20 research outputs found
Atomic trajectory characterization in a fountain clock based on the spectrum of a hyperfine transition
We describe a new method to determine the position of the atomic cloud during
its interaction with the microwave field in the cavity of a fountain clock. The
positional information is extracted from the spectrum of the F=3,mF=0 to
F=4,mF=-1 hyperfine transition, which shows a position dependent asymmetry when
the magnetic C-field is tilted by a few degrees with respect to the cavity
axis. Analysis of this spectral asymmetry provides the horizontal
center-of-mass position for the ensemble of atoms contributing to frequency
measurements. With an uncertainty on the order of 0.1 mm, the obtained
information is useful for putting limits on the systematic uncertainty due to
distributed cavity phase gradients. The validity of the new method is
demonstrated through experimental evidence.Comment: 6 figures, submitted to PR
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Prospects for magnetic field communications and location using quantum sensors
Signal attenuation limits the operating range in wireless communications and location. To solve the reduced range problem, we can use low-frequency signals in combination with magnetic sensing. We propose the use of an optically pumped magnetometer as a sensor and realize a proof-of-principle detection of binary phase shift keying (BPSK) modulated signals. We demonstrate a ranging enhancement by exploiting both the magnetometer’s intrinsic sensitivity of below 1 pT/Hz1/2 and its 1 kHz operating bandwidth through the use of BPSK signals.</p
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Field-polarization sensitivity in rf atomic magnetometers
We demonstrate the sensitivity of a sensor based on an optically pumped radio-frequency (rf) atomic magnetometer to the polarization state of the detected rf magnetic field and measure >36 dB difference in amplitude sensitivity for opposite circular-field polarizations. This sensitivity could be used to create sensors that would allow signal detection while suppressing unwanted rf fields using polarization rejection, in contrast to traditional gradiometry configurations. Additionally, such a sensor will be orientation-sensitive, as the phase of the detected signal is shown to depend on the angle between the sensor’s detection axis and the direction to the transmitter.</p
Femtosecond frequency comb measurement of absolute frequencies and hyperfine coupling constants in cesium vapor
We report measurements of absolute transition frequencies and hyperfine
coupling constants for the 8S_{1/2}, 9S_{1/2}, 7D_{3/2}, and 7D_{5/2} states in
^{133}Cs vapor. The stepwise excitation through either the 6P_{1/2} or 6P_{3/2}
intermediate state is performed directly with broadband laser light from a
stabilized femtosecond laser optical-frequency comb. The laser beam is split,
counter-propagated and focused into a room-temperature Cs vapor cell. The
repetition rate of the frequency comb is scanned and we detect the fluorescence
on the 7P_{1/2,3/2} -> 6S_{1/2} branches of the decay of the excited states.
The excitations to the different states are isolated by the introduction of
narrow-bandwidth interference filters in the laser beam paths. Using a
nonlinear least-squares method we find measurements of transition frequencies
and hyperfine coupling constants that are in agreement with other recent
measurements for the 8S state and provide improvement by two orders of
magnitude over previously published results for the 9S and 7D states.Comment: 14 pages, 14 figure
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Pulsed operation of a miniature scalar optically-pumped magnetometer
A scalar magnetic field sensor based on a millimeter-size 87 Rb vapor cell is described. The magnetometer uses nearly copropagating pump and probe laser beams, amplitude modulation of the pump beam, and detection through monitoring the polarization rotation of the detuned probe beam. The circularly polarized pump laser resonantly drives a spin precession in the alkali atoms at the Larmor frequency. A modulation signal on the probe laser polarization is detected with a lock-in amplifier. Since the Larmor precession is driven all-optically, potential cross talk between sensors is minimized. And since the pump light is turned off during most of the precession cycle, large offsets of the resonance, typically present in a single-beam Bell–Bloom scheme, are avoided. At the same time, relatively high sensitivities can be reached even in millimeter-size vapor cells: The magnetometer achieves a sensitivity of 1 pT/Hz 1/2 in a sensitive volume of 16 mm 3 , limited by environmental noise. When a gradiometer configuration is used to cancel the environmental noise, the magnetometer sensitivity reaches 300 fT/Hz 1/2 . We systematically study the dependence of the magnetometer performance on the optical duty cycles of the pump light and find that better performance is achieved with shorter duty cycles, with the highest values measured at 1.25% duty cycle.</p
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Scalar Magnetometry Below 100 fT/Hz1=2 in a Microfabricated Cell
Zero-field optically-pumped magnetometers are a room-temperature alternative to traditionally used superconducting sensors detecting extremely weak magnetic fields. They offer certain advantages such as small size, flexible arrangement, reduced sensitivity in ambient fields offering the possibility for telemetry. Devices based on microfabricated technology are nowadays commercially available. The limited dynamic range and vector nature of the zero-field magnetometers restricts their use to environments heavily shielded against magnetic noise. Total-field (or scalar) magnetometers based on microfabricated cells have demonstrated subpicotesla sensitivities only recently. This work demonstrates a scalar magnetometer based on a single optical axis, 18 (<inline-formula> <tex-math notation="LaTeX">3\times 3\times 2 </tex-math></inline-formula>)mm 3 microfabricated cell, with a noise floor of 70 fT/Hz 1/2 . The magnetometer operates in a large static magnetic field range, and and is based on a simple optical and electronic configuration that allows the development of dense sensor arrays. Different methods of magnetometer interrogation are demonstrated. The features of this magnetic field sensor hold promise for applications of miniature sensors in nonzero field environments such as unshielded magnetoencephalography (MEG) and brain-computer interfaces (BCI).</p
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An Atomic Sensor for Direct Detection of Weak Microwave Signals
This paper demonstrates direct detection of weak signals at microwave frequencies based on parametric frequency conversion. The atomic medium is optically pumped by a resonant light field and prepared in a coherent atomic superposition by a weak microwave field. The coherent atomic superposition causes a parametric modulation of the polarization of a probe light field at the microwave field frequency. An upper limit magnetic field component sensitivity of 1.2(1.0) pT/Hz 1/2 , corresponding to 3.7(3.1)-<inline-formula> <tex-math notation="LaTeX">\mu </tex-math></inline-formula>V/cm/Hz 1/2 electric field component sensitivity, is achieved at ~6.835 GHz with a 33-mm 3 vapor cell.</p