Physics 321 - HeNe Laser Lab Report

Physics 321 - HeNe Laser Lab Report - Alex Ryng 10/01/07...

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Alex Ryng 10/01/07 Physics 321 Professor Dunham The Helium Neon Laser The helium-neon laser is a common component of scientific instrumentation; this lab concentrates on understanding and gaining facility in using a HeNe laser through a hands on experience with the various optical components of a working laser. Demonstration of proper alignment to achieve lasing and the experimental replication of Malus’s Law complete the introduction to HeNe lasers.
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I. INTRODUCTION Experimental physics, at the beginner level, requires the ability to set up, fine tune, and reproduce desired results consistently. Understanding the principles of HeNe laser operation, including the energy pump, optical gain medium, and optical resonator, is the basis of the experiment. The 3-mW HeNe laser gets its power from a 1400-V DC power supply that maintains a glow discharge in the glass tube. The discharge current of 5 mA is limited by a 91-kΩ ballast resistor. The discharge can act as an optical gain medium once a population inversion has been established; a population inversion occurs when incident photons on the gas discharge will have a higher probability of being replicated in the stimulated emission process rather than the absorption process. Creating an optical resonator with two highly reflective mirrors placed along the axis of discharge, emitted photons along the axis of the cavity interact with each other in a process called stimulated emission, emitting 6328 Å light. The photon multiplication process creates many photons of the same polarization and wavelength that reflect off the mirrors in the optical resonator structure, creating a lasing action. II. PROCEDURE Setting up the lab, although time consuming, is very methodical. Using a commercial HeNe laser to assist in alignment and an alignment note card to help keep the alignment laser beam at a uniform height above the table, I was able to fine tune the alignment laser from the source to the last high reflectivity cavity mirror and back to the aperture of the commercial laser. Adjusting the last hemispherical mirror before the HeNe plasma tube and the distance between the mirror on the translation stage and the brewster window, I honed in on a series of converging and diverging concentric rings that
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This lab report was uploaded on 04/18/2008 for the course PHYS 321 taught by Professor Dunham during the Spring '08 term at Middlebury.

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Physics 321 - HeNe Laser Lab Report - Alex Ryng 10/01/07...

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