Kemal Tekce's research while affiliated with University of Münster and other places

... Complex inhomogeneous fields can be characterized via their singularities and topological structures. Polarization singularities (e.g., the C points or C lines where polarization is circular) have been analyzed in detail for optical fields [7][8][9][10][11][12][13][14], and it was found that the orientation of the 3D polarization ellipse in a vicinity of a generic (nondegenerate) C point has a nontrivial Möbius-strip topology [13][14][15][16][17][18][19][20]. Recently, some of us argued that the same topological structures can appear naturally in inhomogeneous sound waves [21] and the present work is in a line of emerging studies of the vector properties of sound waves. ...

... However, measuring those propagating fields has been very challenging. In the last few decades, metrology tools that are considered 'paraxial' (like classical interference) have been disregarded [2,3,1] due to the nano-scale structure and 3D polarization of tightly focused vector beams. ...

... Obviously, the output had a lower brightness but more uniform field intensity distribution, which resulted from the diffraction effect of the SLM. In the previous works, the fast varied on-demand structured light fields could be produced by regulating pump beam profiles traditionally [69][70][71][72]. The utilization of the digital device (SLM, DMD) makes the quick adjusting of the pump intensity profiles possible. ...

... 2(a) and 2(b). Similar intensity distributions are generated if we focus the vectorial flower structure without a phase vortex [31,34,70]. In this case, as outlined in [34], the number of focal intensity lobes is related to the singularity index σ 12 or, more precisely, the number of ζ-lines of the input field given by |σ 12 − 2|: Purely radially oriented states as found on ζ-lines create maxima in longitudinal components, thus, |E z | 2 includes |σ 12 − 2| maxima. ...

... In 3D vector fields, the topological structures exhibit intriguing shapes, for instance the topological knots [33][34][35][36][37] evolved from the curves of singularities in 2D fields, and the polarization Möbius strips [5,6,28,38,39] corresponding to the star-, lemon-, monstar-structures around C-points in 2D vector fields. While, in 2D vector fields, there also exist other interesting topological structures: the topological flowers and spider webs [40][41][42][43][44]. They are formed in the higher-order singular beams consisting of only linear polarization with spatially varying orientation [45,46]. ...

... Frequency conversion processes, mainly second harmonic generation (SHG), have been demonstrated in various femtosecond laser-inscribed waveguide frequency converters. Meeting the phase-matching condition is a precondition to achieve efficient SHG, by either birefringence phase matching (BPM) [89] or quasi phase matching (QPM) [90][91][92][93][94][95]. ...