Tunable Narrowband Terahertz Source and Accessories for Near-Field Nano-Spectroscopy and Nano-Imaging
Abstract
Terahertz (THz) radiation opens transformational fundamental science possibilities in physics, chemistry, biology, and neuroscience, as well as various novel applications in communication, defense, remote probing, and non-invasive imaging. The THz spectral region (~0.1 THz to ~20 THz) spans the energy scales of many fundamental excitations in solids that include lattice vibrations, superconductivity, electronic spin excitations, and plasmon polaritons. This equipment proposal is to request a tunable THz source along with necessary accessories (THz optics and detector) for research and research related educational purposes. The THz source will provide a narrowband terahertz radiation with a wide tuning range and a bandwidth of less than 100 GHz. The THz source will be integrated with scattering type scanning near-field optical microscope (s-SNOM) for THz nanoscale spectroscopic imaging experiments. The THz system includes all optical, mechanical, and electronic components for the generation of THz waves as well as the software to control the tuning. Integration of the THz source to the s-SNOM will make it a highly capable, rare piece of equipment. The THz source outputs a divergent tunable beam. The out beams will be collimated and focused using parabolic mirrors to the s-SNOM tip for single frequency nanoscale near-field THz spectroscopy and imaging experiments. s-SNOM allows interferometric measurements where the scattered THz field from the tip-sample junction is mixed with an interference beam reflected from a reference mirror. The scattered signal and the reference signals are mixed at a beam splitter and directed to a detector. The detector signal is demodulated at higher harmonics of the sum of the tip resonance frequency and the reference mirror frequency using lock-in amplifier. The signal is then processed by a computer to result in amplitude and phase optical images simultaneously with topography. s-SNOM enables to operate at ultrahigh spatial resolution even at THz spectrum region since resolution is not dependent on the frequency of the excitation of light used but by the apex radius of the tip, which is in the order of ~20 nm. This enables nanoscale imaging and spectroscopy by utilization of the long wavelengths corresponding to the far-infrared fingerprint vibrations. It will also be utilized for far-field spectroscopic measurements. The requested integrated THz/s-SNOM equipment will provide new nanoscale real space imaging capabilities at THz frequencies in research areas that are at the heart of the mission of DoD. These include (i) real-space imaging and investigation of spin plasmon waves in topological insulators (ii) spectroscopic characterization of semiconductor dislocations, interfaces, defects, and a THz probing carrier density variations as function of depth in semiconductors, (iii) development and characterization of novel THz nanolaser, and (iv) spectroscopic imaging and characterization of THz adiabatic nanofocusing plasmonic devices. The research and research related education capabilities that will be provided by the THz source, will promote undergraduate and graduate laser spectroscopy and imaging education at GSU. The proposed research enabled by the THz source will offer participating students, including those from underrepresented groups with advanced multidisciplinary skills, from THz spectroscopy and nanoscale imaging at THz frequencies to using analytical tools in tackling challenging materials science problems.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Apr 18, 2017
- Source ID
- W911NF1610495
Entities
People
- Yohannes Abate
Organizations
- Army Contracting Command
- Georgia State University
- Office of the Secretary of Defense