Phys.org October 1, 2024 When reflected from an interface, a laser beam generally drifts and tilts away from the path predicted by ray optics, an intriguing consequence of its finite transverse extent. For twisted light, such beam shifts manifest even more dramatically: upon reflection, a field containing a high-order optical vortex is expected to experience not only geometrical shifts, but an additional splitting of its high-order vortex into a constellation of unit-charge vortices, a phenomenon known as topological aberration. In an experiment an international team of researchers (Finland, Brazil) observed topological aberration effect verified through the deformation of vortex constellations […]
Category Archives: Light
Light momentum turns pure silicon from an indirect to a direct bandgap semiconductor
Phys.org September 20, 2024 Photons do not carry sufficient momentum to induce indirect optical transitions in semiconducting materials, such as silicon, necessitating the assistance of lattice phonons to conserve momentum. Therefore, silicon is a less attractive material for a wide variety of optoelectronic applications. An international team of ranchers (Russia, Israel, USA – UC Irvine) introduced an alternative strategy to fulfill the momentum-matching requirement in indirect optical transitions. They demonstrated that when confined to scales below ∼3 nm, photons acquired sufficient momentum to allow electronic transitions at the band edge of Si without the assistance of a phonon. Confined photons […]
Generating spin currents directly using ultrashort laser pulses
Phys.org September 13, 2024 An international team of researchers (USA – UC Berkeley, Lawrence Berkeley National Laboratory, France, Canada, Germany, Austria) measured the light-driven response of a magnetic multilayer structure made of thin alternating layers of cobalt and platinum at the few-femtosecond timescale. They observed how light rearranges the magnetic moment during and after excitation. The results revealed a sub-5 fs spike of magnetization in the platinum layer, which followed the shape of the driving pulse. They interpreted the observations as light-driven spin injection across the metallic layers of the structure. The light-triggered spin current was strikingly short, largely outpacing […]
New method improves understanding of light-wave propagation in anisotropic materials
Phys.org September 17, 2024 Although structurally anisotropic materials are ubiquitous in several application fields, their accurate optical characterization remains challenging due to the lack of general models linking their scattering coefficients to the macroscopic transport observables and the need to combine multiple measurements to retrieve their direction-dependent values. An international team of researchers (Italy, Slovenia, Germany) developed an improved method for the experimental determination of light-transport tensor coefficients from the diffusive rates measured along all three directions, based on transient transmittance measurements and a generalized Monte Carlo model. They applied their method to the characterization of light-transport properties in two […]
Printing 3D photonic crystals that completely block light
Nanowerk September 12, 2024 Fabricating photonic crystals with a complete photonic bandgap in the visible spectrum presents at least two important challenges: achieving a material refractive index > ~2 and a three-dimensional patterning resolution better than ~280 nm. Researchers in Singapore developed a titanium ion-doped resin (Ti-Nano) for high-resolution printing by two-photon polymerization lithography. After printing, the structures were heat-treated in air to induce lattice shrinkage and produced titania nanostructures. The attainted three-dimensional photonic crystals with patterning resolution as high as 180 nm and refractive index of 2.4–2.6. Optical characterization revealed ~100% reflectance within the photonic crystal bandgap in the visible range. They showed […]
Reconfigurable sensor can detect particles 0.001 times the wavelength of light
Phys.org August 27, 2024 The exceptional point, a spectral singularity widely existing in non-Hermitian systems, provides an indispensable route to enhance the sensitivity of optical detection. However, the exceptional point of the systems is set once the system is built or fabricated, and machining errors make it hard to reach such a state precisely. An international team of researchers (China, Spain, Singapore) developed a highly tunable and reconfigurable exceptional point system, i.e., a single spoof plasmonic resonator suspended above a substrate and coupled with two freestanding Rayleigh scatterers. Their design offered great flexibility to control exceptional point states, enabling them […]
Ultrathin quantum light sources: Scientists show excitonic interactions boost efficiency of entangled photon generation
Phys.org August 19, 2024 Researchers in Singapore have showed that the efficiency of spontaneous parametric down-conversion (SPDC) could be improved by harnessing many-body excitonic interactions present in the non-linear optical crystal. They showed that excitonic resonances and interexciton transitions could enhance the probability of SPDC. They benchmarked their ab initio many-body calculations using experimental polar plots of second harmonic generation in NbOI2, demonstrating the relevance of excitons in the nonlinear response. A strong double-exciton resonance in 2D NbOCl2 led to significant enhancement in the second order susceptibility. According to the researchers their work paves the way for the realization of […]
Controlling magnetism with polarized light: Non-thermal pathway uses inverse Faraday effect
Phys.org July 5, 2024 Coherent light-matter interactions mediated by opto-magnetic phenomena like the inverse Faraday effect (IFE) are expected to provide a non-thermal pathway for ultrafast manipulation of magnetism on timescales as short as the excitation pulse itself. As the IFE scales with the spin-orbit coupling strength of the involved electronic states, photo-exciting the strongly spin-orbit coupled core-level electrons in magnetic materials appears as an appealing method to transiently generate large opto-magnetic moments. An international team of researchers (Germany, France, Canada, Italy, Spain, Slovenia, Sweden, UK) investigated this scenario in a ferrimagnetic GdFeCo alloy by using intense and circularly polarized […]
Researchers demonstrate new way to ‘squeeze’ infrared light
Science Daily June 10, 2024 Recent theoretical studies have suggested that transition metal perovskite oxide membranes can enable surface phonon polaritons in the infrared range with low loss and much stronger subwavelength confinement than bulk crystals. Such modes, however, have not been experimentally observed so far. An international team of researchers (USA – North Carolina State University, Lawrence Berkeley National Laboratory, Stanford University, SLAC National Accelerator Laboratory, Switzerland) studied the phonon polaritons in a 100 nm thick freestanding crystalline membrane of SrTiO3 transferred on metallic and dielectric substrates. They observed a symmetric-antisymmetric mode splitting which gave rise to epsilon-near-zero and Berreman […]
Internet can achieve quantum speed with light saved as sound
Phys.org April 15, 2024 An international team of researchers (Denmark, Croatia) demonstrated a memory for light based on optomechanically induced transparency. They achieved a long storage time by leveraging the ultralow dissipation of a soft-clamped mechanical membrane resonator, which oscillated at MHz frequencies. At room temperature, they demonstrated a lifetime T1≈23 ms and a retrieval efficiency η≈40% for classical coherent pulses. According to the researchers the storage of quantum light is possible at moderate cryogenic conditions (T≈10K) and such systems could find applications in emerging quantum networks, where they could serve as long-lived optical quantum memories by storing optical information in […]