Major Concepts of Physics PHY 102 – Lecture #  Syracuse University Lecture #19 How does a laser work? April 6 th Spring 2016 Prof. Liviu Movileanu Room 211, Physics Bldg., Major Concepts of Physics PHY102

1.Review from Lecture #18 2.Electron energy levels in a solid (Section 28.9) 3.How does a laser work? (Section 28.9) 4.Announcements Lecture objectives Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Orbitals and ground-state configuration Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Conceptual example 28.4 Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Energy levels for atomic subshells Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Major Concepts of Physics PHY 102 – Lecture #  Syracuse University Energy levels in bands

Major Concepts of Physics PHY 102 – Lecture #  Syracuse University Electron energy levels in conductors, semiconductors, and insulators

2 nd April 2007PHY 102: Major Concepts in Physics8 Absorption/Emission of Photons Photon energy E photon = E final - E initial The frequency f of the emitted photon must is determined by E photon = hf = (hc)/ Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

2 nd April 2007PHY 102: Major Concepts in Physics9LASER Light Amplification by Stimulated Emission of Radiation Laser beams are –Coherent –Intense –They have a single frequency –Narrow Can be generated in several ways Wide applications in science, technology and biomedical applications Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Spontaneous Vs Stimulated emission Major Concepts of Physics PHY 102 – Lecture #  Syracuse University Different photons with different Different photons with the same

2 nd April 2007PHY 102: Major Concepts in Physics11 Laser generation process Three steps –Energy absorption (pumping) Absorbs light energy / electrical energy Atoms in material move to higher energy state –Spontaneous emission Material emits light to move from higher (unstable) energy state to lower (more stable) energy state spontaneously –Stimulated emission Spontaneously emitted light triggers other high energy atoms to lose energy and emit light This step produces a highly coherent laser beam Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Major Concepts of Physics PHY 102 – Lecture #  Syracuse University Laser generation process

2 nd April 2007PHY 102: Major Concepts in Physics13 Review of concepts Energy levels of electrons bound to atoms are discrete –These finite, discrete values are unique to the atom (Emission/Absorption Spectroscopy) An atom at a higher energy state emits light (photons) to return to a lower energy state –Atoms are unstable at higher energy states Finite number of energy levels implies finite wavelengths of energy emitted or absorbed Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

2 nd April 2007PHY 102: Major Concepts in Physics14 Ruby Laser Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

PHY 102: Major Concepts in Physics15 Ruby laser First laser ever made (1960 by Ted Maiman, Hughes Aircraft company) Emits pulses of visible light at a wavelength of nm Used in holography, non-destructive testing, hair removal Three level laser Active laser gain medium is a synthetic ruby rod –Mostly made up of Al 2 O 3 and doped with Cr 3+ ions Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

2 nd April 2007PHY 102: Major Concepts in Physics16 Ruby Laser working Step 1: Excitation Step 2: Radiation Loss Step 3: Electron Accumulation (population inversion) Step 4: Spontaneous fall Step 5: Stimulated emission Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

2 nd April 2007PHY 102: Major Concepts in Physics17 Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

Major Concepts of Physics PHY 102 – Lecture #  Syracuse University He-Ne Laser

2 nd April Helium-Neon laser Small gas laser emitting nm light Gain medium is a mixture of helium and neon combined in a low pressure cavity Pumped by 1000 V, mA signal applied between cathode and anode Electrical signal pumps helium from ground to excited states High energy helium atoms collide with neon atoms in ground state till population inversion occurs This triggers lasing action Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

2 nd April 2007PHY 102: Major Concepts in Physics20 Applications of lasers Scientific –Spectroscopy –Microscopy –Photochemistry –Optical Tweezers Medical –Eye surgery (LASIK,…) –Dental procedures –Cosmetic surgery (hair removal) –Imaging Industrial and commercial –Cutting, welding –Optical communications –Rangefinder / surveying –Pattern engraving –Barcode readers –Laser printers –Photolithography Military –Laser Sight –Illuminator –Satellite obstruction and tracking Consumer electronics –CD, DVD reading and writing –Holographic displays Entertainment –Laser light shows,… Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

2 nd April 2007PHY 102: Major Concepts in Physics21 Simple problem on lasers Major Concepts of Physics PHY 102 – Lecture #  Syracuse University

1. Reading. 1. Reading. This material is partly covered in the textbook (Sections 28.8 and 28.9; pages ); Conceptual examples 28.4 and Homework. 2. Homework. HW#8 (Lectures 16-17) is due on this week’s workshop. HW#9 (Lectures 18-19), which is now posted online, is due on next week’s workshop. 3. Laboratory on this week. Workshop #10 – Lasers. 4. Next week topics. We move on “Nuclear Physics” (Chapter 29).Announcements Major Concepts of Physics PHY 102 – Lecture #  Syracuse University 22