William M Fairbank, Jr

Professor
B.A., Pomona College, 1968; Ph.D., Stanford University, 1974.
Fellow, American Physical Society.

Ultra Sensitive Analysis

Single Atom Detection
Single atoms are detected in our laboratory through the burst of photons they absorb and emit as they pass through a dye laser beam whose wavelength is in resonance with the atom. Recently we have also detected photon bursts from single fast ions for the first time. We are now developing a new radioisotope dating technique, called Photon Burst Mass Spectroscopy (PBMS), capable of measuring isotope ratios down to the 10-15 level.

A second method of single atom detection we have used is called resonance ionization spectroscopy (RIS). We are working on a new technique for ultrasensitive analysis of solid samples, called SIRIS (Sputter-Initiated RIS). In SIRIS an ion beam vaporizes by sputtering a microscopic portion of the sample. RIS is them used to selectively count the atoms of a particular element in this region of the sample.

Fundamental Physics
We have used the SIRIS method to look for atoms containing new elementary particles which may exist around us at very low concentrations but have so far escaped detection. A new SIMS instrument with a microfocus ion gun will allow us to apply SIRIS to the ultrasensitive analysis of semiconductor quantum wells, solar cells and devices grown at Colorado State University and in other laboratories. We are also collaborating with nuclear physicists to use both RIS and laser fluorescence methods to study short-lived nuclei created by accelerators.

Laser Spectroscopy
Our work in high-precision spectroscopy includes hyperfine structure and isotope shift studies and absolute wavelength measurements which test fundamental theories such as quantum electrodynamics. We are also investigating a new effect we discovered in resonance ionization with broadband lasers in which odd-mass isotopes have a different response from even isotopes.