Abstract-Femtosecond pulse with THz repetition frequency based on the coupling between quantum emitters and a plasmonic resonator

Shilei Li, Yinxing Ding, Rongzhen Jiao, Gaoyan Duan, and Li Yu

https://journals.aps.org/pra/abstract/10.1103/PhysRevA.97.033811

Nanoscale pulsed light is highly desirable in nano-integrated optics. In this paper, we obtained femtosecond pulses with THz repetition frequency via the coupling between quantum emitters (QEs) and plasmonic resonators. Our structure consists of a $V$-groove (VG) plasmonic resonator and a nanowire embedded with two-level QEs. The influences of the incident light intensity and QE number density on the transmission response for this hybrid system are investigated through semiclassical theory and simulation. The results show that the transmission response can be modulated to the pulse form. And the repetition frequency and extinction ratio of the pulses can be controlled by the incident light intensity and QE number density. The reason is that the coupling causes the output power of nanowire to behave as an oscillating form, the oscillating output power in turn causes the field amplitude in the resonator to oscillate over time. A feedback system is formed between the plasmonic resonator and the QEs in the nanowire. This provides a method for generating narrow pulsed lasers with ultrahigh repetition frequencies in plasmonic systems using a continuous wave input, which has potential applications in generating optical clock signals at the nanoscale.

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Abstract-Charge transfer plasmon resonances across silver-molecule-silver junctions: Estimating the Terahertz conductance of molecules at near-infrared frequencies

Lin Wu,   Shu Fen Tan ,   Michel Bosman,   Joel K.W. Yang,  Christian A. Nijhuis and   Ping Bai  

RSC Adv., 2016, Accepted Manuscript

DOI: 10.1039/C6RA16826D
Received 30 Jun 2016, Accepted 18 Jul 2016
http://pubs.rsc.org/en/content/articlelanding/2016/ra/c6ra16826d#!divAbstract

Quantum plasmon resonances have been recently observed across molecular tunnel junctions made of two plasmonic resonators bridged by a self-assembled monolayer (SAM). The energy of this quantum plasmon mode, i.e., the tunneling charge transfer plasmon (tCTP), depends on the properties of the molecules bridging the gaps. The present work extends these studies theoretically using a generalized space-charge corrected electromagnetic model to a wider range of SAM structures (with various molecular lengths and conductances) sandwiched between silver nanocubes, which could support different types of CTP resonances in addition to tCTP. The space-charge corrected electromagnetic model treats the charge injection and charge transport separately, and assumes a Drude expression (with damping frequency on the order of driving frequency) to model the space-charge limited transport problem. Our theoretical modelling of these organic-inorganic hybrid structures establishes a one-to-one relationship between the conductivity of the SAM and the resonant energy of the CTP modes. Considering that the SAM consists of a finite number of molecules bridging the two nanocubes in a parallel arrangement, we introduce a method to estimate the molecular conductance at the CTP resonant frequency. Experimental results from two types of SAMs were examined as a proof-of-concept: the THz conductance is estimated to be 0.2G0 per EDT (1,2-ethanedithiolate) molecule at 140 THz and 0.4G0 for a BDT (1,4-benzeneditiolate) molecule at 245 THz. This approach paves the way of using plasmonic oscillations for measuring the THz conductance of single molecules at near-infrared frequencies.

Abstract-Quantum Plasmon Resonances Controlled by Molecular Tunnel Junctions

1. Shu Fen Tan1, 
2. Lin Wu2, 
3. Joel K.W. Yang3,4, 
4. Ping Bai*,2, 
5. Michel Bosman*,3, 
6. Christian A. Nijhuis*,1,3,5,6
7. 1. http://www.sciencemag.org/content/343/6178/1496.abstract

-Author Affiliations

1. ¹Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore.
2. ²Institute of High Performance Computing, A*STAR (Agency for Science, Technology and Research), 1 Fusionopolis Way, 16-16 Connexis North, Singapore 138632, Singapore.
3. ³Institute of Materials Research and Engineering, A*STAR, 3 Research Link, Singapore 117602, Singapore.
4. ⁴Singapore University of Technology and Design, 20 Dover Drive, Singapore 138682, Singapore.
5. ⁵Graphene Research Center, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore.
6. ⁶Solar Energy Research Institute of Singapore (SERIS), National University of Singapore, Singapore 117574, Singapore.

1. ↵*Corresponding author. E-mail: baiping@ihpc.a-star.edu.sg (P.B.), michel.bosman@gmail.com (M.B.),christian.nijhuis@nus.edu.sg (C.A.N.)

Quantum tunneling between two plasmonic resonators links nonlinear quantum optics with terahertz nanoelectronics. We describe the direct observation of and control over quantum plasmon resonances at length scales in the range 0.4 to 1.3 nanometers across molecular tunnel junctions made of two plasmonic resonators bridged by self-assembled monolayers (SAMs). The tunnel barrier width and height are controlled by the properties of the molecules. Using electron energy-loss spectroscopy, we directly observe a plasmon mode, the tunneling charge transfer plasmon, whose frequency (ranging from 140 to 245 terahertz) is dependent on the molecules bridging the gaps.

Researchers create circuits that operate at ‘hundreds of terahertz’

Author Graham Pitcher

http://www.newelectronics.co.uk/electronics-news/researchers-create-circuits-that-operate-at-hundreds-of-terahertz/60698/

Circuits that are said to operate at hundreds of terahertz have been designed and fabricated by researchers at the National University of Singapore. The team says its work has the potential to revolutionise high speed electronics, nanoscale optoelectronics and nonlinear optics. 

The development is based on a new physical process called quantum plasmonic tunnelling. Current photonic elements are large, but operate at frequencies of 100THz, while current nanoelectronic devices are much smaller, making it difficult to combine the properties of both.

According to researchers, it has long been known that light can interact with certain metals and can be captured in the form of plasmons – ultra fast oscillations of electrons that can be manipulated at the nanoscale. Quantum plasmon modes have been predicted to occur at atomic scales and have been difficult to investigate.

In its study, the research team demonstrated that quantum plasmonics is possible at scales that are useful for real applications, then fabricated an element of a molecular electronic circuit using two plasmonic resonators. These structures, which can capture light in the form of plasmons, are bridged by a single molecule thick layer that switches on the quantum plasmonic tunnelling effects, enabling the circuits to operate at terahertz frequencies.

The work was led by Assistant Professor Christian Nijhuis from the National University of Singapore's Faculty of Science and Dr Bai Ping and Dr Michel Bosman from A*STAR.

Dr Bosman used advanced electron microscopy techniques to visualise and measure the optoelectronic properties of these structures at nanometre resolution. The measurements revealed the existence of the quantum plasmon mode and that its speed could be controlled by varying the molecular properties of the devices.

By performing quantum corrected simulations, Dr Bai confirmed that quantum plasmonic properties could be controlled in the molecular electronic devices at high frequencies.

Asst Prof Nijhuis said: "We are excited by the new findings. Our team is the first to observe the quantum plasmonic tunneling effects directly. This is also the first time that a research team has demonstrated theoretically and experimentally that very fast switching at optical frequencies are possible in molecular electronic devices."

The researchers will now address the integration of these devices into real electronic circuits.