Femtosecond-laser-induced periodic self-organized nanostructures (FLIPSON)
Category: femtosecond optics, directed self-assembly, photochemistry, laser-induced surface periodic structures.
Application: laser based nanofabrication, sub-wavelength optics.
Directed self-organization is to use external stimuli such as temperature, stress, electromagnetic fields, etc, to influence the global organization of constituent components in a deterministic fashion. In this work we have observed light as a driving force for DSO of tungsten atoms during laser chemical vapor deposition to form periodic nanostructures. This could lead to new fabrication schemes of large-area templates for data storage, catalysts, and sensors.
Selected publication (see Publication for complete list)
1. H. Zhang, M. Tang, J. McCoy, and T. Her, “Deposition of tungsten nanogratings induced by a single femtosecond laser beam,” Optics Express 15 5937 (2007).
2. Mingzhen Tang, Haitao Zhang, and Tsing-Hua Her, “Self-assembly of tunable and highly-uniform tungsten nanogratings induced by femtosecond laser with nanojoule energy,” Nanotechnology 18 (2007) 485304 (5pp).
3. Tsing-Hua Her, “Femtosecond-Laser-Induced Periodic Self-Organized Nanostructures,” appeared in Comprehensive Nanoscience and Technology, edited by David Andrews, Greg Scholes, and Gary Wiederrecht, published by Elsevier (Dec. 2010).
4. Haitao Zhang, Terry T. Xu, Mingzheng Tang, Tsing-Hua Her, and Shu-you Li, “Selective growth of tungsten oxide nanowires via a vapor-solid process,” J. Vacuum Science and Technology B 28 (2), pp. 310-315 (2010).
Dispersive wavelength modulation spectroscopy
Category: laser modulation spectroscopy, femtosecond laser frequency comb, single-particle absorption spectroscopy, balanced detection.
Application: homeland security, early cancer detection, quantum information science, environmental monitoring, combustion diagnostics, atmospheric sensing, analytical chemistry.
Quantum objects and nanostructures, such as quantum dots, molecules, nanowires, proteins, and molecular motors, are building blocks and fundamental machineries for many physical, chemical and biological processes. On the other hand, explosives and biohazard molecules such as TNT and anthrax pose significant thread to homeland security. Sensitive and early detection of these quantum-sized objects is therefore very crucial for many applications in physics, chemistry, biology, medicine, and national defense.
Conventional wavelength modulation spectroscopy (WMS) is a well-established sensitive detection method by modulating the absorption of molecules with laser wavelength. This method, however, is not applicable to molecules at room temperature as they typically have much large absorption bandwidth than traditional laser can afford. In this research, we are investigating a new technique using femtosecond supercontinuum to accomplish the required wavelength sweep. This technique, if successful, can become a new imaging modality for material and biomedicine study. Students who are interested in this work please contact THRG for more information.