Physicists Discover Effect that Turns Physics of Semiconductor Lasers "Upside Down"

Researchers at the Technische Universität Darmstadt have found a new method for generating tunable wavelengths, as well as more easily switching back and forth between two wavelengths, employing quantum-dot lasers. Prospective application fields are biomedicine and nanosurgery.

Darmstadt physicists have discovered an effect that turns the physics of semiconductor lasers “upside down.” Laser action in semiconductor lasers usually starts off with emission of photons corresponding to transitions originating from the lowest energy level. Emission of high energetic, i.e., short-wavelength, photons does not normally commence until the pumping current has been increased to well above the lasing threshold. Under the EU’s “FAST-DOT” project, researchers from the Semiconductor Optics Group at the Technische Universität Darmstadt’s Institute for Applied Physics headed by Prof. Dr. Wolfgang Elsäßer have recently discovered that, under some circumstances, quantum-dot lasers do emit first short-wavelength photons and then long-wavelength photons. Elsäßer explained that “this inverted hierarchy of emission states that we are the first to discover effectively allows generating intentionally custom-tailored wave­lengths covering a wavelength range of interest in many applications. Furthermore, the method not only allows switching back and forth between two wavelengths and but also exploiting beneficially effects occurring in the laser systems involved for improving pulse parameters.” Following up on that work, the Darmstadt researchers engaged in the “FAST-DOT” project plan to explore applications of the easier means for switching between wave­lengths, whose underlying physics they have discovered.

Medical applications of nanostructured quantum-dot lasers

Quantum-dot lasers operable at high pulse-repetition rates are capable of reaching pulse energies that will allow modifying living cells, e.g., making accurately controlled incisions in cell structures, while minimizing the attendant effects on cellular environments. Summarizing their capabilities, Elsäßer stated that, “They may be employed as high-precision scalpels, with which cell structures may be parted in controlled manners.” In addition, certain cell organelles might be deactivated or individual intracel­lular or extracellular molecules activated, which would open up unforeseen opportunities in molecular surgery, which allows making incisions two-thousand times finer than a human hair. In the future, these quntum dot lasers might allow destroying cancer cells very specifically or applying them simultaneously either for corneal surgery or diagnostics.