W. Z. Zhao

A computer-based digital feedback control of frequency drift of multiple lasers

We report a method to monitor and control laser frequencies with an optical cavity and a digital feedback system. A frequency-stabilized He–Ne laser provides the reference that is transferred to several other lasers using a scanning Fabry–Perot cavity. A personal computer-based multifunction data acquisition system generates the scan wave form, and reads the detector outputs synchronously with the cavity scan. The computer determines the positions of all of the peaks in the scan, and generates output signals to control the laser frequencies. It also provides a visual display of cavity spectra. We have successfully used the setup to achieve a long-term lock of the lasers for magneto-optical trapping of radioactive francium atoms.

7S(1/2) ? 9S(1/2) two-photon spectroscopy of trapped francium.

We report on the spectroscopic measurement of the {sup 210}Fr 9{ital S}{sub 1/2} energy obtained by two-photon excitation of atoms confined and cooled in a magneto-optic trap. The resonant intermediate level 7{ital P}{sub 3/2} is the upper state of the trapping transition. We have measured the energy difference between the 9{ital S}{sub 1/2} state and the 7{ital S}{sub 1/2} ground state to be 25671.021{plus_minus}0.006 cm{sup {minus}1}. {copyright} {ital 1996 Optical Society of America.}We report on the spectroscopic measurement of the (210)Fr 9S(1/2) energy obtained by two-photon excitation of atoms confined and cooled in a magneto-optic trap. The resonant intermediate level 7P(3/2) is the upper state of the trapping transition. We have measured the energy difference between the 9S(1/2) state and the 7S(1/2) ground state to be 25 671.021 +/- 0.006 cm(-1).

Laser trapping of radioactive francium atoms

Abstract The difficult problem of quickly slowing and cooling nuclear reaction products so that they can be injected into a laser trap has been solved by several groups and there are now strong efforts to work with the trapped atoms. The atoms are confined in the trap to a small spatial volume of the order of 1 mm3, but more importantly, they are also confined in velocity, which makes them an ideal sample for spectroscopic measurements with other lasers. We have recently trapped radioactive francium and have embarked on a program to further study the francium atom as a prelude to a test of the Standard Model analogous to previous work with Cs. Our sample of 3 min 210Fr now contains over 20 000 atoms, and is readily visible with an ordinary TV camera. We work on-line with the accelerator, and continuously load the trap to replace losses due to decay and collisions with background gas. We have maintained a sample of Fr atoms in the trap for over 10 hours, with occasional adjustment of the trapping laser frequency to account for drifts. The proposed test of the Standard Model will require accurate calculation of its atomic properties. We are currently testing these calculations by measuring other predicted quantities.