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Wavelength Selection Devices 1. Absorption Filters 2. Interference Filters 3. Prism Monochromators 4. Grating Monochromators 5. Interferometers

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1. Absorption Filters Optical material containing an absorber that permits transmission only at certain wavelengths

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2. Interference Filter A sandwich of at least two parallel optical flats that transmit only rays that undergo constructive interference.

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3. Prism Monochromator Wavelength selection device containing a movable prism.

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Snells Law of Refraction n 1 sin 1 = n 2 sin 2

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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

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Reflection Grating:

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Linear Dispersion D l D l = f D a = dx/d where: f = focal length (of monochromator) x = distance (along focal plane)

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Spectral Bandpass (s or ) s = RLD w where: w = slit width (mm) s in nm Reciprocal Linear Dispersion (RLD) RLD = D l -1 =d/dx nm/mm

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Echelle prism ICP Camera

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Rowland Circle

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Limitations??

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5. Interferometer Allows multiple wavelengths to fall on the detector simultaneously. Corrects for interference patterns to calculate the signal at different wavelengths.

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Fabrey-Perot Interferometer

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Michelson Interferometer

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Interferometer Advantages 1. Fellgets Advantage (multiplex) 2. Jacquinots Advantage (throughput) 3. Wavelength Accuracy

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Interferometer Disadvantages 1. Fellgets Disadvantage (multiplex) 2. Low wavelengths 3. $$$ for high resolution