Lattice Induced Transparency in Metasurfaces

Lattice modes are intrinsic to the periodic structures and their occurrence can be easily tuned and controlled by changing the lattice constant of the structural array. Previous studies have revealed excitation of sharp absorption resonances due to lattice mode coupling with the plasmonic resonances. Here, we report the first experimental observation of a lattice induced transparency (LIT) by coupling the first order lattice mode (FOLM) to the structural resonance of a metamaterial resonator at terahertz frequencies. The observed sharp transparency is a result of the destructive interference between the bright mode and the FOLM mediated dark mode. As the FOLM is swept across the metamaterial resonance, the transparency band undergoes large change in its bandwidth and resonance position. Besides controlling the transparency behaviour, LIT also shows a huge enhancement in the Q-factor and record high group delay of 28 ps, which could be pivotal in ultrasensitive sensing and slow light device applications.Comment: 5 figure

Effects of temperature and ground-state coherence decay on enhancement and amplification in a Δ\Delta atomic system

We study phase-sensitive amplification of electromagnetically induced transparency in a warm ${}^{85}$Rb vapor wherein a microwave driving field couples the two lower-energy states of a {\Lambda} energy-level system thereby transforming into a {\Delta} system. Our theoretical description includes effects of ground-state coherence decay and temperature effects. In particular, we demonstrate that driving-field-enhanced electromagnetically induced transparency is robust against significant loss of coherence between ground states. We also show that for specific field intensities, a threshold rate of ground-state coherence decay exists at every temperature. This threshold separates the probe-transmittance behavior into two regimes: probe amplification vs probe attenuation. Thus, electromagnetically induced transparency plus amplification is possible at any temperature in a {\Delta} system

DESIGN AND CONSTRUCTION OF SCIENTIFIC APPARATUS FOR COLD ATOM EXPERIMENTS

Master'sMASTER OF SCIENC

Elucidating the effects of radiant and sub-radiant interactions in terahertz metamaterials

This thesis discusses the study and implications of near- field interactions mediated by radiant and sub-radiant resonant modes in passive metamaterials (MMs), MEMS actuated active MMs and semiconductor-metamaterial heterostructures at terahertz frequencies. The thesis is divided into two parts, where the fi rst part of the thesis includes fi rst three chapters (Chaps. 2, 3 and 4) that discusses on the phenomena of metamaterial induced transparency and lattice induced transparency in the metamaterial structures at terahertz frequencies. Theoretical analysis using classical coupled oscillators model is proposed to unravel the interaction mechanisms that reveals the radiant and subradiant type of Fano interference effects in the system. These systems show strong slow light effects with large enhancement in the group delay of the pulse through the medium. Further, the implications of the competing electric and magnetic near- field interactions on the transmission characteristics of the medium have shown to exhibit resonant invisibility effects showing an active control of effective permittivity and permeability of the medium. Second part of the thesis (Chap. 5 and Chap. 6) focuses on the demonstration of excitation and active modulation of sharp Fano resonances in a MEMS metamaterial and semiconductor-metamaterial hybrid heterostructure systems. Excitation of Fano resonance in MEMS metamaterial by introducing out-of plane structural asymmetry exhibits anisotropic coupling that results in the multiple-input-output (metahysteresis) characteristics in its near- and far-fi eld optical properties. This exhibits exciting features such as NAND and XOR logical operations, where XOR function can show direct implications in the one-time pad (OTP) secured cryptographic channel for sub-terahertz wireless communications. Further, an active control of Fano resonance in a heterostructure consisting of solution processed CH3NH3PbI3/PbI2 semiconductors spin coated on a metamaterial structure is discussed that exhibits ultrasensitive and ultrafast modulation of Fano resonance in the metamaterial structure, respectively (Chap. 6). Additionally, a new signature of localized plasmon-phonon quasiparticles sensing and interference effects are observed and elucidated using the coupled oscillator model. This phenomenon reveals a strong resonant interactions between the elementary excitations that can be actively controlled by optically pumping the sample using a femtosecond pulse. The thesis concludes by discussing the importance and the future prospectives of the conducted studies.Doctor of Philosoph

Tailoring the Electromagnetically Induced Transparency and Absorbance in Coupled Fano-Lorentzian Metasurfaces: A Classical Analog of a Four-Level Tripod Quantum System

Absorbance spectra of a near-field coupled Fano-Lorentzian metasurfaces are explored. A strong absorption window develops from the transparency background by coupling a LC resonance to the electromagnetically induced transparency band. This classical behavior can be analoged to a quantum four-level tripod system, where the interference between a bright and two dark modes gives rise to this observation.MOE (Min. of Education, S’pore)Accepted versio

Color-sensitive ultrafast optical modulation and switching of terahertz plasmonic devices

2D micro‐nanostructured metal films with hole arrays show promising features such as the extraordinary transmission of light. Such systems are interesting in the field of subwavelength photonics and nonlinear optics due to their high field confinement in addition to their inherent spectral scalability and frequency selective response. Several active schemes to control the extraordinary transmission are recently demonstrated. However, these dynamic devices do not reveal any obvious color‐dependent modulation of the resonant transmission behavior. Here, color‐sensitive ultrafast modulation of extraordinary resonant transmission of terahertz (THz) waves through 2D metallic hole arrays is demonstrated. Pumping the silicon beneath the metallic array with light of different colors and identical fluences exhibit significantly different ultrafast switching dynamics and modulation. The color‐dependent sensitivity and control of THz waves at an ultrafast timescale provide an extra degree of freedom that opens up new opportunities for future applications in active subwavelength optics, optoelectronics, and all‐optical switching of THz photonic devices.MOE (Min. of Education, S’pore)Accepted versio

Active control and switching of broadband electromagnetically induced transparency in symmetric metadevices

Electromagnetically induced transparency (EIT) arises from coupling between the bright and dark mode resonances that typically involve subwavelength structures with broken symmetry, which results in an extremely sharp transparency band. Here, we demonstrate a tunable broadband EIT effect in a symmetry preserved metamaterial structure at the terahertz frequencies. Alongside, we also envisage a photo-active EIT effect in a hybrid metal-semiconductor metamaterial, where the transparency window can be dynamically switched by shining near-infrared light beam. A robust coupled oscillator model explains the coupling mechanism in the proposed design, which shows a good agreement with the observed results on tunable broadband transparency effect. Such active, switchable, and broadband metadevices could have applications in delay bandwidth management, terahertz filtering, and slow light effects.MOE (Min. of Education, S’pore)Published versio