Mid-IR Lasers for High Ultra-Precision Spectroscopy Instruments
MDL lasers have enabled measurements of greenhouse gases, their isotopes, and reactive intermediates in the troposphere and the stratosphere (OH, H2O, HDO, CH4, HCl, and C2H6) on the order of parts-per-trillion (ppt) concentrations via integrated cavity output spectroscopy (ICOS) and cavity ring-down spectroscopy techniques. Tunable laser absorption spectroscopy (TLAS) is a versatile and robust method for gas sensing with applications ranging from industry to Earth and planetary science. Together with techniques such as wavelength-modulation spectroscopy, TLAS with simple absorption cells is capable of detection limits on the order of parts per million, which is sufficient for many applications of interest. However, for weaker-absorbing molecules or measurements that require higher sensitivity, a cavity-enhanced method, such as cavity ring-down spectroscopy, is often used and requires light sources capable of emitting tens of milliwatts of single-mode power due to the low coupling of the light into a high-finesse cavity.
In collaboration with the epitaxial growth expertise of Naval Research Laboratory and MDL’s semiconductor laser fabrication expertise, JPL has delivered high-power interband cascade lasers emitting at 3.38 µm for integration in Harvard Professor Anderson’s ICOS instrument and Caltech Professor Okumura’s cavity ring-down spectrometer. Professor Anderson’s research is focused on investigating the relationship between climate change and stratospheric ozone depletion at mid-latitudes by measuring ppt levels of HCl and HDO, while Professor Okumura’s spectrometer targets fugitive natural gas emissions such as ethane to determine if the shift towards natural gas energy production exacerbates climate change. The technological accomplishment of MDL lasers has enabled cutting-edge science. Ultimately, the lasers developed at MDL have bridged the long-standing gap in commercially available laser technologies and have enabled state-of-the-art spectroscopy techniques for atmospheric science.UV dosage levels in the summer: increased risk of ozone loss from convectively injected water.*
*Images courtesy of Professor James G. Anderson and illustrated by Rob Stanope, Harvard University.