nonadjacent energy levels of said.
  • four energy level system is achieved, and m'eans'supplying to and abstracting from the solid signal povver of "frequency corresponding to the negative temperature in the solid.
  • Receiving apparatus in accordance with claim 14 further characterized in that the source of signals is an antenna.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Optics & Photonics (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Control Of Motors That Do Not Use Commutators (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)
  • Stabilization Of Oscillater, Synchronisation, Frequency Synthesizers (AREA)
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US616004A 1956-10-15 1956-10-15 Uninterrupted amplification key stimulated emission of radiation from a substance having three energy states Expired - Lifetime US2909654A (en)

Priority Applications (10)

Application Number Priority Date Filing Date Title
NL221512D NL221512A (da) 1956-10-15
US616004A US2909654A (en) 1956-10-15 1956-10-15 Uninterrupted amplification key stimulated emission of radiation from a substance having three energy states
GB31853/57A GB880478A (en) 1956-10-15 1957-10-11 Improvements in microwave signal circuit-arrangements
DEB46369A DE1095326B (de) 1956-10-15 1957-10-11 Vorrichtung zur Verstaerkung, Erzeugung oder Frequenzumwandlung eines Mikrowellensignals
CH1157361A CH378378A (de) 1956-10-15 1957-10-12 Anordnung zur Kopplung eines rauscharmen Verstärkers mit einer Belastung
DK191961AA DK106678C (da) 1956-10-15 1957-10-12 Forstærkerkobling med et forstærkende element med negativ modstandskarakteristik.
CH359757D CH359757A (de) 1956-10-15 1957-10-12 Vorrichtung zur Verstärkung, Erzeugung oder Frequenzumwandlung eines Mikrowellensignals
DK348157AA DK114073B (da) 1956-10-15 1957-10-12 Anordning til forstærkning, frembringelse eller frekvenstransformation af mikrobølgesignaler.
FR749407A FR1267115A (fr) 1956-10-15 1957-10-14 Dispositif pour amplifier ou engendrer un signal à hyperfréquence ou pour transformer sa fréquence
NL6605677A NL6605677A (da) 1956-10-15 1966-04-28

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Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2981894A (en) * 1961-04-25 scovil
US2988636A (en) * 1960-04-22 1961-06-13 Research Corp Parametric amplifier antenna
US2990518A (en) * 1961-06-27 Braunstein
US2997581A (en) * 1961-08-22 Frequency converter
US3002156A (en) * 1961-09-26 pumped solid state maser
US3009123A (en) * 1960-04-26 1961-11-14 Bell Telephone Labor Inc Tunable two mode cavity resonator
US3013217A (en) * 1958-04-30 1961-12-12 Int Standard Electric Corp Maser type oscillator
US3018443A (en) * 1958-05-20 1962-01-23 Rca Corp Parameric amplifier with lower frequency pumping
US3023367A (en) * 1962-02-27 Maser
US3072859A (en) * 1959-12-01 1963-01-08 Ibm Four spin flip maser with single maser action
US3075156A (en) * 1957-05-02 1963-01-22 Varian Associates Gyromagnetic method and apparatus
US3117282A (en) * 1960-06-21 1964-01-07 Gen Electric Maser recovery system
US3175164A (en) * 1958-06-30 1965-03-23 Ibm Non-linear resonant apparatus
US3177445A (en) * 1965-04-06 Harmonic generator using equally spaced energy levels
US3201708A (en) * 1965-08-17 Ports oh
US3210674A (en) * 1965-10-05 Pushxpush l lower frequency pumped maser
US3210673A (en) * 1960-01-05 1965-10-05 Tavkozlesi Ki Hydrogen maser for generating, amplifying and/or frequency modulating microwave energy
US3237132A (en) * 1960-01-21 1966-02-22 Okaya Akira Dielectric microwave resonator
US3281600A (en) * 1966-10-25 Stimulated gamma ray emission
US4063195A (en) * 1976-03-26 1977-12-13 Hughes Aircraft Company Parametric frequency converter
US20080231275A1 (en) * 2007-03-21 2008-09-25 Kirstin Jattke Magnetic resonance method and apparatus for automatically determining objects that attenuate penetrating radiation
WO2013175235A1 (en) * 2012-05-25 2013-11-28 Imperial Innovations Limited Device and method for generating stimulated emission of microwave or radio frequency radiation
US20150214687A1 (en) * 2012-08-17 2015-07-30 The Secretary Of State For Business Innovation & Skills Of Her Majesty's Britannic Government Maser assembly

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3978417A (en) * 1975-02-12 1976-08-31 Nasa Reflected-wave maser

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2445895A (en) * 1942-12-31 1948-07-27 Bell Telephone Labor Inc Coupling arrangement for use in wave transmission systems
US2762872A (en) * 1954-12-01 1956-09-11 Robert H Dicke Microwave amplifier employing a microwave resonant gas as the amplifying element

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2445895A (en) * 1942-12-31 1948-07-27 Bell Telephone Labor Inc Coupling arrangement for use in wave transmission systems
US2762872A (en) * 1954-12-01 1956-09-11 Robert H Dicke Microwave amplifier employing a microwave resonant gas as the amplifying element

Cited By (26)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3281600A (en) * 1966-10-25 Stimulated gamma ray emission
US2990518A (en) * 1961-06-27 Braunstein
US2997581A (en) * 1961-08-22 Frequency converter
US3002156A (en) * 1961-09-26 pumped solid state maser
US3210674A (en) * 1965-10-05 Pushxpush l lower frequency pumped maser
US2981894A (en) * 1961-04-25 scovil
US3201708A (en) * 1965-08-17 Ports oh
US3023367A (en) * 1962-02-27 Maser
US3177445A (en) * 1965-04-06 Harmonic generator using equally spaced energy levels
US3075156A (en) * 1957-05-02 1963-01-22 Varian Associates Gyromagnetic method and apparatus
US3013217A (en) * 1958-04-30 1961-12-12 Int Standard Electric Corp Maser type oscillator
US3018443A (en) * 1958-05-20 1962-01-23 Rca Corp Parameric amplifier with lower frequency pumping
US3175164A (en) * 1958-06-30 1965-03-23 Ibm Non-linear resonant apparatus
US3072859A (en) * 1959-12-01 1963-01-08 Ibm Four spin flip maser with single maser action
US3210673A (en) * 1960-01-05 1965-10-05 Tavkozlesi Ki Hydrogen maser for generating, amplifying and/or frequency modulating microwave energy
US3237132A (en) * 1960-01-21 1966-02-22 Okaya Akira Dielectric microwave resonator
US2988636A (en) * 1960-04-22 1961-06-13 Research Corp Parametric amplifier antenna
US3009123A (en) * 1960-04-26 1961-11-14 Bell Telephone Labor Inc Tunable two mode cavity resonator
US3117282A (en) * 1960-06-21 1964-01-07 Gen Electric Maser recovery system
US4063195A (en) * 1976-03-26 1977-12-13 Hughes Aircraft Company Parametric frequency converter
US20080231275A1 (en) * 2007-03-21 2008-09-25 Kirstin Jattke Magnetic resonance method and apparatus for automatically determining objects that attenuate penetrating radiation
US7859261B2 (en) * 2007-03-21 2010-12-28 Siemens Aktiengesellschaft Magnetic resonance method and apparatus for automatically determining objects that attenuate penetrating radiation
WO2013175235A1 (en) * 2012-05-25 2013-11-28 Imperial Innovations Limited Device and method for generating stimulated emission of microwave or radio frequency radiation
US9293890B2 (en) 2012-05-25 2016-03-22 Imperial Innovations Limited Device and method for generating stimulated emission of microwave or radio frequency radiation
US20150214687A1 (en) * 2012-08-17 2015-07-30 The Secretary Of State For Business Innovation & Skills Of Her Majesty's Britannic Government Maser assembly
US9608396B2 (en) * 2012-08-17 2017-03-28 The Secretary Of State For Business, Innovation And Skills Of Her Magesty's Britannic Government Maser assembly

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Publication number Publication date
DE1095326B (de) 1960-12-22
NL6605677A (da) 1968-04-25
GB880478A (en) 1961-10-25
DK106678C (da) 1967-03-06
CH359757A (de) 1962-01-31
CH378378A (de) 1964-06-15
DK114073B (da) 1969-05-27
NL221512A (da)

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