Electromagnetically induced grating

Electromagnetically Induced Grating (EIG) is a physics phenomenon based on light interference (or, more generally, on electromagnetic fields) where an interference pattern is used to build a dynamic spatial diffraction grating in matter.

Introduction

Electromagnetically induced gratings (EIG) is a process of optics and atomic physics concerned with the creation and laser-detection of induced gratings and patterns in material structures. EIGs are dynamically created by light interference on optically resonant materials and rely on population inversion and/or optical coherence properties of the material. They were first demonstrated with population gratings on atomic atoms [Mitsunaga et al., Phys. Rev. A 59, 4773 (1999)] . EIGs can be used for purposes of atomic/molecular velocimetry [ http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6TVF-3WV9PT7-B&_user=10&_rdoc=1&_fmt=&_orig=search&_sort=d&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=2a7c3bf5a89ee50260d196a4e2f6c543] , to probe the material optical properties such as coherence and population life-times [Phys. Rev. A 65, 033803 B (2002).] , and switching and routing of light [Brown AW, Xiao, M, Opt. Lett. 30, 699 2005 ; Su XM, Ham BS, Dynamic control of the photonic band gap using quantum coherencePhys. Rev. A 71, 013821 (2005) ] . Related but different effects are thermally induced gratings and photolithography gratings.

Phase matching conditions for the EIG

The phase-matching conditions for the EIG for the plane-wave approximation is given by the simple geometric relation:

,

where the angles are given according to Fig. 2, $omega\_1$ and $omega\_2$ are the frequencies of the writing (W, W') and reading beam (R), respectively, and n is the effective index of refraction of the medium.

Types of EIG

Matter Gratings: The writing lasers form a grating by modulating density of matter or by localizing matter (trapping) on the regions of maxima (or minima) of the writing interference fields. A thermal grating is an example. Matter gratings have slow dynamics (milisenconds) compared to population and phase gratings (potentially nanoseconds and faster).

Population Gratings: The writing lasers are resonant with optical transitions in the matter and the grating is formed by optical pumping. (See Fig. 3)

Coherence Gratings: A grating where the writing lasers form a coherent matter pattern. An example is a pattern of electromagnetically induced transparency

Applications

Usually two lasers at an angle are used to build an EIG. The EIG is used to diffract a third laser, to monitor the behavior of the underlying substrate where the EIG was written or to serve as a switch for one of the lasers involved in the process.

ee also

*Atomic coherence
*Electromagnetically Induced Transparency
*Bragg's law

References

Primary work

* Laser-induced thermal grating effects in flames, S Williams,La Rahn, Ph Paul, JW Forsman, RN Zare Opt. Lett. 19:2121, 1681-1683, 1994
* [http://prola.aps.org/abstract/PRA/v65/i3/e033803 Electromagnetically induced gratings in a degenerate open two-level system, G.C.Cardoso, J.W.R. Tabosa, Phys. Rev. A 65, 033803 (2002)]

References