From physics to biology, temperature is often a critical factor. Most existing techniques (e.g., ovens, incubators, ...) only provide global temperature control and incur strong inertia. Thermoplasmonic heating is drawing increasing interest by giving access to fast, local, and contactless optical temperature control. However, tailoring temperature at the microscale is not straightforward since heat diffusion alters temperature patterns. In this article, we propose and demonstrate an accurate and reconfigurable microscale temperature shaping technique by precisely tailoring the illumination intensity that is sent on a homogeneous array of absorbing plasmonic nanoparticles. The method consists in (i) calculating a Heat Source Density (HSD) map, which precompensates heat diffusion, and (ii) using a wavefront engineering technique to shape the illumination and reproduce this HSD in the nanoparticle plane. After heat diffusion, the tailored heat source distribution produces the desired microscale temperature pattern under a microscope. The method is validated using wavefront-sensing-based temperature imaging microscopy. Fast (sub-s), accurate, and reconfigurable temperature patterns are demonstrated over arbitrarily shaped regions. In the context of cell biology, we finally propose a methodology combining fluorescence imaging with reconfigurable temperature shaping to thermally target a given population of cells or organelles of interest, opening new strategies to locally study their response to thermal activation.

Mesoscopic Photonic Crystals (MPhCs) are composed of alternating natural or artificial materials with compensating spatial dispersion. In their simplest form, as presented here, MPhCs are composed by the periodic repetition of a MPhC supercell made of a short slab of bulk material and a short slab of Photonic Crystal (PhCs). Therefore, MPhCs present a multiscale periodicity with a subwavelength periodicity within each PhC slab and with a few-wavelength periodicity for its supercell. Thanks to this mesoscopic structure, MPhCs allow the self-collimation of light, through a mechanism called mesoscopic self-collimation (MSC), along both directions of high symmetry and directions oblique with respect to the MPhCs slab interfaces. Here, we propose a new design method useful for conceiving MPhCs that allow MSC under oblique incidence, avoiding in-plane scattering and ensuring propagation via purely guided modes, without out-of-plane radiation losses. In addition, the proposed method allows a systematic search for optimal MSC structures, which also simultaneously satisfy the impedance matching condition at MPhC interfaces, thus reducing the effect of multiple reflections between bulk-PhC interfaces. The proposed design method has the advantage of an extreme analytical simplicity and it allows direct design of oblique-incidence MPhC structures. Its accuracy is validated through Finite Difference Time Domain simulations and the MSC performances of the designed structures are evaluated, in terms of angular direction, beam waist, overall transmittance, and through discussion of a Figure of Merit that accounts for residual beam curvature. This simple yet powerful method can pave the way for the design of advanced MSC-based photonic interconnects and circuits that are immune to crosstalk and out-of-plane losses.

Active suspended membranes are an ideal test-bench for experimenting with novel laser geometries and principles. We show that adding thin AlGaAs barrier near the top and bottom Air/GaAs interfaces of the membrane significantly reduces the carriers non-radiative recombinations and decreases the threshold of test photonic crystal test lasers. We review the existing literature on photonic crystal membrane fabrication and propose an overview of the significant defects that can be induced by each fabrication step. Finally we propose a complete processing scheme that overcome most of these defects.

Mesoscopic photonic crystals (MPhC) are composed of alternating photonic crystal slabs (PhC) and homogeneous material. MPhC structures combine PhC dispersive properties (self-collimation and slow light, among others) with reflectivity control (Bragg mirrors). One of the most studied properties of MPhC is mesoscopic selfcollimation (MSC). MSC occurs when PhC dispersion properties compensate the natural divergence of light in homogeneous material [1]. However, MSC is only visible if the energy properly propagates throughout the structure, it is thus crucial to control undesirable reflections at each interface. Different methods, relying on complex Fourier modal analysis [2], allow reflectivity control using an impedance-based approach such as half-holes or comet-like holes between each interface. These methods have fabrication limitations (not circular holes) and may need long and complex calculations. We propose a method based on a fast and simple multiscale approach. In constrast to [3] we prioritize perfect antireflection at the different interfaces, instead of perfect self-collimation. At the µm-scale, we first model the MPhC as a multilayer Bragg structure. By solving simple Bragg equations we determine a first set of parameters ensuring perfect antireflection. At the nm-scale, we then take into account the PhC dispersion properties to search for MSC solutions within the first set of parameters. With this approach, we obtain a complete set of MPhC geometries that ensures reflectivity control and correct MSC (i.e. low beam divergence), without the need for long numerical simulations. To validate our model, we use FDTD [4] simulations to study light propagation through the previously determined MPhC (Figures 1b, 1c, 1d).