Multidimensional structures of intrinsically controlled complex laser pulses (Conference Presentation)

Laser pulses in either laboratory or industry are typically complex objects. Unlike the classical electro-magnetic wave with uniform polarization distribution along the flat wave-front or a general vector beam under the paraxial approximation, the real light pulses, such as the pulses from the high power multimode fiber laser and the dechirped femtosecond pulses with structured wave-front, spectrum and polarization distributions, usually have non-vanishing component in the propagation direction. Therefore, the description of a general vectorial laser pulse should be implemented in multi-dimensional way, for the light is the combination of a three-dimensional(3D) vector field (electric field E) and a 3D pseudovector field (magnetic field B) in the 3D Euclidean space (R3). Here we report on a novel technique for the multi-dimensional characterization which includes the spatiotemporal amplitude and phase information as well as the vectorial features in 3D Euclidean space of the complex laser pulses, such as the intrinsically controlled femtosecond pulses with higher-order Poincare sphere beams and vectoral spherical beams. A two-steps-based polarization-sensitive Mach–Zehnder interferometer temporal scan technique was used, at the first time, to capture the complete information of the pulses. The corresponding measurement device, placed on the collimated and attenuated beam at the laser output is consists of a special Mach–Zehnder interferometer, a polarizing beam-splitter and charge-coupled device (CCD) cameras. The reference beam with vertical and horizontal polarization is exported from the cavity and attenuated to a suitable intensity by using a neutral-density filter. After 3D phase unwrapping, removal of the reference curvature, correction of achromatic wave-front distortions, spectral phase and amplitude reconstructions, as well as the measurement for the intrinsic phase of the reference pulse, the complete information of the pulse, include the phase information of the three electronic components, will be obtained. This new measurement capability opens the way to in-depth characterizations and optimizations of the complex laser pulses and ultimately to the study of new phenomena of multimode fiber laser generated laser pulse as well as the interactions between materials and structured ultra-short laser beams.