Birefringent Phase Matching | previous | next | feedback |
Definition: a technique of phase matching based on the birefringence of a crystal material
Birefringent phase matching is a technique for achieving phase matching of a nonlinear process by exploiting the birefringence of a nonlinear crystal. For example, the process of frequency doubling of a 1064-nm beam in a lithium niobate (LiNbO3) crystal can be phase-matched by using the ordinary polarization for the pump beam and the extraordinary polarization for the second-harmonic beam. When the appropriate crystal temperature is set, the birefringence just cancels the chromatic dispersion. The dispersion alone would normally lead to the higher refractive index for the second-harmonic light, so that phase matching would not be possible.
Figure 1: Birefringent noncritical phase matching of frequency doubling in LBO with a pump wavelength of 1064 nm. The beams propagate in the X direction, the pump wave is polarized in the Z direction, and the second-harmonic wave in the Y direction. At 149°C, the birefringence compensates the effect of chromatic dispersion, so that the refractive indices for both waves are equal.
The common forms of birefringent phase matching are
- noncritical phase matching with beam propagation along an axis of the index ellipsoid (see Figure 1)
- critical phase matching where the angle dependence of the extraordinary refractive index is exploited.
A common alternative to birefringent phase matching is quasi-phase matching (QPM).
See also: quasi-phase matching, phase matching, nonlinear frequency conversion
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