Daniel Wasserman

Physics Asst. Prof. Daniel Wasserman loves photons – those quanta (units) of visible light or other forms of electromagnetic radiation that possess both particle and wave characteristics. As assistant director of UMass Lowell’s Photonics Center, his research deals mainly with the properties and applications of light and other forms of radiant energy, including ways to generate and control them.

“I’m interested in anything that emits, detects and interacts with light,” he says, “specifically, mid-infrared light.” This light, which is invisible to the human eye, has a wavelength of 2 to 30 microns (millionths of a meter). Wasserman and his graduate students, Troy Ribaudo, Rajesh Lakkimsetti and Karen Freitas, are working on a new approach to the study of “active surface plasmons.”
 
“Basically, surface plasmons are hybrid waves that propagate along the interface between a metal and a dielectric, or non-conducting, material,” explains Wasserman. “In the metal, the surface plasmon would look like a sea of electrons oscillating back and forth and propagating almost like a sound wave. In the dielectric – in our case, we’re using a Gallium-Arsenide substrate as our dielectric – the surface plasmon looks like a light wave trapped at the surface of the dielectric. These two waves co-propagate along the metal/dielectric interface. Typically, the frequencies at which you can excite these waves, using an external light source, are determined by the material properties of both the metal and the dielectric, as well as the geometry of the metal layer. The ‘active’ part of the term comes from the fact that we’ve come up with ways of electronically controlling the resonant frequency of surface plasmons excited at a metal/semiconductor interface.”

According to Wasserman, their research, which has been funded as a collaboration with Sandia National Laboratories, is significant because they are taking a completely novel approach to the field. “We’re thinking about devices based on surface plasmons as not simply passive optical elements but as optoelectronic devices, which greatly enhances the number of applications for them and their overall utility,” he says.

His team’s findings were recently featured in the journal Laser Focus World. “Being able to actively control surface plasmons has many potential commercial, biomedical and military applications,” says Wasserman. “For instance, people have talked about using surface-plasmon-based gratings as filters that allow a certain range of wavelengths to pass through and exclude others. If you’re able to electronically tune these filters, their utility increases dramatically and they could be applied to numerous technologies, such as flat-panel displays.”

Wasserman is also interested in using active surface plasmons for sensing applications. “Imagine using them as a compact, low power on-chip spectrometer for biomedical diagnostics and monitoring,” he says. “For example, by bringing the incident light into ‘contact’ with a molecule on the surface of the plasmonic structure, you could measure the ammonia content in the breath of patients undergoing dialysis to monitor their kidney function.”
 
There are some military applications as well, specifically as defense countermeasures, where a tunable plasmonic structure could direct a high-power laser beam onto an incoming missile and steer it away from its target.

But Wasserman’s work doesn’t stop there. “I’m actually putting together a project to do single photon quantum communications with mid-IR photons, as well as continuing my work with quantum cascade lasers and quantum dot nanostructures,” he says. Visit Wasserman's website for more information about his research.