IRG 1 FRG 1 – THz Plasmonics

Team

Dr. Ajay Nahata (Professor), Dr. Berardi Sensale Rodriguez (Professor), Dr. Mikhail Raikh (Professor), Dr. Valy Vardeny (Professor), Sara Arezoomandan (Graduate Student),  Ashish Chanana (Graduate Student), Barun Gupta (Graduate Student), Shashank Pandey (Graduate Student), Ting Zhang (Graduate Student), Hui Zhou (Graduate Student).

 

Research Objective

Development of devices for guiding and confinement of Terahertz radiation (THz) on sub wavelength scales.

Particularly involving:

  • Design, fabrication and characterization of metal surfaces structures with sub wavelength dimension for guiding and confinement of THz radiation.
  • Design and characterization of plasmonic device for enhanced THz radiation to be used as near field probing device.
  • Development of stretchable plasmonic structures using liquid metal (Eutectic GaIn).
  • Exploring new fabrication techniques to create THz plasmonic devices.
  • Characterization of plasmonic device using THz Imaging.
  • Generation and detection of THz radiation using new sources.

 

Approach

Structuring the metal surface with sub wavelength structures allows for the existence of surface plasmon polaritons (SPP) mode at the interface between structured surface and the dielectric (air). THz-SPP offers exciting capabilities such as enhanced transmission, guiding and confinement of propagating Electric field.

Details

Terahertz radiation is region of electromagnetic spectrum between the microwave and the infrared region. Generation, detection and routing of the Terahertz radiation is critically important for development in the field of material characterization, security imaging and biochemical detection.

a) THz Devices

Guided Wave Devices

Our approach is to extend the concept of SPP at optical frequency to THz regime, where by structuring the metal surface, we achieve confined and guided propagation of THz radiation. The structured metal surface with holes acts as an effective medium whose dielectric properties can be varied by changing the dimension of holes.

Waveguide devices which can control the properties of SPP in all 3 dimensions require a complex geometrical design which is impossible to create via conventional techniques of laser ablation and micro fabrication. Using 3 D printing complex structures which allow for conformal transport of SPP are created.

THz Waveshaping Devices

b) Liquid metal based plasmonics

Liquid metals support SPP at THz frequencies and serve to create exciting plasmonic metamaterials with stretchable feature. Eutectic GaIn metal is injected into a Polydimethylsiloxane (PDMS polymer) mold which is created using soft lithography techniques. Liquid metal has viscosity similar to water and it can be injected and extracted from the polymer mold to change the depth of holes in the mold, it is a potential active THz device.

c) Terahertz Sources and Detectors

A non linear polymer embedded in metal waveguide allows for coherent generation and detection of THz radiation. Metal waveguide allows for broadband propagation of optical pump, probe and THz beam, enabling phase matched interaction of beams over longer interaction lengths. “All optical” approach for generation and detection of THz overcomes the problems of source power, detector sensitivity and THz frequency response.

Surface plasmon polariton concept is extended in the field of photoconductive dipole antenna to develop a THz detector for multiband THz radiation with increased sensitivity. The antenna incorporates a corrugated metals structure that surrounds the dipole. Each periodically spaced groove in the corrugation couples to the THz SPP which then propagates along the structure to be detected by the dipole.

Results

a) THz Devices

Guided Wave Devices

The devices created via 3D printing are coated with layer of Au to create plasmonic devices. The 3D device allow for bound propagation of THz waveform along various complex shapes.

Detailed explanation of loss of SPP as the plane of propagation varies at different angle from the input plane.

b) Liquid Metal based Plasmonics

The metal ink injected in the PDMS mold forms a stretchable structure. As the sample I stretched the dimensions of the holes and periodicity change which then modulates the spectrum of the transmitted THz beam. The resulting spectrum depends on the feature of transformed holes upon being stretched.

c) THz sources and detectors

The non linear polymer embedded in the metal waveguide generates a broadband THz radiation with average optical power needed less than 10 mW. In contrast the average optical power needed for 1 mm thick ZnTe crystal is ~ 200 mW. Thus the throughput efficiency of the generated THz radiation is ~ 20 times better than the generation of THz radiation through conventional non linear optical crystal.

The detection of multimode THz radiation is done with increased sensitivity by increasing the aperture opening of the center corrugation in the SPP based photoconductive dipole antenna.