Analytical Instrumental Laboratory CHEM 314W Sources, Optics, and Monochromators Readings: Ch 7 1. Watch the laser video (minutes 3:45-­‐9:00) and describe in your own words how a laser works. 2. In the diagram of an echellette monochromator below, label the path of two monochromatic wavelengths after the diffraction grating. Using the information from above, correctly identify the paths for 488, 532 and 600 nm. Explain your reasoning and state the applicable equation. 1 Analytical Instrumental Laboratory CHEM 314W 3. Sources Characteristics of a good source 4. Line sources-­‐ one or few wavelengths Lasers Hollow Cathode Lamp (HCL) Electrodeless discharge lamp (EDL) 2 5. Continuum Sources-­‐ broad spectrum of wavelengths UV Visible IR 6. Wavelength Selection Filters Monochromators 1. 2. 7. Pieces of a Monochromator Entrance slits Collimating lens or mirror Prism or grating Focusing element Exit slit in focal plane 8. Prisms vs gratings Characteristic Prism Common Angular dispersion Dispersion 3 Analytical Instrumental Laboratory CHEM 314W Grating Analytical Instrumental Laboratory CHEM 314W 9. Prism Geometries 60° Prism-­‐ Bunsen prism 2x 30° Prism-­‐ cornu prism 30° Prism with mirrored back-­‐ Littrow prism 10. Grating Monchromators Typical dimensions Echellette 4 Analytical Instrumental Laboratory CHEM 314W Echelle 11. If polychromatic visible light is incident at an angle of 20 degrees on a 1400 grooves per millimeter echellette diffraction grating, determine the angle of first order diffraction of light with wavelengths of 488, 532, and 600nm. 12. Monochromator Performance Characteristics 1. Spectral purity 2. Dispersion Angular Linear 3. Resolving power 5 Analytical Instrumental Laboratory CHEM 314W 4. Light gathering power 14. Slits Characteristics and purpose monochromator slits 15. Slit width and resolution-­‐ No Free Lunch Bandwidth Effective bandwidth Take-­‐home message re slits: 6 Analytical Instrumental Laboratory CHEM 314W What did you learn today? What remains unclear?
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