1. 7.2 Notes The Microscope continued

2. Objectives Appreciate how a polarizing microscope is designed to characterize polarized light Appreciate how a microspectrophotometer can be used to examine trace physical evidence Compare and contrast the image formation mechanism of a light microscope to that of a scanning electron microscope Outline some forensic applications of the scanning electron microscope

3. Microspectrophotometer Combination of computerized spectrophotometer and microscope Allows for viewing a small particle under the microscope Allows for the a beam of light directed at the particle to obtain an absorption spectrum

4. Microspectro. cont. Visual inspection of color is essential in examining paint, fiber, ink evidence Used to distinguish counterfeit and authentic currency by comparing spectral patterns of inked lines on currency Useful in determining fiber and paint chip chemicals

5. Scanning Electron Microscope (SEM) A beam of electrons on the specimen from a tungsten filament Electrons are focused by electromagnets The upper layers of the specimen rebound electrons Rebounded electrons collected by a cathode ray tube or the TV

6. SEM cont. Emitted electrons are converted into an image High magnification, high resolution, great depth of focus 10x to 100,000 x Can be used to determine elemental composition of a specimen by coupling with an X-ray Can be used to tell if a suspect has recently fired a gun