12.2.2. Four-Wave Mixing (FWM) 4849 12.2.3. Dye Aggregation 4850 12.2.4. Optoelectronic Nanodevices 4850 12.3. Sensor 4851 12.3.1. Chemical Sensor 4851 12.3.2. Biological Sensor 4851 12.4. Catalysis 4852 13. Conclusion and Perspectives 4852 14. Abbreviations 4853 15. Acknowledgements 4854 16. References 4854 * Corresponding author E-mail: tpal@chem.iitkgp.ernet.in. † Raidighi College. § Indian Institute of Technology. 4797 Chem. Rev. 2007, 107, 4797−4862

Interparticle Coupling Effect on the Surface Plasmon Resonance of Gold Nanoparticles: From Theory to Applications

We present a quantum description of a planar microcavity photon mode strongly coupled to a semiconductor intersubband transition in presence of a two-dimensional electron gas. We show that, in this kind of system, the vacuum Rabi frequency ${\ensuremath{\Omega}}_{R}$ can be a significant fraction of the intersubband transition frequency ${\ensuremath{\omega}}_{12}$. This regime of ultrastrong light-matter coupling is enhanced for long-wavelength transitions, because for a given doping density, effective mass and number of quantum wells, the ratio ${\ensuremath{\Omega}}_{R}∕{\ensuremath{\omega}}_{12}$ increases as the square root of the intersubband emission wavelength. We characterize the quantum properties of the ground state (a two-mode squeezed vacuum), which can be tuned in situ by changing the value of ${\ensuremath{\Omega}}_{R}$, e.g., through an electrostatic gate. We finally point out how the tunability of the polariton quantum vacuum can be exploited to generate correlated photon pairs out of the vacuum via quantum electrodynamics phenomena reminiscent of the dynamical Casimir effect.

Quantum vacuum properties of the intersubband cavity polariton field

We present a full quantum theory for the dissipative dynamics of an optical cavity in the ultrastrong light-matter coupling regime, in which the vacuum Rabi frequency is a significant fraction of the active electronic transition frequency and the antiresonant terms of the light-matter coupling play an important role. In particular, our model can be applied to the case of intersubband transitions in doped semiconductor quantum wells embedded in a microcavity. The coupling of the intracavity photonic mode and of the electronic polarization to the external, frequency-dependent, dissipation baths is taken into account by means of quantum Langevin equations in the input-output formalism. In the case of a time-independent vacuum Rabi frequency, exact analytical expressions for the operators are obtained, which allows us to characterize the quantum dissipative response of the cavity to an arbitrary initial condition (vacuum, coherent field, thermal excitation). For a vacuum input in both the photonic and electronic polarization modes, the ground state of the cavity system is a two-mode squeezed vacuum state with a finite population in both photonic and electronic modes. These excitations are, however, virtual and cannot escape from the cavity: for a vacuum input, a vacuum output is found, without any trace of the intracavity squeezing. For a coherent photonic input the linear optical response spectra (reflectivity, absorption, transmission) have been studied, and signatures of the ultrastrong coupling have been identified in the asymmetric and peculiar anticrossing of the polaritonic eigenmodes. Finally, we have calculated the electroluminescence spectra in the case of an incoherent electronic input: the emission intensity in the ultrastrong coupling regime results in being significantly enhanced as compared to the case of an isolated quantum well without a surrounding cavity.

https://hal.archives-ouvertes.fr/hal-00080977/document

Input- output theory of cavities in the ultrastrong coupling regime : The case of time-independent cavity parameters

Local fields in the electrodynamics of mesoscopic media

The development of surface-enhanced Raman scattering (SERS)-active substrates for cancer gene detection is described. The detection method uses Raman active dye-labeled DNA gene probes, self-assembled monolayers, and nanostructured metallic substrates as SERS-active platforms. The mercaptohexane-labeled single-stranded DNA (SH−(CH2)6-ssDNA)/6-mercapto-1-hexanol system formed on a silver surface is characterized by atomic force microcopy. The surface-enhanced Raman gene (SERGen) probes developed in this study can be used to detect DNA targets via hybridization to complementary DNA probes. The probes do not require the use of radioactive labels and have a great potential to provide both sensitivity and selectivity. The effectiveness of this approach and its application in cancer gene diagnostics (BRCA1 breast cancer gene) are investigated.

Surface-Enhanced Raman Scattering Substrate Based on a Self-Assembled Monolayer for Use in Gene Diagnostics

In a nonlocal semiclassical local-field approach and by using a simple one-band model in which the conduction-band nonparabolicity is taken into account in an energy-dependent effective-mass scheme, we have derived a rigorous expression for the p-polarized optical intersubband absorption coefficient of a multiple-quantum-well (MQW) structure inside an asymmetric Fabry-P\'erot microcavity. For a GaAs/${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$As MQW structure sandwiched between a GaAs/AlAs distributed Bragg reflector and vacuum, we performed numerical calculations of the optical-absorption spectra for different parameters such as the cavity length, the angle of incidence, the electron concentration, and the number of quantum wells (QW's) in the structure. In the strong-coupling regime, our results show that the so-called Rabi splitting of the absorption spectrum, which is due to the electromagnetic interactions between the cavity modes and the intersubband modes, is increased in size with an increase in the QW number and in the sheet electron density. The contrast of the splitting is also found to be strongly dependent of these parameters. Finally, it is demonstrated that the Rabi splitting of the intersubband absorption line can be easily tuned by varying either the cavity length or the angle of incidence.

Rabi splitting of the optical intersubband absorption line of multiple quantum wellsinside a Fabry-Pérot microcavity

Using a microscopic local-field formulation, the linear optical absorption of a multiple-quantum-well (MQW) structure associated with intersubband transitions is investigated. Taking as a starting point a fundamental self-consistent integral equation for the local field, the p-polarized electric-field distribution inside each quantum well in the MQW structure is studied. It is demonstrated that the local field is essentially determined from a set of linear algebraic equations. Within the infinite-barrier approximation with an effective well width, numerical calculations of the optical absorption spectra are presented for a GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As multiple quantum well for different parameters such as the two-dimensional (sheet) electron concentration, the angle of incidence, and the number of wells. The numerical results show that the local-field effect leads to a notable blueshift of the peak-position energy in the absorption spectra as the sheet density of the electrons is increased, and that for larger angles of incidence the electromagnetic interaction among quantum wells gives rise to a significant broadening of the absorption peak when the number of wells is sufficiently large.

Local-field effect on the linear optical intersubband absorption in multiple quantum wells.

A nonlocal analysis of the infrared second-harmonic generation associated with intersubband transitions in a symmetric semiconductor quantum-well structure is presented. Taking as a starting point a fundamental self-consistent integral equation for the local field, the p-polarized first-harmonic field inside the quantum well is studied. By using the infinite-barrier wave functions and taking into account only the two lowest subbands, analytical expressions are obtained for the local field. The result of the local-field calculation at the first-harmonic frequency, in turn, is used to calculate the p-polarized second-harmonic local field. The conversion efficiency of the second-harmonic generation from the quantum well is thus determined. Numerical calculations of the frequency and angular spectra of the second-harmonic intensities are presented for a symmetric GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$As quantum well. The numerical results show that strong second-harmonic generation occurs in the vicinity of the resonance frequencies for both the first- and second-harmonic local field inside the quantum well. The influence of the dynamic local-field interaction of the electrons on the optical second-harmonic generation is investigated. It is demonstrated that the dynamic screening can lead to a notable upward shift of the locations of the resonant peaks in the frequency spectra of the second-harmonic conversion coefficient.

Local-field study of the optical second-harmonic generation in a symmetric quantum-well structure.

Taking as a starting point the Liouville equation for the one-body density matrix operator, a general expression for the third-order nonlinear current density responsible for the optical Kerr effect associated with intersubband transitions in a quantum well is derived by use of the perturbative expansion method. The nonlinear current density is related to the local field inside the quantum well via a nonlocal relation. By combining the field-induced nonlinear part of the current density with the Maxwell equation, a nonlinear integral equation for the local field is established. For a two-level quantum well, the integral equation is solved exactly. The nonlinear optical reflectivity, transmittance, and absorbance of the quantum well in turn are obtained. Numerical calculations of the light-induced change of the optical spectra are presented for a Al0.5Ga0.5As/GaAs/Al0.5Ga0.5 As quantum well. The numerical results show that the optical reflectivity and absorbance decrease, and the transmittance increases as the optical intensity of the incident light is increased. In the case where the quantum-well structure is heavily doped, a notable light-induced red-shift of the location of the resonance peak in the optical spectra stemming from the combined local-field effect and field-induced population redistribution is predicted.

https://iopscience.iop.org/article/10.1088/0031-8949/52/1/021/pdf

Ansheng Liu

Papers

Rabi splitting of the optical intersubband absorption line of multiple quantum wellsinside a Fabry-Pérot microcavity

Local-field effect on the linear optical intersubband absorption in multiple quantum wells.

Local-field study of the optical second-harmonic generation in a symmetric quantum-well structure.

Nonlocal theory of the intersubband optical Kerr effect in a semiconductor quantum well

Local-field-resonant Optical Paramagnetic Response of a Metallic Quantum Well