Abstract

Second-order nonlinear optical effects are electric-dipole-forbidden in centrosymmetric materials. Second-order processes are therefore attractive tools to study surfaces and interfaces. When higher multipole (magnetic-dipole and electric-quadrupole) contributions are taken into account, second-order processes can occur also in the bulk of centrosymmetric materials. Separation of surface and bulk nonlinearities has been a long standing problem. Quantitative separation has recently been achieved through the polarization dependence of the surface and bulk response,¹ which opens the door for the development of materials with potentially high multipolar bulk response.² The bulk response for second-harmonic generation (SHG) is best accessed in a geometry with two incident fundamental beams, which intersect in the sample. The finite overlap of the two beams and the resulting varying interaction strength along the beam propagation direction precludes reliable calibration of the multipolar nonlinearity using the traditional Maker fringe technique. In this Paper, we present a novel technique that takes advantage of the two-beam geometry and allows absolute calibration of the multipolar response against a known reference material.

© 2007 IEEE