Quasi-Bessel beams with longitudinally varying polarization state generated by employing spectrum engineering.

We report on the generation and control of quasi-Bessel beams having not only a uniform axial intensity but also a longitudinally varying polarization state. Based on the optimization routine of the spatial spectrum of the so-called Durnin ring, we generate quasi-Bessel beams possessing longitudinally variant axial intensity with linear or sinusoidal envelopes. By utilizing a Sagnac interferometer, we create and coaxially composite two orthogonally polarized beams with complementary axial intensities to form quasi-Bessel beams with uniform axial intensity but a longitudinally varying polarization state. Furthermore, we demonstrate the possibility and flexibility of manipulating the trajectory, speed, and period of polarization state transformation upon propagation. Our results may enable Bessel beams to be used in other applications including optical communications, material processing, and polarimetry.