Summer 2021 Undergrad Research

After having no undergraduates in the laboratory last summer due to the pandemic, thankfully it was possible to have them back this summer. We had a great group this summer:

Allison Earnhardt from Purdue in the UM-Physics REU program
Joel Greenfield
Jacob McMurtry
Claire Montague from Hamilton College, supported by an NSF REU supplement
Jason Zeng, supported by an NSF REU supplement

Diode Frequency Combs

We have demonstrated new, miniaturized lasers known as diode frequency combs. These lasers provide a platform to launch precision measurement and spectroscopy techniques out of the lab and into widespread use. The goal is to demonstrate that these lasers can be used to rapidly acquire absorption spectra of gaseous molecules to monitor the concentrations of hazardous gasses or environmental pollutants in real time. 

Artists depiction of the setup for performing dual comb spectroscopy using a diode laser.

Frequency combs are lasers which emit a spectrum of many discrete, equally spaced colors. These lasers are useful for a variety of applications. In particular, they can be used to measure the properties of molecules and atoms with great precision, stabilize two atomic clocks against each other, and have even been employed to measure the radius of the proton.

When the output of two combs are combined, high resolution absorption spectra of molecules in a gas can be acquired with a combination of rapid data acquisition time and precision which is not achievable any other way. This technique, known as dual-comb spectroscopy, is an ideal candidate for use in accurately measuring gas concentrations in real time in a variety of settings. For instance, one can imagine using dual-comb spectroscopy to monitor the environmental emissions of an oil well or the concentration of noxious gasses in a hazardous environment.

Typically, a host of complex laser equipment to generate the ‘comb,’ rendering combs impractical for applications outside of the laboratory. Our new lasers require no such equipment, with two dozen devices fitting roughly within a grain of rice. Our combs are efficient enough to be powered by two household AA batteries, cheap to manufacture, and can provide the platform for miniature precision spectrometers to be widely deployed.

We have shown that our devices fit the definition of frequency combs. Furthermore, we used two lasers on the same device to conduct dual-comb spectroscopy and take precision absorption spectra of hydrogen cyanide gas. Finally, we showed that these combs can be battery powered, proving that our combs are ready to take precision spectroscopy outside of the laboratory.

M. W. Day, M. Dong, B. C. Smith, R. C. Owen, G. C. Kerber, T. Ma, H. G. Winful, and S. T. Cundiff, “Simple Single-Section Diode Frequency Combs,”  APL Photonics 5, 121303 (2020) (2020).