Simultaneous reduction of particulate matter and NOx emissions using 4-way catalyzed filtration systems

The next generation of diesel emission control devices includes 4-way catalyzed filtration systems (4WCFS) consisting of both NOx and diesel particulate matter (DPM) control. A methodology was developed to simultaneously evaluate the NOx and DPM control performance of miniature 4WCFS made from acicular mullite, an advanced ceramic material (ACM), that were challenged with diesel exhaust. The impact of catalyst loading and substrate porosity on catalytic performance of the NOx trap was evaluated. Simultaneously with NOx measurements, the real-time solid particle filtration performance of catalyst-coated standard and high porosity filters was determined for steady-state and regenerative conditions. The use of high porosity ACM 4-way catalyzed filtration systems reduced NOx by 99% and solid and total particulate matter by 95% when averaged over 10 regeneration cycles. A "regeneration cycle" refers to an oxidizing ("lean") exhaust condition followed by a reducing ("rich") exhaust condition resulting in NOx storage and NOx reduction (i.e., trap "regeneration"), respectively. Standard porosity ACM 4-way catalyzed filtration systems reduced NOx by 60-75% and exhibited 99.9% filtration efficiency. The rich/lean cycling used to regenerate the filter had almost no impact on solid particle filtration efficiency but impacted NOx control. Cycling resulted in the formation of very low concentrations of semivolatile nucleation mode particles for some 4WCFS formulations. Overall, 4WCFS show promise for significantly reducing diesel emissions into the atmosphere in a single control device. © 2013 American Chemical Society.

Wideband-tuneable, nanotube mode-locked, fibre laser.

Ultrashort-pulse lasers with spectral tuning capability have widespread applications in fields such as spectroscopy, biomedical research and telecommunications. Mode-locked fibre lasers are convenient and powerful sources of ultrashort pulses, and the inclusion of a broadband saturable absorber as a passive optical switch inside the laser cavity may offer tuneability over a range of wavelengths. Semiconductor saturable absorber mirrors are widely used in fibre lasers, but their operating range is typically limited to a few tens of nanometres, and their fabrication can be challenging in the 1.3-1.5 microm wavelength region used for optical communications. Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness. Here, we engineer a nanotube-polycarbonate film with a wide bandwidth (>300 nm) around 1.55 microm, and then use it to demonstrate a 2.4 ps Er(3+)-doped fibre laser that is tuneable from 1,518 to 1,558 nm. In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems.

Gain saturation in 60-fs mode-locked semiconductor laser

A passively mode-locked optically-pumped InGaAs/GaAs quantum well laser with an intracavity semiconductor saturable absorber mirror emits sub-100-fs pulses. Pulse energy declines steeply as pulse duration is reduced below 100 fs due to gain saturation. © 2010 Optical Society of America.