1. Progress of the Laser Spectroscopy Program at Bridgewater State College Greg Surman, Brian Keith, and Edward Deveney Department of Physics, Bridgewater State College, Bridgewater, MA 02325 We report on the development of our laser spectroscopy program at BSC; our new 100 mW Toptica tunable diode laser and some preliminary measurements on Rb on our way toward Dopplerfree saturated absorption spectroscopy and 1-D cooling and trapping. Abstract Our Experimental Setup Results and Future Hyperfine versus Fine Structure 1. A.M. Fox. Dept. of Physics and Astronomy. PHY332: Atomic and Laser Physics. Lecture Notes. University of Sheffield, England. 2. Am. J. Phys., Vol. 64, No. 11, November 1996. Doppler-Free Saturated Absorption: Laser Spectroscopy. 3. Am. J. Phys., Vol. 65 (5), May 1997. Temperature Dependence of Doppler-broadening in rubidium : An undergraduate experiment. 4. Am. J. Phys. 72 (5), May 2004. The role of hyperfine pumping in multilevel systems exhibiting saturated absorption. 5. http://members.aol.com/WSRNet/tut/ut3.htm.http://members.aol.com/WSRNet/tut/ut3.htm References We have seen fluorescence, an indication of excitation of Rubidium. We have explored Doppler-broadened fine structure of Rb-87. We have crossed the pump and the probe beam and examined Doppler-broadened fine structure. We have encountered a lot of noise. Employ a lock-in amplifier to decrease the noise. Examine natural linewidth Totally eliminate Doppler broadening in order to fully examine the hyperfine structure of Rubidium Rubidium is excited! Fluorescence Exploring Rubidium Hyperfine Structure Transitions between the |1 ½ 3/2 > and |0 ½ ½ > states provide a good look at hyperfine structure Energy level transitions are stimulated by quantized amounts of energy Probabilities and rates of transitions between states are governed by Fermi’s Golden Rule Fermi’s Golden Rule Governs Transition Probabilities The Rate of Transition is independent of time This means that the probability of an atom decaying does not increase with time We can derive the transition matrix from the magnetic vector potential expanded about a specific time, say t = 0: We were looking for Hyperfine structure We found Doppler broadened Fine structure Fine structure is caused by spin-spin interactions (smaller…) Hyperfine structure is caused by interactions with the small magnetic moment of the nucleus (MUCH smaller!!!) Moving charged particles act like little magnets (dipoles) The field of these magnets interact with other particles in the atom Eureka!!! Excited about Excitation Laser Diode System A laser is an intense, coherent beam of light of a single wavelength. A diode laser works on the basis of population inversion. Population inversion can be reached by taking advantage of metastable states. A steady rate of electrons decay as a result, emitting photons in the process. Photons bounce off mirrors and some get through the partially reflected mirror. As more photons get created the probability that they will exist in the same state increases. This creates an intense, monochromatic beam. Pondering the hyperfine structure of the Rubidium atom Class 3b diode laser and other equipment Laser light sees some atoms in the gas cell as redshifted some as blueshifted, and some neither. This gives rise to the Doppler broadening of the natural linewidth which is gaussian in nature. Electrons orbiting nuclei can only be excited by precise energies. This broadening “masks” the natural linewidth. Doppler Broadening Experimentally observed spectral line of Rb-87 where f is increasing to the left. This line is Doppler broadened.