Investigation of the sum of orbital angular momentum generated by conical diffraction

International audienceThe conical diffraction (CD) of a wave propagating along the optical axis of a biaxial crystal is an intriguing phenomenon with nowadays applications including imaging or optical communications. More the emerging light can have a fractional or integer orbital angular momentum (OAM). The measurement of the OAM of a beam is not an easy task, especially for non-integer values. We operated the CD of two 1053 and 1047 nm beams with a KGW crystal, in various input and output polarization states. Then the sum-frequency has been obtained with a KTP phase matched crystal located near the second Raman spike. The integer or fractional OAM of both the fundamental and sum-frequency waves have been visualized with the cylindrical lens method. All the experimental patterns: far field, near field and field in the focal plane of the cylindrical lens, are quite well described by a self-consistent model based on plane waves propagation and their interferences. Sum of OAM due to quadratic nonlinear conversion is evidenced from experimental and calculated patterns