Marcos R. Cardoso

Femtosecond lasers for processing glassy and polymeric materials

Novel materials have been developed to meet the increasing mechanical, electrical and optical properties required for technological applications in different fields of sciences. Among the methods available for modifying and improving materials properties, femtosecond laser processing is a potential approach. Owing to its precise ablation and modification capability, femtosecond laser processing has already been employed in a broad range of materials, including glasses and polymers. When ultrashort laser pulses are focused into a transparent material, the intensity at the focus can become high enough to induce nonlinear optical processes. Here, we report on femtosecond (fs) laser microfabrication in special glasses and polymers. Initially, we describe fs-laser micromachining on the surface of copper doped borate and borosilicate glasses. Subsequently, we present results on two-photon induced polymerization to fabricate microstructures containing fluorescent dyes for manufacturing optical microcavities. Both approaches are promising for designing optical and photonics micro/nanodevices.

Label-free oligonucleotide biosensor based on dual-peak long period fiber grating

We report the simplification and development of biofunctionalization methodology based on one-step 1-ethyl-3-(3- dimethylaminopropyl)carbodiimide (EDC)-mediated reaction. The dual-peak long period grating (dLPG) has been demonstrated its inherent ultrahigh sensitivity to refractive index (RI), achieving 50-fold improvement in RI sensitivity over a standard LPG sensor used in low RI range. With the simple and efficient immobilization of unmodified oligonucleotides on sensor surface, dLPG-based biosensor has been used to monitor the hybridization of complementary oligonucleotides showing a detectable oligonucleotide concentration of 4 nM with the advantages of label-free, real-time, and ultrahigh sensitivity.

Characterization of polymer fiber Bragg grating with ultrafast laser micromachining

We report that the main photosensitive mechanism of poly(methyl methacrylate)-based optical fiber Bragg grating (POFBG) under ultraviolet laser micromachining is a complex process of both photodegradation and negative thermo-optic effect. We found experimentally the unique characteristics of Bragg resonance splitting and reunion during the laser micromachining process providing the evidence of photodegradation, while the mean refractive index change of POFBG was measured to be negative confirming further photodegradation of polymer fiber. The thermal-induced refractive index change of POFBG was also observed by recording the Bragg wavelength shift. Furthermore, the dynamic thermal response of the micromachined-POFBG was demonstrated under constant humidity, showing a linear and negative response of around -47.1 pm/°C.

Effects in ultrafast laser micromachining PMMA-based optical fibre grating

Ultrafast laser owns extreme small beam size and high pulse intensity which enable spatial localised modification either on the surface or in the bulk of materials. Therefore, ultrafast laser has been widely used to micromachine optical fibres to alter optical structures. In order to do the precise control of the micromachining process to achieve the desired structure and modification, investigations on laser parameters control should be carried out to make better understanding of the effects in the laser micromachining process. These responses are important to laser machining, most of which are usually unknown during the process. In this work, we report the real time monitored results of the reflection of PMMA based optical fibre Bragg gratings (POFBGs) during excimer ultraviolet laser micromachining process. Photochemical and thermal effects have been observed during the process. The UV radiation was absorbed by the PMMA material, which consequently induced the modifications in both spatial structure and material properties of the POFBG. The POFBG showed a significant wavelength blue shift during laser micromachining. Part of it attributed to UV absorption converted thermal energy whilst the other did not disappear after POFBG cooling off, which attributed to UV induced photodegradation in POF.

Improved response time of laser etched polymer optical fiber Bragg grating humidity sensor

The humidity sensor made of polymer optical fiber Bragg grating (POFBG) responds to the water content change in fiber induced by the change of environmental condition. The response time strongly depends on fiber size as the water change is a diffusion process. The ultrashort laser pulses have been providing an effective microfabrication method to achieve spatial localized modification in materials. In this work we used the excimer laser to create different microstructures (slot, D-shape) in POFBG to improve its performance. A significant improvement in the response time has been achieved in a laser etched D-shaped POFBG humidity sensor.

Femtosecond laser induced periodic surface structures on hydrogenated amorphous silicon thin films

We report a study of fs-laser micromachining on the structure and surface morphology of hydrogenated amorphous silicon thin films using Raman spectroscopy and scanning electron and atomic force microscopy.

Production of copper nanoparticles by femtosecond laser micromachining in borosilicate glass

Femtosecond laser pulses were used to induce the precipitation of copper nanoparticles into three-dimensionally well-defined regions of borosilicate glass. Such results open new perspectives for the development of new photonic devices.

Excitation of Microstructures Fabricated by Two-photon Polymerization Through Silica Nanowires

We use two-photon polymerization to fabricate microstructures containing rodhamine 6G. Such microstructures were excited through silica nanowires, by coupling light to the standard end of the fiber. Such results open new opportunities for micro-optical devices.

Obtaining Superhydrophobic Surfaces By Laser Micromachining

This study presents three distinct laser methods, based on interference of a CW laser and pulsed laser ablation to create microstructures on polymeric surfaces.

Spectral-domain measurement of photo-induced birefringence in polymer

We report a new method to study the photo-induced birefringence in polymers based on spectral fringes observed with white-light polarized light transmission. Here, a photo-induced birefringence in polymeric film was used to add a phase shift on the fringes pattern of one given reference thick waveplate. Basically, the period of the fringes and phase shift carry information about the thickness and birefringence of the reference waveplate and the film, respectively. The optical fringes were detected by a linear array spectrometer. We measured a birefringence induced by polarized argon-ion laser at 514 nm on azopolymer MDI-DR19 film.