Two-photon absorption spectrometers for near infrared.

We present a Silicon-based Charge-Coupled Device (Si-CCD) sensor applied as a cost-effective spectrometer for femtosecond pulse characterization in the Near Infrared region in two different configurations: two-Fourier and Czerny-Turner setups. To test the spectrometer's performance, a femtosecond Optical Parametric Oscillator with a tuning range between 1100 and 1700 nm and a femtosecond Erbium-Doped Fiber Amplifier at 1582 nm were employed. The nonlinear spectrometer operation is based on the Two-Photon Absorption effect generated in the Si-CCD sensor.

Effect of oils on the transmission properties of a terahertz photonic crystal.

The transmission properties of a photonic crystal immersed in several different oils have been characterized using terahertz time domain spectroscopy in the spectral range of 0.3-1.5 THz.

Sub-wavelength continuous THz imaging system based on interferometric detection.

We have developed a continuous wave sub-wavelength terahertz (THz) imaging system that combines two prominent classical optical techniques: solid immersion microscopy and interferometric detection. This combination allows for resolution beyond the diffraction limit at 703 GHz. We experimentally demonstrate sub-wavelength spatial resolution working with a relatively low-cost pyroelectric detector and with both high and low contrast samples.

Photolithographically-patterned C-MEMS graphene by carbon diffusion through nickel.

In recent years the most studied carbon allotrope has been graphene, due to the outstanding properties that this two-dimensional material exhibits; however, it turns out to be a difficult material to produce, pattern, and transfer to a device substrate without contamination. Carbon microelectromechanical systems are a versatile technology used to create nano/micro carbon devices by pyrolyzing a patterned photoresist, making them highly attractive for industrial applications. Furthermore, recent works have reported that pyrolytic carbon material can be graphitized by the diffusion of carbon atoms through a transition metal layer.

Fluorescence of serotonin in the visible spectrum upon multiphotonic photoconversion.

The vital molecule serotonin modulates the functioning of the nervous system. The chemical characteristics of serotonin provide multiple advantages for its study in living or fixed tissue. Serotonin has the capacity to emit fluorescence directly and indirectly through chemical intermediates in response to mono- and multiphoton excitation.

Low-energy/pulse response and high-resolution-CMOS camera for spatiotemporal femtosecond laser pulses characterization @ 1.55 μm.

In this work, we present a commercial CMOS (Complementary Metal Oxide Semiconductor) Raspberry Pi camera implemented as a Near-Infrared detector for both spatial and temporal characterization of femtosecond pulses delivered from a femtosecond Erbium Doped Fiber laser (fs-EDFL) @ 1.55 µm, based on the Two Photon Absorption (TPA) process. The capacity of the device was assessed by measuring the spatial beam profile of the fs-EDFL and comparing the experimental results with the theoretical Fresnel diffraction pattern.

Emergent ultra-long-range interactions between active particles in hybrid active-inactive systems.

Particle-particle interactions determine the state of a system. Control over the range of such interactions as well as their magnitude has been an active area of research for decades due to the fundamental challenges it poses in science and technology. Very recently, effective interactions between active particles have gathered much attention as they can lead to out-of-equilibrium cooperative states such as flocking.

Effect of velocity on microdroplet fluorescence quantified by laser-induced fluorescence.

Microdroplets generated inside microfluidic devices have been widely used as miniaturized chemical and biological reactors allowing important reductions in experimental fluid volumes and making it possible to carry out high-throughput assays. Laser-induced fluorescence (LIF) is commonly used to detect and quantify the product, marker or cell content inside each individual droplet. In this work, we employed this technique to characterize the response of in-flow microdroplets filled with fluorescein dye at different laser powers and flow velocities.

Huygens' Principle: Exact wavefronts produced by aspheric lenses.

We obtain simple exact formulas for the refracted wavefronts through plano-convex aspheric lenses with arbitrary aspheric terms by considering an incident plane wavefront propagating along the optical axis. We provide formulas for the zero-distance phase front using the Huygens' Principle and the Malus-Dupin theorem. Using the fact that they are equivalent, we have in the second method found a way to use an improper integral, instead of the usual evaluated integral, to arrive at these formulas.

Null Ronchi-Hartmann test for a lens.

A method to design Ronchi-Hartmann screens for improved alignment in the testing of fast plano-convex spherical lenses is presented. We design null screens that produce aligned straight fringes for observed patterns. The designs of these null screens are based on knowledge of the caustic by refraction.

Nanopositioning for polarimetric characterization.

A positioning system with approximately nanometer resolution has been developed based on a new implementation of a motor-driven screw scheme. In contrast to conventional positioning systems based on piezoelectric elements, this system shows remarkably low levels of drift and vibration, and eliminates the need for position feedback during typical data acquisition processes. During positioning or scanning processes, non-repeatability and hysteresis problems inherent in mechanical positioning systems are greatly reduced using a software feedback scheme.

Cavity-enhanced magnetooptical observation of magnetization reversal in individual single-domain nanomagnets.

Optical studies of nanoscale magnets promise access to ultrafast magnetization dynamics but are challenging because of limited spatial resolution. We demonstrate that cavity enhancement of the magnetooptical Kerr effect increases the sensitivity in nanomagnetooptics significantly. Magnetization switching in individual single-domain magnets in both far-field and near-field Kerr microscopy is observed, and scaling laws are determined.