Frequency-conversion of vector vortex beams with space-variant polarization in single-pass geometry

Abstract

Nonlinear frequency conversion processes depend on the polarization state of the interacting beams. On the other hand, vector vortex beams have space-variant polarization in the transverse beam plane. In light of these two points, is it possible to do nonlinear frequency conversion of the vector vortex beam in single-pass geometry and retain the characteristics of the beam? To address this question, here, we report an experimental scheme for single-pass second harmonic generation (SHG) of vector vortex beams. Using an ultrafast Ti:Sapphire laser of pulse width ∼17 fs and a set of spiral phase plates in a polarization based Mach–Zehnder interferometer (MZI), we have generated vector vortex beams of order as high as lp = 12 at an average power of 860 mW. Using two contiguous bismuth borate crystals with the optic axis orthogonal to each other, we have frequency-doubled the near-IR vector vortex beam into visible vector vortex beam with order as high as lsh = 24. The maximum output power of the vector vortex beam of order, lsh = 2, is measured be as high as 20.5 mW at a single-pass SHG efficiency of 2.4%. Controlling the delay in MZI, we have preserved the vector vortex nature of both the pump and frequency-doubled beams. Measurement on the mode purity confirms the generation of high quality vector vortex beams at pump and SHG wavelengths. This generic scheme can be used to generate vector vortex beams across the electromagnetic spectrum in all time scales, continuous-wave to ultrafast.

All-optical input-agnostic polarization transformer via experimental Kraus-map control

“…Many quantum information technologies also utilize the polarization degree-of-freedom of light [11][12][13][14] . In addition, ultrafast vector beams 15 with tailored spatial and temporal polarization shaping 16 have the potential to be used in studies of chiral molecules and magnetic materials 17 . In all of these varied applications of polarization, the ability to transform one state of polarization (SOP, or simply "state") to another is a key enabling technology.…”

Nonlinear optics with structured light

“…Since nonlinear wave mixing depends on both the spatial mode and polarization DoFs, it might seem that a inhomogenous polarization structure would be bound to change when frequency converted. In fact, frequency conversion of vector structured beams has been characterized as producing non-trivial scalar patterns in type-II SHG 80,81 and having an altered vector structure when generated in SHG with sandwiched crystals 82 and using a Sagnac loop 83 . In this sense, the inhomogeneous state of polarization has been proposed as a control parameter for nonlinear process 50,84 .…”

Vectorial light-matter interaction -- exploring spatially structured complex light fields

“…The challenge here is to maintain the inhomogeneous polarization structure of the fundamental mode. This can be achieved in two complementary approaches: either by using two cascading type I crystals, [134][135][136] each addressing one polarization component of the beam at a time, or interferometrically, by separating the polarization components and performing independent SHG. The latter has been demonstrated in a Mach-Zehnder configuration 137 but is more commonly performed in Sagnac interferometers.…”