Abstract-Magneto –THz spectroscopy in spinel superconductors LiTi2O4 thin films

Yue Huang, Jie Yuan, Kui Jin, Wei Zhang, Kimberly Reichel, and Daniel M. Mittleman

https://www.osapublishing.org/abstract.cfm?uri=cleo_qels-2018-FF2D.2&origin=search

We observed a clear superconducting gap at 2.0meV and a coherent peak in the strong spin fluctuation compounds LiTi2O4 using continues wave (CW) terahertz spectroscopy. The superconducting state was strongly suppressed by magnetic fields.

© 2018 The Author(s)

Thesis defense-Devices Based on Parallel-Plate Waveguides for Terahertz Application

Speaker: Kimberly Reichel
Doctoral Candidate

Devices Based on Parallel-Plate Waveguides for Terahertz Application

Friday, April 15, 2016
1:00 PM  to 3:00 PM 
300  Brockman Hall for Physics
http://events.rice.edu/index.cfm?EventRecord=28440

The promise of terahertz (THz) frequencies for technological applications is wide, spanning from wireless communications for faster downloads to non-destructive imaging for security screening. Although the potential is high, there is a lack of the basic devices necessary to make these prospects a reality. One essential component for any electromagnetic wave technology is a waveguide, which as the name implies can guide light waves, like a hose would direct water from the source to the desired target location. Several waveguide types have been introduced for THz frequencies, one of the most promising of which is the parallel-plate waveguide (PPWG). The PPWG is attractive based on its superior waveguiding perforxmance of efficient input coupling and low losses, but additionally it serves as an excellent platform for other purposes. The projects presented in this dissertation highlight a few new functionalities incorporated into, and enabled by, a PPWG for sensing, filtering, and splitting. First, we characterize a high quality factor resonator integrated into a PPWG used for microfluidic sensing. Typically, the characterization of the frequency-dependent electric field profile inside a narrowband resonator is challenging, either due to limited optical access or to the perturbative effects of invasive probes. In our situation however, the geometry of the PPWG allows for direct access to the resonant cavity via the open sides of the waveguide and a novel implementation of the air-biased coherent detection (ABCD) method permits non-invasive probing. Through both experiment and simulation, we see the narrowband frequencies trapped in the resonator and also discover an unexpected broadband asymmetric field distribution due to the resonator inside the waveguide, yielding new information that is not available in the far field. Second, we investigate a narrowband tunable filter based on extraordinary optical transmission (EOT) through a 1D array of subwavelength holes inside a PPWG. EOT is an effect where at a particular frequency 100% of the light is transmitted through an array of holes with diameters much smaller than the wavelength. We demonstrate that the output resonant frequency depends strongly on the input mode of the waveguide, where excitation with the TEM waveguide mode mimics EOT in a 2D array in free space, while the TE1 waveguide mode is vastly different. Through this disparity of outcomes between the two different waveguide excitation modes, we can better understand the resonant transmission process. We show that the surface plasmon theoretical description is invalid for the TE1 resonance, and instead use impedance matching to properly predict the resonances in both TE1 and TEM. Additionally, we show that the device can be used as a tunable filter at THz frequencies by simply changing the separation between the two waveguide plates. Third, we demonstrate a THz variable power splitter based on a PPWG T-junction excited by the TE1 waveguide mode. By integrating a small triangular septum into the waveguide plate, we are able to direct the THz light down to either one of the two output channels with precise control over the coupling ratio between the waveguide outputs. We find good agreement between experiment and simulation in both amplitude and phase. We show that the coupling ratio varies exponentially with the septum translation offset and that nearly 100% transmission can be achieved. The splitter operates over almost the entire range in which the waveguide is single mode, providing a sensitive and broadband method for power splitting. By incorporating our innovations along the already propagating path of THz waves inside a waveguide, we establish multiple functional capabilities into one universal platform. The hope of this work is that these devices will ultimately serve as fundamental building blocks to make everyday THz applications a reality. 

Abstract-Terahertz Microfluidic Sensing Using a Parallel-plate Waveguide Sensor

Astley, Victoria
Reichel, Kimberly
Mendis, Rajind
Mittleman, Daniel M.
http://scholarship.rice.edu/handle/1911/78893?show=full

Refractive index (RI) sensing is a powerful noninvasive and label-free sensing technique for the identification, detection and monitoring of microfluidic samples with a wide range of possible sensor designs such as interferometers and resonators [1,2]. Most of the existing RI sensing applications focus on biological materials in aqueous solutions in visible and IR frequencies, such as DNA hybridization and genome sequencing. At terahertz frequencies, applications include quality control, monitoring of industrial processes and sensing and detection applications involving nonpolar materials. Several potential designs for refractive index sensors in the terahertz regime exist, including photonic crystal waveguides [3], asymmetric splitring resonators [4], and photonic band gap structures integrated into parallel-plate waveguides [5]. Many of these designs are based on optical resonators such as rings or cavities. The resonant frequencies of these structures are dependent on the refractive index of the material in or around the resonator. By monitoring the shifts in resonant frequency the refractive index of a sample can be accurately measured and this in turn can be used to identify a material, monitor contamination or dilution, etc. The sensor design we use here is based on a simple parallel-plate waveguide [6,7]. A rectangular groove machined into one face acts as a resonant cavity (Figures 1 and 2). When terahertz radiation is coupled into the waveguide and propagates in the lowest-order transverse-electric (TE1) mode, the result is a single strong resonant feature with a tunable resonant frequency that is dependent on the geometry of the groove [6,8]. This groove can be filled with nonpolar liquid microfluidic samples which cause a shift in the observed resonant frequency that depends on the amount of liquid in the groove and its refractive index [9]. Our technique has an advantage over other terahertz techniques in its simplicity, both in fabrication and implementation, since the procedure can be accomplished with standard laboratory equipment without the need for a clean room or any special fabrication or experimental techniques. It can also be easily expanded to multichannel operation by the incorporation of multiple grooves [10]. In this video we will describe our complete experimental procedure, from the design of the sensor to the data analysis and determination of the sample refractive index.

Abstract-High-Q terahertz Fano resonance with extraordinary transmission in concentric ring apertures

Jie Shu, Weilu Gao, Kimberly Reichel, Daniel Nickel, Jason Dominguez, Igal Brener, Daniel M. Mittleman, and Qianfan Xu  »View Author Affiliations

http://www.opticsinfobase.org/oe/abstract.cfm?uri=oe-22-4-3747

Optics Express, Vol. 22, Issue 4, pp. 3747-3753 (2014)

We experimentally demonstrate a polarization-independent terahertz Fano resonance with extraordinary transmission when light passes through two concentric subwavelength ring apertures in the metal film. The Fano resonance is enabled by the coupling between a high-Q dark mode and a low-Q bright mode. We find the Q factor of the dark mode ranges from 23 to 40, which is 3~6 times higher than Q of bright mode. We show the Fano resonance can be tuned by varying the geometry and dimension of the structures. We also demonstrate a polarization dependent Fano resonance in a modified structure of concentric ring apertures.

© 2014 Optical Society of America

Abstract-High-Contrast Terahertz Wave Modulation by Gated Graphene Enhanced by Extraordinary Transmission through Ring Apertures

Weilu Gao , Jie Shu , Kimberly Reichel , Daniel V. Nickel , Xiaowei He , Gang Shi , Robert Vajtai ,Pulickel M Ajayan , Junichiro Kono , Daniel M. Mittleman , and Qianfan Xu

Nano Lett., Just Accepted Manuscript

DOI: 10.1021/nl4041274

Publication Date (Web): February 3, 2014

Copyright © 2014 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/nl4041274

Gate-controllable transmission of terahertz (THz) radiation makes graphene a promising material for making high-speed THz wave modulators. However, to date, graphene-based THz modulators have exhibited only small on/off ratios due to small THz absorption in single-layer graphene. Here we demonstrate a ~50% amplitude modulation of THz waves with gated single-layer graphene by the use of extraordinary transmission through metallic ring apertures placed right above the graphene layer. The extraordinary transmission induced ~7 times near-filed enhancement of THz absorption in graphene. These results promise CMOS-compatible THz modulators with tailored operation frequencies, large on/off ratios, and high speeds, ideal for applications in THz communications, imaging, and sensing.