Person:
Gómez Calderón, Óscar

First Name

Óscar

Last Name

Gómez Calderón

URI

https://hdl.handle.net/20.500.14352/79942

Affiliation

Universidad Complutense de Madrid

Faculty / Institute

Óptica y Optometría

Department

Óptica

Area

Optica

Identifiers

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Now showing 1 - 8 of 8

Squeezing in a Lambda-type three-level atom via spontaneously generated coherence
(Physical review A, 2005) Gonzalo Fonrodona, Isabel; Antón Revilla, Miguel Ángel; Carreño Sánchez, Fernando; Gómez Calderón, Óscar
The squeezing spectrum of the fluorescent light is investigated for a laser-driven three-level atom of the Lambda configuration when quantum interference of the decay channels is accounted for. We show that when the two atomic transitions contribute to the detected fluorescence field, squeezing at certain frequency intervals is obtained in both the weak- and the high-Rabi-frequency regimes even for equally decay rates of the transitions. Unlike in two-level atoms in free space, squeezing can be obtained in both the in-phase and out-of-phase quadrature spectra although in different spectral regions. We also show that the squeezing spectrum can be controlled by an adequate selection of the Rabi frequencies and atomic detunings. Another remarkable effect is that squeezing can be achieved with proper relative phases of the driving fields. We provide an analytical description in the dressed basis which accounts for the main features of the squeezing spectra obtained from the numerical work.
Plasmon-enhanced terahertz emission in self-assembled quantum dots by femtosecond pulses
(Journal of Applied Physics, 2014) Carreño Sánchez, Fernando; Antón Revilla, Miguel Ángel; Melle Hernández, Sonia; Gómez Calderón, Óscar; Cabrera Granado, Eduardo; Cox, Joel; Singh, Mahi R.; Egatz-Gómez, Ana
A scheme for terahertz (THz) generation from intraband transition in a self-assembled quantum dot (QD) molecule coupled to a metallic nanoparticle (MNP) is analyzed. The QD structure is described as a three-level atom-like system using the density matrix formalism. The MNP with spherical geometry is considered in the quasistatic approximation. A femtosecond laser pulse creates a coherent superposition of two subbands in the quantum dots and produces localized surface plasmons in the nanoparticle which act back upon the QD molecule via dipole-dipole interaction. As a result, coherent THz radiation with a frequency corresponding to the interlevel spacing can be obtained, which is strongly modified by the presence of the MNP. The peak value of the terahertz signal is analyzed as a function of nanoparticle's size, the MNP to QD distance, and the area of the applied laser field. In addition, we theoretically demonstrate that the terahertz pulse generation can be effectively controlled by making use of a train of femtosecond laser pulses. We show that by a proper choice of the parameters characterizing the pulse train a huge enhancement of the terahertz signal is obtained.
From nearly tilted waves to cavity phase solitons in broad area lasers with squeezed vacuum
(Physical review letters, 2004) Gómez Calderón, Óscar; Cabrera Granado, Eduardo; Antón Revilla, Miguel Ángel; Gonzalo Fonrodona, Isabel; Carreño Sánchez, Fernando; Guerra, J. M.
Phase domains and phase solitons in two-level amplifying media damped by a squeezed vacuum are predicted for the first time. Two different types of pattern formation are found depending on the relative value of the cavity detuning to the squeezed parameter: the usual one in lasers via a supercritical Hopf bifurcation and a new one via pitchfork bifurcation.
Optical pumping of a single hole spin in a p-doped quantum dot coupled to a metallic nanoparticle
(Physical review B, 2013) Antón Revilla, Miguel Ángel; Carreño Sánchez, Fernando; Melle Hernández, Sonia; Gómez Calderón, Óscar; Cabrera Granado, Eduardo; Singh, Mahi R.
The preparation of quantum states with a defined spin is analyzed in a hybrid system consisting of a p-doped semiconductor quantum dot (QD) coupled to a metallic nanoparticle. The quantum dot is described as a four-level atom-like system using the density matrix formalism. The lower levels are Zeeman-split hole spin states and the upper levels correspond to positively charged excitons containing a spin-up, spin-down hole pair and a spin electron. A metallic nanoparticle with spheroidal geometry is placed in close proximity to the quantum dot, and its effects are considered in the quasistatic approximation. A linearly polarized laser field drives two of the optical transitions of the QD and produces localized surface plasmons in the nanoparticle which act back upon the QD. The frequencies of these localized plasmons are very different along the two principal axes of the nanoparticle, thus producing an anisotropic modification of the spontaneous emission rates of the allowed optical transitions which is accompanied by local-field corrections. This effect translates into a preferential acceleration of some of the optical pathways and therefore into a fast initialization of the QD by excitation with a short optical pulse. The population transfer between the lower levels of the QD and the fidelity is analyzed as a function of the nanoparticle's aspect ratio, the external magnetic field, and the Rabi frequency of the driving field. It is also shown that the main effect of the local-field corrections is a lengthening of the time elapsed to reach the steady-state. The hole spin is predicted to be successfully cooled from 5 to 0.04 K at a magnetic field of 4.6 T applied in the Voigt geometry.
Slow light in molecular-aggregate nanofilms
(Physical review letters, 2011) Cabrera Granado, Eduardo; Díaz García, Elena; Gómez Calderón, Óscar
We study slow-light performance of molecular aggregates arranged in nanofilms by means of coherent population oscillations. The molecular cooperative behavior inside the aggregate enhances the delay of input signals in the gigahertz range in comparison with other coherent population oscillation-based devices. Moreover, the problem of residual absorption present in coherent population oscillation processes is removed. We also propose an optical switch between different delays by exploiting the optical bistability of these aggregates.
Optical bistability in lasers induced by active molecules with a large permanent dipole moment
(Physical review A, 2002) Gómez Calderón, Óscar; Melle Hernández, Sonia; Gonzalo Fonrodona, Isabel
We study a single-mode laser system, whose active medium consists of molecules with a large difference between excited and ground electrical permanent-dipole moments, In this case, the Maxwell-Bloch equations Lire further coupled by nonlinear terms involving the ratio between this difference between the dipoles and the transition dipole moment. It is found that these new terms lead to multiple stationary solutions. From the linear stability analysis, we demonstrate the bistable (or multistable) character of the lasing solutions.
Transverse effects in the laser threshold due to electronic-vibrational coupling
(Physical review A, 1998) Gómez Calderón, Óscar; Gonzalo Fonrodona, Isabel
Transverse effects in the laser threshold, originated by electronic-vibrational coupling in the active centers, are analyzed theoretically by means of the semiclassical two-level Maxwell-Bloch equations. A single longitudinal mode is considered. It is found that the first laser threshold suffers modifications depending on the electronic-vibrational coupling strength. This coupling imposes certain conditions for the selection of a particular transverse spatial state and provides the minimum wavelength that can appear in the transverse pattern. The nature of the bifurcation and the stability of the homogeneous and critical traveling waves are analyzed.
Superluminal and slow light in Lambda-type three-level atoms via squeezed vacuum and spontaneously generated coherence
(Physical review A, 2005) Carreño Sánchez, Fernando; Gómez Calderón, Óscar; Antón Revilla, Miguel Ángel; Gonzalo Fonrodona, Isabel
We study the dispersion and absorption spectra of a weak probe in a Delta-type three-level atomic system with closely ground sublevels driven by a strong field and damped by a broadband squeezed vacuum. We analyze the interplay between the spontaneous generated coherence and the squeezed field on the susceptibility of the atomic system. We find that by varying the intensity of the squeezed field the group velocity of a weak pulse can change from subluminal to superluminal. In addition we exploit the fact that the properties of the atomic medium can be dramatically modified by controlling the relative phase between the driving field and the squeezed field, allowing us to manipulate the group velocity at which light propagates. The physical origin of this phenomenon corresponds to a transfer of the atomic coherence from electromagnetically induced transparency to electromagnetically induced absorption. Besides, this phenomenon is achieved under nearly transparency conditions and with negligible distortion of the propagation pulse.