New media for magneto-optics

Introduction

Magneto-optical phenomena are traditionally studied in crystals and atomic vapors, and less often in liquids. Although crystals are more robust and easier to work with, they have some very important disadvantages. The most important ones are broad spectral lines of atoms in crystal lattices arising due to thermal vibrations of the atoms. This practically eliminates possibility of observation of the nonlinear magneto-optical effects in crystals. To the contrary, spectral lines in dilute atomic vapors at room-temperature are not broadened due to atom-atom interactions and the linewidths are determined by an inverse lifetimes of the atomic states. This allows observation of nonlinear magneto-optical effects with very low light intensities.
Recent developments in solid-state and atomic physics, as well as in photonics offer a number of new media with properties attractive for studies of linear and nonlinear magneto-optical phenomena. These media are gas-filled holey fiber, diamonds with color centers, quantum dots, crystal doped with rare-earth atoms, photonic crystals. Some of these media are currently under consideration in context of magneto-optical research in the Center.

Holey fibers filled with atomic vapors

Photonic crystals are 3D-structures with spatial modulation of a refractive index in at least one of the directions. Modulation of the refractive index in a given direction changes conditions for light propagation in that direction which may lead to formation of photonic bandgaps, i.e., finite ranges of frequencies that can be transmitted trough the crystal. A specific example of the photonic crystal is a photonic-crystal fiber in which the index is modulated perpendicular to the fiber's axis. The refractive-index modulation may be achieved by introduction of air channels along the fiber axis. Such air channels enable: 1) transmission of light of the frequency that is strongly absorbed in the fiber material via fiberís air holes, 2) filling the fiber with gases or liquids. The possibility of filling the fibers with gases is particularly interesting for nonlinear and quantum optics. It allows one to study interaction between light and atomic vapors under special physical conditions; atoms filling the fibers are well localized while the intensity of the light within the air holes is very high. The ability of fabrication vapor cells based on photonic-crystal fibers will have a big impact on the development of opto-electronics enabling miniaturization of many components such as frequency references, optical delay lines, optical clocks, etc. Recently, a number of interesting nonlinear atomic phenomena were demonstrated with photonic-crystal fibers, for example, saturation spectroscopy, stimulated Raman scattering, electromagnetically induced transparency, and slow light. The research conducted in the Center is focused on application of the photonics-crystal fibers for magneto-optical studies. The long term aim is to construct sensitive all-optical magnetic-field sensor based on hollow fibers.

Diamonds with color centers

Another interesting medium for nonlinear and quantum optical studies are diamonds with nitrogen-vacancy (NV) centers. In such a system, nitrogen occupying the vacancy in the crystal lattice acts as a color center absorbing visible and emitting ultra-violet light. Absorption or emission of the radiation is associated with a nitrogen electron transition between two magnetic states. A superposition between different electronic states can be effectively generated by means of optical and radio-frequency spectroscopy. Since the individual centers are relatively well insulated from spins of carbon atoms, the superposition can be preserved for long time (up to μs) even at room-temperature. The long relaxation times make the diamonds extremely interesting for nonlinear and quantum optics, and quantum information. Recently, a number of interesting optical applications of diamonds with color centers were demonstrated. The medium is intensively explored for quantum-information processing and quantum cryptography. Another interesting application is magnetometry. The possibility of magnetic-field measurements with a sensitivity of a few fT/√Hz with spatial resolution ranging from micro- to millimeters was demonstrated. Due to this fact diamonds are particularly interesting for the works conducted in the Center for Magneto-Optical Research.

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Last updated: 05.04.2011