Schematic of plasmon excitation of (a)surface plasmon polaritons exists in a metadielectric interface with electromagnetic fields. a) metamaterial with a negative refractive index.[10] (b) hyper metalens.[11] (c) metamaterial for optical timing [12]. Figure 1.4.2 FDTD mode profile results for plasmonic nonlinear metasurfaces. a)-(b) Top view of the cross-section of the normalized Ez field distribution on the resonator monitored in the MQW at frequencies FF (ω) (a) and TH (3ω) (b). Ziji is the transition dipole moment element and Eijis is the transition energy of intersubband transitions between electronic subbands i and j, respectively.
Top view of SEM image of metasurface resonators. a) circular resonator (b) kite-shaped resonators. a) - (b) Side view schematic of metasurface resonators. b) Metal-connected plasmonic antennas from top to bottom (c)-(d) Simulation results of finite difference time domain (FDTD) of reflection. Red line means the monopole mode profile can be displayed, the bull line means the dipole mode profile can be displayed. Red line means the monopole mode profile can be displayed, the bull line means the dipole mode profile can be displayed. c)-(e) mode profile of monopole and dipole peak in pair.
Figure 2.1.7 Figure 2.1.7 FDTD mode profile results of the top-bottom metal coupled kite-shaped plasmonic nonlinear metasurfaces. Top cross section of the normalized Ez field distribution on the resonator at the (a) Fundamental Frequency (ω) and (b) Third Harmonic frequencies. Simulation and experiment results of linear reflection spectra of the nonlinear metasurface for designed metasurface.
The experimental result of nonlinear characterization. a) In fundamental frequency, 9um, the THG signal in lock-in amplifier. b) The THG signal in variation in laser FF power.
Introduction
- Nonlinear polarizations
- Third harmonic generation
- Plasmonic Resonances
- Metasurfaces
- Giant Nonlinearity in MQWs based Nonlinear metasurface
- Motivation
The three photons with the same frequency interact with the nonlinear material, including natural materials such as molecules, nonlinear crystals and plasmonic materials, which is the newly emerging research field. Since the nonlinear response in nature nonlinear materials are not strong enough to develop in applications, it necessarily needs strong bulk material to withstand the high intensity for experimentally controlling the nonlinear signal, but on the large scale of bulk material the reason is for fundamental and harmonic signals to have different propagation speeds within the media. Schematic representation of the plasmonic excitation (a) Surface plasmon polaritons exist in a metaelectric interface with electromagnetic fields.
In the optical regime, the electromagnetic field of the incident waves interacts with the plasma electron near the metal surface and thus excites a common oscillation that propagates along the interface. Only the TM (transverse magnetic) mode can induce excitation in the metal layer, so the SPP dispersion relation is described as. For the existing SPP, it must be a positive value, since almost precious metals fulfill the spectral range of transmittance, and the real part must be negative. The dispersion ratio SPP means >.
With artificially designed meta-atoms, the amplitude, phase and polarization of scattered light from the structure can be designed on a scale much shorter than the working wavelength, as this can be a subwavelength scale. The difficulty here is not limited, there are more serious problems, such as the difficulty to fabricate and integrate with the applications. a) metamaterial with negative refractive index.[10] (b) hypermetals.[11] (c)metamaterial for optical clocks [12]. Metasurfaces open new horizons in overcoming the scale limitation in controlling the propagation of electromagnetic waves with the light-matter interactions down to the subwavelength regime.
Unlike metamaterials, metasurfaces can be defined as an optically thin layer of metamaterial, whose thickness is smaller than the operating wavelength, as it is specified as a 2D regime. Like metamaterials, new features such as reconfigurable light paths, beamforming, and on-chip optical radiation can be achieved by integrating dynamically tunable components, gain medium, or nonlinear materials. When using MQWs in the nonlinear medium, the peak intensity of the third harmonic can be defined as 5.
The problem is from equation (1.4.1) the nonlinear medium thickness is smaller than the wavelength, it is proportional to the square of the thickness , the thickness of the order of subwavelength causes the intensity of the third harmonic to decrease. By designing the MQWs in the right way, it can be designed in the intersubband transition that occurs with 3 or 4 energy bands. the electron moves to the quantized energy band in the conduction band or valence band structure, called an intersubband transition. For Third Harmonic Generation in MQW, the nonlinear sensitivity can be described as5. where, is the average doping density, ω is the input frequency, is the electron charge, ℏΥ is the transition linewidth, ℏ is the transition energy, and is the dipole moment between energy states i and j. MQWs cannot resonate in free-space electromagnetic field propagation, so they combine with the plasmonic structure in the induced field Ez.
For these two problems solved, the motivation for the development of the previous research can be found in the Reference [18]. Therefore, in the side view it is much like SRR (Split ring resonator) magnetic dipole moment due to the electron moving the upper metal to the lower metal.
![Figure 1.1.1 (a)THG from the nonlinear crystal [24] (b)THG from nonlinear metasurface [4]](https://thumb-ap.123doks.com/thumbv2/123dokinfo/10493746.0/13.892.122.766.393.689/figure-thg-nonlinear-crystal-24-thg-nonlinear-metasurface.webp)
THG Metasurface with Monopole-Dipole Interaction
- Design of MQWs
- Metasurface design result
- Fabrication of the antennas
- Experiment approach
- MQWs Intersubband absorption measurment
- Nonlinear Optical Characterization
- Conclusion
Zij is the transition dipole moment element and Eij is the transition energy of the intersubband transitions between the electronic subbands i and j respectively (b) As a function of the pump wavenumber, the third-order nonlinear susceptibility of the MQW structure in (a). Second, due to the growth characteristic of the MQW, which makes it have a high susceptibility only in the normal to the surface, the structure can be caused by a high Ezfield within the MQW regions (nonlinear media). The next step to the design is confirmed that the "monopole mode" is formed when the metal is connected above and below. a)-(b) side view of metasurface resonators. b) Plasmonic antennas coupled to the top and bottom metal elements (c)-(d) Finite difference time domain (FDTD) simulation results of reflection.
So check the mode profile of 9um, Figure 3.1.4. e) and (f), besides the non-connected structure mode profile at 9um shown exact dipole mode file, it is clear that when connected top-bottom metal make monopole-like mode. It's a fairly simple change, but the result is quite unexpected. the pair of two resonators in mirror symmetry for interaction with each other, The traditional dipole mode splits into trailing dipole modes. a) side view schematic of of meta-surface resonators. Figure 2.1.7 FDTD mode profile results of the top-bottom metal coupled kite shape plasmonic nonlinear metasurfaces.
Place the sample in the solution until the reaction that changed the color of the surface between solution and sample is uniform. The former wet etching process opens the bottom metal-bonded MQWs layer. Due to the growth direction, only TM-polarized light with an E-field component was absorbed by the intersubband transitions.
For the MQW's intersubband absorption measurement, unpolarized mid-IR light passes through the polarizer and is then converted to TM-polarized light from the Fourier Transform Infrared Spectrometer (FTIR, Bruker Vertex 70) and passes through a chopper and linear polarizer and is focused on a facet of the multipath sample by a ZnSe lens. 407, which agreed well with the calculated values shown in Figure 3.3.1.(b) The measured transition line widths were 2ℏ ≈ 24 , 2ℏ ≈ 34.6 and 2ℏ ≈ 44 for the and 1–4 absorption coefficients, respectively. for each transition peak was calculated.7 taking into account the sample geometry and the thickness of the MQW layer was 400 nm thick, and the number of passages the MQW layer is reasonably estimated to be 3 times. The imaginary part of the out-of-plane dielectric constant of the MQW layer e^ which relates to the absorption and it can be expressed as
2.3.2) where w denotes the pumping frequency, ecore denotes the average dielectric constant of the undoped semiconductor, Neis average bulk doping density, i.e. the electron charge, and ℏ is energy, ℏ is linewidth and is dipole moment between and subband energy level. The dielectric constant of the MQW for the in-plane E-field polarization (∥) can be expressed as. Using the calculated dielectric constants of the MQW for the out-of-plane ( ) and in-plane ( ∥ ) E-field polarizations, it is applied to the designed MQW layer in the FDTD simulation.
The polarization states of the input and output beams are monitored by a sample mounted on a rotary stage and a polarizer. The QCL wavelength is 9 um (MQW absorption peak) fixed. Input peak intensity and power were measured with a power and energy meter (PM100D, Thorlabs) in front of the collimating lens.
Outlook
Taking into account the saturation effect when the structure is designed, the effective susceptibility is defined with saturation by multiplying the factors. Traditionally, the effective susceptibility value has high value in the same condition where saturation is high. It makes effective non-linearity has been reduced, but with the monopole structure which can make waste of mode quite easier, it can differentiate the effective chi modes.
With multiplication of the saturation value in mode split effective chi, relaxing region in high saturation and the other mode dominates the effective chi in large region.
Conclusion
Summary
