Scanning electron microscopy combined with microchemical analysis has evolved into one of the most widely used instruments in forensic science today. In particular, the environmental scanning electron microscope (SEM) in conjunction with energy dispersive spectroscopy (EDS), has created unique opportunities in forensic science in regard to the examination of trace evidence; i.e. the examination of evidence without altering the evidence with conductive coatings, thereby enabling criminalists to solve cases that were previously considered unsolvable. Two cold cases were solved at URI using a JEOL 5900 LV SEM in conjunction with EDS. A cold case murder and a cold missing person case will be presented from the viewpoint of the microscopist and will include sample preparation, as well as image and chemical analysis of the trace evidence using electron microscopy and optical microscopy.
In our previous work, we reported the optimum design for 10 km and 50 km length fibers for a distributed erbium doped fiber amplifier(DEDFA), based on a comprehensive computer model. This design contained an erbium doping concentration of 20 - 22 parts per billion, V of 1.775 with a signal wavelength of 1555 nm using low signal powers, -30 dBm, and bidirectionally pumping at 1480 nm. This paper investigates the effects of operating a DEDFA at the optimum doping concentration with large input signal power in which the ASE has a greater effect on the overall performance. The final issue addressed is the noise figure under similar circumstances.
With theoretical modeling, we optimize the fiber design for distributed erbium-doped fiber amplifiers which maintain a constant signal level across 10 - 100 km lengths. A constant signal level is maintained by fully inverting an amplifier with very low doping concentrations in the 10 - 50 ppb range. Included in the analysis are the pump wavelength, pumping configuration, erbium doping concentration, noise, temperature effects, macrobending loss and chromatic dispersion. We found that the optimum design would consist of a V value of 1.775 with a corresponding doping concentration of approximately 22 ppb.