Slides from my talk at the APS

1. Lasers in the Undergraduate Laboratory: Precision Measurement for the Masses Chad Orzel Union College Department of Physics and Astronomy

2. History 1957-8: Townes & Schawlow, Gould proposals 1960: First (pulsed) ruby laser Theodore Maiman First (CW) gas laser (HeNe) Javan, Bennett, Herriott 1962: First semiconductor laser Hall, Fenner, Kingsley, Soltys, Carlson 1970: CW heterostructure lasers Alferov, Panish

3. Applications Medical: Laser surgery, laser therapy Industrial: Laser cutting, welding Telecommunications: Diode lasers Fiber lasers Fiber optics

4. Lasers in Science Lasers have become an indispensible tool in modern science: Session B5: Five Legacies from the Laser J15.00001 : Laser-combined STM and probing ultrafast transient dynamics L10.00006 : Laser-Assisted Single Molecule Refolding P10.00009 : A remote control for the C. elegans nervous system Session V27: Focus Session: Attosecond Science and Strong Field Chemical Physics I

5. Precision Measurement My opinion: most impressive applications are in precision measurement At this meeting: Session Q27: Focus Session: New Trends in Spectroscopy III (Wed 11:15-2:15) Session T4: Keithly Award Session: Precision Time and Frequency Measurements (Wed 2:30-5:30) Laser spectroscopic methods, interferometry, pulse timing World’s best measurements mostly involve lasers

6. Lasers for Undergraduates Can do laser measurements “on the cheap” Discuss three experiments, make analogy to real techniques 1) Lunar Laser Ranging  Measuring Speed of Light Intro mechanics/ sophomore modern physics 2) LIGO Index of Refraction of Air Sophomore modern physics 3) Atomic Clocks Laser Spectroscopy of Rubidium Junior/senior level advanced lab Can’t match precision of real experiments  Can get basic idea

7. Resources Lawrence University Keck Foundation Report 2005 NECUSE Modern Optics Group Laboratory Resource Book 1991

8. Lunar Laser Ranging Retro-reflector arrays left on Moon by Apollo missions Round-trip time gives Earth-Moon distance ~ mm precision (out of 380,000,000 m) http://www.physics.ucsd.edu/~tmurphy/apollo/

9. Speed of Light Lab Measuring the speed of light Used in intro calculus-based mechanics class sophomore modern physics class Pulsed diode laser Send beam across lab and back Record pulse time w/ digital scope

10. Speed of Light Data Distance across lab: 15.87 ±0.02 m Travel time: 52.8 ± 0.1 ns c = 3.01 ± 0.07 ×108 m/s Good agreement (<1%) Simple procedure Introduce instrumentation, uncertainty analysis

11. LIGO Laser Interferometer Gravitational wave Observatory Kilometer-scale Michelson Interferometer Detect small changes in length of arms Sensitive to ~10-18m shifts http://www.ligo.caltech.edu/ Hanford, WA Livingston, LA

12. Michelson Interferometer Sophomore modern physics lab HeNe laser, PASCO sensor, computer Commercial interferometer apparatus Also use in Jr/ Sr elective Modern Classical Optics (Assemble from components, measure Na D line splitting)

13. Index of Refraction of Air

14. Interference Fringes Record light intensity using computer Count fringes as air pumped out of cell 18.25 ± 0.25 fringes Dn = 1.92±0.03×10-4

15. Index of Refraction Data

16. Laser-Cooled Atomic Clocks Second defined in terms of hyperfine splitting of Cs ground state Ramsey interferometry, fountain geometry Current standards good to Basis for GPS navigation, etc. NIST F-1 Boulder CO

17. Laser Spectroscopy of Rubidium Experiment for Physics 300: “Modern Experimental Physics” Required Jr/Sr level lab course 2-4 faculty lead students through 6-8 experiments in 10 weeks Experiments include: X-ray diffraction, Rutherford scattering, PIXE Mössbauer spectroscopy, molecular spectroscopy Spectroscopy: Two-part experiment, 2-3 weeks: 1) Calibration of Fabry-Perot Interferometer 2) Measurement of Rb ground state hyperfine splitting

18. Fabry-Perot Calibration Determine free spectral range of homemade confocal FPI Follow procedure in AJP 73, 1135 (2005) Students given paper, asked to determine procedure to be followed

19. Fabry-Perot Calibration Measure transmission spectrum using multi-mode HeNe Inter-mode spacing measured by beat note Serves as frequency reference for calibration of free spectral range

20. Laser Spectroscopy of Rubidium Free-running diode laser @780 nm (ThorLabs) Scan frequency by current sweep Use FPI as frequency reference Students given lab from Brandenberger report, asked to determine procedure to be followed Introduce hyperfine structure, laser spectroscopy

21. Rubidium Spectrum (out of 384 THz) Ultimately limited by laser/Doppler width Improve with grating, saturated absorption (Student data: Bartell, Handin, Miles, Pathak 2009)

22. Beyond Course Work Laser experiments provide ample opportunities for research experience Laser-related projects at Union Laser cooling and trapping Optical tweezers Laser light scattering Laser cleaning/ art restoration Single-photon interference etc. (saturated absorption lock signal in Kr data recorded by B. Miles) Essential capstone of undergraduate education

23. Conclusions Lasers are central to many modern precision measurements “Cheap” and “easy” experiments can introduce idea of lasers as measurement tools in undergraduate laboratories Opportunity to introduce modern techniques, data reduction, uncertainty analysis, etc. Acknowledgements: S. Maleki J. Newman J. Marr J. Sheehan C. Fletcher R. Bonventre B. Bartell A. Handin B. Miles S. Pathak