5 results
14 - Detection of nuclear magnetic resonance with atomic magnetometers
- from Part II - Applications
-
- By M. P. Ledbetter, University of California, I. Savukov, Los Alamos National Laboratory, S. J. Seltzer, University of California, D. Budker, University of California
- Edited by Dmitry Budker, University of California, Berkeley, Derek F. Jackson Kimball, California State University, East Bay
-
- Book:
- Optical Magnetometry
- Published online:
- 05 May 2013
- Print publication:
- 07 March 2013, pp 265-284
-
- Chapter
- Export citation
-
Summary
Introduction
Nuclear magnetic resonance (NMR) is a powerful analytical tool for elucidation of molecular form and function, finding application in disciplines including medicine (magnetic resonance imaging), materials science, chemistry, biology, and tests of fundamental symmetries [1–6]. Conventional NMR relies on a Faraday pickup coil to detect nuclear spin precession. The voltage induced in a pickup coil is proportional to the rate of change of the magnetic flux through the coil. Hence, for a given nuclear spin polarization, the signal increases linearly with the Larmor precession frequency of the nuclear spins. Since the thermal nuclear spin polarization is also linear in the field strength, the overall signal is roughly proportional to B2, motivating the development of stronger and stronger magnetic fields. Additionally, an important piece of information in NMR is the so-called chemical shift, which effectively modifies the gyromagnetic ratios of the nuclear spins depending on their chemical environment. This produces different precession frequencies for identical nuclei on different sites of a molecule, and the separation in precession frequencies is linear in the magnetic field. For these reasons, tremendous expense has been spent on the development of stronger magnets. Typical spectrometers feature 9.4 T superconducting magnets, corresponding to 400 MHz proton precession frequencies, and state-of-the-art NMR facilities may feature 24 T magnets, corresponding to 1 GHz proton precession frequency. While the performance of such machines is impressive, there are a number of drawbacks: superconducting magnets are immobile and expensive (roughly §500 000 for a 9.4 T magnet and console) and require a constant supply of liquid helium.
13 - Remote detection magnetometry
- from Part II - Applications
-
- By S. M. Rochester, University of California, J. M. Higbie, Bucknell University, B. Patton, University of California, D. Budker, University of California, R. Holzlöhner, Bucknell University, D. Bonaccini Calia, Laser Systems Department
- Edited by Dmitry Budker, University of California, Berkeley, Derek F. Jackson Kimball, California State University, East Bay
-
- Book:
- Optical Magnetometry
- Published online:
- 05 May 2013
- Print publication:
- 07 March 2013, pp 251-264
-
- Chapter
- Export citation
-
Summary
Introduction
Shortly after the inception of atomic magnetometry, alkali-vapor magnetometers were being used to measure the Earth's magnetic field to unprecedented precision. During the same era, Bell and Bloom first demonstrated all-optical atomic magnetometry through synchronous optical pumping [1] (see Chapters 1 and 6). In this approach, optical-pumping light is frequency- or amplitude-modulated at harmonics of the Larmor frequency ωL to generate a precessing spin polarization within an alkali vapor at finite magnetic field [2, 3]. Although this technique received considerable attention from the atomic physics community for its applicability to optical pumping experiments, Earth's-field alkali-vapor atomic magnetometers continued to rely on radiofrequency (RF) field excitation for several decades (see Chapter 4). Upon the advent of diode lasers addressing alkali and metastable helium transitions, synchronously pumped magnetometers experienced a revival beginning in the late 1980s. In recent years, such magnetometers have found applications in nuclear magnetic resonance detection [4] (see also Chapter 14), quantum control experiments [5], and chip-scale devices intended for spacecraft use [6] (see also Chapters 7 and 15).
All-optical magnetometers possess several advantages over devices that employ RF coils. RF-driven magnetometers can suffer from cross-talk if two sensors are placed in close proximity, since the AC magnetic field driving resonance in one vapor cell can adversely affect the other. All-optical magnetometers are free from such interference. When operated in self-oscillating mode [7], RF-driven magnetometers require an added ±90° electronic phase shift in the feedback loop to counter the intrinsic phase shift between the RF field and the probe-beam modulation.
1 - General principles and characteristics of optical magnetometers
- from Part I - Principles and techniques
-
- By D. F. Jackson Kimball, California State University, E. B. Alexandrov, Ioffe Physical Technical Institute, D. Budker, University of California
- Edited by Dmitry Budker, University of California, Berkeley, Derek F. Jackson Kimball, California State University, East Bay
-
- Book:
- Optical Magnetometry
- Published online:
- 05 May 2013
- Print publication:
- 07 March 2013, pp 3-24
-
- Chapter
- Export citation
8 - Optical magnetometry with nitrogen-vacancy centers in diamond
- from Part I - Principles and techniques
-
- By V. M. Acosta, University of California, D. Budker, University of California, P. R. Hemmer, Texas A &, M University, J. R. Maze, Pontificia Universidad Catolica, R. L. Walsworth, Harvard-Smithsonian Center for Astrophysics
- Edited by Dmitry Budker, University of California, Berkeley, Derek F. Jackson Kimball, California State University, East Bay
-
- Book:
- Optical Magnetometry
- Published online:
- 05 May 2013
- Print publication:
- 07 March 2013, pp 142-166
-
- Chapter
- Export citation
-
Summary
Introduction
While atomic magnetometers can measure magnetic fields with exceptional sensitivity and without cryogenics, spin-altering collisions limit the sensitivity of sub-millimeter-scale sensors [1]. In order to probe magnetic fields with nanometer spatial resolution, magnetic measurements using superconducting quantum interference devices (SQUIDs) [2–4] as well as magnetic resonance force microscopes (MRFMs) [5–8] have been performed. However, the spatial resolution of the best SQUID sensors is still not better than a few hundred nanometers [9] and both sensors require cryogenic cooling to achieve high sensitivity, which limits the range of possible applications. A related challenge that cannot be met with existing technology is imaging weak magnetic fields over a wide field of view (millimeter scale and beyond) combined with sub-micron resolution and proximity to the signal source under ambient conditions.
Recently, a new technique has emerged for measuring magnetic fields at the nanometer scale, as well as for wide-field-of-view magnetic field imaging, based on optical detection of electron spin resonances of nitrogen-vacancy (NV) centers in diamond [10–12]. This system offers the possibility to detect magnetic fields with an unprecedented combination of spatial resolution and magnetic sensitivity [8, 12–15] in a wide range of temperatures (from 0 K to well above 300 K), opening up new frontiers in biological [10, 16, 17] and condensed-matter [10, 18, 19] research. Over the last few years, researchers have developed techniques for nanoscale magnetic imaging in bulk diamond [11, 12, 20] and in nanodiamonds [21–23] along with scanning probe techniques [10, 24].
6 - Optical magnetometry with modulated light
- from Part I - Principles and techniques
-
- By D. F. Jackson Kimball, California State University, S. Pustelny, Jagiellonian University, V. V. Yashchuk, Lawrence Berkeley National Laboratory, D. Budker, University of California
- Edited by Dmitry Budker, University of California, Berkeley, Derek F. Jackson Kimball, California State University, East Bay
-
- Book:
- Optical Magnetometry
- Published online:
- 05 May 2013
- Print publication:
- 07 March 2013, pp 104-124
-
- Chapter
- Export citation
-
Summary
Introduction
Soon after the development of optical magnetometers based on the radio-optical double resonance method (see Chapter 4), it was realized by Bell and Bloom [1] that an alternative method for optical magnetometry was to modulate the light used for optical pumping at a frequency resonant with the Larmor precession of atomic spins. In a Bell-Bloom optical magnetometer, circularly polarized light resonant with an atomic transition propagates through an atomic vapor along a direction transverse to a magnetic field B. Atomic spins immersed in B precess at the Larmor frequency ΩL, and when the light intensity is modulated at Ωm = ΩL, a resonance in the transmitted light intensity is observed. The essential ideas of the Bell–Bloom optical magnetometer are reviewed in Chapter 1 (Section 1.2), and can be summarized in terms of what Bell and Bloom termed optically driven spin precession: in analogy with a driven harmonic oscillator, in a magnetic field B atomic spins precess at a natural frequency equal to ΩL and the light acts as a driving force oscillating at the modulation frequency Ωm. From another point of view, the Bell-Bloom optical magnetometer can be described in terms of synchronous optical pumping: when Ωm = ΩL, there is a “stroboscopic” resonance in which atoms are optically pumped into a spin state stationary in the frame rotating with ΩL. Depending on the details of the atomic structure, the spin state stationary in the rotating frame can be either a dark state that does not interact with the modulated light or a bright state for which the strength of the light–atom interaction is increased.