17th IEEE International Conference on Micro Electro Mechanical Systems. Maastricht MEMS 2004 Technical Digest
This paper describes the fabrication of chip-scale alkali atom vapor cells, for use in highly min... more This paper describes the fabrication of chip-scale alkali atom vapor cells, for use in highly miniaturized atomic frequency references, using silicon micromachining and anodic bonding technology. The cells consist of silicon cavities with internal volume ranging from a few mm3 to less than 1 mm3. The cells were filled with cesium and nitrogen buffer gas either by chemical reaction of cesium chloride and barium azide, or by direct injection of elemental miurn within a controlled anaerobic environment. Cesium optical absorption spectra were obtained from the cells, and coherent population trapping resonances with linewidths of about 1 kHz were measured.
2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, 2008
This paper reports on a method for improving the optical efficiency of micromachined reflectors i... more This paper reports on a method for improving the optical efficiency of micromachined reflectors integrated in rubidium vapor cells. A hybrid bulk micromachining and multilayer thin film process is used to form the reflectors on angled sidewalls, which redirect laser light through the vapor cell and back toward the plane of the source with reduced optical power loss. The optical return efficiency of two paired dielectric reflectors is shown to be improved by as much as eight times over silicon reflectors alone. The D 1 absorption line in a one cubic millimeter miniature alkali 87 Rb vapor cell by use of two integrated thin film reflectors is experimentally demonstrated.
A scalar magnetic field sensor based on a millimeter-size 87 Rb vapor cell is described. The magn... more 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.
We demonstrate a miniature microfabricated saturated absorption laser spectrometer. The system co... more We demonstrate a miniature microfabricated saturated absorption laser spectrometer. The system consists of miniature optics, a microfabricated Rb vapor cell, heaters, and a photodetector, all contained within a volume of 0.1 cm 3. Saturated absorption spectra were measured with a diode laser at 795 nm. They are comparable to signals obtained with standard table-top setups, although the rubidium vapor cell has an interior volume of only 1 mm 3. We discuss the performance and prospects for using such systems as a miniature optical wavelength reference, compatible with transportable instruments.
We have studied the noise in the optical rotation of a linearly polarized laser beam transmitted ... more We have studied the noise in the optical rotation of a linearly polarized laser beam transmitted through a spin-polarized 133 Cs vapor as a function of its frequency detuning from the optical resonance. Our measurements demonstrate the direct conversion of the laser-frequency noise into optical rotation noise by the dispersive response of the atomic vapor. We describe this noise-conversion process in terms of a simple model that can be used to optimize the performance of atomic devices, such as atomic magnetometers, that use optical rotation as their operational signal.
A scalar magnetic field sensor based on a millimeter-size 87 Rb vapor cell is described. The magn... more 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.
A multichannel imaging system is presented, consisting of 25 microfabricated optically-pumped mag... more A multichannel imaging system is presented, consisting of 25 microfabricated optically-pumped magnetometers. The sensor probes have a footprint of less than 1 cm<sup>2</sup> and a sensitive volume of 1.5 mm × 1.5 mm × 1.5 mm and connect to a control unit through optical fibers of length 5 m. Operating at very low ambient magnetic fields, the sensor array has an average magnetic sensitivity of 24 fT/Hz<sup>1/2</sup>, with a standard deviation of 5 fT/Hz<sup>1/2</sup> when the noise of each sensor is averaged between 10 and 50 Hz. Operating in Earth's magnetic field, the magnetometers have a field sensitivity around 5 pT/Hz<sup>1/2</sup>. The vacuum-packaged sensor heads are optically heated and consume on average 76 ± 7 mW of power each. The heating power is provided by an array of eight diode lasers. Magnetic field imaging of small probe coils was obtained with the sensor array and fits to the expected field pattern agree well with...
IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003
We report on the fabrication of millimetersized vapor cells and their performance in atomic clock... more We report on the fabrication of millimetersized vapor cells and their performance in atomic clocks based on coherent population trapping (CPT). We discuss two fabrication techniques. The first one is based on hollow-core pyrex fibers, fused with a CO 2 laser or micro-torch, and the second one involves anodic bonding of micro-machined silicon wafers to pyrex. Key aspects of the discussion are the performance of the cell in frequency references, the potential for further miniaturization of the cells and the ability to manufacture them on a large scale with reproducible performance.
Following the rapid progress in the development of optically pumped magnetometer (OPM) technology... more Following the rapid progress in the development of optically pumped magnetometer (OPM) technology for the measurement of magnetic fields in the femtotesla range, a successful assembly of individual sensors into an array of nearly identical sensors is within reach. Here, 25 microfabricated OPMs with footprints of 1 cm(3) were assembled into a conformal array. The individual sensors were inserted into three flexible belt-shaped holders and connected to their respective light sources and electronics, which reside outside a magnetically shielded room, through long optical and electrical cables. With this setup the fetal magnetocardiogram of a pregnant woman was measured by placing two sensor belts over her abdomen and one belt over her chest.The fetal magnetocardiogram recorded over the abdomen is usually dominated by contributions from the maternal magnetocardiogram, since the maternal heart generates a much stronger signal than the fetal heart. Therefore, signal processing methods hav...
We report on the measurement of somatosensory-evoked and spontaneous magnetoencephalography (MEG)... more We report on the measurement of somatosensory-evoked and spontaneous magnetoencephalography (MEG) signals with a chip-scale atomic magnetometer (CSAM) based on optical spectroscopy of alkali atoms. The uncooled, fiber-coupled CSAM has a sensitive volume of 0.77 mm(3) inside a sensor head of volume 1 cm(3) and enabled convenient handling, similar to an electroencephalography (EEG) electrode. When positioned over O1 of a healthy human subject, α-oscillations were observed in the component of the magnetic field perpendicular to the scalp surface. Furthermore, by stimulation at the right wrist of the subject, somatosensory-evoked fields were measured with the sensors placed over C3. Higher noise levels of the CSAM were partly compensated by higher signal amplitudes due to the shorter distance between CSAM and scalp.
2006 IEEE International Frequency Control Symposium and Exposition, 2006
We describe the first local oscillator (LO) that demonstrates viability in terms of performance, ... more We describe the first local oscillator (LO) that demonstrates viability in terms of performance, size, and power, for chip-scale atomic clocks (CSAC) and has been integrated with the physics package at the National Institute of Standards and Technology (NIST) in Boulder, CO. This voltage-controlled oscillator (VCO) achieves the lowest combined size, DC power consumption, phase noise, and thermal frequency drift among those previously reported, while achieving a tuning range large enough to compensate for part tolerances but small enough to permit precision locking to an atomic resonance. We discuss the design of the LO and the integration with the NIST physics package. I.
2010 IEEE International Frequency Control Symposium, 2010
Atomic magnetometers based on absorption or polarization rotation of light in an alkali vapor hav... more Atomic magnetometers based on absorption or polarization rotation of light in an alkali vapor have recently demonstrated sensitivities rivaling those of superconducting quantum interference devices (SQUIDs) [1]. Miniaturization of such devices containing vapor cells fabricated with microelectro-mechanical (MEMS) technology has been the focus of development for the better part of the last decade. In this paper, we describe a portable magnetometry system with a sensitivity below 50 fT/ √ Hz at 100 Hz. The atomic magnetometer consists of a microfabricated sensor head that is fiber coupled to a control module consisting of a laser and electronics. We describe the construction of this system and present the results of sensitivity measurements with an emphasis on identifying and characterizing the source of 1/f (flicker) noise. This portable magnetometer system was developed to measure magnetocardiograms (MCG) of human subjects inside a shielded environment [2].
Proceedings of the 2002 IEEE International Frequency Control Symposium and PDA Exhibition (Cat. No.02CH37234)
We consider theoretically the expected performance of ultra-small vapor-cell frequency references... more We consider theoretically the expected performance of ultra-small vapor-cell frequency references with cell volumes below 1 mm3. The short-term stability is found to degrade as the size is reduced. The amount of degradation depends on whether a buffer gas or wall coating is used for the atomic confinement. Preliminary experimental results with all-optical excitation indicate that the atomic Q-factor behaves as expected.
We demonstrate an optically pumped 87Rb magnetometer in a microfabricated vapor cell based on a z... more We demonstrate an optically pumped 87Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the 87Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.
Proceedings of the National Academy of Sciences, 2008
We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consi... more We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consisting of a microfluidic channel and a microfabricated vapor cell (the heart of an atomic magnetometer). Detection occurs at zero magnetic field, which allows operation of the magnetometer in the spin-exchange relaxation-free (SERF) regime and increases the proximity of sensor and sample by eliminating the need for a solenoid to create a leading field. We achieve pulsed NMR linewidths of 26 Hz, limited, we believe, by the residence time and flow dispersion in the encoding region. In a fully optimized system, we estimate that for 1 s of integration, 7 × 10 13 protons in a volume of 1 mm 3 , prepolarized in a 10-kG field, can be detected with a signal-to-noise ratio of ≈3. This level of sensitivity is competitive with that demonstrated by microcoils in 100-kG magnetic fields, without requiring superconducting magnets.
A thermal vapor of three-level atoms irradiated by two copropagating laser beams of suitable freq... more A thermal vapor of three-level atoms irradiated by two copropagating laser beams of suitable frequencies exhibits the phenomenon of coherent population trapping, leading to an electromagnetically induced transparency ͑EIT͒. When a mirror reflects the beams back onto themselves one finds that depending on the position along the resulting standing wave the fluorescence intensity from the sample ͑cesium in our case͒ decreases ͑EIT͒ or even increases ͓electromagnetically induced absorption ͑EIA͔͒ with a period on the centimeter scale. An intuitive picture is based on the interference of coherent dark states but the explanation of the EIA effect requires consideration of Doppler effects in the thermal vapor. This allows for a quantitative comparison between experimental and calculated results.
We demonstrate very high-contrast coherent population trapping 1 (CPT) resonances by using four-w... more We demonstrate very high-contrast coherent population trapping 1 (CPT) resonances by using four-wave mixing in 87 Rb atoms. In the experiment, we take advantage of the spectral overlap between F =2→ FЈ and F =3→ FЈ optical resonances on the D1 line of 87 Rb and 85 Rb atoms, respectively, to eliminate the DC-light background from the CPT resonance signal. We observe a CPT resonance with a contrast in the range of 90%, compared with a few percent achieved by alternative methods.
We propose and demonstrate a novel technique for increasing the amplitude of coherent population ... more We propose and demonstrate a novel technique for increasing the amplitude of coherent population trapping (CPT) resonances in open ⌳ systems. The technique requires no complex modifications to the conventional CPT setup and is compatible with standard microfabrication processes. The improvement in the CPT resonance amplitude as a function of intensity of the excitation light agrees well with the theory based on ideal open and closed ⌳ systems.
17th IEEE International Conference on Micro Electro Mechanical Systems. Maastricht MEMS 2004 Technical Digest
This paper describes the fabrication of chip-scale alkali atom vapor cells, for use in highly min... more This paper describes the fabrication of chip-scale alkali atom vapor cells, for use in highly miniaturized atomic frequency references, using silicon micromachining and anodic bonding technology. The cells consist of silicon cavities with internal volume ranging from a few mm3 to less than 1 mm3. The cells were filled with cesium and nitrogen buffer gas either by chemical reaction of cesium chloride and barium azide, or by direct injection of elemental miurn within a controlled anaerobic environment. Cesium optical absorption spectra were obtained from the cells, and coherent population trapping resonances with linewidths of about 1 kHz were measured.
2008 IEEE 21st International Conference on Micro Electro Mechanical Systems, 2008
This paper reports on a method for improving the optical efficiency of micromachined reflectors i... more This paper reports on a method for improving the optical efficiency of micromachined reflectors integrated in rubidium vapor cells. A hybrid bulk micromachining and multilayer thin film process is used to form the reflectors on angled sidewalls, which redirect laser light through the vapor cell and back toward the plane of the source with reduced optical power loss. The optical return efficiency of two paired dielectric reflectors is shown to be improved by as much as eight times over silicon reflectors alone. The D 1 absorption line in a one cubic millimeter miniature alkali 87 Rb vapor cell by use of two integrated thin film reflectors is experimentally demonstrated.
A scalar magnetic field sensor based on a millimeter-size 87 Rb vapor cell is described. The magn... more 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.
We demonstrate a miniature microfabricated saturated absorption laser spectrometer. The system co... more We demonstrate a miniature microfabricated saturated absorption laser spectrometer. The system consists of miniature optics, a microfabricated Rb vapor cell, heaters, and a photodetector, all contained within a volume of 0.1 cm 3. Saturated absorption spectra were measured with a diode laser at 795 nm. They are comparable to signals obtained with standard table-top setups, although the rubidium vapor cell has an interior volume of only 1 mm 3. We discuss the performance and prospects for using such systems as a miniature optical wavelength reference, compatible with transportable instruments.
We have studied the noise in the optical rotation of a linearly polarized laser beam transmitted ... more We have studied the noise in the optical rotation of a linearly polarized laser beam transmitted through a spin-polarized 133 Cs vapor as a function of its frequency detuning from the optical resonance. Our measurements demonstrate the direct conversion of the laser-frequency noise into optical rotation noise by the dispersive response of the atomic vapor. We describe this noise-conversion process in terms of a simple model that can be used to optimize the performance of atomic devices, such as atomic magnetometers, that use optical rotation as their operational signal.
A scalar magnetic field sensor based on a millimeter-size 87 Rb vapor cell is described. The magn... more 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.
A multichannel imaging system is presented, consisting of 25 microfabricated optically-pumped mag... more A multichannel imaging system is presented, consisting of 25 microfabricated optically-pumped magnetometers. The sensor probes have a footprint of less than 1 cm<sup>2</sup> and a sensitive volume of 1.5 mm × 1.5 mm × 1.5 mm and connect to a control unit through optical fibers of length 5 m. Operating at very low ambient magnetic fields, the sensor array has an average magnetic sensitivity of 24 fT/Hz<sup>1/2</sup>, with a standard deviation of 5 fT/Hz<sup>1/2</sup> when the noise of each sensor is averaged between 10 and 50 Hz. Operating in Earth's magnetic field, the magnetometers have a field sensitivity around 5 pT/Hz<sup>1/2</sup>. The vacuum-packaged sensor heads are optically heated and consume on average 76 ± 7 mW of power each. The heating power is provided by an array of eight diode lasers. Magnetic field imaging of small probe coils was obtained with the sensor array and fits to the expected field pattern agree well with...
IEEE International Frequency Control Sympposium and PDA Exhibition Jointly with the 17th European Frequency and Time Forum, 2003. Proceedings of the 2003
We report on the fabrication of millimetersized vapor cells and their performance in atomic clock... more We report on the fabrication of millimetersized vapor cells and their performance in atomic clocks based on coherent population trapping (CPT). We discuss two fabrication techniques. The first one is based on hollow-core pyrex fibers, fused with a CO 2 laser or micro-torch, and the second one involves anodic bonding of micro-machined silicon wafers to pyrex. Key aspects of the discussion are the performance of the cell in frequency references, the potential for further miniaturization of the cells and the ability to manufacture them on a large scale with reproducible performance.
Following the rapid progress in the development of optically pumped magnetometer (OPM) technology... more Following the rapid progress in the development of optically pumped magnetometer (OPM) technology for the measurement of magnetic fields in the femtotesla range, a successful assembly of individual sensors into an array of nearly identical sensors is within reach. Here, 25 microfabricated OPMs with footprints of 1 cm(3) were assembled into a conformal array. The individual sensors were inserted into three flexible belt-shaped holders and connected to their respective light sources and electronics, which reside outside a magnetically shielded room, through long optical and electrical cables. With this setup the fetal magnetocardiogram of a pregnant woman was measured by placing two sensor belts over her abdomen and one belt over her chest.The fetal magnetocardiogram recorded over the abdomen is usually dominated by contributions from the maternal magnetocardiogram, since the maternal heart generates a much stronger signal than the fetal heart. Therefore, signal processing methods hav...
We report on the measurement of somatosensory-evoked and spontaneous magnetoencephalography (MEG)... more We report on the measurement of somatosensory-evoked and spontaneous magnetoencephalography (MEG) signals with a chip-scale atomic magnetometer (CSAM) based on optical spectroscopy of alkali atoms. The uncooled, fiber-coupled CSAM has a sensitive volume of 0.77 mm(3) inside a sensor head of volume 1 cm(3) and enabled convenient handling, similar to an electroencephalography (EEG) electrode. When positioned over O1 of a healthy human subject, α-oscillations were observed in the component of the magnetic field perpendicular to the scalp surface. Furthermore, by stimulation at the right wrist of the subject, somatosensory-evoked fields were measured with the sensors placed over C3. Higher noise levels of the CSAM were partly compensated by higher signal amplitudes due to the shorter distance between CSAM and scalp.
2006 IEEE International Frequency Control Symposium and Exposition, 2006
We describe the first local oscillator (LO) that demonstrates viability in terms of performance, ... more We describe the first local oscillator (LO) that demonstrates viability in terms of performance, size, and power, for chip-scale atomic clocks (CSAC) and has been integrated with the physics package at the National Institute of Standards and Technology (NIST) in Boulder, CO. This voltage-controlled oscillator (VCO) achieves the lowest combined size, DC power consumption, phase noise, and thermal frequency drift among those previously reported, while achieving a tuning range large enough to compensate for part tolerances but small enough to permit precision locking to an atomic resonance. We discuss the design of the LO and the integration with the NIST physics package. I.
2010 IEEE International Frequency Control Symposium, 2010
Atomic magnetometers based on absorption or polarization rotation of light in an alkali vapor hav... more Atomic magnetometers based on absorption or polarization rotation of light in an alkali vapor have recently demonstrated sensitivities rivaling those of superconducting quantum interference devices (SQUIDs) [1]. Miniaturization of such devices containing vapor cells fabricated with microelectro-mechanical (MEMS) technology has been the focus of development for the better part of the last decade. In this paper, we describe a portable magnetometry system with a sensitivity below 50 fT/ √ Hz at 100 Hz. The atomic magnetometer consists of a microfabricated sensor head that is fiber coupled to a control module consisting of a laser and electronics. We describe the construction of this system and present the results of sensitivity measurements with an emphasis on identifying and characterizing the source of 1/f (flicker) noise. This portable magnetometer system was developed to measure magnetocardiograms (MCG) of human subjects inside a shielded environment [2].
Proceedings of the 2002 IEEE International Frequency Control Symposium and PDA Exhibition (Cat. No.02CH37234)
We consider theoretically the expected performance of ultra-small vapor-cell frequency references... more We consider theoretically the expected performance of ultra-small vapor-cell frequency references with cell volumes below 1 mm3. The short-term stability is found to degrade as the size is reduced. The amount of degradation depends on whether a buffer gas or wall coating is used for the atomic confinement. Preliminary experimental results with all-optical excitation indicate that the atomic Q-factor behaves as expected.
We demonstrate an optically pumped 87Rb magnetometer in a microfabricated vapor cell based on a z... more We demonstrate an optically pumped 87Rb magnetometer in a microfabricated vapor cell based on a zero-field dispersive resonance generated by optical modulation of the 87Rb ground state energy levels. The magnetometer is operated in the spin-exchange relaxation-free regime where high magnetic field sensitivities can be achieved. This device can be useful in applications requiring array-based magnetometers where radio frequency magnetic fields can induce cross-talk among adjacent sensors or affect the source of the magnetic field being measured.
Proceedings of the National Academy of Sciences, 2008
We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consi... more We demonstrate remote detection of nuclear magnetic resonance (NMR) with a microchip sensor consisting of a microfluidic channel and a microfabricated vapor cell (the heart of an atomic magnetometer). Detection occurs at zero magnetic field, which allows operation of the magnetometer in the spin-exchange relaxation-free (SERF) regime and increases the proximity of sensor and sample by eliminating the need for a solenoid to create a leading field. We achieve pulsed NMR linewidths of 26 Hz, limited, we believe, by the residence time and flow dispersion in the encoding region. In a fully optimized system, we estimate that for 1 s of integration, 7 × 10 13 protons in a volume of 1 mm 3 , prepolarized in a 10-kG field, can be detected with a signal-to-noise ratio of ≈3. This level of sensitivity is competitive with that demonstrated by microcoils in 100-kG magnetic fields, without requiring superconducting magnets.
A thermal vapor of three-level atoms irradiated by two copropagating laser beams of suitable freq... more A thermal vapor of three-level atoms irradiated by two copropagating laser beams of suitable frequencies exhibits the phenomenon of coherent population trapping, leading to an electromagnetically induced transparency ͑EIT͒. When a mirror reflects the beams back onto themselves one finds that depending on the position along the resulting standing wave the fluorescence intensity from the sample ͑cesium in our case͒ decreases ͑EIT͒ or even increases ͓electromagnetically induced absorption ͑EIA͔͒ with a period on the centimeter scale. An intuitive picture is based on the interference of coherent dark states but the explanation of the EIA effect requires consideration of Doppler effects in the thermal vapor. This allows for a quantitative comparison between experimental and calculated results.
We demonstrate very high-contrast coherent population trapping 1 (CPT) resonances by using four-w... more We demonstrate very high-contrast coherent population trapping 1 (CPT) resonances by using four-wave mixing in 87 Rb atoms. In the experiment, we take advantage of the spectral overlap between F =2→ FЈ and F =3→ FЈ optical resonances on the D1 line of 87 Rb and 85 Rb atoms, respectively, to eliminate the DC-light background from the CPT resonance signal. We observe a CPT resonance with a contrast in the range of 90%, compared with a few percent achieved by alternative methods.
We propose and demonstrate a novel technique for increasing the amplitude of coherent population ... more We propose and demonstrate a novel technique for increasing the amplitude of coherent population trapping (CPT) resonances in open ⌳ systems. The technique requires no complex modifications to the conventional CPT setup and is compatible with standard microfabrication processes. The improvement in the CPT resonance amplitude as a function of intensity of the excitation light agrees well with the theory based on ideal open and closed ⌳ systems.
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