Fluence

About: Fluence is a research topic. Over the lifetime, 6156 publications have been published within this topic receiving 94486 citations.

Ultrashort-pulse laser machining of dielectric materials

Abstract: There is a strong deviation from the usual τ1/2 scaling of laser damage fluence for pulses below 10 ps in dielectric materials. This behavior is a result of the transition from a thermally dominated damage mechanism to one dominated by plasma formation on a time scale too short for significant energy transfer to the lattice. This new mechanism of damage (material removal) is accompanied by a qualitative change in the morphology of the interaction site and essentially no collateral damage. High precision machining of all dielectrics (oxides, fluorides, explosives, teeth, glasses, ceramics, SiC, etc.) with no thermal shock or distortion of the remaining material by this mechanism is described.

Laser‐cleaning techniques for removal of surface particulates

Abstract: Flash laser heating using short‐pulsed laser irradiation of a surface is demonstrated to be a promising new approach for effective removal of particulate contaminations of sizes as small as 0.1 μm. This is very useful because micron‐ and submicron‐sized particulates adhere tenaciously onto a solid surface, and conventional cleaning techniques are inadequate for removal. Several varieties of the new laser‐cleaning techniques have been developed by us as well as by others. For example, the pulsed laser irradiation can be used with or without the simultaneous deposition of a thin liquid film on the surface to be laser cleaned. The laser wavelength can also be chosen so that absorption occurs mainly at the sample surface, or in the liquid, or in the particulate, or in a combination of these. In this paper, we discuss and compare examples of these different approaches. We find that laser cleaning with highest efficiency is achieved by choosing a laser wavelength that is strongly absorbed by the surface together with pulse depositing a water film of thickness on the order of microns on the surface momentarily before the pulsed laserirradiation. This permits the effective removal of particles smaller than ∼20 μm, down to as small as 0.1 μm, from a solid surface using a modest ultraviolet laser fluence of ∼0.1 J/cm2.

Excimer laser etching of polyimide

Abstract: It is reported that thin films of polyimide are efficiently etched in air at pulsed excimer laser wavelengths of 248, 308, and 351 nm. Etch rate versus incident fluence data are found to obey a Beer–Lambert etching relation. Sharp laser fluence thresholds for significant etching are found to correlate with the wavelength‐dependent absorption coefficient. The absorbed energy density required to initiate significant etching is found, within experimental error, to be independent of the wavelengths examined. It is felt that this information demonstrates the predominantly thermal nature of the laser etching mechanism. Additionally, infrared spectroscopy and coupled gas chromatography/mass spectroscopy were used to identify several gases evolved during pulsed laser etching of polyimide in both air and vacuum.

Dynamics of UV laser ablation of organic polymer surfaces

Abstract: A model based on a time‐dependent treatment of the ablation of organic polymer surfaces by UV laser radiation is proposed. It relates the dynamics of the etching process to the experimental parameters such as the fluence, wavelength, and the width of the laser pulse. The model is applied to poly(methyl methacrylate) and to polyimide in order to predict the etch characteristics quantitatively and to compare them systematically to the experimental results. This model accounts for a wide variety of observations such as fluence thresholds, wavelength‐dependent etch rates, ‘‘incubation’’ pulses, filtering by photofragments, fast intrapulse etching, thermal contributions, and even the influence of pulse compression so that a consistent picture of the mechanisms underlying the ablation process becomes apparent.