Ainara Rodriguez

Fabrication of high quality sub-micron Au gratings over large areas with pulsed laser interference lithography for SPR sensors

Metallic gratings were fabricated using high energy laser interference lithography with a frequency tripled Nd:YAG nanosecond laser. The grating structures were first recorded in a photosensitive layer and afterwards transferred to an Au film. High quality Au gratings with a period of 770 nm and peak-to-valley heights of 20-60 nm exhibiting plasmonic resonance response were successfully designed, fabricated and characterized.

Photonic structures in diamond based on femtosecond UV laser induced periodic surface structuring (LIPSS)

We study the fabrication of photonic surface structures in single crystal diamond by means of highly controllable direct femtosecond UV laser induced periodic surface structuring. By appropriately selecting the excitation wavelength, intensity, number of impinging pulses and their polarization state, we demonstrate emerging high quality and fidelity diamond grating structures with surface roughness below 1.4 nm. We characterize their optical properties and study their potential for the fabrication of photonic structure anti-reflection coatings for diamond Raman lasers in the near-IR.

System Requirement Analysis of Laser Interference Nanolithography

This paper presents a system requirement analysis of multi-beam laser interference nanolithography for nanoscale structuring of materials including seven sections: introduction, formation of multi-beam laser interference patterns, user requirements, system architecture, experiments, discussions and conclusions. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results. The environmental effect and technological potential were also discussed.

Enhancement of surface area and wettability properties of boron doped diamond by femtosecond laser-induced periodic surface structuring

We demonstrate the formation of laser-induced periodic surface structures (LIPSS) in boron-doped diamond (BDD) by irradiation with femtosecond near-IR laser pulses. The results show that the obtained LIPSS are perpendicular to the laser polarization, and the ripple periodicity is on the order of half of the irradiation wavelength. The surface structures and their electrochemical properties were characterized using Raman micro-spectroscopy, in combination with scanning electron and atomic force microscopies. The textured BDD surface showed a dense and large surface area with no change in its structural characteristics. The effective surface area of the textured BDD electrode was approximately 50% larger than that of a planar substrate, while wetting tests showed that the irradiated area becomes highly hydrophilic. Our results indicate that LIPSS texturing of BDD is a straightforward and simple technique for enhancing the surface area and wettability properties of the BDD electrodes, which could enable higher current efficiency and lower energy consumption in the electrochemical oxidation of toxic organics.

Ultrafast laser inscription of volume phase gratings with low refractive index modulation and self-images of high visibility

Ultrafast laser inscription of volume phase gratings with low index contrast and self-images with visibility of 0.96 is demonstrated. It is also demonstrated that phase differences of π/2 for visible light are achievable with only one layer of structures induced in bulk borosilicate glass by direct laser writing. The fabrication method avoids the stitching of several layers of structures and significantly reduces the time of process. The increment of visibility with the induced phase difference is proved and results are compared with the expected for planar phase gratings.

Interference lithography processes with high-power laser pulses

Laser interference lithography (LIL) is concerned with the use of interference patterns generated from two or several coherent beams of laser radiation for the structuring of materials. This paper presents the work on the processes based on resists and direct writing with laser interference lithography. In the work, a four-beam laser interference system was used as a submicrometer structuring tool in which a high-energy pulsed, frequency-tripled and TM polarized Nd:YAG laser (355 nm) with a coherent length of 3 m, energy power up to 320 mJ/cm2, pulse duration of 8 ns and 10 Hz repetition rate was used as a light source. The experimental results were achieved with 2-beam and 4-beam interference patterning. The processes can be used to define submicron surface relieves in large areas for use in the field of MEMS.

Formation of 4-beam laser interference patterns for nanolithography

This paper presents a theoretical analysis of formation of 4-beam laser interference patterns for nanolithography. Parameters of 4-beam interference patterns including the pattern amplitude, period, orientation and uniformity were discussed. Analytical expressions were obtained for the spatial distribution of radiation of the interfering beams as a function of their amplitudes, phases, angles of incidence on the sample, and polarization planes with computer simulation and experimental results.

Volume polarization gratings inscribed in glass with femtosecond lasers

The discovery of the formation of nanogratings when irradiating fused silica glass with ultrashort laser pulses in 2003 may have opened a new generation of compact and long life time optical devices. 3D-writing, thermal stability up to 1000 oC and virtually unlimited lifetime at room temperature make optics based on nanogratings of great potential for compact sensors or devices that work in adverse environmental conditions [1]. In addition, nanogratings behave as subwavelength structures in the visible and NIR spectrum, so that they allow micro-sized waveplates with controllable retardance and fast-axis orientation and, thus, they are expected to allow the fabrication of almost any design of polarization device in glass [2]. In this work we study volume polarization gratings (VPOG) in glass with special focus on the self-imaging of the grating produced by the Talbot effect. The experimental results are compared with the theoretical planar polarization gratings described by Scalar Diffraction Theory.

Mask-less lithography of diamond films using shaped ultrafast UV pulses

Atomic-scale manipulation of carbon based surfaces, such as diamond, has an enormous potential for the construction of future nano-scale, photonic and optoelectronic devices. Diamond, when compared to other group IV covalent semiconductors, is particularly interesting; not only its tightly packed and strongly bound crystal lattice is an ideal environment for extreme physics, but it also offers advantages in terms of heat conductivity, hardness and transparency for multitude of applications. The development of diamond transistors [1], single photon sources for quantum computation based on diamond [2] or high power diamond optics and lasers [3] have benefited from developments on high precision diamond processing greatly.

Patterning and Optical Properties of Materials at the Nanoscale

The discovery of novel material properties at the nanoscale has aroused a great amount of interest in the fabrication of structures at the sub-micro and nano scales. In this chapter the most promising non-conventional sub-micro and nano fabrication techniques together with the optical characterization techniques which have been developed in recent years to address the novel photonic and plasmonic properties of structured materials are revised.