Clément Lafargue

Spectra, thresholds, and modal fields of a kite-shaped microcavity laser

We investigate the lasing spectra, threshold gain values, and emission directionalities for a two-dimensional microcavity laser with a “kite” contour. The cavity modes are considered accurately using the linear electromagnetic formalism of the lasing eigenvalue problem with exact boundary and radiation conditions. We develop a numerical algorithm based on the Muller boundary integral equations discretized using the Nystrom technique, which has theoretically justified and fast convergence. The influence of the deviation from the circular shape on the modal characteristics is studied numerically for the modes polarized in the cavity plane, demonstrating opportunities of directionality improvement together with preservation of a low threshold. These advantageous features are shown for the perturbed whispering-gallery modes of high-enough azimuth orders. Other modes can display improved directivities while suffering from drastically higher threshold levels. Experiments based on planar organic microcavity lasers confirm the coexistence of Fabry–Perot-like and whispering-gallery-like modes in kite-shaped cavities and show good agreement with the predicted far-field angular diagrams.

Three-dimensional microlasers based on polymer fibers fabricated by electrospinning

We report three-dimensional mirror-less lasing from non-cylindrical dye doped polystyrene fibers drawn using an electrospinning procedure where the fiber cross-sectional shape and dimension could be controlled. Signatures of three dimensional etalon like modes were observed corresponding to the transverse and axial quantization of the wave vector. Low lasing thresholds of the order of 200 nJ were achieved along with moderate Q factors.

Three-dimensional organic microlasers with low lasing thresholds fabricated by multiphoton and UV lithography

Cuboid-shaped organic microcavities containing a pyrromethene laser dye and supported upon a photonic crystal have been investigated as an approach to reducing the lasing threshold of the cavities. Multiphoton lithography facilitated fabrication of the cuboid cavities directly on the substrate or on the decoupling structure, while similar structures were fabricated on the substrate by UV lithography for comparison. Significant reduction of the lasing threshold by a factor of ~30 has been observed for cavities supported by the photonic crystal relative to those fabricated on the substrate. The lasing mode spectra of the cuboid microresonators provide strong evidence showing that the lasing modes are localized in the horizontal plane, with the shape of an inscribed diamond.

Three-dimensional emission from organic Fabry-Perot microlasers

We measured the far-field emission patterns in three dimensions of flat organic dye microlasers using a solid angle scanner. Polymer-based microcavities of ribbon shape (i.e., Fabry-Perot type) were investigated. Out of plane emission from the cavities was observed, with significant differences for the two cases of resonators either fully supported by the substrate or sustained by a pedestal. In both cases, the emission diagrams are accounted for by a model combining diffraction at the cavity edges and reflections from the substrate.

Localized lasing modes of triangular organic microlasers

We investigated experimentally the ray-wave correspondence in organic microlasers of various triangular shapes. Triangular billiards are of interest since they are the simplest cases of polygonal billiards and the existence and properties of periodic orbits in triangles are not yet fully understood. The microlasers with symmetric shapes that were investigated exhibited states localized on simple periodic orbits, and their lasing characteristics like spectra and far-field distributions could be well explained by the properties of the periodic orbits. Furthermore, asymmetric triangles that do not feature simple periodic orbits were studied. Their lasing properties were found to be more complicated and could not be explained by periodic orbits.

Strong Electro‐Optic Effect and Spontaneous Domain Formation in Self‐Assembled Peptide Structures

Short peptides made from repeating units of phenylalanine self‐assemble into a remarkable variety of micro‐ and nanostructures including tubes, tapes, spheres, and fibrils. These bio‐organic structures are found to possess striking mechanical, electrical, and optical properties, which are rarely seen in organic materials, and are therefore shown useful for diverse applications including regenerative medicine, targeted drug delivery, and biocompatible fluorescent probes. Consequently, finding new optical properties in these materials can significantly advance their practical use, for example, by allowing new ways to visualize, manipulate, and utilize them in new, in vivo, sensing applications. Here, by leveraging a unique electro‐optic phase microscopy technique, combined with traditional structural analysis, it is measured in di‐ and triphenylalanine peptide structures a surprisingly large electro‐optic response of the same order as the best performing inorganic crystals. In addition, spontaneous domain formation is observed in triphenylalanine tapes, and the origin of their electro‐optic activity is unveiled to be related to a porous triclinic structure, with extensive antiparallel beta‐sheet arrangement. The strong electro‐optic response of these porous peptide structures with the capability of hosting guest molecules opens the door to create new biocompatible, environmental friendly functional materials for electro‐optic applications, including biomedical imaging, sensing, and optical manipulation.

Dielectric equilateral triangle microresonators: integral equations and semi-classical physics approaches

We investigate in detail the resonant properties of a 2D dielectric cavity with an equilateral triangle shape, using a numerical integral equations approach and a semiclassical approach. The homogeneous Müller boundary equations are used to calculate the resonant modes of a dielectric triangle in a wide range of frequencies. It is shown that the modes of dielectric triangles localized on families of periodic orbits can be well described in terms of a semiclassical superscar model. Special attention is given to the families of resonances based on the inscribed triangle periodic orbit.

Out-of-plane modes in three-dimensional Fabry-Perot microlasers

Microlasers are involved in a broad range of devices for numerous research applications. However, the mode structures of three-dimensional microlasers without rotational symmetry are largely unexplored. Previous studies of such cavities revealed lasing modes exclusively localized on periodic orbits in the plane parallel to the substrate, which is to say that the associated momentum vectors are concentrated in the plane. In this paper, we characterize three-dimensional, polymer-based Fabry-Perot (i.e., ribbon-shaped) microcavities and demonstrate that such cavities exhibit modes with momentum vectors out of the substrate plane. These results constitute a proof-of-principle and motivate follow-up studies with more complex three-dimensional geometries.Microlasers are involved in a broad range of devices for numerous research applications. However, the mode structures of three-dimensional microlasers without rotational symmetry are largely unexplored. Previous studies of such cavities revealed lasing modes exclusively localized on periodic orbits in the plane parallel to the substrate, which is to say that the associated momentum vectors are concentrated in the plane. In this paper, we characterize three-dimensional, polymer-based Fabry-Perot (i.e., ribbon-shaped) microcavities and demonstrate that such cavities exhibit modes with momentum vectors out of the substrate plane. These results constitute a proof-of-principle and motivate follow-up studies with more complex three-dimensional geometries.

Strong electro-optic effect in self assembled peptide nanofibers

Low-cost biocompatible nanomaterials with opto-electronic properties are highly desirable as they may open avenue onto new biomedical imaging or sensing technologies. It was recently unveiled that short peptides self-assemble into various micro- and nano-structures including tubes, tapes and fibrils. These structures were found to possess striking mechanical, electrical and optical properties, which are rarely seen in organic materials. Here, we focus on the electro-optic (EO) properties of di- and tri-phenylalanine self-assembled peptide fiber structures and characterize them by using a home built EO phase microscope (PLEOM). This prototypal set-up is based on a highly sensitive interferometric scheme allowing to detect electric-field driven optical phase shifts at the focal point of the microscope objective. The Pockels effect requires a breaking of centro-symmetry, which is intrinsic to the ferroelectric phase in oxide crystals or to molecular crystals of adequate symmetry, or also in statistically oriented molecular assemblies such as biological tissues or membranes.

Dynamical control of square microlaser emission via its symmetry classes

For two decades, microcavities have been widely studied due to their numerous applications, from microlasers on chip [1] to biological or chemical sensing [2]. One of the main concerns is the control of the light propagation inside the resonator and its emission in one or several selected directions. Here, we focus on the square microlaser because it emits very narrow emission lobes [3], and we report a new mechanism to dynamically suppress or enhance some of these lobes by means of the polarization of the pump beam. This method is based on the control of the coherent superposition of degenerate modes belonging to different symmetry classes. This generic concept can be further extended to other cavity shapes.