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Modality is a generic concept of wave-optics at the basis of optical information and communications. One of the challenges of photonics technologies based on optical orbital angular momentum consists in the production of a modal content for both the azimuthal and radial degrees of freedom. This basically requires shaping the complex amplitude of an incident light beam, which is usually made up from adaptive spatial light modulators or bespoke devices. Here, we report on the experimental attempt of a recent theoretical proposal [Opt. Lett. 42, 1966 (2017)] toward the production of various optical vortex modes of the Laguerre–Gaussian type relying on the spin–orbit interaction of light. This is done in the visible domain from optical elements made out of silica glass. The idea consists in exploiting the combined effects of azimuthally-varying geometric phase with that of radially-varying propagation features. The proposed approach can be readily extended to any wavelength as well as to other families of optical modes, although some dynamic phase problems remain to be solved to make it a turnkey technology.

Polarization singularities and topological polarization structures are generic features of inhomogeneous vector wave fields of any nature. However, their experimental studies mostly remain restricted to optical waves. Here, we report the observation of polarization singularities, topological Möbius-strip structures, and skyrmionic textures in 3D polarization fields of inhomogeneous sound waves. Our experiments are made in the ultrasonic domain using nonparaxial propagating fields generated by space-variant 2D acoustic sources. We also retrieve distributions of the 3D spin density in these fields. Our results open the avenue to investigations and applications of topological features and nontrivial 3D vector properties of structured sound waves.

We report on ab initio simulation of fluid interface deformations induced either by acoustic or optical radiation pressure. This is done by solving simultaneously the scalar wave propagation equation and the two-phase flow equations using the boundary element method. Using dimensional analysis, we show that interface deformation morphogenesis is universal, i.e. depends on the same dimensionless parameters in acoustics and electromagnetics. We numerically investigate a few selected phenomena -- in particular the shape of large deformations, the slenderness transition and its hysteresis -- and compare with existing and novel experimental observations. Qualitative agreement between the numerical simulations and experiments is found when the mutual interaction between wave propagation and wave-induced deformations is taken into account. Our results demonstrate the leading role of the radiation pressure in morphogenesis of fluid interface deformations and the importance of the propagation-deformation interplay .

International audience; Spin–orbit photonic devices usually rely on 2D (transverse) material structuring and are designed for optimal coupling between the polarization state and the spatial degrees of freedom at a given wavelength. Exploiting the third dimension (longitudinal) provides ways to bypass monochromatic limitations. Within a singular optics framework, here we show that chiral liquid crystals endowed with non-singular 3D helix axis orientational distribution exhibit transmissive broadband spin–orbit optical vortex generation as well as an optical diode effect. These results are in stark contrast to the properties of spin–orbit optical elements fabricated from chiral liquid crystals with a uniform orientation of the helix axis, which are reflective devices that process forward and backward propagating waves equally. Moreover, the similarities between the proposed 3D chiral structure and that of the cuticle of some insects invites considering spin–orbit photonics from a biological perspective.

Geometric phase optical elements made of space-variant anisotropic media customarily find their optimal operating conditions when a half-wave retardance condition is fulfilled, which allows imparting polarization-dependent changes to an incident wavefront. In practice, intrinsic limitations of a man-made manufacturing process or a finite spectrum of a light source lead to a deviation from the ideal behavior. This implies an implementation of strategies to compensate for the associated efficiency losses. Here, we report on how the intrinsic tunable features of self-engineered liquid crystal topological defects can be used to enhance rejection capabilities of spectrally tunable vector vortex coronagraphs. We also discuss the extent of which current models enable to design efficient devices. The simplicity and decent performance of our approach offer the possibility to an amateur astronomy community to consider the use of vortex coronography.

We report on free-space strategy for electromagnetic concealment of three-dimensional macroscopic objects in the optical domain owing to unique energy flow redirection capabilities enabled by optical phase singularities. We propose and implement the generation of a quasi-nodal volume based on optical vortex Fourier processing, which inhibits light scattering from objects placed inside. The proof of concept is made by numerical simulations and the experimental implementation is carried out in the visible domain by using geometric phase vortex phase masks. Optical cloaking demonstration is made by using stainless steel sphere as the object to be concealed. The geometric phase nature of the vortex masks confers polarization independent features to the device and makes it possible to implement in a reflection mode.

International audience; Agile management of the optical orbital angular momentum encompasses temporal, spatial, and spectral aspects that, once combined, offer new perspectives in our way to manipulate light. To date the spectral control is mainly limited to tunable operating wavelength and polychromatic capabilities. Recently, a multispectral approach has been proposed [Phys. Rev. Lett. 121, 213901 (2018)] to achieve independent orbital angular momentum state control on multiple spectral channels. Here we report on the design, fabrication and implementation of a solid-state multispectral approach that consists of arrays of optical diamond micro-metasurfaces. Obtained device exhibits superior performances with respect to the original attempt, both regarding the spectral vortex purity, the ability to deal with high photon flux, and the orbital angular momentum diversity across the spectrum. These results motivate further development of metasurface-based integrated spin-orbit photonics technologies.

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Among the properties of light that dictate its mechanical effects, polarization has held a special place since the mechanical identification of the photon spin1. Nowadays, little surprise might be expected from the mechanical action of linearly polarized weakly focused (paraxial) beams on transparent and homogeneous dielectrics. Still, here we unveil vectorial optomechanical effects mediated by the material anisotropy and the longitudinal field component inherent to real-world beams2,3. Experimentally, this is demonstrated by using an elastic anisotropic medium prone to exhibit a sensitive and reversible effect, that is, a nematic liquid crystal, and our results are generalized to vector beams4. This represents an alternative to irreversible damaging approaches restricted to strongly non-paraxial fields5. The reported creation of multiple self-induced lenses from a single beam also open up topology assisted all-optical information routing strategies. Moreover, our findings point out the transverse internal optical energy flows (spin and orbital)6 as novel triggers to tailor structured optical nonlinearities. Researchers demonstrate vectorial optomechanical effects using a nematic liquid crystal and report creation of multiple self-induced lenses from a single beam.

International audience; Structuring light attracts continuous research effort due to its impactful applications in optical information and communications, laser material processing, optical imaging, or optical manipulation of matter. In particular, femtosecond laser direct writing of photoresists is a technology dedicated to the creation of optically isotropic free-form 3D micro-optical elements with size, spatial resolution, and surface quality that qualify to demanding integrated optics needs. Here, we report on the design, production, and characterization of dielectric metasurface birefringent optical retarders made from femtosecond laser 3D printing technology whose polarization conversion efficiency is more than 10 times larger than that previously reported Wang et al., Appl. Phys. Lett. 110, 181101 (2017)]. As the flexibility of the fabrication process allows considering arbitrary orientation of the artificially engineered optical axis, these results open up for 3D printed geometric phase optical elements.

International audience; We demonstrate that the orbital angular momentum of radiating waves can be used to drive a mechanical oscillator, an option that has remained elusive to date on experimental grounds whatever the nature of the waves. This is done using an amplitude-modulated ultrasonic wave interacting with a centimeter-size torsional pendulum. Achieved resonant quantitative measurements of the acoustic radiation torque and material properties set the basis for orbital-angular-momentum-based metrology applications and possibly cooling of the rotational degree of freedom of macroscopic objects.

International audience; Topological solitons are non-singular but topologically nontrivial structures in fields, which have fundamental significance across various areas of physics, similar to singular defects. Production and observation of singular and solitonic topological structures remain a complex undertaking in most branches of science – but in soft matter physics, they can be realized within the director field of a liquid crystal. Additionally, it has been shown that confining liquid crystals to spherical shells using microfluidics resulted in a versatile experimental platform for the dynamical study of topological transformations between director configurations. In this work, we demonstrate the triggered formation of topological solitons, cholesteric fingers, singular defect lines and related structures in liquid crystal shells. We show that to accommodate these objects, shells must possess a Janus nature, featuring both twisted and untwisted domains. We report the formation of linear and axisymmetric objects, which we identify as cholesteric fingers and skyrmions or elementary torons, respectively. We then take advantage of the sensitivity of shells to numerous external stimuli to induce dynamical transitions between various types of structures, allowing for a richer phenomenology than traditional liquid crystal cells with solid flat walls. Using gradually more refined experimental techniques, we induce the targeted transformation of cholesteric twist walls and fingers into skyrmions and elementary torons. We capture the different stages of these director transformations using numerical simulations. Finally, we uncover an experimental mechanism to nucleate arrays of axisymmetric structures on shells, thereby creating a system of potential interest for tackling crystallography studies on curved spaces.

We quantitatively report on the rotational mechanical effect of wave orbital angular momentum on matter by nondissipative vortex mode conversion. Our experiments consist of ultrasonic waves reflected off freely spinning helical acoustic mirrors that are capillary trapped at a curved air-water interface. Considering helical mirrors with integer topological charges these results represent the demonstration of the experiment proposed by Allen et al. originally introduced in the optical domain [Phys. Rev. A 45, 8185 (1992)PLRAAN1050-294710.1103/PhysRevA.45.8185], whose quantitative implementation remains elusive to date whatever the nature of the wave. The study is further generalized to helical mirrors with fractional charges.

We report on the conversion of an infrared vector beam into THz vortex beams using a ZnTe cubic crystal. We provide a theoretical analysis demonstrating how an infrared vector beam with the azimuthal order l can be transformed into a THz beam endowed with an orbital angular moment content that consists of optical vortices with topological charge ±2l. Experimentally, quasi-monochromatic THz vortex beams with topological charges +2 and −2 are produced and characterized both in amplitude and phase using real-time two-dimensional imaging of the terahertz electric field.

International audience; We report on the experimental demonstration of chirality-selective mechanical separation of randomly distributed assemblies of right-handed and left-handed chiral microparticles by optical means. Chiral-resolution experiments are made using two-dimensional emulsions of chiral-liquid-crystal droplets under the action of circularly polarized laser beams and do not require information on the initial location of the particles. Also, we numerically identify that the cooperative effects of hydrodynamic interactions mediated by the viscous fluid surrounding the particles can speed up the enantioseparation process.

International audience; We propose an approach to achieve achromatic pure geometric phase shaping of light from anisotropic media by exploiting the fundamental laws of electromagnetic waves. Its practical implementation requires a cover layer made of a dispersive isotropic medium. The approach applies to any anisotropic material and any geometric phase spatial distribution and preserves the geometric phase reversal upon the reversal of the incident polarization handedness. An experimental demonstration is made over the whole visible range but can be extended to any wavelength range without conceptual issues.

We report on a chiral optical Stern-Gerlach experiment where chiral liquid crystal microspheres are selectively displaced by means of optical forces arising from optical helicity gradients. The present Newtonian experimental demonstration of an effect predicted at molecular scale [New J. Phys. 16, 013020 (2014)NJOPFM1367-263010.1088/1367-2630/16/1/013020] is a first instrumental step in an area restricted so far to theoretical discussions. Extending the Stern-Gerlach experiment legacy to chiral light-matter interactions should foster further studies, for instance towards the elaboration of chirality-enabled quantum technologies or spin-based optoelectronics.

International audience; Spontaneously formed liquid crystal topological defects under external fields offer a nature-assisted route to the creation of geometric phase optical vortex generators (q-plates). Here we report on the consequences of the unavoidable swirled transverse spatial distribution of the optical axis of such optical elements on the beam shaping and we propose a swirl-compensation scheme based on the arithmetic of geometric phase optical elements.

International audience; We report on a programmable liquid crystal spatial light modulator enabling independent orbital angular momentum state control on multiple spectral channels. This is done by using electrically controllable “topological pixels" that independently behave as geometric phase micro-optical elements relying on selfengineered liquid crystal defects. These results open interesting opportunities in optical manipulation, sensing, imaging, and communications, as well as information processing. In particular, spectral vortex modulation allows considering singular spatiotemporal shaping of ultrashort pulses which may find applications in many areas such as material processing, spectroscopy, or elementary particles acceleration.

International audience; Photonics have developed greatly over the last several decades and brought about a variety of new concepts in communica tions, sensing, solar energy and many other fields. With the emerging applications of quantum technologies and all optical data processing, the impact of photonics on technology is unde niable, as evidenced through the International Year of Light and Light based Technologies in 2015.

This corrects the article DOI: 10.1103/PhysRevLett.120.213903.

International audience; We present and test the integration of a static orbital angular momentum mode multiplexer with a dynamical geometric-phase optical element, enabling on-demand spin-controlled angular momentum multiplexing. A diffractive optic multiplexer fabricated by 3D high-resolution electron beam lithography performs a conformal mapping for the conversion from linear to azimuthal phase gradients. The latter is functionalized by a dynamic spin-orbit add-on that consists of a self-engineered electrically activated liquid crystal optical vortex generator having large clear-aperture and high-resolution. By combining several functionalities based on the optical angular momentum of light in a compact manner, the proposed hybrid device could find applications in next-generation high-dimensional mode switchers and routers based on orbital angular momentum.

In this work we reveal an influence of polarization of the laser beam on polymerization in direct laser writing. It was experimentally found that the width of suspended lines fabricated in SZ2080, OrmoComp and PETA (pentaerythritol triacrylate) pre-polymers directly depends on the incident polarization and is largest when the angle between the electric field vector and the sample translation direction is α = 90° and the smallest when α = 0°. The size of polymerized structures is consistent with theoretical simulations based on vectorial Debye theory. Experiments were performed by using average laser power corresponding to the middle value of the fabrication window. Polarization was found to be affecting feature sizes while structuring various widespread photoresists, the observed variation was material dependent and measured from 5 to 22% in the line-width. The performed study proves that polarization can be used as a variable parameter for fine tuning of the voxel's aspect ratio.

International audience; Molecular machines operated by light have been recently shown to be able to produce oriented motion at the molecular scale 1,2 as well as do macroscopic work when embedded in supramolecular structures 3–5. However, any supramolecular movement irremediably ceases as soon as the concentration of the interconverting molecular motors or switches reaches a photo-stationary state 6,7. To circumvent this limitation, researchers have typically relied on establishing oscillating illumination conditions—either by modulating the source intensity 8,9 or by using bespoke illumination arrangements 10–13. In contrast, here we report a supramolecular system in which the emergence of oscillating patterns is encoded at the molecular level. Our system comprises chiral liquid crystal structures that revolve continuously when illuminated, under the action of embedded light-driven molecular motors. The rotation at the supramolecular level is sustained by the diffusion of the motors away from a localized illumination area. Above a critical irradiation power, we observe a spontaneous symmetry breaking that dictates the directionality of the supramolecular rotation. The interplay between the twist of the supramolecu-lar structure and the diffusion 14 of the chiral molecular motors creates continuous, regular and unidirectional rotation of the liquid crystal structure under non-equilibrium conditions.

International audience; We report on the design, fabrication, and experimental characterization of reflective geometric phase optical elements enabling the generation of scalar and vectorial high-order Laguerre-Gauss optical beams over a broad spectral range. This is made possible by combining azimuthal and radial structuring of helix-based liquid-crystal films exhibiting the circular Bragg reflection phenomenon. By extending the previously introduced concept of Bragg-Berry optical elements to the polychromatic shaping of the radial degrees of freedom and showing their combination with azimuthal ones, this work suggests that spectrally broadband spin-orbit processing of optical information over multiple spatial degrees of freedom can be further considered on experimental grounds.

International audience; Geometric phase optical elements based on structured anisotropy are widely used for phase shaping via their orienta-tional degree of freedom. To date, amplitude shaping via space-variant retardance is much less investigated, a practical reason being that the spin-orbit interaction of light couples retardance with the dynamic part of the optical phase. Inspired by the complementary diffractive elements associated with Babinet's principle, a bilayered subwavelength grating design is proposed in order to cancel out the spatial modulation of the dynamic phase usually associated with space-variant birefringent phase retardation. This concept is illustrated in the framework of single-mode Laguerre Gauss –beam shaping.

International audience; Optical vortex phase masks are now installed at many ground-based large telescopes for high-contrast astronomical imaging. To date, such instrumental advances have been restricted to the use of helical phase masks of the lowest even order, while future giant telescopes will require high-order masks. Here we propose a single-stage on-axis scheme to create high-order vortex coronagraphs based on second-order vortex phase masks. By extending our approach to an off-axis design, we also explore the implementation of multiple-star vortex coronagraphy. An experimental laboratory demonstration is reported and supported by numerical simulations. These results offer a practical roadmap to the development of future coronagraphic tools with enhanced performances.

International audience; Artificially engineered geometric phase optical elements may have tunable photonic functionalities owing to their sensitivity to external fields, as is the case for liquid crystal based devices. However, liquid crystal technology combining high-resolution topological ordering with tunable spectral behavior remains elusive. Here, by using a magnetoelectric external stimulus, we create robust and efficient self-engineered liquid crystal geometric phase vortex masks with a broadly tunable operating wavelength, centimeter-size clear aperture, and high-quality topological ordering.

Observing and taming unusual effects arising from non-trivial light-matter interaction has always triggered scientists to better understand Nature and develop technological tools towards implementing novel applications. Recently, several unusual optomechanical effects have been unveiled when subtle spin-orbit interactions come at play to build up optical forces and torques that are hardly seen in everyday life, such as negative optical radiation pressure, transverse optical forces, or left-handed optical torques. To date, there are only a few experimental proposals to reveal these effects despite tremendous conceptual advances. In particular, spin-dependent lateral forces and their angular analog are done either at the expense of direct observations or at the cost of specific instrumental complexity. Here we report on naked-eye identification of light-induced spin-dependent lateral displacements of centimeter-sized objects endowed with structured birefringence. Its angular counterpart is also discussed and the observation of left-handed macroscopic rotational motion is reported. The unveiled effects are ultimately driven by lateral optical force fields that are five orders of magnitude larger than those reported so far. These results allow structured light-matter interaction to move from a scientific curiosity to a new asset for the existing multidisciplinary optical manipulation toolbox across length scales. In addition, this highlights the spin-orbit optomechanics of anisotropic and inhomogeneous media, which is just beginning to be explored.

International audience; We propose to couple the optical orientational nonlinearities of liquid crystals with their ability to self-organize to tailor them to control space-variant-polarized optical fields in a nonlinear manner. Experimental demonstration is made using a liquid crystal light valve that behaves like a light-driven geometric phase optical element. We also unveil two original nonlinear optical processes, namely self-induced separability and nonseparability. These results contribute to the advancement of nonlinear singular optics that is still in its infancy despite 25 years of effort, which may foster the development of nonlinear protocols to manipulate high-dimensional optical information both in the classical and quantum regimes.

International audience; By making use of the spin angular momentum of light, rotational frequency shifts of harmonic waves generated by spinning nonlinear media have been observed.

The realization of geometric phase optical device operating over a broad spectral range is usually confronted with intrinsic limitations depending of the physical process at play. Here we propose to use chiral nematic liquid crystal slabs with helical ordering that varies in three dimensions. Namely, gradient-pitch cholesterics endowed with in-plane space-variant angular positioning of the supramolecular helix. By doing so, we show that the recently introduced Bragg-Berry mirrors [Opt. Lett. {\bf 41}, 3972-3975 (2016)] can be endowed with ultra-broadband spectral range. Experimental demonstration is made in the case of ultra-broadband optical vortex generation in the visible domain. These results offer practical solution to the polychromatic management of the orbital angular momentum of light combining the circular Bragg reflection of chiral media with the Berry phase., Comment: 11 pages, 13 figures

International audience; Structured light beams, such as optical vortices, vector beams, and non-diffracting beams, have been recently studied in a variety of fields, such as optical manipulations, optical telecommunications, nonlinear interactions, quantum physics, and 'super resolution' microscopy.. Their unique physical properties, such as annular intensity profile, helical wavefront and orbital angular momentum, give rise to a plethora of new, fundamental light-matter interactions and device applications. Recent progress in nanostructured materials, including metamaterials and metasurfaces, opened new opportunities for structured light generation on the microscale that exceed the capabilities of bulk-optics approaches such as computer generated holography and diffractive optics. Furthermore, structured optical fields may interact with matters on the subwavelength scale to yield new physical effects, such as spin-orbital momentum coupling. This special issue of Optics Express focuses on the state-of-the-art fundamental research and emerging technologies and applications enabled by the interplay of " structured light " and " structured materials " .

Three dimensional (3D) fast (< 0.5 hour) printing of micro-optical elements down to sub-wavelength resolution over 100 micrometers footprint areas using femtosecond (fs-)laser oscillator is presented. Using sub-1 nJ pulse energies, optical vortex generators made of polymerised grating segments with an azimuthally changing orientation have been fabricated in SZ2080 resist; width of polymerised rods was ~150 nm and period 0.6-1 micrometers. Detailed phase retardance analysis was carried out manually with Berek compensator (under a white light illumination) and using an equivalent principle by an automated Abrio implementation at 546 nm. Direct experimental measurements of retardance was required since the period of the grating was comparable (or larger) than the wavelength of visible light. By gold sputtering, transmission-type optical vortex generators were turned into reflective ones with augmented retardance, n.h defined by the form birefringence, n, and the height h = 2d where d is the thickness of the polymerised structure. Retardance reached 315 nm as measured with Berek compensator at visible wavelengths. Birefringent phase delays of 180 degrees (or half-wavelength) required for high purity vortex generators can be made based on the proposed approach. Optical vortex generators for telecom wavelengths with sub-wavelength patterns of azimuthally oriented gratings are amenable by direct laser polymerisation., Pacific Rim Laser Damage 2017: Optical Materials for High Power Lasers (PLD17); Shanghai, China 21 - 24 May 2017. Invited talk

We propose a topological beam-shaping strategy of terahertz beams using geometric phase elements made of space-variant birefringent slabs. Quasi-monochromatic terahertz vortex beams are produced and characterized both in amplitude and phase from the reconstructed real-time two-dimensional imaging of the electric field. Nonseparable superpositions of such vortex beams are also obtained and characterized by two-dimensional polarimetric analysis. These results emphasize the versatility of the spin-orbit electromagnetic toolbox to prepare on-demand structured light endowed with polarization-controlled orbital angular momentum content in the terahertz domain, which should find many uses in future terahertz technologies.

International audience; Reflective geometric phase flat optics made from chiral anisotropic media recently unveiled a promising route towards polychromatic beam shaping. However, these broadband benefits are strongly mitigated by the fact that flipping the incident helicity does not ensure geometric phase reversal. Here we overcome this fundamental limitation by a simple and robust add-on whose advantages are emphasized in the context of spin-to-orbital angular momentum mapping.

International audience; We propose to use a femtosecond direct laser writing technique to realize dielectric optical elements from photo-resist materials for the generation of structured light from purely geometrical phase transformations. This is illustrated by the fabrication and characterization of spin-to-orbital optical angular momentum couplers generating optical vortices of topological charge from 1 to 20. In addition, the technique is scalable and allows obtaining microscopic to macroscopic flat optics. These results thus demonstrate that direct 3D photopolymerization technology qualifies for the realization of spin-controlled geometric phase optical elements.

International audience; We propose a topological beam-shaping strategy of terahertz (THz) beams using geometric phase elements made of space-variant birefringent slabs. Quasi-monochromatic THz vortex beams are produced and characterized both in amplitude and phase from the reconstructed real-time two-dimensional imaging of the electric field. Nonseparable superpositions of such vortex beams are also obtained and characterized by two-dimensional polarimetric analysis. These results emphasize the versatility of the spin-orbit electromagnetic toolbox to prepare on-demand structured light endowed with polarization-controlled orbital angular momentum content in the THz domain, which should find many uses in future THz technologies.

International audience; We propose the development of a high contrast imaging technique enabling the simultaneous and selective nulling of several light sources. This is done by realizing a reconfigurable multiple vortex phase mask made of a liquid crystal thin film on which local topological features can be addressed electro optically. The method is illustrated by reporting on a triple star optical vortex coronagraphy laboratory demonstration, which can be easily extended to higher multiplicity. These results allow considering the direct observation and analysis of worlds with multiple suns and more complex extrasolar planetary systems.

International audience; We explore the spin-orbit nature of the optical torque exerted on chiral liquid-crystal microspheres exhibiting circular Bragg reflection. Experimental investigation relies on the direct optomechanical observation of spinning liquid-crystal droplets immersed in water and held in a circularly polarized laser levitator. More generally, we anticipate that the total angular momentum transfer per photon may depart from the commonly assumed spin-only ±2¯ h contribution, when the topological features of the illuminated microsphere are taken into account.

International audience; We report on a self-induced strategy to achieve high-contrast optical imaging, without the need for any man-made optical masks, which relies on the self-induced spin-to-orbital angular momentum conversion phenomenon. This is experimentally demonstrated by realizing a laboratory demonstration of self-eclipsing of a light source following the generation of a self-adapted vectorial optical vortex transmission mask. The proposed concept, namely the realization of an alignment-free optical vortex corona-graph, may inspire the development of future generations of smart astronomical imaging instruments.

The generation of a left-handed torque that acts in the opposite direction to light's natural spin angular momentum is reported. The effect is achieved by sending circularly polarized light into an azimuthally patterned birefringent glass disk. Optical forces and torques are two mechanical degrees of freedom available to manipulate matter, and form the basis of optical tweezing strategies1,2. In contrast to the Keplerian intuition that objects should be pushed downstream an incident photon flux, the concept of ‘negative’ optical forces has recently been described3,4 and has triggered many developments5,6,7,8,9,10,11,12,13,14. Here, we report on the counterintuitive angular analogue of negative optical forces by demonstrating that circularly polarized Gaussian light beams give rise to torque with opposite sign to that of the incident optical angular momentum. Such a ‘left-handed’ mechanical effect is demonstrated by the use of an inhomogeneous and anisotropic transparent macroscopic medium. Practical difficulties associated with the direct observation of optically induced spinning of a macroscopic object are circumvented via the rotational Doppler effect15,16. These results shed light on spin–orbit optomechanics and equip the left-handed optomechanical toolbox with angular features.

International audience; Here, we report on the experimental demonstration that highly efficient self-induced spin-orbit optical vortex generation can be achieved by using standard liquid crystal materials and surface treatment agents. This is done by revisiting the recent attempt by Zolot’ko and coworkers to produce self-induced liquid crystal vortex plates using the dc electric field [I. A. Budagovsky, S. A. Shvetsov, and A. S. Zolot’ko, Mol. Cryst. Liq. Cryst. 637, 47 (2016)] that remains, so far, limited to moderate efficiencies. The phenomenon is the result of the self-back-action of light arising from the spontaneous creation of a liquid crystal topological defect. These results demonstrate photo-electric interface activation as a candidate towards the development of a self-adapted spinorbit photonic toolbox, thus enabling agile management of the orbital angular momentum of light.