Electromagnetically induced grating

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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.

Figure 1: Possible beam configuration to write and read an EIG. The period of the grating is controlled bu the angle θ. The writing and reading frequencies are not necessarily the same. E_B is referred as the "backward" reading beam and ER is the signal obtained by diffraction on the grating.
Figure 1: Possible beam configuration to write and read an EIG. The period of the grating is controlled bu the angle θ. The writing and reading frequencies are not necessarily the same. E_B is referred as the "backward" reading beam and ER is the signal obtained by diffraction on the grating.

Contents

[edit] 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 [1] . EIGs can be used for purposes of atomic/molecular velocimetry [2], to probe the material optical properties such as coherence and population life-times[3], and switching and routing of light [4]. Related but different effects are thermally induced gratings and photolithography gratings.

[edit] Phase matching conditions for the EIG

Figure 2: Phase matching condition for EIG diffraction.
Figure 2: Phase matching condition for EIG diffraction.

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

sinβ = n(ω1 / ω2)sin(θ / 2),

where the angles are given according to Fig. 2, ω1 and ω2 are the frequencies of the writing (W, W') and reading beam (R), respectively, and n is the effective index of refraction of the medium.

[edit] Types of EIG

Figure 3: Difference between a "matter grating" a "population grating". The smileys :-( and :-) represent ground and optically excited atoms, respectively.
Figure 3: Difference between a "matter grating" a "population grating". The smileys :-( and :-) represent ground and optically excited atoms, respectively.

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

[edit] 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.

[edit] See also

[edit] References

[edit] Primary work

[edit] References

  1. ^ Mitsunaga et al., Phys. Rev. A 59, 4773 (1999)
  2. ^ 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
  3. ^ Phys. Rev. A 65, 033803 B (2002).
  4. ^ Brown AW, Xiao, M, Opt. Lett. 30, 699 2005 ; Su XM, Ham BS, Dynamic control of the photonic band gap using quantum coherence Phys. Rev. A 71, 013821 (2005)