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Chapter I Brief Introduction...
Optical Rectification
The optical rectification is defined as the ability to induce a dc voltage
between the electrodes placed on the surface of the crystal when an intense
laser beam is directed into the crystal [15]. Equation (1.7) shows the term
responsible for optical retification.
1.3 Some Important Parameters of NLO Process
follows:
Some of the important parameters of NLO process are summarized as
Phase-matching
Many of the practical problems associated with optical frequency
mixing come from the distributed nature of the mixing process. Particularly,
the difference in the phase velocities of the interacting waves of different
frequencies in the Nonlinear medium produces a phase difference that
accumulates along the length of the device and significantly limits the
efficiency of the mixing process. In order to obtain high conversion efficiency,
the phase vectors of input beams and generated beams have to be matched
ΔK=k3-k2-k1=2π(n3/λ3−n2/λ2−n1/λ1)=0. Where, ΔK is phase mismatching, ki is
phase vector at λi and ni is refractive index at λi. In low power case, the
relationship between conversion efficiency and phase mismatching is:
η PL(deff Sin(ΔKL)/ΔKL) 2
12
(1.8)
Where, deff is the effective Nonlinear coefficient , L is the crystal length , P is
the input power density and Δ K is the phase mismatching.
It is clear that the conversion efficiency will drop dramatically if ΔK increases
and the same has been given in the figure (1.9).