A microlens array optic was fabricated for laser surface microstructuring of polymer surfaces. The optic contains a hexagonal close-packed monolayer of SiO2 microspheres, held together by an adhesive substance and supported on fused silica glass. The array is placed in direct contact with the target substrate and is exposed to UV light at a wavelength of 193 nm. During this exposure, the SiO2 spheres act as microlenses, which focus the incoming laser light, but also enhance the optical near-field intensity underneath each microsphere. A large number of identical structures are produced simultaneously using this type of direct laser ablation, which leads to a highly efficient process. The ablated holes are approximately 1.8 µm in diameter, with a pitch of 8.4 µm and a depth of 80 nm. This microlens array has many advantages over other types of array, including the fact that it is inexpensive and easy to fabricate. An important feature is that it can transmit light at a wavelength less than 300 nm, which makes it suitable for laser surface patterning.
Laser Induced Periodic Surface Structures (LIPSS) may have numerous applications, ranging from biomaterial applications to LCDs, microelectronic fabrication and photonics. However, in order to control the development of these structures for their particular application, it is necessary to understand how they are generated.
We report our work on investigating the melting that occurs during LIPSS formation. LIPSS were generated on three polymer surfaces - polyethylene terephthalate (PET), amorphous polycarbonate (APC) and oriented crystalline polycarbonate (OPC) - which were irradiated with a polarized ArF excimer laser (193 nm) beam with fluences between 3 and 5 mJ/cm<sup>2</sup>.
The structures were imaged using a Transmission Electron Microscope (TEM), which facilitated investigation of changes in the polymer structures and consequently the depth of the melt zone that accompanies LIPSS generation.
We also present theoretical calculations of the temperature-depth profile due to the interaction of the low fluence 193 nm laser beam with the polymer surfaces and compare these calculations with our experimental results.
Bone-bonding implants include some of the commonest biomaterials currently used. The useful lifetimes of these materials are limited in part by the capacity of the material to support an intimate bond with the tissue in which they are implanted. A number of materials currently used have either good mechanical properties but poor biological responses, or have the ability to form suitable bonds with bone but lack the requisite strength, wear resistance, etc. In particular, polymeric materials have generally been shown to be inert with respect to bone. We report on our work on developing methods to surface treat polymers to encourage colonisation by bone, either for clinical implantation or in vitro tissue engineering applications. Polymers were treated by one of two methods; either 1) using an excimer laser to machine arrays of grooves in the surface; the periodicity of the grooves was varied from a few hundred nanometers to 10 μm; or 2) using an excimer lamp to affect the chemistry of the surface layer by breaking surface bonds and incorporating atmospheric oxygen. Surface structures of samples treated by method 1 were examined using Scanning Electron Microscopy (SEM), White Light Intereferometry and Atomic Force Microscopy (AFM) and surfaces of samples treated by method 2 were examined by using contact angle measurements which indicated a higher surface energy. The difference in cellular response to the control surfaces and modified surfaces was investigated. In conclusion, these methods provide viable means for altering polymers and may generate improved polymers for bone-bonding applications.
Fused biconic tapered (FBT) couplers are essential components in today's telecommunications networks where they are used for a number of different applications. The manufacturing process consists of aligning two adjacent fibres from which the buffer has been stripped, and subsequently heating and stretching them, creating an input taper, output taper either side of the fused coupling region. It is the coupling region where energy transfer between cores is possible; this gives the device its main characteristics, and the basic geometry can be used to create a range of devices such as 3 dB splitters, tap couplers, WDMs, etc. Low losses for these devices are achievable if made with reference to the adiabatic approximation. In this paper we report the development of a laser-based rig for the manufacture of couplers in which a CO<sub>2</sub> laser replaces the gas torch typically used as a heat source in modern manufacturing processes. In addition to the use of a laser source, we describe the integration of advanced optical techniques and feedback mechanisms to improve the workstation's reliability and flexibility. These characteristics should be advantageous for efficient manufacture of standard devices and novel devices for niche applications.
Cellular reactions to implantable medical devices are dominated by the surface properties of materials from which the device is constructed. Consequently, in recent times much effort has been expended on modifying material surface properties to control bioactivity. We examine the effect of exposing surfaces to ultra-violet (UV) light from excimer lasers (λ = 193nm) in a room air environment. Working below the threshold of ablation, samples of nylon-12 and PET were treated. Physical and chemical studies of the surfaces following treatment demonstrated an increase in sample hydrophilicity, though no significant increases in roughness were recorded. Spectroscopic analyses revealed increased oxygen content in the surface layers while there were no chemical alterations in the bulk material. The assessment of in vitro interactions concerning the polymer samples and 3T3 fibroblast cells was conducted using cell counting, viability assays and a confocal microscopic analysis of cytoskeletal fluorescent staining. Results from cell counting and the viability tests confirmed that, subsequent to treatment, there was an increase in cell population on the surface, while improved spreading and activity was observed by confocal microscopy.