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1.
Figure 1

Figure 1. Vortex beams.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

Schematics of the vortex-beam optical field employed in the present work. Shown are the wavefront helical structures for vortex topological charges q=±1 and q=±3 (in the latter case, the wavefront is composed of three intertwined helical surfaces, here shown in different colours for clarity) and, in the last example, the associated doughnut-shaped transverse intensity distribution.

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.
2.
Figure 4

Figure 4. Two- and three-dimensional AFM maps of a light-induced polymer spiral structure.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

(a) Two-dimensional AFM image of the topographical structure obtained at the sample surface when the polymer is illuminated by a focused q=10 vortex beam. The distances between the two green and the two red cursors, taken along the corresponding lines passing through the structure centre, are 1.2 and 2.7 μm, respectively. These values are consistent with the inner and outer diameters of the laser spot shown in Fig. 2c. (b) Three-dimensional rendering of the same AFM map.

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.
3.
Figure 5

Figure 5. Spiral relief patterns obtained for different illumination doses.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

AFM images of the topographical structures obtained for varying illumination intensity and fixed time of exposure (and polarization direction), for topological charge q=10. The white arrow indicates the polarization direction. Different panels correspond to different values of the laser power injected in the microscope: (a) 15 μW; (b) 18 μW; (c) 21 μW; (d) 29 μW; (e) 41 μW; (f) 54 μW. Similar results are obtained for varying time of exposure at fixed intensity.

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.
4.
Figure 7

Figure 7. Evolution of the light-induced surface relief patterns as a function of the vortex-beam topological charge.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

The topological charge increases when moving from the top to the bottom of the figure. (a) Topographical AFM map of the pattern obtained with a q=1 vortex beam, linearly polarized as indicated by the white arrow. (b) Corresponding simulation based on our model. (c) and (d), same as for panels a and b, respectively, but in the case q=2. (e) and (f), in the case q=5. (g) and (h), in the case q=10. The scale bars of all the AFM maps correspond to 900 nm. The simulated area in panels b, d and f has a diameter of 4 times the wavelength, whereas in panel h, it has a diameter of 7.3 times the wavelength.

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.
5.
Figure 3

Figure 3. Optical apparatus.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

The laser beam (from a Nd:YVO4 continuous-wave frequency-duplicated laser), after a beam expander (lenses L1 and L2), is reflected by mirror M1 onto a computer-controlled SLM, which is programmed for visualizing a pitchfork hologram (kinoform) generating the desired LG-like beam with a prescribed topological charge. Next, the first-order diffracted beam is selected via an iris located in the focal plane of a lens (L3). After recollimation (lens L4), the beam is sent through a half-wave plate (HWp) for rotating the input polarization and finally imaged by external lens L5 and the internal lens system of the microscope (including tube lens LT and the microscope objective OBJ) to the sample plane, positioned at the polymer surface. The dashed lines mark the image planes reproducing the optical field after SLM diffraction. Segments fi denote the focal lengths of the corresponding lenses Li.

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.
6.
Figure 6

Figure 6. Surface relief patterns corresponding to the various terms appearing in our model.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

(a) Contribution to the surface relief pattern resulting from the second-derivative term x2|Ex|2 appearing in our model, based on the simulations of the optical field at the focus, for a tightly focused q=5 vortex beam, linearly polarized along the y-axis. The relief scale is in arbitrary units. The simulated area is a circle of four times the light wavelength in diameter. (bi), Same as in panel a, for the other field-derivative terms appearing in our model and displayed above each panel. (j) Total surface relief pattern obtained by combining all terms as in Equation (2), with the constants' values set to: c1=0; c2=1; c3=0; cB=8 (c2/λ). (km) Same as for panels hj, respectively, when the vortex beam charge is inverted to q=−5 (all other terms remain unchanged).

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.
7.
Figure 2

Figure 2. Light-induced surface relief patterns on the azo-polymer film.. From: Light-induced spiral mass transport in azo-polymer films under vortex-beam illumination.

(a) Absorption spectrum of the azo-polymer used in this work. Inset: polymer structure. (b) Surface relief pattern induced by a focused Gaussian beam (topological charge q=0). The material displacement leads to a two-lobed pattern oriented along the beam polarization direction (y-axis), as already reported in previous works78. (c) Optical micrograph of the intensity pattern of a LG-like vortex beam having topological charge q=10, focused by a 1.3 NA oil-immersion microscope objective on the surface of a coverslip where a metallic mirror is inserted in the place of the sample. (d) Optical micrograph of the polymer surface relief pattern generated by the focused q=10 vortex beam (linearly polarized along the y-direction). The image is taken by means of the same objective used to illuminate the sample. (e) AFM image of the same surface relief pattern as in panel d. (f) Optical micrograph of the intensity pattern when the vortex handedness is inverted (topological charge q=−10; still linearly polarized along the y-direction). (g) Optical micrograph of the polymer surface relief pattern induced after inverting the vortex handedness. (h) AFM image of the same structure as in panel g. (i) Optical micrograph of the intensity pattern obtained for a vortex beam with q=10, when the light polarization direction is rotated by 90° (so as to be parallel to the x-axis). (j) AFM surface relief pattern corresponding to the illumination conditions of panel i: the two arms of the spiral are rotated by 90°, as compared with the pattern shown in panel e. The white arrow in panels e, h and j indicates the polarization direction of the light. The scale bars in panels c–j correspond to 1 μm.

Antonio Ambrosio, et al. Nat Commun. 2012 August 7;3:989.

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