Gas Phase Terahertz Lasers Make a Comeback
Gas phase optically pumped far infrared (OPFIR) lasers were once the most powerful sources of radiation in the challenging terahertz spectral region. Unfortunately, these lasers were enormous, often filling an entire optical table to produce milliwatts of power and requiring a different gas each time a different wavelength was needed. Consequently, when more compact, more tunable alternative sources of terahertz radiation were discovered, OPFIR lasers were largely abandoned. However, in the mid-1980’s Prof. Frank De Lucia, then of the Duke Physics Department, recognized that a more compact version of OPFIR lasers was possible, and with then student and now Adjunct Professor Henry Everitt of the Duke Physics Department, they discovered that OPFIR lasers worked at much higher pressures and with much more tunability than their enormous commercial counterparts.
By 1990 the basic understanding had been worked out, but the complexity of the problem evaded accurate theoretical modeling. Fast forward to 2010 when Prof. Everitt, also a senior scientist with the Army's Aviation and Missile RD&E Center, partnered with researchers at the Army-funded MIT Institute for Soldier Nanotechnologies to develop such a model in hopes of designing optimized OPFIR laser cavities. The breakthrough came in 2016 when MIT graduate student Fan Wang, working with Prof. Everitt and MIT faculty Steven Johnson, Marin Soljacic, and John Joannopoulos, reformulated the problem and developed a model that precisely predicted the observed behavior with no adjustable parameters. To their surprise, they discovered that operating the laser in the unprecedented high pressure regime actually improved the efficiency a factor of ten higher than commercial lasers and within a factor of three of the maximum possible efficiency! This breakthrough, recently reported in the Proceedings of the National Academy of Science, heralds the possible rebirth of OPFIR lasers as powerful, efficient, tunable sources of terahertz radiation.
Photo caption: Duke Prof. Henry Everitt and MIT graduate student Fan Wang operate the compact OPFIR laser.