1. Spectrophotometer Light Sources: Lasers

2. L.A.S.E.R. • Acronym for: light amplification by stimulated emission of radiation • Basic principle of lasing: population inversion • Laser light is typically monochromatic – emitting only one wavelength • Cost as varied as possible wavelength range: from two-dollar pointers to million-dollar devices www.howstuffworks.com/laser www.answers.com/topic/laser

3. Laser Wavelengths www.howstuffworks.com/laser

4. Energy Absorption • Energy absorption propels molecules to a higher energy level. • In order for the molecules to move to the excited state, they must absorb energy from heat, light or electricity. www.howstuffworks.com/laser

5. Population Inversion • Higher energy levels must be more “populated” than lower levels in order for lasing to occur. • Once in the excited state, the molecule will begin returning to the ground state, resulting in the release of energy in the form of a photon. - www.howstuffworks.com/laser - Harris, Daniel C. Quantitative Chemical Analysis. 6th ed. New York: W.H. Freeman and Company, 2003.

6. Energy Emission • From the excited state, molecules begin to relax, releasing energy in the form of photons of specific wavelengths (colors), determined by the state of the electron’s energy at release. www.howstuffworks.com/laser

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8. Properties of Laser Light • Consists of only one wavelength (monochromatic). • Wave fronts of all the photons are “launched in unison,” all moving in step with the others (coherent). • Strong, concentrated, tight beam (directional). www.howstuffworks.com/laser

9. Types of Lasers • excimer:reactive gases (e.g.: chlorine and fluorine), mixed with inert gases (e.g.: argon, krypton or xenon). When electrically stimulated, a pseudo molecule (dimer) is produced. (λ = UV range when lased)* • gas:primary output of visible red light. CO2 lasers emit energy in the far-infrared; used for cutting hard materials. * UV light is most difficult to obtain due to it high energy wavelength. www.howstuffworks.com/laser

10. Types (cont.) • solid-state:lasing material distributed in a solid matrix (λ=1064nm; IR) • dye: use complex organic dyes (e.g.: rhodamine 6G) in liquid solution or suspension as lasing media (broad wavelength range). • semiconductor: (aka: diode lasers); are not solid-state lasers, but electronic devices. Generally very small and use low power, found in laser printers and cd-players. www.howstuffworks.com/laser