Generation of ultra-long optical needles with dual-ring cosine filter

Abstract

Combining the advantages of phase and amplitude modulation, we designed a dual-ring cosine filter which was consisted by an inner and outer ring, and the two rings have different number of paired cosine phase. Using the dual-ring cosine filter, ultra-long longitudinally polarized optical needles were obtained by tight focusing radially polarized Bessel-Gaussian beams with single lens system. And the obtained optical needles have depth of focus of 268λ, lateral full width of 0.37λ at half height, beams quality of 94% and axial uniformity of 95%. In addition, we found that the depth of focus of obtained optical needles can be further stretched and the lateral dimension can be further compressed by increasing the number of paired cosine phase. The ultra-long optical needles were appropriately applied in the fields of optical beams lithography, laser direct writing, particle acceleration and optical trapping.

The generation of ultra-long longitudinally polarized optical needle with multi-belt complex phase filter

“…By now, reversing electric dipole array radiation, vector beam wavefront modulation, paraxial spherical mirrors focusing and phase mask modulation were main methods for the generation of optical needles [12][13][14][15][16][17][18][19][20]. In addition, optical needles can be also generated by focusing radially polarized beams using a high-numerical aperture (NA) lens and diffractive optical elements (DOEs) with belts [1,16,[21][22][23][24][25][26][27][28][29]. The optical needles modulated by DOEs have longer depth of focus (DOF), narrower transverse size and higher beam quality due to the special amplitude modulation and phase modulation of DOE in tightly focusing system.…”