Gerd Marowsky

Sub-micron grating formation in Ta2O5-waveguides by femtosecond UV-laser ablation

Abstract Sub-micron-period surface gratings on Ta2O5 waveguide layers were produced by ablation with a sub-ps-UV-laser. The structure is generated by projection imaging of a primary transmission grating mask. A grating of 500 nm period with a surface modulation depth of 10 nm on a sample area of about 300 μm×300 μm can be produced with a single laser pulse of about 100 mJ/cm2 at 248 nm. Adjustment of the modulation depth to specific requirements can be accomplished by varying laser fluence or pulse number. The structures can be used as grating couplers.

F2-lasers: High-Resolution Optical Processing System for Shaping Photonic Components

A high-resolution 157-nm optical system has been developed for the first time to microprocess optical materials with record short-wavelength F2-laser radiation. The F2-laser photons drive strong material interactions in silica glasses for microsculpting surfaces and for imprinting internal refractive index structures. The high-resolution optics deliver a homogenized beam of high on-target fluence (approximately 2.5 J/cm2) for ablation of fused silica and other wide bandgap optical materials. The system resolution is approaching 1-micron lateral and less than 100-nm depth - sub-wavelength features appropriate for defining optical communication components at 1.55-micrometers wavelength. This paper describes this novel processing system and offers prospects for F2-laser microfabrication and trimming of photonic components in the telecommunication and general optics manufacturing fields.

High-resolution F2-laser machining of micro-optic components

The F2-laser Nano fabrication Facility at the University of Toronto delivers high-fluence 157-nm radiation at high resolution to micro fabricate high-finesse silica-based optical components. The 7.9-eV photons drive strong material interactions near the band-edge states of fused silica and related glasses that help avoid microcrack formation, a common limitation of longer wavelength laser. The strong interactions provide for small and smooth excisions, offering depth control on a scale of tens of nanometers. A 157-nm beam homogenization system and a 25x Schwarzschild lens provided a uniform on-target fluence of 9 J/cm2 in a 0.25 mm by 0.25 mm field. Larger work are was enabled by synchronously driving the projection mask and target motion stages. The 0.4 NA lens supported the formation of high- aspect channel walls and surface-relief features as small as approximately 500 nm. Both mask projection and direct writing technique were employed. The novel aspects of the optical beam delivery system are presented together with results on fabricating micro-channels, cutting optical fiber, fabricating surface relief grating and cylindrical lens. The results demonstrate broad application directions for fabricating telecommunication devices, general optical and photonic components, and biological devices.

Fluorescence measurements on nanotiter plates

Two different highly sensitive and fast but low-cost instruments for fluorescence measurements on nanotiter plates or other high density sample arrays are presented. Both instruments use 635 nm diode lasers for the detection of Cy5 fluorescence. In the first device all cavities of the nanotiter plate are illuminated simultaneously and the fluorescence is detected spatially resolved by a charge-coupled device camera within a few seconds. The second system uses an on-chip microscanner for the sequential illumination of the samples and the fluorescence is detected by a simple photomultiplier tube. Both instruments have originally been developed for environmental analysis by immunochemical labeling but they can also be used for other medical and biological purposes where analyte concentrations have to be determined.

Fabrication of diffractive phase elements by F2-laser ablation of fused silica

F2-laser ablation at 157 nm was used for generating sub-micron surface relief structures on fused silica to define binary diffractive phase elements (DPE). A pattern array of 128 x 128 pixels was excised using the F2 laser in combination with a high resolution processing system comprising of CaF2 beam-homogenization optics and a high-resolution Schwarzschild reflective objective. A square projection mask provided precise excisions in less than 10 x 10 μm2 spots, having sub-μm depths that were controlled by the laser fluence and the number of laser pulses to provide for the required phase delay between ablated and non-ablated pixels. Thus a diffractive phase element (DPE) optimized for first order in the UV spectral range was made. A four-level DPE design computed by the Iterative Fourier Transform Algorithm (IFTA) will be described for generating an arbitrary irradiation pattern without the point symmetry of a two level design.

Environmental analysis by laser-induced fluorescence detection on nano titer plates

A small, fast and low cost device for the measurement of analyte concentrations on nano titer plates is desired. By immuno chemical labelling with dyes these analyte concentrations can be determined by laser induced fluorescence detection. A first highly sensitive instrument for fluorescence excitation and detection has been developed. It is based on a diode laser and a CCD camera. Further reduction in price and size is leading to a second system that uses a micro scanner for the sequential illumination of the NTP. The development of this second instrument is still in progress.

Ablation of solid targets with UV femtosecond pulses

Ablation of submicron structures on metals and semiconductors is presented using subpicosecond laser pulses at 248 nm. Morphology changes as a function of pulse duration have been investigated. The dynamics of the surface modification has been studied using a pump-probe technique. Diffracted signals of a probe beam on laser induced gratings provide information on the dynamics of the electron phonon interaction, melting and material removal simultaneously. For metals, in the first 5 - 10 ps following irradiation the electron-phonon relaxation dominates the process, followed by melting, expansion and violent material ejection. For semiconductors, rapid amorphization of the surface occurs within a couple of hundred femtoseconds following irradiation, with less pronounced indication for the development of molten material.