1. Light Emission

2. Today’s Topics Excitation Emission Spectra Incandescence –Absorption Spectra

3. Excitation/De-Excitation Electron raised to higher energy level Electron emits photon when it drops back down to lower energy level E~f E = hf (h is Planck’s constant – more later) h = 6.626 x 10 -34 Js

4. Incandescence Glowing while at a high temperature Caused by Electrons emit Peak frequency depends on Intensity of radiation depends on Frequency is proportional to the absolute temperature

5. Emission Spectra Continuous Spectra – Bright Line Spectra

6. Absorption Spectra

7. Spectrum produced by sun is not continuous – Similar lines in spectra produced by Lines indicate the sun and stars are Joseph Fraunhofer (1787-1826) Fraunhofer Lines

8. Hydrogen

9. Fluorescence Photon Electron

10. Fluorescent Lamp

11. LASER L A through S E of R

12. Lasing Medium is Pumped Optic or electric pumping Increased population inversion

13. Stimulated Emission Incoming photon whose frequency corresponds Emitted photon --

14. Laser Optical Pumping Multiple Reflections Coherent Light

15. Interference in CDs Laser shines light onto track of CD Discs have “pits” in the surface Sensor reads signal from laser CD Burners

16. Constructive Interference When entire beam reflects from the “pit” or when entire beam reflects from the “land” – constructive interference results – “on”

17. Destructive Interference “Pits” are ¼ above the “land” When part of beam reflects from “pit” and part from “land” Destructive interference – interpreted as “off”

18. Laser Scans Disc Intensity of the reflected light varies as the disc rotates. Intensity is measured and interpreted as a series of ones and zeros (digital information). Information is then relayed to other systems that interpret it.

19. Holography

20. Viewing a Hologram