|
The Pockels effect (after Friedrich Carl Alwin Pockels who studied the effect in 1893), or Pockels electro-optic effect, produces birefringence in an optical medium induced by a constant or varying electric field. In the Pockels effect, also known as the linear electro-optic effect, the birefringence is proportional to the electric field. In the Kerr effect, the refractive index change (birefringence) is proportional to square of the field. The Pockels effect occurs only in crystals that lack inversion symmetry, such as lithium niobate or gallium arsenide and in other noncentrosymmetric media such as electric-field poled polymers or glasses. ==Pockels cells== Pockels cells are voltage-controlled wave plates. The Pockels effect is the basis of the operation of Pockels cells. Pockels cells may be used to rotate the polarization of a beam that passes through. See applications below for uses. A transverse Pockels cell consists of two crystals in opposite orientation, which together give a zero-order wave plate when the voltage is turned off. This is often not perfect and drifts with temperature. But the mechanical alignment of the crystal axis is not so critical and is often done by hand without screws; while misalignment leads to some energy in the wrong ray (either ''e'' or ''o''for example, horizontal or vertical), in contrast to the longitudinal case, the loss is not amplified through the length of the crystal. The electric field can be applied to the crystal medium either longitudinally or transversely to the light beam. Longitudinal Pockels cells need transparent or ring electrodes. Transverse voltage requirements can be reduced by lengthening the crystal. Alignment of the crystal axis with the ray axis is critical. Misalignment leads to birefringence and to a large phase shift across the long crystal. This leads to polarization rotation if the alignment is not exactly parallel or perpendicular to the polarization. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Pockels effect」の詳細全文を読む スポンサード リンク
|