Physics II Lab w answers_Part_64

Physics II Lab w answers_Part_64 - Appendix Lasers...

Info icon This preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
139 Appendix: Lasers Introduction: The light emitted from a conventional light source is(like sodium lamp) is said to be incoherent because the radiation emitted from different atoms do not, in general, bear any definite phase relationship with each other. On the other hand, the light emitted from a laser has a very high degree of coherence and is almost perfectly collimated. Laser is an acronym for Light Amplification by Stimulated Emission of Radiation. The basic principle involved in lasing action is the phenomenon of stimulated emission, which was predicted by Einestein in 1917. Einestein argued that when an atom is in the excited state, it can make a transition to a lower energy state through the emission of electromagnetic radiation; however, in contrast to the absorption process, the emission ca be occur in two different ways: i). The first is referred to as spontaneous emission in which an atom in the excited state emits radiation even in the absence of any incident. It is thus not stimulated by any incident signal but occurs spontaneously. ii) The second is referred to as stimulated emission in which an incident signal of appropriate frequency triggers an atom in an excited state to emit radiation. Using the phenomenon of stimulated emission, C.H. Townes and A.H. Schawlow, in 1958, worked out the principle of the laser. Stimulated Emission: Consider a gas enclosed in a vessel containing free atoms having a number of energy levels, at least one of which is metastable. By shining white light into this gas many can be excited, through resonance, from the ground state to excited states. As the electron drop back, many of them will become trapped in the metastable states. If the pumping light is
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern