Brain function depends on simultaneous electrical, chemical and mechanical signaling at the cellular level. This multiplicity has confounded efforts to simultaneously measure or modulate these diverse signals in vivo. Here we present fiber probes that allow for simultaneous optical stimulation, neural recording and drug delivery in behaving mice with high resolution. These fibers are fabricated from polymers by means of a thermal drawing process that allows for the integration of multiple materials and interrogation modalities into neural probes. Mechanical, electrical, optical and microfluidic measurements revealed high flexibility and functionality of the probes under bending deformation. Long-term in vivo recordings, optogenetic stimulation, drug perturbation and analysis of tissue response confirmed that our probes can form stable brain-machine interfaces for at least 2 months. We expect that our multifunctional fibers will permit more detailed manipulation and analysis of neural circuits deep in the brain of behaving animals than achievable before.

Multifunctional fibers for simultaneous optical, electrical and chemical interrogation of neural circuits in vivo

Joining of dissimilar materials is one of the challenging tasks facing modern manufacturers. Dissimilar joining technologies find applications in many sectors including microelectronics, medical, optoelectronics and microsystems. The tiny geometry of the joints and the different optical and thermal properties of the materials makes laser welding one of the most suitable production methods. This paper presents the results of an investigation into laser welding of dissimilar metals without filler materials using a 350 W pulsed Nd:YAG laser. The mixing behaviour of the materials in the fusion zone, the microstructure, the presence of defects, hardness and residual stress of the joints were all investigated.

Characterisation of dissimilar joints in laser welding of steel–kovar, copper–steel and copper–aluminium

Fiber lasers have seen progressive developments in terms of spectral coverage and linewidth, output power, pulse energy, and ultrashort pulse width since the first demonstration of a glass fiber laser in 1964. Their applications have extended into a variety of fields accordingly. In this paper, the milestones of glass fiber laser development are briefly reviewed and recent advances of high-power continuous wave, Q-switched, mode-locked, and single-frequency fiber lasers in the 1, 1.5, 2, and 3 μm regions and their applications in such areas as industry, medicine, research, defense, and security are addressed in detail.

Fiber lasers and their applications [Invited]

This critical review is motivated by an increasing interest of the microfluidics community in developing complete Lab-on-a-Chip solutions based on thin and flexible films (Lab-on-a-Foil). Those implementations benefit from a broad range of fabrication methods that are partly adopted from well-established macroscale processes or are completely new and promising. In addition, thin and flexible foils enable various features like low thermal resistance for efficient thermocycling or integration of easily deformable chambers paving the way for new means of on-chip reagent storage or fluid transport. From an economical perspective, Lab-on-a-Foil systems are characterised by low material consumption and often low-cost materials which are attractive for cost-effective high-volume fabrication of self-contained disposable chips. The first part of this review focuses on available materials, fabrication processes and approaches for integration of microfluidic functions including liquid control and transport as well as storage and release of reagents. In the second part, an analysis of the state of Lab-on-a-Foil applications is provided with a special focus on nucleic acid analysis, immunoassays, cell-based assays and home care testing. We conclude that the Lab-on-a-Foil approach is very versatile and significantly expands the toolbox for the development of Lab-on-a-Chip solutions.

Lab-on-a-Foil: microfluidics on thin and flexible films

Absorber-free transmission and butt-welding of different polymers were performed using thulium fiber laser radiation at the wavelength 2 μm. The relations between the laser process conditions and the dimensions and quality of the seam were investigated by means of optical and phase-contrast microscopy. Mechanical properties of the weld joints were studied in tensile strength tests. Laser-welded polyethylene samples revealed a tensile strength of greater than 80% of the bulk material strength. Transmission welding of different polymer combinations featured the formation of different joint classes depending on the spectral properties. The experiments demonstrate new application areas of mid-IR fiber laser sources for materials processing.

Welding of polymers using a 2 μm thulium fiber laser

Laser Assisted Joining of Plastic Metal Hybrids

Laser applications in microtechnology

Fibre laser welding for packaging of disposable polymeric microfluidic-biochips

In laser transmission welding of thermoplastics the optical properties of the joining parts determine the quality of the welding result. Especially, the scattering of laser radiation in the transparent welding part has an impact on weld seam properties. This scattering is caused by additives. For polycarbonate (PC) with different additives the transmittance, the reflectance and the collimated transmittance are measured with a UV-VIS-NIR spectrometer. From this data, the optical properties, such as scattering coefficient, absorption coefficient, and anisotropy factor are calculated. The calculations are made with the aid of the four-flux model of radiation transport in the diffusive approximation. The results show that the additives have a significant influence on the scattering coefficient. For most additives under consideration the scattering is forward directed, which means that most of the radiation is transmitted into the absorbing welding part. However, the power density distribution of the transmitted radiation may differ significantly from PC without additives. So, the weld seam may also differ due to different additives. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 451–455, 2010

Alexander Olowinsky

Papers

Welding of polymers using a 2 μm thulium fiber laser

Laser Assisted Joining of Plastic Metal Hybrids

Laser applications in microtechnology

Fibre laser welding for packaging of disposable polymeric microfluidic-biochips

Optical characterization of polycarbonate: Influence of additives on optical properties