Robust, Tunable Diode Lasers for Environmental Monitoring

Tunable diode laser spectroscopy (TDLS) is one of the most versatile and powerful detection technologies. Essentially, any contaminant can be detected, and with emerging cavity-enhanced techniques, sensitivities can be in the parts per trillion. Despite this tremendous potency, however, widespread use of TDLS has been prevented largely by the lack of economical, reliable, and wavelength-versatile tunable diode lasers. Currently available tunable diode lasers are either: (1) not robust and expensive (such as mechanically tuned lasers that are vibration sensitive and can cost up to $20,000), or (2) only exist at a few specific center wavelengths and have limited tunability (such as distributed feedback lasers that typically can tune only 2 nm around only select wavelengths). During this project, Vescent Photonics, Inc., developed an all solid-state laser that will be extremely robust, compact (comparable in size to a book of matches), widely tunable (greater than 90 nm, likely limited by the diode gain curve), and accommodating to wavelengths from 400 nm to 2 µm (any semiconductor diode chip can be used as the gain medium). This remarkable new laser design, termed WECSL (pronounced "wexl"), is enabled by an innovative electrooptic technology. In Phase I, Vescent Photonics, Inc., demonstrated an unprecedented voltage-tuned index of n greater than 0.02, which, for = 1 µm light, provides 200 waves of voltage controlled optical phase delay per centimeter of propagation. Furthermore, through detailed modeling and experiments, the feasibility of using this technology to construct all solid-state tunable diode lasers was demonstrated. The goal of this Phase II research project is to build three different WECSL lasers with center wavelengths at 670 nm, 1,824 nm, and 1,954 nm, which can probe NO2, NO, and N2O, respectively. Finally, to illustrate the utility of the WECSL for TDLS, demonstration spectra for each NOx species will be recorded. The potential commercial applications are many. First, environmental monitoring is a diverse and expanding market, with applications including in situ factory monitoring, mobile emissions monitoring, and fenceline detection, for example. When combined with ultra-sensitive cavity-enhanced detection techniques, applications exist for weapons detection and medical breath analyses. Outside of monitoring, a large market for tunable diode lasers is telecommunications, where precise control over wavelength enables increased bandwidth through optical fibers. Finally, tunable diode lasers find utility in the growing field of fiber-sensors.