cell.html

In our first experiment, a vapor cell polarimeter (photograph of layout; schematic diagram) constructed by Kyle Downey '96 and others was used to measure absorption and Faraday rotation of laser light interacting with thallium in a heated quartz vapor cell. A 1.283m external cavity diode laser (ECDL) drives both magnetic dipole (M1) and electric quadrupole (E2) transitions between the 6P_1/2 and 6P_3/2 states. Using the M1 absorptivity to calibrate the number density (the M1 linestrength is known precisely without detailed wavefunction knowledge), our measurement of the relative E2 absorptivity provides a test of the atomic wavefunctions required to calculate this quantity. Precise knowledge of E2 is also essential in the precision measurement of PNC within this transition. Here is a sample of recent data (Faraday Rotation[F=0] ; Transmission signal[F=0]; Faraday Rotation[F=1]; Transmission Signal[F=1]) and a nonlinear least squares fit to a function which in each case includes a superposition of four Voigt profiles (two excited-state hyperfine sublevels for each of two isotopes). This measurement was the subject of Leo Tsai ('98) thesis. Peter Nicholas ('98) also contributed substantially to the development of software for data acquisition and analysis. This experiment was completed in the summer of 1998, and a paper describing the results has recently appeared in Physical Review A (see Pub. #1 below).

II. Vapor cell spectroscopy of Tl at 378 nm using a frequency-doubled diode laser
In our second experiment, we used a commercial bowtie external resonant cavity (manufactured by Laser Analytical Systems), to generate. Now we can turn our attention to the 'strongly allowed' electric dipole transition in thallium ( 6P_1/2- 7S_1/2), still using the vapor cell apparatus (see relevant Energy levels). Given the large hyperfine splittings (HFS) in the relevant states, and the large isotope shift, all six absorption peaks are resolved even in the presence of substantial Doppler broadening. There is a bit of a checkered history in the 7S_1/2state HFS measurements, which we have resolved, and we have improved the measurement of the isotope shift by a factor of 50. By scanning our diode laser over ~25 GHz, we can tune the UV light continuously over the complete HFS of both ground and excited states. Since the ground-state HFS has been measured to very high precision, it can be used to calibrate our excited-state HFS measurement. We also monitor the transmission of two independent Fabry-Perot cavities for frequency linearization and calibration. (see schematic, photo of optical system). Our postdoc David Richardson, with able help of Rob Lyman ('99) and more recently Andrew Speck ('00), we worked to collect and analyze hundreds of UV spectra to determine HFS and isotope shift values with unprecedented precision. Please see publication #2 below which describes these results.