Coating-free mirrors for high precision interferometric experiments

Thermal noise in mirror optical coatings may not only limit the sensitivity of future gravitational-wave detectors in their most sensitive frequency band but is also a major impediment for experiments that aim to reach the standard quantum limit or cool mechanical systems to their quantum ground state. We present the design and experimental characterization of a highly reflecting mirror without any optical coating. This coating-free mirror is based on total internal reflection and Brewster-angle coupling. In order to characterize its performance, the coating-free mirror was incorporated into a triangular ring cavity together with a high quality conventional mirror. The finesse of this cavity was measured using an amplitude transfer function to be about F≃4000. This finesse corresponds to a reflectivity of the coating-free mirror of about R≃99.89%. In addition, the dependence of the reflectivity on rotation was mapped out

Shape-induced force fields in optical trapping

Advances in optical tweezers, coupled with the proliferation of two-photon polymerization systems, mean that it is now becoming routine to fabricate and trap non-spherical particles. The shaping of both light beams and particles allows fine control over the flow of momentum from the optical to mechanical regimes. However, understanding and predicting the behaviour of such systems is highly complex in comparison with the traditional optically trapped microsphere. In this Article, we present a conceptually new and simple approach based on the nature of the optical force density. We illustrate the method through the design and fabrication of a shaped particle capable of acting as a passive force clamp, and we demonstrate its use as an optically trapped probe for imaging surface topography. Further applications of the design rules highlighted here may lead to new sensors for probing biomolecule mechanics, as well as to the development of optically actuated micromachines

Inkjet Printing Based Mono-layered Photonic Crystal Patterning for Anti-counterfeiting Structural Colors

Photonic crystal structures can be created to manipulate electromagnetic waves so that many studies have focused on designing photonic band-gaps for various applications including sensors, LEDs, lasers, and optical fibers. Here, we show that mono-layered, self-assembled photonic crystals (SAPCs) fabricated by using an inkjet printer exhibit extremely weak structural colors and multiple colorful holograms so that they can be utilized in anti-counterfeit measures. We demonstrate that SAPC patterns on a white background are covert under daylight, such that pattern detection can be avoided, but they become overt in a simple manner under strong illumination with smartphone flash light and/or on a black background, showing remarkable potential for anti-counterfeit techniques. Besides, we demonstrate that SAPCs yield different RGB histograms that depend on viewing angles and pattern densities, thus enhancing their cryptographic capabilities. Hence, the structural colorations designed by inkjet printers would not only produce optical holograms for the simple authentication of many items and products but also enable a high-secure anti-counterfeit techniqueope

Three-dimensional microfabrication using two-photon-activated chemistry

Photochemical reactions which can be activated by the simultaneous absorption of two photons provide a means for single-step fabrication of complex 3D microstructures. These types of structures are needed for a wide range of applications, including microfluidics, electrooptics, and micro-electromechanical systems. We have shown that chromophores can be engineered to have both large two-photon absorptivities as well as an efficient means for activating chemical processes, such as radical polymerization, subsequent to the photoexcitation. Chromophores designed following this strategy two-photon-activate the radical polymerization of acrylates at lower incident laser powers than conventional UV initiators. Efficient two-photon photopolymer resins based on these chromophores were used in the fabrication of complex microarchitectures, such as photonic bandgap structures and tapered waveguides. We have devised a strategy which allows this approach to be extended to other chemical systems