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Lasers in the Undergraduate Laboratory: Precision Measurement for the Masses


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Slides from my talk at the APS

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Lasers in the Undergraduate Laboratory: Precision Measurement for the Masses

  1. 1. Lasers in the Undergraduate Laboratory: Precision Measurement for the Masses<br />Chad Orzel<br />Union College Department of Physics and Astronomy<br />
  2. 2. History<br />1957-8: Townes & Schawlow, Gould proposals <br />1960: First (pulsed) ruby laser<br /> Theodore Maiman<br /> First (CW) gas laser (HeNe)<br />Javan, Bennett, Herriott<br />1962: First semiconductor laser<br /> Hall, Fenner, Kingsley, Soltys, Carlson<br />1970: CW heterostructure lasers<br />Alferov, Panish<br />
  3. 3. Applications<br />Medical:<br /> Laser surgery, laser therapy<br />Industrial: <br /> Laser cutting, welding<br />Telecommunications:<br /> Diode lasers<br /> Fiber lasers<br /> Fiber optics<br />
  4. 4. Lasers in Science<br />Lasers have become an indispensible tool in modern science:<br />Session B5: Five Legacies from the Laser<br />J15.00001 : Laser-combined STM and probing <br /> ultrafast transient dynamics<br />L10.00006 : Laser-Assisted Single Molecule Refolding<br />P10.00009 : A remote control for the C. elegans nervous system<br />Session V27: Focus Session: Attosecond Science and <br /> Strong Field Chemical Physics I<br />
  5. 5. Precision Measurement<br />My opinion: most impressive applications are in precision measurement<br />At this meeting:<br />Session Q27: Focus Session: New Trends in Spectroscopy III<br /> (Wed 11:15-2:15)<br />Session T4: Keithly Award Session: Precision Time <br /> and Frequency Measurements (Wed 2:30-5:30)<br />Laser spectroscopic methods, interferometry, pulse timing <br />World’s best measurements mostly involve lasers<br />
  6. 6. Lasers for Undergraduates<br />Can do laser measurements “on the cheap”<br />Discuss three experiments, make analogy to real techniques<br />1) Lunar Laser Ranging  Measuring Speed of Light<br />Intro mechanics/ sophomore modern physics<br />2) LIGO Index of Refraction of Air<br />Sophomore modern physics<br />3) Atomic Clocks Laser Spectroscopy of Rubidium<br />Junior/senior level advanced lab<br />Can’t match precision of real experiments<br /> Can get basic idea<br />
  7. 7. Resources<br />Lawrence University<br />Keck Foundation Report<br />2005<br />NECUSE Modern Optics Group<br />Laboratory Resource Book<br />1991<br />
  8. 8. Lunar Laser Ranging<br />Retro-reflector arrays left on Moon by Apollo missions<br />Round-trip time gives Earth-Moon distance<br />~ mm precision (out of 380,000,000 m)<br /><br />
  9. 9. Speed of Light Lab<br />Measuring the speed of light<br />Used in intro calculus-based mechanics class<br />sophomore modern physics class<br />Pulsed diode laser<br />Send beam across<br /> lab and back<br />Record pulse time<br /> w/ digital scope<br />
  10. 10. Speed of Light Data<br />Distance across lab:<br />15.87 ±0.02 m<br />Travel time:<br />52.8 ± 0.1 ns<br />c = 3.01 ± 0.07 ×108 m/s<br />Good agreement (<1%)<br />Simple procedure<br />Introduce instrumentation,<br /> uncertainty analysis<br />
  11. 11. LIGO<br />Laser Interferometer Gravitational wave Observatory<br />Kilometer-scale Michelson Interferometer<br />Detect small changes in length of arms<br />Sensitive to ~10-18m shifts<br /><br />Hanford, WA<br />Livingston, LA<br />
  12. 12. Michelson Interferometer<br />Sophomore modern<br /> physics lab<br />HeNe laser, PASCO<br /> sensor, computer<br />Commercial interferometer<br /> apparatus<br />Also use in Jr/ Sr elective<br /> Modern Classical Optics<br /> (Assemble from components, measure Na D line splitting)<br />
  13. 13. Index of Refraction of Air<br />
  14. 14. Interference Fringes<br />Record light intensity<br /> using computer<br />Count fringes as air<br /> pumped out of cell<br />18.25 ± 0.25 fringes<br />Dn = 1.92±0.03×10-4<br />
  15. 15. Index of Refraction Data<br />
  16. 16. Laser-Cooled Atomic Clocks<br />Second defined in terms of hyperfine<br /> splitting of Cs ground state<br />Ramsey interferometry,<br /> fountain geometry<br />Current standards good to<br />Basis for GPS navigation, etc.<br />NIST F-1<br />Boulder CO<br />
  17. 17. Laser Spectroscopy of Rubidium<br />Experiment for Physics 300:<br />“Modern Experimental Physics” <br />Required Jr/Sr level lab course<br />2-4 faculty lead students through<br /> 6-8 experiments in 10 weeks<br />Experiments include: X-ray diffraction, Rutherford scattering, PIXE<br />Mössbauer spectroscopy, molecular spectroscopy<br />Spectroscopy: Two-part experiment, 2-3 weeks:<br />1) Calibration of Fabry-Perot Interferometer<br />2) Measurement of Rb ground state hyperfine splitting<br />
  18. 18. Fabry-Perot Calibration<br />Determine free spectral<br /> range of homemade<br />confocal FPI<br />Follow procedure in <br /> AJP 73, 1135 (2005)<br />Students given paper, asked<br /> to determine procedure to<br /> be followed<br />
  19. 19. Fabry-Perot Calibration<br />Measure transmission spectrum<br /> using multi-mode HeNe<br />Inter-mode spacing measured by beat note<br />Serves as frequency reference for calibration of free spectral range<br />
  20. 20. Laser Spectroscopy of Rubidium<br />Free-running diode laser<br /> @780 nm (ThorLabs)<br />Scan frequency by<br /> current sweep<br />Use FPI as frequency<br /> reference<br />Students given lab from Brandenberger report, asked to determine<br /> procedure to be followed<br />Introduce hyperfine structure, laser spectroscopy<br />
  21. 21. Rubidium Spectrum<br />(out of 384 THz)<br />Ultimately limited by<br /> laser/Doppler width<br />Improve with grating,<br /> saturated absorption<br />(Student data: Bartell, Handin, Miles, Pathak 2009)<br />
  22. 22. Beyond Course Work<br />Laser experiments provide <br /> ample opportunities for<br /> research experience<br />Laser-related projects at Union<br />Laser cooling and trapping<br />Optical tweezers<br />Laser light scattering<br />Laser cleaning/ art restoration<br />Single-photon interference<br />etc.<br />(saturated absorption lock signal in Kr<br /> data recorded by B. Miles)<br />Essential capstone of undergraduate education<br />
  23. 23. Conclusions<br />Lasers are central to many modern precision measurements<br />“Cheap” and “easy” experiments can introduce idea of lasers<br /> as measurement tools in undergraduate laboratories<br />Opportunity to introduce modern techniques, data reduction,<br /> uncertainty analysis, etc.<br />Acknowledgements:<br />S. Maleki<br />J. Newman<br />J. Marr<br />J. Sheehan<br />C. Fletcher<br />R. Bonventre<br />B. Bartell<br />A. Handin<br />B. Miles<br />S. Pathak<br />