Qing Yang Steve Wu

Sub-wavelength nano-electrode structures to improve the performance of terahertz photomixers

By utilizing the sub-wavelength metallic structures in the active region of the photomixer, the confinement and concentration of electric field from optical pump lasers on a photoconductive substrate can be efficiently achieved as these sub-wavelength metallic structures are exhibiting the nano-antenna effect over a high index photoconductive substrate. Designing the sub-wavelength metallic structures, branch-like nano-electrodes structures, a new strategy to improve carrier capture was developed in which more carrier collection points occupy across the area of the pumping laser source. These branch-like nano-electrode structures were found to improve THz emission intensity of a photomixer by approximately one order of magnitude and optical-to-THz conversion efficiency by 10 times higher than that of photomixer with one row of nano-electrodes separated by the same 100nm gap. The enhancement is attributed to a more efficient collection of generated carriers due to a more intense electric field under the branch-like nano-electrodes structures. This is coupled with increased effective areas where strong tip-to-tip THz field enhancements were observed. The more efficient THz photomixer will greatly benefit the development of continuous wave THz imaging and spectroscopy system.

Retraction Note to: Retraction: Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer

enhancement compared with a photomixer with conventional interdigitated electrodes, which we used as a reference device. We estimated the powers of the devices based on the blackbody power of a Hg lamp, as described in the Methods section and shown in Fig. 3b of this Article. After receiving a communication from J. Mangeney, R. Colombelli, E. Peytavit, J. F. Lampin, M. Jarrahi, S. Barbieri, M. Wanke and M. A. Belkin, we measured the absolute output of our device using a loaned pyrodetector (Gentec-EO, THZ1.5B-BL-USB). We measured the absolute output power to be about 1 mW, instead of 100 mW as initially estimated and shown in Fig. 3b. Due to this error, we wish to retract the Article, even though the reported relative enhancement and the idea of using nanogap electrodes are still valid. We apologize to the readers for any adverse consequences that may have resulted from the paper’s publication. Retraction: Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer

Surface plasmon enhanced optical transmission through subwavelength apertures with carbon nanotubes

Optical transmission through subwavelength holes perforated in metal films in the Terahertz region is enhanced through the coupling of spoof surface plasmons (SSPs) and light. It is known that light transmitted inside the subwavelength hole cavity peaks at certain wavelengths, which correspond to the excitation of the SP modes. This transmission is boosted as the SP modes in both sides of the metal are matched. In this paper, we show that hybridization of plasmonic metal hole-arrays with semiconducting single-walled carbon nanotubes leads to enhanced transmission.

Continuous wave Terahertz photomixer from low temperature grown GaAs with high carrier mobility

Low temperature GaAs grown by an MBE system exhibiting Hall carrier mobility of 5000 cm2/v.s. is fabricated into continuous-wave (CW) Terahertz (THz) photomixers utilizing a dual-dipole antenna with an interdigitated feed structure. The characteristics of the CW THz photomixer are presented.