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.Comment: 10 pages, 7 figure

High slope efficiency and high refractive index change in direct-written Yb-doped waveguide lasers with depressed claddings

We report the first Yb:ZBLAN and Yb:IOG10 waveguide lasers fabricated by the fs-laser direct-writing technique. Pulses from a Titanium-Sapphire laser oscillator with 5.1 MHz repetition rate were utilized to generate negative refractive index modifications in both glasses. Multiple modifications were aligned in a depressed cladding geometry to create a waveguide. For Yb:ZBLAN we demonstrate high laser slope efficiency of 84% with a maximum output power of 170 mW. By using Yb:IOG10 a laser performance of 25% slope efficiency and 72 mW output power was achieved and we measured a remarkably high refractive index change exceeding Δn = 2.3 × 10(-2).Guido Palmer, Simon Gross, Alexander Fuerbach, David G. Lancaster and Michael J. Withfor

Integrated photonic building blocks for next-generation astronomical instrumentation I: the multimode waveguide

We report on the fabrication and characterization of composite multimode waveguide structures that consist of a stack of single-mode waveguides fabricated by ultrafast laser inscription. We explore 2 types of composite structures; those that consist of overlapping single-mode waveguides which offer the maximum effective index contrast and non overlapped structures which support multiple modes via strong evanescent coupling. We demonstrate that both types of waveguides have negligible propagation losses (to within experimental uncertainty) for light injected with focal ratios >8, which corresponds to the cutoff of the waveguides. We also show that right below cutoff, there is a narrow region where the injected focal ratio is preserved (to within experimental uncertainty) at the output. Finally, we outline the major application of these highly efficient waveguides; in a device that is used to reformat the light in the focal plane of a telescope to a slit, in order to feed a diffraction-limited spectrograph.Comment: 15 pages, 11 figures, accepted to Optics Expres

Simultaneous second- and third- order spectral phase control of Ti:sapphire laser pulses using achromatic doublet prisms

The standard technique commonly utilized to introduce large amounts of negative group delay dispersion (GDD) into the beam path of ultrashort laser pulses with low insertion losses is the use of a pair of prisms in a double pass configuration. However, one disadvantage of this approach is the unavoidable introduction of additional high-order spectral phase errors, most notably third-order dispersion (TOD) due to the characteristics of the refractive index of available optical materials. In this paper we provide an overview of the dispersive properties of more than 100 common types of optical glasses, used either as a bulk stretcher or in a prism compressor configuration. In addition, we present a novel method that enables independent control of GDD and TOD in a prism-only setup. The performance of different prism combinations is analyzed numerically, and design guidelines are given.4 page(s

Single-stage Pulse Compression and High-Energy Supercontinuum generation from a Chirped-pulse oscillator

We demonstrate the generation of high-energy supercontinuum pulses by coupling the uncompressed pulses of a Ti:sapphire Chirped-pulse oscillator into a microstructure fibre which features a highly anomalous dispersion at the centre wavelength of the laser.3 page(s

Femtosecond laser direct-writing of waveguide Bragg gratings in a quasi cumulative heating regime

Waveguide Bragg gratings (WBGs) were directly inscribed into Alkaline Earth Boro-Aluminosilicate glass samples in a single process step at high fabrication speeds. We utilized a 5.1 MHz femtosecond oscillator to exploit high repetition rate heat accumulation effects. The pulse energy was modulated using a Pockels cell in order to fabricate waveguides that contain a periodic array of nano-structures inside their core. We have demonstrated, for the first time, that the transient build-up of heat accumulation within the sample can lead to the formation of a permanent nano-void. This effect can be exploited to fabricate WBGs at high speeds.9 page(s

Direct femtosecond laser written waveguides in bulk Ti³⁺: sapphire

We report on direct inscription of type-II waveguides in bulk titanium-doped sapphire with an ultrafast chirpedpulse oscillator. Ti³⁺:Sapphire is of particular interest due to its large emission bandwidth which enables a broadband tunability and generation of ultra-short pulses. However, its lasing threshold is high and powerful high brightness pump sources are required. The fabrication of a waveguide in Ti³⁺:Sapphire could thus enable the fabrication of low-threshold tunable lasers and broadband fluorescence sources. The latter are of interest for optical coherence tomography where the obtainable resolution scales with the bandwidth of the light source. The fabricated waveguides are formed in-between two laser induced damage regions. This technique has been applied to other crystalline materials (e.g. LiNbO3) but not in Ti3+:Sapphire, yet. The size of the structural changed regions is strongly dependent on the writing laser polarization. These damage regions of changed structure cause a stress-field inside the crystalline lattice which consequently increases the refractive index to form a waveguide. The written structures exhibit a strong birefringence and two waveguides that support orthogonal polarized modes are formed between each pair of damage lines. Linearly polarized light parallel to the crystal's surface is guided between the two damage regions while a waveguide for the orthogonal polarization is formed underneath. The propagation properties of the waveguides are characterized by their near-field profiles and insertion losses with respect to the writing parameters. Further the fluorescence output power is measured and the emission spectra of the waveguides are compared to the bulk material.8 page(s

Ultrafast direct written waveguide Bragg gratings utilizing a high pulse energy femtosecond oscillator

Direct written Waveguide Bragg gratings (WBGs) were fabricated in Borosilicate. We utilized a 5.1 MHz femtosecond oscillator exploiting heat accumulation and micro-structuring effects. By synchronizing a Pockels cell to the translation of the sample the pulse energy was modulated between the cumulative heating regime and the micro-damaging regime. We present and characterize WBGs fabricated in a single step at high process speeds.4 page(s

Dynamics of waveguide writing using a high pulse energy (600 nJ) MHz femtosecond oscillator

We study waveguide writing in various transparent dielectric materials using a highly flexible chirped-pulse femtosecond oscillator (CPO) as the laser source. This unique device allows us to investigate an unprecedented parameter range up to 5.2 MHz in repetition rate, 50 fs-2 ps in pulse duration and up to 600 nJ in energy per pulse. Thus the CPO closes the gap between high energy amplifier- and high repetition oscillator-direct waveguide writing.1 page(s

Fabrication of fully integrated antiresonant reflecting optical waveguides using the femtosecond laser direct-write technique

Utilizing a recently developed two-step fabrication process, we have experimentally demonstrated what is to the best of our knowledge the first ever integrated antiresonant reflecting optical waveguide (ARROW), directly inscribed into bulk optical glass. The waveguide consists of an array of high-index contrast rods that surround an unmodified core. The transmission spectrum reveals the formation of discrete bandgaps that can be tuned by varying the diameter of the individual rods.3 page(s