One of our science friends (who happens to have a Ph.D in Physics) says that Moore’s Law is quickly coming to an end. Moore’s Law states that the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years.  “It’s approaching its asymptote,” he says.  (An asymptotic function is a function that “increases or decreases until it approaches some fixed value (i.e., the asymptote), at which point it levels off.” We know that because we looked it up.)  According to our science friend, the ability to pack more transistors onto a chip is going to soon hit a roadblock having to do with mask size (we don’t pretend to understand that part); it will be the “end of silicon” and the beginning of – what? Our science friend likes the concept of “optical processors” and thinks that Quantum Cascade Lasers (QCLs) may be one way to get there.

Quantum Cascade Lasers (QCLs) are semiconductor lasers that emit in the mid- to far-infrared portion of the electromagnetic spectrum.  Unlike traditional lasers, QCLs achieve laser emission “through the use of intersubband transitions in a repeated stack of semiconductor multiple quantum well heterostructures.”  There is a whole lot more language like that in the article linked above.  Terms such as “valence bands” and “conduction band” and “superlattice” and “one-dimensional multiple quantum well confinement” permeate and we’d be lying if we said it made sense.  This part seemed to make some sense, though:  “in a unipolar QCL, once an electron has undergone an intersubband transition and emitted a photon in one period of the superlattice, it can tunnel into the next period of the structure where another photon can be emitted. This process of a single electron causing the emission of multiple photons as it traverses through the QCL structure gives rise to the name cascade and makes a quantum efficiency of greater than unity possible which leads to higher output powers than semiconductor laser diodes.”

The October 2009 edition of National Defense magazine has an article on QCLs.  The article does not focus on the efficiency noted above, but instead on the size of the laser.  QCLs are a lot smaller than conventional lasers.  Combine efficiency and flexibility and smaller size together, and you get a potential breakthrough.  Our science friend thinks the breakthrough will revolutionize computer processing and perhaps he’s right.  We also note that there are several near-term defense and homeland security applications inherent in the QCL concept, as well. The Wikipedia article (link above) states that “when used in multiple-laser systems, intrapulse QCL spectroscopy offers broadband spectral coverage that can potentially be used to identify and quantify complex heavy molecules such as those in toxic chemicals, explosives, and drugs.” In addition, the National Defense article predicts that “one day they [QCLs] may provide the military with directional infrared countermeasures, target illumination, chemical warfare warning and search-and-rescue capabilities ….”

The National Defense article discusses the work of Pranalytica, a small R&D contractor based in Santa Monica, CA. Pranalytica specializes in tunable laser spectroscopy-based gas sensing and in QCLs.  According to its website, on May 19, 2009 the company shipped its first 2 Watt room temperature QCL system. The article states that Pranalytica’s QCL systems can produce the right wavelength needed to disable the guidance system of heat-seeking anti-aircraft missiles, and can also produce long-range infrared illuminators using wavelengths that are invisible to commercial cameras commonly used by opposition forces as detectors.  According to the article, “only NATO allies and U.S. forces have technologies that can see this kind of light ….”

On June 24, 2009 Pranalytica announced that DARPA had selected it to “continue its involvement in the Efficient Midinfrared Laser (EMIL) program.”  According to the company’s press release, “The project was created to fill the need of the Department of Defense (DoD) for directional infrared countermeasures (DIRCM), advanced stand-off chemical sensors, and Laser Radar (LADAR). Potential non-military applications include DIRCM protection of civilian airliners from shoulder-fired missiles, detection of toxic industrial gases, atmospheric pollution monitoring and free-space optical communications.”  In addition to the DARPA contract, Pranalytica also claims a grant from the National Institutes of Health for medical diagnostics and various other contracts and grants from DARPA, NIST/ATP, and the Department of Agriculture.  Clearly, Pranalytica’s products offer potential breakthroughs to a diverse set of stakeholders.  The company’s future looks bright!