Light induced conch-shaped relief in an azo-polymer film

Abstract

We have discovered that a novel chiral structured surface relief (termed 'conch'-shaped surface relief) with a height of over 1 mm can be formed in an azo-polymer film merely by employing circularly polarized optical vortex irradiation with a total angular momentum of j 5 62. The temporal evolution of the conch-shaped surface relief in the azo-polymer film was also observed. The results provide physical insight into how the angular momentum of light is transferred to a material through mass transport by cis-trans photo-isomerization. Such conch-shaped surface reliefs with chirality, in which functional chemical composites can be doped, enable new applications, such as planar chiral metamaterials, plasmonic holograms, and identification of chiral chemical composites.S urface relief holograms 1-3 on azo-polymer films have been widely investigated through mass transport owing to a driving force based on an optical gradient force, anisotropic photo-fluidity, and cis-trans photoisomerization 4-6 . They allow for unique optical devices, such as active waveguides 7 and photonic circuits, by the doping of functional chemical composites, such as laser dyes and metal (or semiconductor, magnetic) nanoparticles into the films.In general, the mass transport driving force acts to direct the azo-polymer from a bright fringe toward a dark fringe along the polarization direction of the light. Thus, a spiral surface relief formation in the azo-polymer film is mostly inhibited by the irradiation of linearly polarized light.An optical vortex, i.e. light with a helical wavefront due to an azimuthal phase singularity, exp(imw) (where m is an integer known as the topological charge), has been widely studied in a variety of fields, such as optical trapping and guiding [8][9][10] , optical telecommunications 11 , and a super resolution microscope 12,13 , because of its unique characteristics, such as its annular intensity profile and orbital angular momentum, mh 14-17 .Recently, Ambrosio et.al. demonstrated spiral surface relief (termed ''spiral relief'' in their work) formation produced through linearly polarized higher-order optical vortex irradiation 18 . Tightly focused higher-order optical vortices can create a spiral surface relief with a shallow depth (10 , 20 nm) through slight mass-transport along an azimuthal direction owing to interference between longitudinal and transverse optical fields. However, there are still no reports on a single-arm chiral surface relief with depth and height on the micro-scale formed in azo polymer films, so far.Circularly polarized light with a helical electric field exhibits spin angular momentum, sh. Thus, the circularly polarized optical vortex has a total angular momentum (the sum vector of the orbital and spin angular momenta), jh, associated with its helicities of both the wavefront and the polarization [19][20][21] . These angular momenta of light are evidenced by the orbital and spinning motions of trapped particles in optical tweezers.Recently, together with another co-worker, we first dem...

Direct laser printing of chiral plasmonic nanojets by vortex beams

“…More importantly, vortex laser pulses, carrying simultaneously orbital (OAM) and spin (SAM) angular momenta, were demonstrated to twist transiently molten metal producing chiral-shaped micron-size needles [10,11]. Later, similar effects were used to produce chiral structures on the surface polymers [12][13][14] and semiconductors [15,16]. Based on their experiments with ablation of bulk tantalum targets [17], the authors revealed that mass transfer and handedness of the produced surface structures are associated with corresponding phase helicity (or OAM), while the polarization helicity (or SAM) accelerates/decelerates the movement of the molten material.…”

“…Recently, in a number of papers an alternative pioneering approach, employing optical radiation with specially designed intensity-, polarization-or phase states, was proposed for fabrication of chiral structures [9][10][11][12][13][14][15][16][17][18][19]. In particular, using inherent chirality of nanoparticles, synthesis of twisted nanoribbons through self-assembly in water solution under irradiation with continuous-wave circularly polarized laser radiation was demonstrated * alex.iacp.dvo@mail.ru [9].…”

Highly intense monocycle terahertz vortex generation by utilizing a Tsurupica spiral phase plate

“…They have potential applications in a variety of research areas, such as optical trapping and manipulation1314, terabit high-speed optical communications1516, and chiral or achiral nanostructure fabrication1718192021. Laguerre-Gaussian (LG) modes, which are eigen modes of the para-axial electromagnetic equation in cylindrical coordinates, are well known as conventional optical vortices.…”

Coherent dynamics of exciton orbital angular momentum transferred by optical vortex pulses

“…Since Allen et al [1] demonstrated that a Laguerre-Gaussian (LG) beam with the azimuthal phase structure exp (i φ) carries an OAM of per photon, research on optical vortices has spread to various fields, including solid-state-device applications such as spintronics [2], information storage [3][4][5], processing [6][7][8], and quantum computation [9]. In such devices, information multiplexing using the OAM degree of freedom may significantly increase information capacity.…”