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11. Optical Pumping of Rubidium Vapor

Measurement of the Zeeman splittings of the ground state of the natural rubidium isotopes; measurement of the relaxation time of the magnetization of rubidium vapor; and measurement of the local geomagnetic field by the rubidium magnetometer. Rubidium vapor in a weak (~.01-10 gauss) magnetic field controlled with Helmholtz coils is pumped with circularly polarized D1 light from a rubidium rf discharge lamp. The degree of magnetization of the vapor is inferred from a differential measurement of its opacity to the pumping radiation.

In the first part of the experiment the energy separation between the magnetic substates of the ground-state hyperfine levels is determined as a function of the magnetic field from measurements of the frequencies of rf photons that cause depolarization and consequent greater opacity of the vapor. The magnetic moments of the ground states of the 85Rb and 87Rb isotopes are derived from the data and compared with the vector model for addition of electronic and nuclear angular momenta.

In the second part of the experiment the direction of magnetization is alternated between nearly parallel and nearly antiparallel to the optic axis, and the effects of the speed of reversal on the amplitude of the opacity signal are observed and compared with a computer model. The time constant of the pumping action is measured as a function of the intensity of the pumping light, and the results are compared with a theory of competing rate processes - pumping versus collisional depolarization.

Student Wiki: Optical Pumping of Rb Vapor

Download Lab Guide in PDF format

References (certificates required)

  1. W. E. Bell and A. L. Bloom,"Optical Detection of Magnetic Resonance in Alkali Metal Vapor", Phys. Rev., 107, pp 1559, (1957)
  2. A. Bloom, "Optical Pumping", Sci. Am., Oct, (1960)
  3. R. L. De Zafra, "Optical Pumping", Am. J. Phys., 28, (1960)
  4. R. Bernheim, Optical pumping; an introduction, (New York, W. A. Benjamin, 1965).
    • Pages 6-8 of this long (270 page) pdf file contain a table of contents.
  5. R. Benumof, "Optical Pumping Theory and Experiment", American Journal of Physics, 33, pp.151-160, (1965)
  6. M. Nagel and F. E. Haworth, "Advanced Laboratory Experiments on Optical Pumping of Rubidium Atoms-Part I: Magnetic Resonance", American Journal of Physics, 34, pp.553-558, (1966)
  7. S. G. Kukolich, "Time Depencend of Quantum-State Amplitudes Demonstrated by Free Precession of Spins", Am. J. Phys., 36, (1968)
  8. F. K. Richtmyer, E. H. Kennard, and J. N. Cooper, Introduction to Modern Physics 6th ed., (New York, McGraw-Hill, 1969), "Atomic Structure and Optical Spectra", pp. 269-305
  9. H. Semat and J. Albright, Introduction to Atomic and Nuclear Physics, (New York, Holt, Rinehart and Winston, 1972), "Optical Spectra and Electronic Structure", Chap. 9, pp. 256-300
  10. R. D. Evans, The Atomic Nucleus, (Malabar, FL, R.E. Krieger, 1982, c1955), "Atomic and Molecular Effects of Nuclear Moment Parity, and Statistics", Chap. 5, pp.181-187

Selected Resources

  1. Geomagnetism: The Magnetic Field of the Earth
  2. Optical Pumping Schematic
  3. Linear Polarizer
  4. Near and Far photodiode detectors
  5. 794.7nm narrow-band optical filter
  6. 3" 17.2cm focal length (near) field lens
  7. 3" 23.3cm focal length (far) field lens
  8. 1/4 wave retarder
  9. MIT variable attenuator
  10. Omega temperature indicator MDSS116-TC-A
  11. Tektronix CMC250 Frequency Counter
  12. MIT Rb lamp
  13. MIT Rb lamp power supply
  14. MIT 3-axis helmholtz coils
  15. MIT helmholtz coil current supply
  16. EG&G HUV 4000B Silicon Photodiode
  17. Circuit Diagram for Lamp Power Supply Panel
  18. Sanyo DL3038-011 Laser Diode (635nm)
  19. Spectra Physics Current Pre-amplifier (Mo.# 70710)
  20. ThorLabs LDC 500 Laser Diode Controler
  21. Documentation on the Power Supplies for MIT Rubidium discharge lamps (By Jim Gray)
  22. Condor Linear DC Power Supplies - 5V @ 1.5A
  23. Asahi Model AP-101 Digital Panel Meter
  24. Omega DP24-T Thermocouple Meter
  25. W. E. Bell, A.L. Bloom and J. Lynch, "Alkali Metal Vapor Spectral Lamps", Review of Scientific Instruments, 32, pp. 688-692, (1961).
  26. R. G. Brewer, "High Intensity Low Noise Rubidium Light Source", Rev. Sci. Instr., 32, pp. 1356-1358, (1961).
  27. D. Shernoff, "Mercury Lamp for Optical Pumping", Rev. Sci. Instr. Vol. 40, pp.
    1418-1419, 1969
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