Observatoire Cantonal De Neuchatel

Ebauches S.a.

Oscilloquartz S.a.

Giovanni Busca

Pascal Rochat

Leland Johnson

Laurent-Guy Bernier

Helmuth-Hugo Brandenberger

Hartmut S Schweda

An atomic maser comprises a walled enclosure (76) defining a resonant cavity (4), and a storage bulb (8) for storing a medium capable of stimulated emission. The storage bulb is a sapphire cylinder (70) that is open at both ends and has two closure members (71,72) for closing the open ends. The closure members are made substantially of titanium and have a coating (73,74) of polyfluoroethene formed on their inner surfaces. At least one of the closure members (71,72) forms part of the walled enclosure.

Atomic maser with cylindrical sapphire storage bulb

An atomic maser includes a circuit (25) for effecting a shift in the frequency of a signal injected into a resonant cavity (4) so as to generate alternately a first and a second signal portion having respectively a frequency greater than and less than the natural frequency of stimulated emission, the first and second signal portions having a periodicity corresponding to a predetermined interrogation period. Circuitry (31,32,33,51,52) is responsive to a signal detected in the cavity (4) to produce an error signal representing the difference between the amplitude of the detected signal in response to the injection of the first and second signal portions. Further circuitry (53,54) adjusts the resonant frequency of the cavity in response to the error signal. A pulse generator 26 and a mixer 28 periodically apply both the first and second signal portions for a limited duration only during the interrogation period.

Active hydrogen maser atomic frequency standard

The atomic frequency standard has a heating element (58) surrounding an enclosure (43) which defines a microwave resonance cavity (42). The heating element supplies heat to an absorption cell (41) located in the cavity. The absorption cell (41) is surrounded by electrodes (45a-45d) which act to enhance and orient the oscillating magnetic field in the region of the absorption cell. Thermally conductive members (47a-47d) connect the electrodes (45a-45d) to the enclosure (43) to better control the temperature of the cell while retaining the advantages due to the presence of the electrodes (45a-45d).

Atomic frequency standard

The passive frequency standard of this invention comprises a cell (42) containing Rb87 and a source of predetermined spectral component which, by optical pumping, empties the level F=1, m.sub.F =0 and populates the level F=2, m.sub.F =0. This source comprises a lamp (40) and an isotopic filter constituted by Rb 85 contained in the cell (42). A helicoidal resonator (44) is tuned to the transition frequency between level F=2, m.sub.F =0 and level F=1, m.sub.F =0. It receives an excitation signal for stimulating such transition from an oscillator via a connector (64). The frequency of the oscillator is slaved to the transition frequency by slave means comprising a photoelectric cell (46) which receives the light from the lamp (40) through the cell (42).

Passive frequency standard

The atomic frequency standard comprises a source of light of a given spectral component, comprising a lamp 2 and an isotopic filter 3. The light arriving in an Rb 87 cell 4 empties the hyperfine level F=1 by optical pumping. Microwave excitation produced by a loop 5 causes the atoms which populated the level F=2, m.sub.F =0, to fall back to the level F=1, m.sub.F =0. Filling of the latter level reduces the transparency of the cell 4, which phenomenon is detected by a photoelectric cell 6 and permits tuning of the microwave excitation to the hyperfine transition frequency. The electromagnetic wave produced by the loop 5 is progressive, which, by the Doppler effect, increases the width of the absorption line of the cell. This increase makes it possible to reduce the control time constant and consequently makes it possible to have a compact frequency standard, with a rapid control action, which can operate in an unfavorable environment.

Atomic frequency standard having microwave loop around absorption cell

The invention, which may be used in particular as a frequency standard, seeks to avoid disturbance in the control action in respect of the cavity 10 by a powerful parasite signal due to the line of stimulated emission. Control of the cavity and control of the oscillator 1 on the line of stimulated emission control in a shared-time mode. A control circuit 40 acts on the carrier by way of a programmable synthesizer 43, the carrier than assuming the successive values .omega..sub.+, .omega..sub.H, .omega..sub.-, .omega..sub.H, .omega..sub.+, etc. in stages. .omega..sub.H is centered on the line of stimulated emission; .omega..sub.+ and .omega..sub.- which are symmetrically shifted interrogate the flanks of the emission line. By means of a signal INH, the control circuit 40 periodically suppresses the output of an active filter 42 and thus interrupts the detection action used for controlling the cavity, during the periods in which .omega..sub.Q is equal to .omega..sub.+  or .omega..sub.-. This detection action occurs only when .omega..sub.Q =.omega..sub.H, and after a damping dead time.

Passive masers having alternately operated oscillator and cavity control

The maser of the invention is particularly suitable for forming a frequency standard, by virtue of its excellent degree of frequency stability. The stimulating signal injected into a hydrogen maser cavity 10 is phase modulated at a single modulating frequency from a source 34 by a modulator 2. Nevertheless, the envelope detected signal picked off from the cavity and detected by a detector 13 includes two error signal components which respectively represent the difference between the carrier frequency of the injected signal and the frequency of the stimulated emission and the difference between the resonance frequency of the cavity and the said carrier frequency. These components are distinguished by their phases and phase shifters 42 and 44 and bring them respectively into phase with the modulating signal for detection in detectors 23 and 33 whose integrated outputs are used to control the oscillator 1 (and hence the said carrier frequency) and the cavity tuning respectively.

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Neuchatel, Switzerland

Giovanni Busca