Spectrophotometer Light Sources: Lasers

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

Laser Wavelengths

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.

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 Harris, Daniel C. Quantitative Chemical Analysis. 6 th ed. New York: W.H. Freeman and Company, 2003.

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.

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).

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. CO 2 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.

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.