Lecture17

A electron e a e a e4 fast spontaneous transifon

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Unformatted text preview: id relaxaFon to ground state 19 OpFcal pumping E4 pump transiFon Fast, spontaneous transiFon E3 “metastable” state SFmulated emission E2 E1 rapid relaxaFon to ground state Strong opFcal excitaFon by an incoherent light source (flash lamp for example) 20 2010: The 50th anniversary of the laser The first laser: Theodore Maiman at Hughes Research Laboratories, May 16, 1960 Ruby laser Flash lamp (opFcal pumping) 694.3 nm Diagram of a ruby laser from LLNL document "Laser Programs, the first 25 years". 21 Electrical pumping Bias voltage accelerates electrons into a gas. EnergeFc electrons collide with atoms. Electrons excite atoms into excited state * A ! A* electron e + A ! e" + A E4 Fast, spontaneous transiFon V  ­ + E3 Hot electron excites populaFon into E4 E1 SFmulated emission E2 rapid relaxaFon to ground state 22 Resonant energy transfer Energy levels between atoms are very closely spaced. Collisions between atoms transfer energy from He (starter gas) to Neon (lasing gas) collisions E4 laser transiFon (visible) collisions laser transiFon (infrared) Ground state Ground state Helium Neon 23 CharacterisFcs of laser light I !f f •  Monochromacity: The linewidth of laser light is much smaller than convenFonal sources. Source Wavelength λ0 Linewidth Δλ (nm) Frequency f0 (Hz) Bandwidth Δf (Hz) Na discharge lamp 589.6 0.1 5x1014 9x1010 Cd low pressure lamp 643.8 0.0013 4.7x1014 9.4x108 He ­Ne Laser 632.8 1x10 ­8 4.7x1014 7.5x103 24 Natural broadening E2 E2 !E " ! / # E1 E1 Level E2 has a limite...
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This document was uploaded on 02/04/2014.

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