A dielectric-film-coated asymmetric single nanoslit is proposed to realize broadband unidirectional generation of surface plasmon polaritons (SPPs). Due to the tight field confinements by the dielectric film and the deep groove in the asymmetric single slit, the transmittance of the SPPs in the groove to the left side considerably decreases. This greatly suppresses the left-propagating SPP generation efficiency for a broad bandwidth. Meanwhile, the right-propagating SPP generation efficiency has a flat spectra range because of the low transmittance, too. So the unidirectional SPP generation with bandwidth of > 100 nm around lambda = 750 nm is experimentally achieved for the device lateral dimension of only 865 nm. (C) 2011 Optical Society of America
Absorption photometers for real time application have been available since the 1980s, but the use of filter-based instruments to derive information on aerosol properties (absorption coefficient and black carbon, BC) is still a matter of debate. Several workshops have been conducted to investigate the performance of individual instruments over the intervening years. Two workshops with large sets of aerosol absorption photometers were conducted in 2005 and 2007. The data from these instruments were corrected using existing methods before further analysis. The inter-comparison shows a large variation between the responses to absorbing aerosol particles for different types of instruments. The unit to unit variability between instruments can be up to 30% for Particle Soot Absorption Photometers (PSAPs) and Aethalometers. Multi Angle Absorption Photometers (MAAPs) showed a variability of less than 5%. Reasons for the high variability were identified to be variations in sample flow and spot size. It was observed that different flow rates influence system performance with respect to response to absorption and instrumental noise. Measurements with non absorbing particles showed that the current corrections of a cross sensitivity to particle scattering are not sufficient. Remaining cross sensitivities were found to be a function of the total particle load on the filter. The large variation between the response to absorbing aerosol particles for different types of instruments indicates that current correction functions for absorption photometers are not adequate.