Optical frequency combs are generated by a special type of laser that produces approximately 400,000 different colors. Indeed, an optical frequency comb is a white-light laser, containing every color in the visible spectrum. The most significant feature of the optical frequency comb is that the different frequencies of the output light are separated from the neighboring frequencies by precisely the same amount. Thus, the frequency comb acts as a optical ruler for light and allows for the measurement of the frequency of light in a way that is quite similar to the way one measures the length of an object by use of a normal ruler. If one knows the separation of the ticks of the ruler, one simply counts the number of ticks to determine the length of an object. Frequency combs solve the problem of measuring the frequency of light by simplifying it to a measurement of the small frequency difference between any two neighboring frequencies. The result is that optical frequency measurements are currently among the most precise measurements in all of science.
The atomic structure of lithium (Li) has aroused a significant amount of theoretical and experimental interest as a system in which precision atomic calculations and spectroscopic measurements can be united to yield scientifically significant results. Atomic calculations have reached the precision where, when combined with precision measurements, the effects of nuclear structure and quantum electrodynamics can be distinguished. Past experimental investigations of Li are in serious disagreement. We are currently working on an experiemnt to measure the isotope shifts, fine structure, hyperfine structure, and absolute optical frequencies of the D1 and D2 transitions in atomic Li. These measurements utilize a stabilized optical frequency comb that exploits the absolute frequency control and calibration provided by the optical frequency comb. This work has received funding from the National Institute of Standards and Technology Precision Measurements Grant (October 2008 - September 2012) and the National Science Foundation, Award Number:1305591.
The large spectral bandwidth and absolute frequency calibration provided by stabilized optical frequency comb make it an intriguing source for atomic spectroscopy. We have been working to extend and further explore the techniques of direct frequency- comb spectroscopy of two-photon transitions in atomic vapor cells. We have developed a theoretical description and understanding of two-photon velocity-selective excitation using direct frequency-comb spectroscopy by studying two-photon excitation of atomic rubidium. This work was done in collaboration with Derek Jackson Kimball's group at California State University - Easy Bay (CSEB). We have applied these techniques to the study of two-photon transitions in atomic potassium.
We are part of the Global Network of Optical Magnetometers for Exotic physics (GNOME). These magnetometers are looking for dark matter in the form of cosmic topological defects of ultra-light axion-like fields. We have constructed a spin-exchange-relaxation free (SERF) magnetometer station based on potassium atoms at Oberlin. More information regarding the collaboration can be found at the GNOME website This work has received funding from the National Science Foundation, Award Number:1707803.