Transcript Slide 1
Wavelength Selection Devices 1. 2. 3. 4. 5. Absorption Filters Interference Filters Prism Monochromators Grating Monochromators Interferometers 1. Absorption Filters Optical material containing an absorber that permits transmission only at certain wavelengths 2. Interference Filter A “sandwich” of at least two parallel optical flats that transmit only rays that undergo constructive interference. 3. Prism Monochromator Wavelength selection device containing a movable prism. Snell’s Law of Refraction n1sin Θ1 = n2sin Θ2 4. Grating Monochromator Wavelength selection device based on the constructive interference of light rays that have traveled different differences to reach the same point. Work via: (1) transmission, or (2) reflection Reflection Grating: Linear Dispersion Dl Dl = f × Da = dx/dλ where: f = focal length (of monochromator) x = distance (along focal plane) Reciprocal Linear Dispersion (RLD) RLD = Dl-1 Spectral Bandpass (s or Δλ) s = RLD × w =dλ/dx where: nm/mm w = slit width (mm) s in nm Camera Echelle prism ICP Rowland Circle Limitations?? 5. Interferometer Allows multiple wavelengths to fall on the detector simultaneously. Corrects for interference patterns to calculate the signal at different wavelengths. Fabrey-Perot Interferometer Michelson Interferometer Interferometer Advantages 1. Fellget’s Advantage (multiplex) 2. Jacquinot’s Advantage (throughput) 3. Wavelength Accuracy Interferometer Disadvantages 1. Fellget’s Disadvantage (multiplex) 2. Low wavelengths 3. $$$ for high resolution