Dry Laser Ablation Research Articles

Selectively accessing the hotspots of optical nanoantennas by self-aligned dry laser ablation.

Plasmonic nanostructures serve as optical antennas for concentrating the energy of incoming light in localized hotspots close to their surface. By positioning nanoemitters in the antenna hotspots, energy transfer is enabled, leading to novel hybrid antenna-emitter-systems, where the antenna can be used to manipulate the optical properties of the nano-objects. The challenge remains how to precisely position emitters within the hotspots. We report a self-aligned process based on dry laser ablation of a calixarene that enables the attachment of molecules within the electromagnetic hotspots at the tips of gold nanocones. Within the laser focus, the ablation threshold is exceeded in nanoscale volumes, leading to selective access of the hotspot areas. A first indication of the site-selective functionalization process is given by attaching fluorescently labelled proteins to the nanocones. In a second example, Raman-active molecules are selectively attached only to nanocones that were previously exposed in the laser focus, which is verified by surface enhanced Raman spectroscopy. Enabling selective functionalization is an important prerequisite e.g. for preparing single photon sources for quantum optical technologies, or multiplexed Raman sensing platforms.

Laser micromachining of silicon in air and ice layer

Thermal damage is an important drawback of laser micromachining process, and several techniques have been developed to control and limit heat induced by laser during the ablation. A novel method presented in this study is to perform the laser micromachining in ice, where the ablation take places while a workpiece is cooled in a thin ice layer. This technique is expected to limit the excessive heat conducting toward the workpiece material and also to prevent the cut debris depositing in the work surface as usually found in the dry laser ablation. Silicon wafer was used as a work sample to be cut in this study. The effects of ice temperature, ice layer thickness and average laser power on cut dimensions were experimentally investigated, and the predictive models for cut width and depth based on energy balance theorem were also formulated in this paper. Although some optical disturbances due to ice-water-vapor transitions limited the cut depth obtained, a clean and narrow cut with small taper angle was achievable when silicon was cut in ice layer. According to the findings of this study, the ice-assisted laser micromachining process could be a promising method for minimizing thermal damage in the laser ablation of silicon. In addition, this technique could also be of high potential for processing other heat-sensitive materials for micro-manufacturing applications.

A Comparison among Dry Laser Ablation and Some Different Water-Laser Co-Machining Processes of Single Crystal Silicon Carbide

Single crystal silicon carbide (SiC) is a new semiconductor material that has a great potential to be widely used. However, SiC is a kind of difficult-to-machine material due to its extreme hardness and brittleness. The present study investigated the machinability of single crystal SiC using dry laser and three different water-laser co-machining processes. The results indicate that using the hybrid laser-waterjet micro-machining to micro-groove single crystal SiC can derive the clean and straight edges and thermal damage-free grooves.

Excimer Laser Smoothing of Endothelial Keratoplasty Grafts

To use excimer laser smoothing passes to reshape Descemet-stripping automated endothelial keratoplasty (DSAEK) endothelial grafts and to evaluate the effect on the donor endothelium. The stromal surface of microkeratome-cut DSAEK grafts was smoothed using excimer laser smoothing passes with masking fluid. Excimer laser hyperopic ablation was used to improve the uniformity of graft thickness within the optical zone. Fourier-domain optical coherence tomography was used to measure endothelial graft pachymetry, plan ablations, and evaluate donor contour. Vital dye staining was performed to assess endothelial cell damage. Scanning electron microscopy images of stromal surfaces were graded on a 5-point scale by masked observers to evaluate surface roughness. Four grafts underwent excimer laser smoothing. Vital dye staining showed no endothelial damage. Microkeratome-cut surfaces treated with laser smoothing (mean grade = 2.04) were smoother than nonsmoothed microkeratome-cut surfaces (mean grade = 4.07; P < 0.01), surfaces that underwent dry laser ablation (mean grade = 3.63; P < 0.01) and manually dissected interfaces (mean grade = 4.75; P < 0.0001). No difference was observed between stromal beds created by peeling Descemet membrane (mean grade = 1.64) compared with surfaces produced by microkeratome cutting followed by laser smoothing (mean grade = 2.04; P = 0.14). One graft underwent combined excimer smoothing and peripheral hyperopic ablation. The center-periphery thickness difference was 15 μm before ablation and 4 μm afterward. Laser smoothing passes can be used to improve the contour and smoothness of DSAEK grafts without damaging donor endothelial cells. Clinical trials are needed to determine whether reshaping donors using excimer laser can deliver improved visual outcomes after DSAEK.