Efficient 1645-nm Er:YAG laser

We report a resonantly fiber-laser-pumped Er:YAG laser operating at the eye-safe wavelength of 1645 nm, exhibiting 43% optical efficiency and 54% incident slope efficiency and emitting 7-W average power when repetitively Q switched at 10 kHz. To our knowledge, this is the best performance (conversion efficiency and average power) obtained from a bulk solid-state Q-switched erbium laser. At a 1.1-kHz pulse repetition frequency the laser produces 3.4-mJ pulses with a corresponding peak power of 162 kW. Frequency doubling to produce 822.5-nm, 4.7-kW pulses at 10 kHz was performed to demonstrate the laser's utility.     

A weight-function approach for determining watershed initial conditions for combustion waves

In many generic combustion models, one finds that a combustionwave will develop with a specific wave speed. However, thereare possible initial temperature profiles which do not evolveinto such waves, but rather die out to the ambient temperature.There can exist, in some models, a clear distinction betweenthose initial conditions that do evolve into combustion wavesand those that do not; this is sometimes referred to as thewatershed initial condition. When fuel consumption is consideredto be negligible, analytical methods can be used to obtain theexact watershed. In this paper, we consider the problem of determiningpseudo-watersheds and ascertaining the relationship betweenthese pseudo-watersheds and the exact watersheds. In the processa novel weight-function approach for infinite spatial domainsis developed.     

Synthesis of cytotoxic cyanobactin,Wewakazole B

We report herein the synthesis of cytotoxic cyanobactin, Wewakazole B through an efficient solution-phase approach. The key steps of the synthesis are the macrocyclic lactamization of linear dodecapeptide and construction of two hexapeptides with three different substituted oxazole rings.     

Low-temperature direct ammonia fuel cells: Recent developments and remaining challenges

Low-temperature direct ammonia fuel cells (DAFCs) are fueled directly by ammonia, a carbon-neutral fuel stored in the liquid state under low pressure. Liquid ammonia has advantages over compressed hydrogen gas, including higher energy density and facilitated distribution and refill. The beginning-of-life performance reported until recently for low-temperature DAFCs has been substantially lower than that of polymer electrolyte fuel cells fueled by hydrogen. We discuss here promising recent advances in electrocatalyst development, cell performance, and cell performance stability for low-temperature DAFCs, including beginning-of-life peak power density of 420 mW/cm², and operation over several days at constant current. In addition, we describe technology gaps that must be closed for low-temperature DAFCs to achieve the performance required for practical applications.     

Mid-infrared ZnGeP2 parametric oscillator directly pumped by a pulsed 2 microm Tm-doped fiber laser

We have demonstrated what we believe to be the first mid-infrared optical parametric oscillator (OPO) pumped directly by a pulsed Tm-doped fiber laser. The Tm-fiber pump laser produces 30 ns pulses with a repetition rate of 30 kHz at a wavelength of 2 microm. The ZnGeP2 (ZGP) OPO produces 20 ns mid-IR pulses in the 3.4-3.9 microm and 4.1-4.7 microm spectral regions simultaneously. More than 658 mW of mid-IR output power has been generated with a total OPO slope efficiency greater than 35%.     

50-mJ,Q-switched, 2.09-microm holmium laser resonantly pumped by a diode-pumped 1.9-microm thulium laser

We report >50-mJ Q-switched energy output from a 2.09-microm Ho:YAG oscillator, resonantly pumped at 1.9-microm by a diode-pumped Tm:YLF laser. We demonstrate a Q-switched-to-normal-mode extraction efficiency of 100% at an output energy of 30 mJ and over 64% at the 50-mJ output level. Operating at 50 mJ (60 Hz) of output, a pulse width of 14 ns is achieved from the holmium oscillator, which corresponds to approximately 3.6 MW of peak power. At the 50-mJ output level, a beam-propagation factor M2 approximately 1.2 is achieved.     

5-W repetitively Q-switched Er:LuAG laser resonantly pumped by an erbium fiber laser

We report a high-average-power, near-diffraction-limited Er:LuAG laser generating 5 W of power at 1.648 microm in either cw or repetitively Q-switched operation. When the laser is Q switched at 9 kHz, we measure 0.52 mJ/pulse. The laser is end pumped by a 20-W erbium fiber laser and achieves >30% optical conversion efficiency and >40% incident slope efficiency. This is, to our knowledge, the highest performance (average power and conversion efficiency) obtained from a bulk solid-state erbium laser.