There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

We present the science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems, targeting an evolution in technology, that might lead to impacts and benefits reaching into most areas of society. This roadmap was developed within the framework of the European Graphene Flagship and outlines the main targets and research areas as best understood at the start of this ambitious project. We provide an overview of the key aspects of graphene and related materials (GRMs), ranging from fundamental research challenges to a variety of applications in a large number of sectors, highlighting the steps necessary to take GRMs from a state of raw potential to a point where they might revolutionize multiple industries. We also define an extensive list of acronyms in an effort to standardize the nomenclature in this emerging field.

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Science and technology roadmap for graphene, related two-dimensional crystals, and hybrid systems

Femtosecond laser micromachining can be used either to remove materials or to change a material's properties, and can be applied to both absorptive and transparent substances. Over the past decade, this technique has been used in a broad range of applications, from waveguide fabrication to cell ablation. This review describes the physical mechanisms and the main experimental parameters involved in the femtosecond laser micromachining of transparent materials, and important emerging applications of the technology. Interactions between laser and matter are fascinating and have found a wide range of applications. This article gives an overview of the fundamental physical mechanisms in the processing of transparent materials using ultrafast lasers, as well as important emerging applications of the technology.

Femtosecond laser micromachining in transparent materials

1.1 Photodynamic Therapy and Imaging
The purpose of this review is to present the current state of the role of imaging in photodynamic therapy (PDT). In order for the reader to fully appreciate the context of the discussions embodied in this article we begin with an overview of the PDT process, starting with a brief historical perspective followed by detailed discussions of specific applications of imaging in PDT. Each section starts with an overview of the specific topic and, where appropriate, ends with summary and future directions. The review closes with the authors’ perspective of the areas of future emphasis and promise. The basic premise of this review is that a combination of imaging and PDT will provide improved research and therapeutic strategies.

PDT is a photochemistry-based approach that uses a light-activatable chemical, termed a photosensitizer (PS), and light of an appropriate wavelength, to impart cytotoxicity via the generation of reactive molecular species (Figure 1a). In clinical settings, the PS is typically administered intravenously or topically, followed by illumination using a light delivery system suitable for the anatomical site being treated (Figure 1b). The time delay, often referred to as drug-light interval, between PS administration and the start of illumination with currently used PSs varies from 5 minutes to 24 hours or more depending on the specific PS and the target disease. Strictly speaking, this should be referred to as the PS-light interval, as at the concentrations typically used the PS is not a drug, but the drug-light interval terminology seems to be used fairly frequently. Typically, the useful range of wavelengths for therapeutic activation of the PS is 600 to 800 nm, to avoid interference by endogenous chromophores within the body, and yet maintain the energetics necessary for the generation of cytotoxic species (as discussed below) such as singlet oxygen (1O2). However, it is important to note that photosensitizers can also serve as fluorescence imaging agents for which activation with light in the 400nm range is often used and has been extremely useful in diagnostic imaging applications as described extensively in Section 2 of this review. The obvious limitation of short wavelength excitation is the lack of tissue penetration so that the volumes that are probed under these conditions are relatively shallow.






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Figure 1


(A) A schematic representation of PDT where PS is a photoactivatable multifunctional agent, which, upon light activation can serve as both an imaging agent and a therapeutic agent. (B) A schematic representation of the sequence of administration, localization and light activation of the PS for PDT or fluorescence imaging. Typically the PS is delivered systemically and allowed to circulate for an appropriate time interval (the “drug-light interval”), during which the PS accumulates preferentially in the target lesion(s) prior to light activation. In the idealized depiction here the PS is accumulation is shown to be entirely in the target tissue, however, even if this is not the case, light delivery confers a second layer of selectivity so that the cytotoxic effect will be generated only in regions where both drug and light are present. Upon localization of the PS, light activation will result in fluorescence emission which can be implemented for imaging applications, as well as generation cytotoxic species for therapy. In the former case light activation is achieved with a low fluence rate to generate fluorescence emission with little or no cytotoxic effect, while in the latter case a high fluence rate is used to generate a sufficient concentration of cytotoxic species to achieve biological effects.

/pdf/imaging-and-photodynamic-therapy-mechanisms-monitoring-and-76rc7acuq5.pdf

Imaging and photodynamic therapy: mechanisms, monitoring, and optimization.

Transparent conductors as solar energy materials: A panoramic review

Current excimer-laser processing techniques can be extended to a broader and more diverse range of materials by moving to the vacuum ultraviolet (VUV; 100-200 nm) spectral region. Most materials are highly opaque in the VUV and the harder photon energy readily breaks chemical bonds, minimizing thermal loading at target surfaces. Further, the short-wavelength radiation affords patterning of sub quarter-micron feature sizes. An experimental survey has been undertaken to evaluate laser etch rates and surface quality produced on several polymer, glass, and semiconductor materials by both ArF and F/sub 2/ excimer lasers, with the hope of defining new processing applications. A summary of this investigation is presented in this paper. >

Vacuum ultraviolet laser ablation of insulators and III-V semiconductors

Asymmetric directional couplers were written inside bulk borosilicate glass by a high repetition rate femtosecond laser. Wavelength-dependent coupling ratios were tuned by laser exposure and coupler geometry, yielding flattened spectral response (plusmn5%) over >400-nm bandwidth.

Wavelength-flattened asymmetric directional couplers written by focused femtosecond laser

Femtosecond Laser Inscribed Waveguides for New Optical Circuit Applications

An open-structure Fabry-Perot resonator with a quality factor of 2400 was fabricated for the first time with colloidal photonic crystal mirrors, demonstrating that colloidal self-assembly can offer new means for creating high resolving power optical devices

Colloidal photonic crystal mirrors for high-resolving-power Fabry-Perots

A femtosecond fiber laser with 100-kHz repetition rate was optimized for 3-D nanostructuring of photoresist. Contrasts in three-photon (1045 nm) and two-photon (522 nm) resolution are presented together with prospects for creating photonic crystal templates and optical phase masks.

Peter R. Herman

Papers

Vacuum ultraviolet laser ablation of insulators and III-V semiconductors

Wavelength-flattened asymmetric directional couplers written by focused femtosecond laser

Femtosecond Laser Inscribed Waveguides for New Optical Circuit Applications

Colloidal photonic crystal mirrors for high-resolving-power Fabry-Perots

Three-dimensional laser nano-structuring: contrast in three-photon and two-photon polymerization of SU-8