Since the discovery of organic azides by Peter Griess more than 140 years ago, numerous syntheses of these energy-rich molecules have been developed. In more recent times in particular, completely new perspectives have been developed for their use in peptide chemistry, combinatorial chemistry, and heterocyclic synthesis. Organic azides have assumed an important position at the interface between chemistry, biology, medicine, and materials science. In this Review, the fundamental characteristics of azide chemistry and current developments are presented. The focus will be placed on cycloadditions (Huisgen reaction), aza ylide chemistry, and the synthesis of heterocycles. Further reactions such as the aza-Wittig reaction, the Sundberg rearrangement, the Staudinger ligation, the Boyer and Boyer-Aube rearrangements, the Curtius rearrangement, the Schmidt rearrangement, and the Hemetsberger rearrangement bear witness to the versatility of modern azide chemistry.

Organic Azides: An Exploding Diversity of a Unique Class of Compounds

The rise in output power from rare-earth-doped fiber sources over the past decade, via the use of cladding-pumped fiber architectures, has been dramatic, leading to a range of fiber-based devices with outstanding performance in terms of output power, beam quality, overall efficiency, and flexibility with regard to operating wavelength and radiation format. This success in the high-power arena is largely due to the fiber’s geometry, which provides considerable resilience to the effects of heat generation in the core, and facilitates efficient conversion from relatively low-brightness diode pump radiation to high-brightness laser output. In this paper we review the current state of the art in terms of continuous-wave and pulsed performance of ytterbium-doped fiber lasers, the current fiber gain medium of choice, and by far the most developed in terms of high-power performance. We then review the current status and challenges of extending the technology to other rare-earth dopants and associated wavelengths of operation. Throughout we identify the key factors currently limiting fiber laser performance in different operating regimes—in particular thermal management, optical nonlinearity, and damage. Finally, we speculate as to the likely developments in pump laser technology, fiber design and fabrication, architectural approaches, and functionality that lie ahead in the coming decade and the implications they have on fiber laser performance and industrial/scientific adoption.

High power fiber lasers: current status and future perspectives [Invited]

Electrochemical Properties of Polyoxometalates as Electrocatalysts.

The field of polyoxometalates (POMs), although a mature field, continues to attract significant attention. The number of publications and patents continues to grow. New researchers are entering the field. The scientific communities of fast-growing new economic/technology powers such as Peoples Republic of China and India are becoming important contributors of the total number of worldwide publications on POMs. Figure 1 depicts the growth of the POM literature per year since 1966. In 1996, according to Chemical Abstracts, nearly 600 refereed publications and over 120 patents were issued in reference to the POM chemistry and technology. Figure 2 shows the countries where the most research activity exists based on publications, and Figure 3 lists the 10 largest patent assignee countries in the world. Japan issues 40% of the worldwide patent literature followed by the USA with ∼17%. The applications of POMs are based on combinations of so-called “value-adding properties” which are summarized in Table 1. From the above-listed properties, the applications of POMs are centered primarily on their redox properties, photochemical response, ionic charge, conductivity, and ionic weights. The majority of the patent and applied literature is devoted to the applications of the Keggin type heteropolyacids (HPA) and their salts. Primarily H3PMo12O40, H3PW12O40, H4SiMo12O40, and H4SiW12O40 are used as the main examples for many applications. Their popularity can be attributed to a large extent to the enormous volume of literature over several decades that describes their fundamental chemistry and to their commercial availability, which makes them convenient starting materials. Approximately two-thirds of the applied chemistry/technology literature describes applications that are based on these POMs. Dimitris E. Katsoulis was born in Athens, Greece in 1955. He received a B.S. degree in Chemistry from University of Athens in 1977. He subsequently joined the research group of Prof. Michael T. Pope at Georgetown University and obtained a Ph.D. degree in 1985. He continued with a postdoctoral assignment at Georgetown University, and in 1988 he joined the Science and Technology function of Dow Corporation in Midland Michigan. He is currently an Associate Research Scientist in the Rigid Materials Science Expertise Center (Central R&D) in Dow Corning. His research interests include hybrid materials, with focus on siloxane-polyoxometalate compositions, sol−gel chemistry, silsesquioxanes, gel systems, polymer matrix composites, and nanocomposites. 359 Chem. Rev. 1998, 98, 359−387

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A Survey of Applications of Polyoxometalates

10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

We have demonstrated a highly efficient cladding-pumped ytterbium-doped fiber laser, generating >2.1 kW of continuous-wave output power at 1.1 µm with 74% slope efficiency with respect to launched pump power. The beam quality factor (M2) was better than 1.2. The maximum output power was only limited by available pump power, showing no evidence of roll-over even at the highest output power. We present data on how the beam quality depends on the fiber parameter, based on our current and past fiber laser developments. We also discuss the ultimate power-capability of our fiber in terms of thermal management, Raman nonlinear scattering, and material damage, and estimate it to 10 kW

/pdf/multi-kilowatt-single-mode-ytterbium-doped-large-core-fiber-8dz20ylqoo.pdf

Multi-kilowatt Single-mode Ytterbium-doped Large-core Fiber Laser

We propose and experimentally demonstrate a simple, passive, and self-referencing wavelength shift detection scheme for use in fiber Bragg grating sensing systems. The demodulation system is based on the interference between two modes in a polarization maintaining fiber loop mirror. Although it involves the use of an interference technique, it is stable compared with other conventional interference demodulators.

A fiber Bragg grating sensor demodulation technique using a polarization maintaining fiber loop mirror

Efficient asymmetric synthesis of 2,3-diamino-3-phenylpropanoic acid derivatives

We have demonstrated a channel-spacing- and wavelength-tunable multiwavelength fiber ring laser based on a semiconductor optical amplifier and a tunable comb filter. By employing the comb filter, multiwavelength operation of up to 23 laser lines with the signal-to-noise ratio over 25 dB and 0.8-nm wavelength spacing was demonstrated at room temperature. The results show that the multiwavelength operation is even and stable. Furthermore, the shift of lasing wavelength and wavelength spacing were continuously controllable in this system

Channel-Spacing- and Wavelength-Tunable Multiwavelength Fiber Ring Laser Using Semiconductor Optical Amplifier

A simple, passive, and self-referencing wavelength shift detection scheme, for use with fiber Bragg grating sensing systems, is described. The system is based on the use of a polarization maintaining fiber loop mirror.

Seunghwan Chung

Papers

Multi-kilowatt Single-mode Ytterbium-doped Large-core Fiber Laser

A fiber Bragg grating sensor demodulation technique using a polarization maintaining fiber loop mirror

Efficient asymmetric synthesis of 2,3-diamino-3-phenylpropanoic acid derivatives

Channel-Spacing- and Wavelength-Tunable Multiwavelength Fiber Ring Laser Using Semiconductor Optical Amplifier

A fiber Bragg grating sensor demodulation technique using a polarization maintaining fiber loop mirror