A novel fabrication method for surface-enhanced Raman scattering (SERS) sensors that used a fast femtosecond (fs) laser scanning process to etch uniform patterns and structures on the endface of a fused silica optical fiber, which is then coated with a thin layer of silver through thermal evaporation is presented. A high quality SERS signal was detected on the patterned surface using a Rhodamine 6G (Rh6G) solution. The uniform SERS sensor built on the tip of the optical fiber tip was small, light weight, and could be especially useful in remote sensing applications.

Nanostructured regular patterns on silicon surface are made by using femtosecond laser irradiations. This is a novel method that can modify the surface morphology of any large material in an easy, fast, and low-cost way. We irradiate a solid surface with a 400-nm double frequency beam from an 800-nm femtosecond laser, while the solid surface is submerged in a liquid or exposed in air. From the study of multiple-pulses and single-pulse irradiations on silicon, we find the morphologies of nanospikes and capillary waves to follow the same distribution and periodicity. Thermal transport near the solid surface plays an important role in the formation of patterns; a simulation was done to fully understand the mechanism of the pattern formation in single pulse irradiation. The theoretical models include a femtosecond laser pulse function, a two-temperature model (2-T model), and an estimation of interface thermal coupling. The evolution of lattice temperature over time will be calculated first without liquid cooling and then with liquid cooling, which has not been well considered in previous theoretical papers. The lifetime of the capillary wave is found to be longer than the solidification time of the molten silicon only when water cooling is introduced. This allows the capillary wave to be frozen and leaves interesting concentric rings on the silicon surface. The regular nanospikes generated on the silicon surface result from the overlapping capillary waves.

A novel low-temperature SnO₂ gas sensor was prepared and studied on silicon nanostructures formed by femtosecond laser irradiation. By applying a bias voltage on the silicon substrate to alter the charge distribution on the surface of the SnO₂, carbon monoxide (CO), and ammonia (NH₃) gas can be distinguished by the same sensor at room temperature. The experimental results are explained with a mechanism that the sensor works at low temperature because of adsorption of gas molecules that trap electrons to the surface of the SnO₂.

Ultrafast laser texturing allows the generation of micro- and nanostructures on steel substrates. Laser-ablated textures show a wide range of structure geometries, from the micro to the nanoscale, which can enable plastic product functionalization. Polymer processing technologies are used to replicate mold textures on a large manufacturing scale. To enable new product functionalities, developing novel texture geometries is critical. The laser-ablated texture dimensions are primarily linked to the laser light properties, such as the laser wavelength, thus limiting the achievable structure shapes. This work uses ultrafast laser to manufacture textures in air and water environments. The effect of the different mediums on structures formation is characterized. The irradiation is performed over a wide range of fluence values. The texture geometry and characteristics are evaluated by scanning electron microscopy. For decreasing fluence values, the structures transitioned from micro bumps, to LIPSS, to nanostructures, regardless of the irradiation environment. Conversely, structure morphology is affected by the irradiation environment. The LIPSS pitch is lower for the underwater environment due to the change in the laser angle of incidence, which changes with the refraction index ratio of the air and water. A novel nano-lamellae texture was generated when irradiating the steel surface underwater at relatively low fluence. The dynamics of different LIPSS generations are discussed, considering the irradiation medium’s optical, thermal, and physical properties.