Toward high laser power beam manipulation with nanophotonic materials: evaluating thin film damage performance.

Nanophotonic materials enable unprecedented control of light-matter interactions, including the ability to dynamically steer or shape wavefronts. Consequently, nanophotonic systems such as metasurfaces have been touted as promising candidates for free-space optical communications, directed energy and additive manufacturing, which currently rely on slow mechanical scanners or electro-optical components for beam steering and shaping. However, such applications necessitate the ability to support high laser irradiances (> kW/cm2) and systematic studies on the high-power laser damage performance of nanophotonic materials and designs are sparse. Here, we experimentally investigate the pulsed laser-induced damage performance (at λ ∼ 1 µm) of model nanophotonic thin films including gold, indium tin oxide, and refractory materials such as titanium nitride and titanium oxynitride. We also model the spatio-thermal dissipation dynamics upon single-pulse illumination by anchoring experimental laser damage thresholds. Our findings show that gold exhibits the best laser damage resistance, but we argue that alternative materials such as transparent conducting oxides could be optimized to balance the tradeoff between damage resistance and optical tunability, which is critical for the design of thermally robust nanophotonic systems. We also discuss damage mitigation and ruggedization strategies for future device-scale studies and applications requiring high power beam manipulation.

Scalable process for mitigation of laser-damaged potassium dihydrogen phosphate crystal optic surfaces with removal of damaged antireflective coating.

We investigate an approach for the recycling of laser-damaged large-aperture deuterated potassium dihydrogen phosphate (DKDP) crystals used for optical switching (KDP) and for frequency conversion (DKDP) in megajoule-class high-power laser systems. The approach consists of micromachining the surface laser damage sites (mitigation), combined with multiple soaks and ultrasonication steps in a coating solvent to remove, synergistically, both the highly adherent machining debris and the laser-damage-affected antireflection coating. We identify features of the laser-damage-affected coating, such as the "solvent-persistent" coating and the "burned-in" coating, that are difficult to remove by conventional approaches without damaging the surface. We also provide a solution to the erosion problem identified in this work when colloidal coatings are processed during ultrasonication. Finally, we provide a proof of principle of the approach by testing the full process that includes laser damage mitigation of DKDP test parts, coat stripping, reapplication of a new antireflective coat, and a laser damage test demonstrating performance up to at least 12 J/cm2 at UV wavelengths, which is well above current requirements. This approach ultimately provides a potential path to a scalable recycling loop for the management of optics in large, high-power laser systems that can reduce cost and extend lifetime of highly valuable and difficult to grow large DKDP crystals.

In vitro antiprotozoal, antimicrobial and antitumor activity of Pavetta crassipes K. Schum leaf extracts.

AIM OF THE STUDY: To study the potential benefit of the traditional medicinal plant Pavetta crassipes K. Schum (Rubiaceae), which is widely distributed throughout West Africa, the methanol and dichloromethane extracts were isolated from the plant leaves to determine if they exhibited antiprotozoal, antibacterial, antifungal or antitumor activity in vitro. MATERIALS AND METHODS: The methanol and dichloromethane extracts and their specific fractions were obtained using bioassay-guided fractionation and investigated for antiproliferative activity in vitro in microorganisms (Staphylococcus aureus, Escherichia coli and Candida albicans), protozoans (Trypanosoma cruzi, Trypanosoma brucei, Leishmania infantum and Plasmodium falciparum), and cancer (U373, PC3, MXT and A549) and normal cell lines (NHDF and MRC-5). RESULTS: Most of the alkaloid fractions investigated exhibited antiproliferative activity in all the cancer cell lines, microorganisms and protozoans studied. CONCLUSIONS: The benefit of Pavetta crassipes as a traditional medicinal remedy was confirmed using antiprotozoal and cytotoxicity assays in vitro. These analyses revealed that the components present in the alkaloid extract of Pavetta crassipes are responsible for its antiprotozoal and cytotoxic efficacy.

Role of molecular charge and hydrophilicity in regulating the kinetics of crystal growth.

The composition of biologic molecules isolated from biominerals suggests that control of mineral growth is linked to biochemical features. Here, we define a systematic relationship between the ability of biomolecules in solution to promote the growth of calcite (CaCO3) and their net negative molecular charge and hydrophilicity. The degree of enhancement depends on peptide composition, but not on peptide sequence. Data analysis shows that this rate enhancement arises from an increase in the kinetic coefficient. We interpret the mechanism of growth enhancement to be a catalytic process whereby biomolecules reduce the magnitude of the diffusive barrier, Ek, by perturbations that displace water molecules. The result is a decrease in the energy barrier for attachment of solutes to the solid phase. This previously unrecognized relationship also rationalizes recently reported data showing acceleration of calcite growth rates over rates measured in the pure system by nanomolar levels of abalone nacre proteins. These findings show that the growth-modifying properties of small model peptides may be scaled up to analyze mineralization processes that are mediated by more complex proteins. We suggest that enhancement of calcite growth may now be estimated a priori from the composition of peptide sequences and the calculated values of hydrophilicity and net molecular charge. This insight may contribute to an improved understanding of diverse systems of biomineralization and design of new synthetic growth modulators.