Daniel M. Wasserman
Electrical and Computer Engineering
1114 Micro and Nanotechnology Lab
208 N. Wright Street
Urbana, Illinois 61801
Ph.D., Electrical Engineering, Princeton University, 2004
- Research Statement:
- My research focuses on both the fundamental investigation, and the subsequent development, of novel optical and opto-electronic structures and devices for applications in the mid-infrared (mid-IR) wavelength range (3-30µm).
The mid-IR is home to the fundamental absorption resonances of many important molecules, as well as the thermal signatures of both living organisms and mechanical systems. The fact that so many things absorb and emit in the mid-IR makes this wavelength range of fundamental importance for medical, environmental, and biological sensing applications, as well as for thermal imaging, countermeasure, and chemical detection technologies for security and defense applications. This also, however, makes the mid-IR a wavelength range of high losses (absorption) and significant background noise (thermal emission). These drawbacks have, for a long time, hamstrung the development of compact, efficient, and cost-effective mid-IR sensing- and defense-related technologies.
However, with the recent development of the quantum cascade laser (QCL), the mid-IR now has a coherent light source suitable to meet the growing desire for mid-IR optical systems. The QCL has opened up the mid-IR to a degree unimaginable only a decade ago. The mid-IR has become a frontier for the study of new physics and next-generation optical devices and systems. My research team sits at the forefront of the expanding interest of the mid-IR, focusing on the development of new mid-IR materials, optical structures or systems, and optoelectronic devices, while at the same time, leading the way to investigations of previously unexplored wavelength ranges. We have pioneered the field of mid-IR designer metals, and are using these materials to investigate subwavelength optics with long-wavelength light, or as we like to say: we are “making the mid-IR nano”. We are developing new optoelectronic devices based on epitaxial nanostructures, for the detection and generation of mid-IR light. At the same time, we are applying the concepts we have demonstrated in the mid-IR to extend our work into the long-avoided Reststrahlen Band, with the intention of being a pioneering group in this largely unexplored wavelength range. The materials and devices we are developing, in addition to illuminating fundamental light-matter interactions on a sub-wavelength scale, will serve as the basis for a new generation of mid-IR photonic systems for a wide range of applications. As we progress, I envision the development of handheld breath analysis systems for real-time patient diagnostics, countermeasure systems designed to protect commercial and military aircraft from surface-to-air missile attacks, lightweight, portable thermal imaging systems, high-speed and efficient chemical sensors, laser arrays for lab-on-a-chip applications, sub-wavelength resolution mid-IR microscope systems, and much, more.
While at UIUC, I have developed collaborations with numerous groups in the College of Engineering (King, Touissant, Kim: MechSE; Li, Goddard, Coleman, Kim, Chuang: ECE; Cunningham, ECE/BioE) and outside the University (Lee, Yale; Podolskiy, UML; Shaner, Brener, Sandia; Halterman, NAVAIR; Boltasseva, Narimanov, Purdue; Hoffman, Jena, Notre Dame; Khurgin, JHU; Zide, UDel), resulting in numerous co-authored papers and joint proposals. I am active in training and mentoring Graduate Research Assistants, and have graduated 4 PhDs from UMass Lowell and am currently advising or co-advising 5 PhD students at UIUC, as well as one post-doctoral researcher. My research is, or has been, supported by the National Science Foundation, the Department of Energy, the Air Force Office of Scientific Research and Air Force Research Lab, as well as by collaborations with government labs (Sandia National Labs) and Industry. This diversity of funding sources is both a measure of the quality of the research performed by my team, and the importance of mid-IR optics and photonics to a wide array of interests, ranging from the scientific (NSF, DOE), to defense and security (AFOSR, AFRL, Sandia), and private industry (Alloy Surfaces, Triton Systems). In my time as an Assistant Professor, I have brought over $2,000,000 in funding to my group, despite the disruption caused by my move from UMass to UIUC.
Representative descriptions of my current research efforts, coarsely divided into sub-thrusts, are given below.
Designer Mid-Infrared Plasmonic Materials:
Plasmonics serves as a catch-all term for a field of optics centered around the interaction of electromagnetic (EM) radiation with free-electron plasmas in conducting (metallic) materials. While plasmonics has been around for centuries (stained-glass windows, for example), it is only recently that our ability to accurately model and fabricate these materials on a subwavelength-scale has led to an explosion of plasmonics-related research efforts. At mid-IR frequencies, subwavelength and/or nanoscale confinement and control of light using ‘traditional’ plasmonic metals (Ag, Au), is not possible. For this reason, my group has demonstrated the potential of heavily doped semiconductor materials as ‘designer’ mid-IR plasmonic metals [1,2]. We have demonstrated that these doped semiconductors can exhibit transitions from dielectric-like to metal-like optical properties, at the plasma-frequency of the material, whose spectral position we can control (Fig. 1). This demonstration has opened the door to a wide range of potential applications and fundamental investigations, as the ability to design and control our metals’ optical properties vastly expands the design space of plasmonic and metamaterial structures. In addition, because our materials are epitaxially grown, they are high-quality (single-crystal) and therefore low-loss, and can be integrated with other, epitaxial materials and devices, in particular opto-electronic structures designed for light detection or emission. Our designer plasmonic metals have served as a launching pad for much of my group’s subsequent research, including:
Epsilon Near Zero (ENZ) Materials:
Recently, materials with dielectric permittivity of, or near, zero (ENZ) have become of significant interest to the metamaterials community for extraordinary properties stemming from the dramatic extension of optical wavelengths at ENZ frequencies. This effect opens the door to ENZ-assisted optical coupling to subwavelength-scale waveguides, and the use of ENZ materials as ‘photonic wires’ for a lumped-circuit element approach to optical circuitry. Recently, we used our doped-semiconductor material, with ENZ at Lambda~8µm, to demonstrate enhanced funneling of light through subwavelength slits patterned over an ENZ layer. Despite the losses associated with the absorption of the highly doped semiconductor, as the slit size decreases, transmission through the ENZ material is actually enhanced when compared to a reference sample fabricated out of undoped GaAs . This work was the basis for our current NSF DMR funding, in which we look to design and characterize subwavelength ENZ waveguides and photonic structures, for the exploration of an exciting new field of physics.
Nanophotonics with Micron_Scale Light:
Our doped semiconductor metals also allow us to develop nanophotonic structures for mid-IR light, no small feat given the disparity between the micron-scale wavelengths of the mid-IR, and the nanoscale. Our first efforts in this direction utilized micro-patterned doped InAs, and demonstrated (with the King group at UIUC) localized heating of these structures using IR AFM characterization . More recently, we demonstrated arrays of nano-antennas capable of enhancing the interaction between long wavelength (Lambda~10µm) light and thin layers of absorbing polymers , an important step towards the development of nanoscale vibrational absorption sensors. This work generated significant press, and we are following it with a concerted effort to develop not only new geometries and materials capable of even stronger enhancement, but to integrate these materials into epitaxially-grown optoelectronic devices for plasmon-enhanced detectors and emitters.
Thermal Signature Control with Metasurface-based 'Thermal Skin':
The thermal signatures of all living and mechanical systems provide an unfortunate opportunity for malicious malicious targeting. Metamaterials, composite materials with subwavelength constituents and tailored optical properties, have been suggested for a variety of futuristic applications, though one could argue that the singular, unifying property of most metamaterial structures is absorption (often undesired and unintended). By Kirchoff’s Law, any absorption resonance of a material or surface results in a corresponding thermal emission signal upon heating. Our group has been one of the first to note that, designed correctly, this absorption can be utilized to develop thin-film selective thermal emitters, with the potential for the development of dynamic ‘thermal skin’. We are developing mechanisms to control the thermal signatures of thin film structures using low-cost, large-area patterning or thin film deposition techniques. In this work, we are tailoring plasmonic, metamaterial, ENZ, or even phononic resonances to selectively emit thermal radiation in designed wavelength bands [6-9].
Quantum Dots and Layered Nanostructures for Mid-IR Applications:
While the QCL has proven to be a revolutionary advance in mid-IR source technology, these novel semiconductor lasers still suffer from i) low wall-plug efficiencies, ii) high threshold current densities, and iii) preferential TM-polarized. A promising path towards overcoming each of these challenges is the utilization of intersublevel transitions in 3D nanostructures (quantum dots). The result, a quantum dot cascade laser (QDCL), has the potential to provide a mid-IR source for low-power consumption and lab-on-a-chip applications. We have currently been working towards the demonstration of such a device, funded through my NSF CAREER program. Early efforts demonstrated light emission from intersublevel transitions in quantum dots (QDs) embedded in a cascade-like structure, as well as the first example of room temperature emission from such a device [10,11]. At UML, I showed strong coupling between intersublevel transitions in QDs and plasmonic cavities , opening a path towards mid-IR nanostructure/plasmonic light sources. More recently, we have demonstrated electroluminescence from top-down patterned QD structures , and developed a novel growth technique for control of QD energies, which we are currently writing up for publication . We are also developing the epitaxial growth capabilities for novel mid-IR detectors (T2SL’s and nBn’s) which we hope to integrate with our new, semiconductor-based, plasmonic materials, in order to demonstrate the potential of mid-IR plasmonics for real-world applications.
 Optics Express, 20, 12155 (2012).
 Journal of Vacuum Science and Technology B, 31, 03C121 (2013).
 Physical Review Letters, 107, 133901 (2011).
 Applied Physics Letters, 102, 152110 (2013).
 Nano Letters, 13, 4560 (2013).
 Optics Express, 18, 25912 (2010).
 Applied Physics Letters, 98, 241105 (2011).
 Optics Express, 21, 9113 (2013).
 "Engineering absorption and blackbody radiation in the far-infrared with surface phonon polaritons on gallium phosphide", submitted to Applied Physics Letters.
 Applied Physics Letters, 81, 2848 (2002).
 Applied Physics Letters, 94, 061101 (2009).
 Nano-Letters, 11, 338 (2011).
 Applied Physics Letters, 101, 103105 (2012).
 “Controlling quantum dot energies using submonolayer bandstructure engineering”, in preparation
- Research Interests:
- Mid-infrared photonics, plasmonics and metamaterials.
Semiconductor physics and devices, molecular beam epitaxy (MBE), nanotechnology, optics, and intersubband transitions in quantum confined structures.
- For more information:
Honors, Recognition, and Outstanding Achievements:
- National Science Foundation Graduate Fellowship (1999-2002)
- Francis Upton Graduate Fellowship, Princeton University (1998-2003)
- Sigma Xi (1997)
- Phi Beta Kappa (1997)
- Magna Cum Laude (1998)
Honors, Recognition, and Outstanding Achievements for Teaching:
- Council on Science and Technology Postdoctoral Teaching Fellowship
- UMass Lowell Department of Physics Excellence in Teaching Award
- List of Teachers Ranked as Excellent by their Students
- Engineering Council Advising Award
- List of Teachers Ranked as Excellent by their Students
- List of Teachers Ranked as Excellent by their Students
Honors, Recognition, and Outstanding Achievements for Research:
- National Science Foundation CAREER Award
- Air Force Office of Scientific Research Young Investigator Award