Max Planck Institute for the Science of Light

Cassie-Baxter superhydrophobic surfaces repel aqueous media by trapping a thin air layer known as plastron. However, current methods to estimate plastron characteristics on such surfaces, either directly through digital still imaging/confocal microscopy or indirectly through contact angle goniometry, are technically challenging and often imprecise. Previously, we demonstrated that the solid-liquid area fraction, which quantifies the fraction of the solid surface that is in direct contact with the surrounding liquid, can be accurately measured by reflectance optical microscopy, provided that the material surface has approximately uniform local reflectivity. To eliminate the complexity associated with optical reflectance measurements, we recently demonstrated that the drop adhesion force correlates linearly with the solid-liquid area fraction. In this study, we advance the drop adhesion force measurements obtained at different environments, compression distances, and during pressurization-hold experiments to reveal whether the plastron sustains external pressure or undergoes gradual collapse. Here, we demonstrate that measuring drop adhesion force is a robust, rapid, and technically simple method for assessing plastron properties under a wide range of environmental and surface conditions. The proposed method provides information on plastron stability within minutes and thus could aid in the design of ultrarepellent surfaces with long-term stability in demanding applications.

In this talk I’ll introduce indefinite causal order— quantum superposition of ordering of events—and show you how it can be done with photons, the fundamental particle of light. We’ll then explore using this trick to communicate via perfectly noisy channels—which is classically impossible—and to measure rotations with completely noisy probes via a channel that erases all information—again, classically impossible. Questions before, during, and after the talk are highly encouraged.

Superhydrophobic surfaces have attracted considerable attention due to their remarkable ability to repel aqueous media by trapping an air layer. However, estimating the solid-liquid area fraction is challenging due to the complexity of their intrinsic properties and the limited resolution of methods for assessing contact area. We demonstrated that solid-liquid area fraction can be measured using reflectance optical microscopy, which provides a millimeter field of view with a micrometer lateral resolution. However, this method depends on the surface's optical characteristics. To simplify these measurements, this study examines the drop adhesive force as a means of quantifying solid-liquid area fraction. Utilizing a controlled experimental setup, we investigated the relationship between drop adhesive forces and solid-liquid area fraction. After considering various surface geometries obtained by laser and electrochemical treatments, we engineered 23 surfaces with solid-liquid area fractions ranging from 0.1% to ∼50%. Our results show that the adhesive force exerted by droplets on these surfaces increases linearly with the degree of air entrapment beneath the liquid. This provides a measurable indicator of their Cassie-Baxter superhydrophobicity. This research advances our fundamental understanding of plastron on superhydrophobic surfaces, facilitating the development of highly repellent, ultraslippery surfaces.

ABSTRACT Laser ablation is a widely used technique for the fabrication of periodic structures on solids to manipulate their surface properties. A fundamental challenge in the formation of laser‐induced periodic surface structures (LIPSS) is ascertaining the correlation between laser parameters and LIPSS characteristics. This study focuses on the characterization of LIPSS in terms of the period of low spatial frequency LIPSS (LSFL) and their homogeneity as a function of single pulse fluence and effective fluence dose in the range from 0.067 to 1.070 J cm −2 and from 50 to 1280 J cm −2 , respectively. Here, a 1064 nm laser with a pulse duration of 13 ps was utilized to create LIPSS on Ti6Al4V alloy. The morphology of the formed structures was analyzed using the two‐dimensional fast Fourier transform method applied to scanning electron microscopy images. Homogeneous LSFL with spatial periods are obtained for effective fluence doses of 50 and 160 J cm −2 . However, an increase in the effective fluence dose up to 640 J cm −2 led to the formation of so‐called large LIPSS and the disappearance of homogeneous LSFL. The evolution of LIPSS that has been observed is attributed to changes in the ratio and absolute values of the ablative and heating components of the laser pulse energy at different single and effective fluence doses. Our study contributes to the development of tailored surfaces with periodic structures on Ti alloys.

Spontaneous symmetry breaking (SSB) plays a central role in many areas of physics, from particle interactions to optical systems. Exceptional points (EPs), where system properties become degenerate, are often believed to occur together with SSB. Here we investigate the intricate relationship between SSB and a specific class of EPs across three distinct, real-world scenarios in nonlinear optics. In these systems, the two phenomena do not coincide; they occur at dislocated points in parameter space, but are interdependent. This recurring behavior across disparate platforms implies that such decoupling is not unique to these optical systems, but likely reflects a more general principle. Our results highlight the need for careful analysis of assumed correlations between SSB and EPs in both theoretical and applied contexts. They deepen our understanding of nonlinear dynamics in optical systems and prompt a broader reconsideration of contexts where EPs and SSB are thought to be interdependent.

High-resolution studies in structural biology are often limited by the challenges of crystallization and low contrast in the cellular native environment. The exquisite labeling specificity of fluorescence microscopy gets around these issues and allows superresolution microscopy, but to date, these works have used chemically fixed samples. To establish light microscopy as a workhorse in structural biology, two main requirements must be fulfilled: near-native sample preservation and near-atomic optical resolution. Here, we introduce single-particle cryogenic light microscopy (spCryo-LM) as a technique that satisfies these key criteria. We adapt established protocols from cryogenic electron microscopy (Cryo-EM) for shock-freezing samples and use a high-vacuum cryogenic shuttle system to transfer them in and out of a liquid-helium cryostat that houses a superresolution fluorescence microscope. By exploiting the enhanced photophysics at low temperature, angstrom precision can be achieved in localizing several fluorophores attached to proteins separated by a few hundred nanometers. We present various characterization studies on vitreous ice, single-molecule photoblinking behavior, and the effects of laser intensity and benchmark our method by resolving the heptameric membrane protein alpha-hemolysin in a synthetic lipid membrane. Additionally, we report on the technique's capability to resolve membrane proteins in their native cellular membrane environment. spCryo-LM enables structural studies of proteins in their native environment without chemical fixation or protein isolation, and can be integrated with other superresolution or spectroscopic techniques. We believe our approach establishes light microscopy as a powerful tool in structural biology and sets the stage for correlative microscopy with Cryo-EM and related techniques.

The first time in‐depth characterization of dibenzoterrylene (DBT) was performed by a combination of various experimental and computational techniques. First structure confirmation and atom assignment were achieved by means of 2D‐NMR and powder X‐ray. DFT methods shed light on the conformational space of DBT and, more importantly, on the complex electronic structure of the molecule. DBT appears to be the first studied molecule, two low‐lying conformers of which have drastically different biradical character. EPR and NMR studies show the effect of solvent on the population of the biradical state. This demonstrates the perspectives of the usage of DBT and its derivatives in spintronics and other quantum technologies.

Scalable, high-speed, small-footprint photonic switching platforms are essential for advancing optical communication. An effective optical switch must operate at high duty cycles with fast recovery times, while maintaining substantial modulation depth and full reversibility. Colloidal nanocrystals, such as indium tin oxide (ITO), offer a scalable platform to meet these requirements. In this work, the transmission of ITO nanocrystals near their epsilon-near-zero wavelength is modulated by two-cycle optical pulses at a repetition rate of one megahertz. The modulator exhibits a broad bandwidth spanning from 2 to 2.5µm. Sensitive fieldoscopy measurements resolve the transient electric-field response of the ITO for the first time, showing that the modulation remains reversible for excitation fluences up to 1.2mJ cm-2 with a modulation depth of 10%, and becomes fully irreversible beyond 3.3mJ cm-2, while reaching modulation depth of up to 20%. Field sampling further indicates that at higher excitation fluences, the relative contribution from the first cycle of the optical pulses is reduced. These findings are crucial for the development of all-optical switching, telecommunications, and sensing technologies capable of operating at terahertz switchingfrequencies.

Fibrosis and persistent inflammation are interconnected processes that inhibit axon regeneration in the mammalian central nervous system (CNS). Here, we show that in zebrafish, the interplay between fibroblasts and immune cells is required for regeneration. Using temporally resolved single-cell transcriptomics, we identify a transient, injury-induced cthrc1a+ fibroblast state with an inflammation-associated, less differentiated, non-fibrotic profile. Ca2+-dependent induction of this fibroblast state precedes and is critical for the initiation of the inflammatory response. Subsequently, cthrc1a+ fibroblasts coordinate the resolution of the neutrophil-driven inflammation. Disruption of these inflammation dynamics alters the mechano-structural properties of the lesion microenvironment and inhibits regeneration and recovery of locomotor function. Thus, zebrafish fibroblasts possess a dual role in inducing and resolving inflammation, which are both required for regeneration. This establishes the biphasic inflammation control by fibroblasts as an important mechanism directing CNS regeneration.

Axions and axion-like particles (ALPs) are well-motivated dark matter (DM) candidates that couple with photons in external magnetic fields. The parameter space around m a ∼ 50 meV remains largely unexplored by haloscope experiments. We present the first prototype of Weakly Interacting Sub-eV Particles (WISP) Searches on a Fiber Interferometer (WISPFI), a table-top, model-independent scheme based on resonant photon–axion conversion in a hollow-core photonic crystal fiber (HC-PCF) integrated into a Mach–Zehnder interferometer (MZI). Operating near a dark fringe with active phase-locking, combined with amplitude modulation, the interferometer converts axion-induced photon disappearance into a measurable signal. A 2 W, 1550 nm laser is coupled with a 1 m-long HC-PCF placed inside a ∼2 T permanent magnet array, probing a fixed axion mass of m a ≃ 49 meV with a projected sensitivity of g a γ γ ≳ 1.3× 10 − 9 GeV−1 for a measurement time of 30 days. Future upgrades, including pressure tuning of the effective refractive index and implementation of a Fabry–Pérot cavity, could extend the accessible mass range and improve sensitivity, establishing WISPFI as a scalable platform to explore previously inaccessible regions of the axion parameter space.