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Quantum Electronics and Laser Science Conference

Magnetometer and frequency standard based on coherently prepared thermal alkali atomic vapors

C. Affolderbach, W R G Kemp, Svenja A. Knappe, A. Nagel, Markus Stähler, R. Wynands

Published May 7, 2000• 1 citation
OpenAlex

Abstract

Summary form only given. We have experimentally investigated the potential of narrow coherent population trapping resonances for precision applications like magnetometry or atomic frequency standards. CPT can be observed in /spl Lambda/ systems where two ground states are coupled to a common excited state by two near-resonant light fields. Effective formation of ground state coherences takes place when the frequency difference of the light fields precisely matches the ground state splitting. This process leads to reduced absorption in the medium (electromagnetically induced transparency) and thus reduced fluorescence intensity (dark resonance) at the optical resonance frequency. Extremely narrow dark resonances can be observed when the two light fields have fixed phase and frequency difference and time-of-flight broadening is suppressed by the use of a buffer gas, making this type of system a promising candidate for precision applications. The /spl Lambda/ systems under study here are the D/sub 2/ lines of Cs, /sup 87/Rb and /sup 85/Rb where the ground state hyperfine splittings are 9.2 GHz, 6.8 GHz, and 3.0 GHz, respectively. Thus in a magnetic field the CPT resonance splits into several Zeeman components whose frequency positions are determined by the Breit-Rabi formula.

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Picotesla magnetometer based on coherently prepared thermal alkali atomic vapors

C. Affolderbach, W. Kemp, Svenja A. Knappe +2 more

Summary form only given. We have experimentally investigated the potential of narrow coherent population trapping (CPT) resonances for precision magnetometry. CPT can be observed in /spl Lambda/ systems where two ground states are coupled to a common excited state by two near-resonant light fields. On resonance, effective formation of long-lived ground state coherences which do not couple in the light fields leads to reduced absorption in the medium ("electromagnetically induced transparency") and thus reduced fluorescence intensity ("dark resonance"). Extremely narrow CPT resonances can be observed when the light fields have fixed phase and frequency difference and time-of-flight broadening is suppressed by the use of a buffer gas, making this type of system a promising candidate for precision applications.

Conference on Lasers and Electro-Optics•Aug 29, 2005•0 citations

Dark resonance spectroscopy in strong magnetic fields

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Summary form only given. We have performed a series of experiments on coherent population trapping (CPT) in the presence of strong magnetic flux densities up to 1 mT. CPT can be observed in /spl Lambda/-systems where two ground states are coupled to a common excited state by two near-resonant light fields. Effective formation of ground state coherences takes place when the frequency difference of the light fields precisely matches the ground state splitting. This process leads to reduced absorption in the medium and thus reduced fluorescence intensity ("dark resonance") at the optical resonance frequency.

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We have experimentally investigated the potential of narrow coherent population trapping (CPT) resonances for precision applications like magnetometry or atomic frequency standards, using the D lines in thermal Cs or Rb vapor. The magnetometer operates by monitoring the position of the Zeeman-shifted outermost resonance component. The central Zeeman component is well suited for frequency standard applications because its position is shifted by magnetic fields only in second order. We derive the required pair of laser fields form a special diode laser by direct modulation of the injection current. Magneto metric sensitivity down to a picotesla and 10-12 relative instability for a finger-sized clock have been achieved in this way. Use of a magnetic gradiometer allows to cancel fluctuations of ambient magnetic fields to a large degree, making possible sensitive measurements even outside magnetically shielded rooms.

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Summary form only given, as follows.The 30 kHz linewidth and extremely steep dispersion of a coherent dark resonance in a caesium vapor cell allows measurements of magnetic fields to about 10 nT in 0.1 s integration time, limited by stray fields. The narrow resonance should make possible a compact frequency standard. In a preliminary experiment the authors used a coherent dark resonance in a 2 cm long caesium vapor cell to measure magnetic fields with about 10-5 uncertainty. Two diode lasers (852 nm wavelength) were phase-locked onto each other with a 9.2 GHz frequency offset, corresponding to the frequency ground state separation of the two caesium levels. The difference frequency is derived from a stable tunable rf source. Absorption spectrum of the caesium coherent population trapping resonance for linear laser polarizations is illustrated; it is split into seven components by a magnetic field parallel to the laser polarization direction. The width of the individual lines is only 130 kHz due to power broadening. The steep slope of the resonance could be used to lock the frequency of the 9.2 GHz rf source. This would provide a compact frequency reference.

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Light Shift of Coherent Population Trapping Resonances

A. Nagel, R. Wynands, Dieter Meschede

We have measured the spectral position of the absorption minimum in a coherent population trapping resonance in thermal cesium vapor as a function of light intensity. The dependence of position on intensity is found to be almost linear. We have furthermore studied the dependence of this light shift on neon bufier gas pressure and flnd a strong reduction for higher pressures. So the addition of a bufier gas not only reduces the linewidth of the resonance but also a very important systematic efiect for precision measurements. An atomic three-level system with two low-lying and long-lived levels (a so-called ⁄ system) can exhibit a two-photon resonance when the difierence frequency of two driving flelds matches the splitting of the two lower levels (flg. 1), !2 i !1 = !12 (1). The resonance is called \dark since one-photon absorption and resonance ∞uorescence are strongly reduced because of the trapping of the atomic population in a coherent superposition state of the two lower levels that is no longer coupled to the light flelds (coherent population trapping, CPT) (2). The two-photon resonance can be very narrow (3, 4), with linewidths rivaling those of the microwave-driven magnetic dipole transition between the two lower atomic states. The use of dark resonances for the construction of atomic radio frequency standards (5) or applications for precision measurements, for instance in magnetometry (6), has been suggested, and flrst steps in this direction have been taken (7). It is an essential requirement for such precision applications to understand the in∞uence of experimental conditions on the position and shape of the resonance under investigation. Because of the flnite dephasing rate between the two lower states the position of the absorption minimum at the dark resonance can depend on intensity (8,1), and in experiments a shift of the center of the resonance (light shift, AC Stark shift) is readily observed (9), as was discussed, for instance, for an atomic beam (5) or in connection with a CPT maser (10). In this letter we report measurements of the light shift of the two-photon resonance that couples two hyperflne ground-state levels of the cesium atoms in a thermal vapor both with and without an additional bufier gas.

European Quantum Electronics Conference (EQEC)•Aug 24, 2005•0 citations

VCSELs in nonlinear spectroscopy: making optical magnetometers and atomic clocks practical

R. Wynands, C. Affolderbach, Leo W. Hollberg +3 more

We have experimentally investigated the potential af narrow coherent population trapping (CPT) resonances for precision applications like magnetometry, miniaturised atomic frequency standards and the determination of atomic g-factors using the D lines in thermal Cs or Rb vapour.

IEEE/LEOS Summer Topical Meetings•Nov 13, 2002•0 citations
Summary form only given. We have experimentally investigated the potential of narrow coherent population trapping resonances for precision applications like magnetometry or atomic frequency standards. CPT can be observed in /spl Lambda/ systems where two ground states are coupled to a common excited state by two near-resonant light fields. Effective formation of ground state coherences takes place when the frequency difference of the light fields precisely matches the ground state splitting. This process leads to reduced absorption in the medium (electromagnetically induced transparency) and thus reduced fluorescence intensity (dark resonance) at the optical resonance frequency. Extremely narrow dark resonances can be observed when the two light fields have fixed phase and frequency difference and time-of-flight broadening is suppressed by the use of a buffer gas, making this type of system a promising candidate for precision applications. The /spl Lambda/ systems under study here are the D/sub 2/ lines of Cs, /sup 87/Rb and /sup 85/Rb where the ground state hyperfine splittings are 9.2 GHz, 6.8 GHz, and 3.0 GHz, respectively. Thus in a magnetic field the CPT resonance splits into several Zeeman components whose frequency positions are determined by the Breit-Rabi formula.
Summary form only given. We have experimentally investigated the potential of narrow coherent population trapping (CPT) resonances for precision magnetometry. CPT can be observed in /spl Lambda/ systems where two ground states are coupled to a common excited state by two near-resonant light fields. On resonance, effective formation of long-lived ground state coherences which do not couple in the light fields leads to reduced absorption in the medium ("electromagnetically induced transparency") and thus reduced fluorescence intensity ("dark resonance"). Extremely narrow CPT resonances can be observed when the light fields have fixed phase and frequency difference and time-of-flight broadening is suppressed by the use of a buffer gas, making this type of system a promising candidate for precision applications.
Summary form only given. We have performed a series of experiments on coherent population trapping (CPT) in the presence of strong magnetic flux densities up to 1 mT. CPT can be observed in /spl Lambda/-systems where two ground states are coupled to a common excited state by two near-resonant light fields. Effective formation of ground state coherences takes place when the frequency difference of the light fields precisely matches the ground state splitting. This process leads to reduced absorption in the medium and thus reduced fluorescence intensity ("dark resonance") at the optical resonance frequency.
We have experimentally investigated the potential of narrow coherent population trapping (CPT) resonances for precision applications like magnetometry or atomic frequency standards, using the D lines in thermal Cs or Rb vapor. The magnetometer operates by monitoring the position of the Zeeman-shifted outermost resonance component. The central Zeeman component is well suited for frequency standard applications because its position is shifted by magnetic fields only in second order. We derive the required pair of laser fields form a special diode laser by direct modulation of the injection current. Magneto metric sensitivity down to a picotesla and 10-12 relative instability for a finger-sized clock have been achieved in this way. Use of a magnetic gradiometer allows to cancel fluctuations of ambient magnetic fields to a large degree, making possible sensitive measurements even outside magnetically shielded rooms.
Summary form only given, as follows.The 30 kHz linewidth and extremely steep dispersion of a coherent dark resonance in a caesium vapor cell allows measurements of magnetic fields to about 10 nT in 0.1 s integration time, limited by stray fields. The narrow resonance should make possible a compact frequency standard. In a preliminary experiment the authors used a coherent dark resonance in a 2 cm long caesium vapor cell to measure magnetic fields with about 10-5 uncertainty. Two diode lasers (852 nm wavelength) were phase-locked onto each other with a 9.2 GHz frequency offset, corresponding to the frequency ground state separation of the two caesium levels. The difference frequency is derived from a stable tunable rf source. Absorption spectrum of the caesium coherent population trapping resonance for linear laser polarizations is illustrated; it is split into seven components by a magnetic field parallel to the laser polarization direction. The width of the individual lines is only 130 kHz due to power broadening. The steep slope of the resonance could be used to lock the frequency of the 9.2 GHz rf source. This would provide a compact frequency reference.
We have measured the spectral position of the absorption minimum in a coherent population trapping resonance in thermal cesium vapor as a function of light intensity. The dependence of position on intensity is found to be almost linear. We have furthermore studied the dependence of this light shift on neon bufier gas pressure and flnd a strong reduction for higher pressures. So the addition of a bufier gas not only reduces the linewidth of the resonance but also a very important systematic efiect for precision measurements. An atomic three-level system with two low-lying and long-lived levels (a so-called ⁄ system) can exhibit a two-photon resonance when the difierence frequency of two driving flelds matches the splitting of the two lower levels (flg. 1), !2 i !1 = !12 (1). The resonance is called \dark since one-photon absorption and resonance ∞uorescence are strongly reduced because of the trapping of the atomic population in a coherent superposition state of the two lower levels that is no longer coupled to the light flelds (coherent population trapping, CPT) (2). The two-photon resonance can be very narrow (3, 4), with linewidths rivaling those of the microwave-driven magnetic dipole transition between the two lower atomic states. The use of dark resonances for the construction of atomic radio frequency standards (5) or applications for precision measurements, for instance in magnetometry (6), has been suggested, and flrst steps in this direction have been taken (7). It is an essential requirement for such precision applications to understand the in∞uence of experimental conditions on the position and shape of the resonance under investigation. Because of the flnite dephasing rate between the two lower states the position of the absorption minimum at the dark resonance can depend on intensity (8,1), and in experiments a shift of the center of the resonance (light shift, AC Stark shift) is readily observed (9), as was discussed, for instance, for an atomic beam (5) or in connection with a CPT maser (10). In this letter we report measurements of the light shift of the two-photon resonance that couples two hyperflne ground-state levels of the cesium atoms in a thermal vapor both with and without an additional bufier gas.