Enrique López-Moreno

Canonical transforms for paraxial wave optics

Paraxial geometric optics in N dimensions is well known to be described by the inhomogeneous symplectic group I2N ∧ Sp(2N, ℜ). This applies to wave optics when we choose a particular (ray) representation of this group, corresponding to a true representation of its central extension and twofold cover \(\tilde \Gamma _N = W_N ^ \wedge Mp(2N,\Re )\). for wave optics, the representation distinguished by Nature is the oscillator one. There applies the theory of canonical integral transforms built in quantum mechanics. We translate the treatament of coherent states and other wave packets to lens and pupil systems. Some remarks are added on various topics, including a fundamental euclidean algebra and group for metaxial optics.

Utilization of a digital-versatile-disc pickup head for benchtop laser microfabrication

Laser microfabrication is now offering interesting solutions to rapidly produce high-resolution photomasks or microstructures. However, most works require expensive commercial lasers and computer numerical control platforms, limiting its use by a large public. In this paper, we report the construction of a simple, custom-made, easily reproducible, automated laser system, based on a DVD optical pickup head. A user-friendly computer interface specifically designed to operate a motorized three-axis platform with micrometric precision controls focus distance and in-plane displacements. Writing performance characterization for both direct ablation and sintering of commercial black toner demonstrated flexibility in tridimensional microfabrication resolution and speed thanks to precise management of laser power and exposure time, with a minimal resolution of 3.1 μm.

Rapid fabrication of on-demand high-resolution optical masks with a CD-DVD pickup unit

A low-cost, direct fabrication technique with a micrometer range resolution has been implemented for rapid prototyping of optical masks for photolithography and structured light and diffraction optics applications. Using a setup based on the optical unit of a compact disc-digital versatile disc burner, a low-energy infrared laser beam was focused on a thin polymeric layer with embedded absorbing carbon nanopowder coated on a transparent glass substrate. This allowed for the generation of a custom-made transparent pattern in a computer numerical control fashion. In addition to its great simplicity and repeatability, the method also enables grayscale contrasts for each pixel individually, and fabricated masks proved to resist high intensities.

The Hong–Ou–Mandel interferometer in the undergraduate laboratory

The Hong?Ou?Mandel interferometer is an optical device that allows us to prove the quantum nature of light experimentally via the quantum amplitude superposition of two indistinguishable photons. We have implemented this experiment as an advanced undergraduate laboratory experience. We were able to overcome well-known difficulties using techniques reported recently by Thomas et al (2009 Rev. Sci. Instrum. 80 036101).

Teaching quantum mechanics with the Hong-Ou-Mandel interferometer

The Hong-Ou-Mandel interferometer is an optical device which allows us to prove experimentally the quantum nature of light via the quantum amplitude superposition of two indistinguishable photons. We have implemented this experiment as an advanced undergraduate laboratory experience. We were able to overcome well known difficulties with this experiment using recently reported techniques by Thomas et al. [Rev. Sci. Instr. 80, 036101 (2009), ].

Energy level structure and quantum phase transitions of spin systems with nonaxially symmetric Hamiltonians

A general spin system with a nonaxially symmetric Hamiltonian containing Jx, Jz-linear and Jz-quadratic terms, widely used in many-body fermionic and bosonic systems and in molecular magnetism, is considered for the variations of general parameters describing intensity interaction changes of each of its terms. For this model Hamiltonian, a semiclassical energy surface (ES) is obtained by means of the coherent-state formalism. An analysis of this ES function, based on catastrophe theory, determines the separatrix in the control parameter space of the system Hamiltonian: the loci of singularities representing semiclassical phase transitions. Here we show that distinct regions of qualitatively different spectrum structures, as well as a singular behavior of quantum states, are ruled by this separatrix: here we show that the separatrix not only describes ground-state singularities, which have been associated with quantum phase transitions, but also reveals the structure of the excited spectrum, distinguishing different quantum phases within the parameter space. Finally, we consider magnetic susceptibility and heat capacity of the system at finite temperature, in order to study thermal properties and thermodynamical phase transitions in the perspective of the separatrix of this Hamiltonian system.

Non-radiative energy transfer between impurity ions in crystals: configuration mixing

Abstract In this work, the non-radiative energy transfer mechanism between a pair of distinct dopant ions in a monocrystalline matrix is reviewed, the transfer mechanism is contemplated as a result of the configuration mixing of the energy levels of the subsystem donor–acceptor couple. When this resonance is considerable, a strong mixing takes place between two of the wave functions of the involved ions, and this mixing results in an increased value of the probability of non-radiative energy transfer. On the other hand, Dexters classical theory for non-radiative energy transfer can be applied as a limiting case when the energy resonance is neglected. The rate of non-radiative energy transfer has been calculated for various systems where this process has been observed, finding that, for specific energy levels of the subsystem pair the calculated non-radiative excitation transfer is in close agreement with the experimentally determined rate.