Metal-coated concave cone in a fused-silica rod as a multi-function plasmonic element.

A collimated light beam parallel to the axis of a fused-quartz cylinder impinging on a 90° apex angle concave cone cut in a quartz rod is transformed into a cylindrical wave by total internal reflection. A thin metal film at the quartz-air interface enables excitation of the plasmon mode at the air side that can polarize the cylindrical wave and/or has the potential to monitor physical, chemical, or biological quantities or events at the inner wall of the cone. The present Letter first analyzes the plasmon coupling mechanism and conditions. It then describes the diamond-grinding technique achieving a smooth cone wall and the finest possible tip. The experimental evidence of the polarization conversion is brought on a diamond-grinded section of fused-silica rod and gold coating of the concave wall.

Modification of Polymeric Surfaces with Ultrashort Laser Pulses for the Selective Deposition of Homogeneous Metallic Conductive Layers.

In recent years, the demand for highly integrated and lightweight components has been rising sharply, especially in plastics processing. One strategy for weight-saving solutions is the development of conductive tracks and layouts directly on the polymer housing parts in order to be able to dispense with the system integration of additional printed circuit boards (PCB). This can be conducted very advantageously and flexibly with laser-based processes for functionalizing polymer surfaces. In this work, a three-step laser-based process for subsequent selective metallization is presented. Conventional injection molded components without special additives serve as the initial substrate. The Laser-Based Selective Activation (LSA) uses picosecond laser pulses to activate the plastic surface to subsequently deposit palladium. The focus is on determining the amount of deposited palladium in correlation to the laser and scan parameters. For the first time, the dependence of the metallization result on the accumulated laser fluence (Facc) is described. The treated polymer parts are characterized using optical and scanning electron microscopy as well as a contact-type profilometer.

Three-dimensional evaluation of subsurface damage in optical glasses with ground and polished surfaces using FF-OCT.

Subsurface damage (SSD) induced during conventional manufacturing of optics contributes mainly to a reduction in the performance and quality of optics. In this paper, we propose the application of full-field optical coherence tomography (FF-OCT) as a high-resolution and nondestructive method for evaluation of SSD in optical substrates. Both ground and polished surfaces can be successfully imaged, providing a path to control SSD throughout the entire optics manufacturing process chain. Full tomograms are acquired for qualitative and quantitative analyses of both surface and SSD. The main requirements for the detection of SSD are addressed. Data processing allows the removal of low-intensity image errors and the automatic evaluation of SSD depths. OCT scans are carried out on destructively referenced glass samples and compared to existing predictive models, validating the obtained results. Finally, intensity projection methods and depth maps are applied to characterize crack morphologies. The experiments highlight differences in crack characteristics between optical glasses SF6 and HPFS7980 and illustrate that wet etching can enhance three-dimensional imaging of SSD with FF-OCT.

Analysis of Melt Pool Characteristics and Process Parameters Using a Coaxial Monitoring System during Directed Energy Deposition in Additive Manufacturing.

The growing number of commercially available machines for laser deposition welding show the growing acceptance and importance of this technology for industrial applications. Their increasing usage in research and production requires process stability and user-friendly handling. A commercially available DMG MORI LT 65 3D hybrid machine used in combination with a CCD-based coaxial temperature measurement system was utilized in this work to investigate what information relating to the intensity distribution of melt pool surfaces could be appropriate to draw conclusions about process conditions. In this study it is shown how the minimal required specific energy for a stable process can be determined, and it is indicated that the evolution of a plasma plume depends on thermal energy within the base material. An estimated melt pool area-calculated by the number of pixels (NOP) with intensities larger than a fixed, predefined threshold-builds the main measure in analysing images from the process camera. The melt pool area and its temporal variance can also serve as an indicator for an increased working distance.

Investigations on the active compensation of the focal shift in scanning systems using a temperature signal.

For the purpose of realizing a fast and cost-efficient manipulation of the laser beam in production applications, such as welding, marking, and cutting, scanner systems in combination with F-Theta objectives are state-of-the-art. Owing to the absorption of the laser beam power and the resulting heat load acting on the optical system, a change of the focal plane (the so-called focal shift) occurs, significantly affecting the behavior during the application process. A linear correlation between the temperature on the optical surface of a standard F-Theta objective and the focal shift was determined whereby the coefficient of determination R2 is higher than 0.99. Furthermore, two industrial welding applications were investigated using this standard objective, and the resulting temperature distribution along the optical surfaces was also investigated. The results show that a single measurement point appears to be sufficient to obtain a capable input signal for a compensation method. A compensation device was implemented and a sufficient reduction of the focal shift was realized for the examined time range.

3D range-modulator for scanned particle therapy: development, Monte Carlo simulations and experimental evaluation.

The purpose of this work was to design and manufacture a 3D range-modulator for scanned particle therapy. The modulator is intended to create a highly conformal dose distribution with only one fixed energy, simultaneously reducing considerably the treatment time. As a proof of concept, a 3D range-modulator was developed for a spherical target volume with a diameter of 5 cm, placed at a depth of 25 cm in a water phantom. It consists of a large number of thin pins with a well-defined shape and different lengths to modulate the necessary shift of the Bragg peak. The 3D range-modulator was manufactured with a rapid prototyping technique. The FLUKA Monte Carlo package was used to simulate the modulating effect of the 3D range-modulator and the resulting dose distribution. For that purpose, a special user routine was implemented to handle its complex geometrical contour. Additionally, FLUKA was extended with the capability of intensity modulated scanning. To validate the simulation results, dose measurements were carried out at the Heidelberg Ion Beam Therapy Center with a 400.41 MeV/u 12C beam. The high resolution dosimetric measurements show a good agreement between simulated and measured dose distributions. Irradiation of the monoenergetic raster plan took 3 s, which is approximately 20 times shorter than a comparable plan with 16 different energies. The combination of only one energy and a 3D range-modulator leads to a tremendous decrease in irradiation time. 'Interplay effects', typical for moving targets and pencil beam scanning, can be immensely reduced or disappear completely, making the delivery of a homogeneous dose to moving targets more reliable. Combining high dose conformity, very good homogeneity and extremely short irradiation times, the 3D range-modulator is considered to become a clinically applicable method for very fast treatment of lung tumours.