Quantitative fs-TALIF in high-pressure NRP discharges: Calibration using VUV absorption spectroscopy

This work presents a femtosecond two-photon absorption laser-induced fluorescence (fs-TALIF) diagnostic for measuring ground-state atomic nitrogen in nanosecond repetitively pulsed (NRP) discharges. Absolute atom density is obtained from the TALIF signal via a novel calibration technique based on one-photon direct absorption measurements performed in a low-pressure DC discharge. The VUV measurements were done at the Soleil synchrotron facility using the high-resolution Fourier-transform spectrometer (minimum linewidth Δ̃ = 0.08 cm-1). The main goal of this work was to develop a quench-free diagnostic technique, which would allow measurements at elevated pressures with high spatial and temporal resolution. Here fs-TALIF measurements of N(4S) are demonstrated in the NRP post-discharge between 1-500 μs after the nanosecond high-voltage pulse. A maximum number density of N-atoms of × − was measured at 1 μs after the pulse when the discharge was operated at 1 bar in pure nitrogen. This corresponds to a dissociation fraction of ~ 0.1 %. The fs-TALIF technique at high laser intensity regime (> 1 TW cm-2) calibrated using VUV absorption was compared with the fs-TALIF at low laser intensity regime (< 100 MW cm-2) calibrated via the well-established non-saturated TALIF technique using krypton as an etalon gas. It was found that the two measurements of N(4S) in the NRP post-discharge agree within a factor of 3. Importantly, the limit of detection of the fs-TALIF at high laser intensity regime was determined to be ()~ e 1/. This is approximately one order of magnitude better than previously reported by ns-TALIF in low-pressure discharges.

Influence of Adding Modifying Elements and Homogenization Annealing on Laser Melting Process of the Modified AlZnMgCu with 4%Si Alloys

AlZnMgCu, the high-strength aluminum alloy, is unsuitable for laser melting applications due to its high hot cracking sensitivity and large solidification temperature range. Adapting this alloy for laser melting processing is a high-demand research issue for extending its use. Thus, this paper investigates the effect of adding 4%Si, 4%Si-Sc+Zr, 4%Si-Ti+B, and homogenization annealing on the laser melting process (LMP) of AlZnMgCu alloy. Homogenization annealing at 500 °C for 6.5 h was selected to dissolve most of the low melting temperature phases into the grain matrix and perform stable alloys for the LMP. The pulsed laser melting process (PLM) was performed on the as-casted and the homogenized samples. The microstructures of the as-casted, the homogenized alloys, and after the LMP were evaluated. In addition, the hardness of the base metal (BM) and laser melted zone (LMZ) were measured. The results revealed that the microstructure was enhanced and refined in the as-cast state by adding the modifiers due to the increasing nucleation potency of solidification sites and the formation of primary Al3(Ti, Zr, Sc) phases. The average grain size was decreased by 15.6 times when adding 4%Si + 0.4%Zr + 0.29%Sc, while it decreased by 10.2 times when adding 4%Si + 1%Ti + 0.2%B. The LMZ of the as-casted samples exhibited a non-uniform distribution of the grains and the elements after the LMP. This was attributed to the evaporation of Zn, Mg during the high laser power process besides the non-uniform distribution of elements and phases in samples during casting. After the laser treating of the homogenized samples with 4%Si-Sc + Zr, uniform columnar grains were formed in the direction of the laser. The presence of Ti and B changed the crystallization nature, resulting in the LMZ with very fine and equiaxed grains due to forming many nucleation centers during solidification. The hardness values have positively increased due to Si addition and adding a combination of Ti + B and Sc + Zr. The maximum hardness was 153.9 ± 5 HV achieved in the LMZ of the homogenized samples of 4%Si + 1%Ti + 0.2%B.

Fast Fabrication of Conductive Copper Structure on Glass Material Using Laser-Induced Chemical Liquid Phase Deposition

Glass is a very stable material at room temperature and has good resistance to gas, bacteria, and organisms. Due to the development of the electronic industry, the industrial demand for creating a conductive pattern on glass is increasing rapidly. To create conductive circuit patterns on the glass surface, non-contact methods based on high energy sources or chemical methods are generally used. However, these methods have disadvantages such as low conductivity, high cost, and size limitations. Processes such as LCLD (laser-induced chemical liquid phase deposition) have been widely studied to solve this problem. However, it has a fatal disadvantage of being slow. Therefore, in this study, various process changes were attempted to improve productivity and conductivity. In particular, sufficient thermal energy was supplied with high laser power for a stable chemical reduction, and the scanning path was changed in various shapes to minimize the ablation that occurs at this time. Through this, it was possible to disperse the overlapped laser energy of high power to widen the activation area of the reduction reaction. With this proposed LCLD process, it is possible to achieve good productivity and fabricate conductive circuit patterns faster than in previous studies.

Thermal effects of thulium: YAG laser treatment of the prostate—an in vitro study

Purpose To objectively determine whether there is potential thermal tissue damage during Tm:YAG laser-based LUTS treatment. Methods Our experimental model was comprised of a prostatic resection trainer placed in a 37 °C water bath. In a hollowed-out central area simulating the urethral lumen, we placed a RigiFib 800 fibre, irrigation inflow regulated with a digital pump, and a type K thermocouple. A second thermocouple was inserted 0.5/1 cm adjacently and protected with an aluminum barrier to prevent it from urethral fluid. We investigated continuous and intermittent 120 W and 80 W laser application with various irrigation rates in eight measurement sessions lasting up to 14 min. Thermal measurements were recorded continuously and in real-time using MatLab. All experiments were repeated five times to balance out variations. Results Continuous laser application at 120 W and 125 ml/min caused a urethral ∆T of ~ 15 K and a parenchymal temperature increase of up to 7 K. With 50 ml/min irrigation, a urethral and parenchymal ∆T of 30 K and 15 K were reached, respectively. Subsequently and in absence of laser application, prostatic parenchyma needed over 16 min to reach baseline body temperature. At 80 W lower temperature increases were reached compared to similar irrigation but higher power. Conclusions We showed that potentially harming temperatures can be reached, especially during high laser power and low irrigation. The heat generation can also be conveyed to the prostate parenchyma and deeper structures, potentially affecting the neurovascular bundles. Further clinical studies with intracorporal temperature measurement are necessary to further investigate this potentially harming surgical adverse effect.

On the in situ elimination of pores during laser powder bed fusion of a titanium alloy

The printing quality of the laser powder bed fusion (LPBF) components largely depends on the presence of various defects such as massive porosity. Thus, the efficient elimination of pores is an important factor to the production of a sound LPBF product. In this work, the efficacy of two in situ laser remelting approaches on the elimination of pores during LPBF of a titanium alloy Ti-6.5Al-3.5Mo-l.5Zr-0.3Si (TC11) were assessed using both experimental and computational methods. These two remelting methods are the surface remelting, and the layer-by-layer printing and remelting. A multi-track and multi-layer phenomenological model was established to compute the evolution of pores with the temperature and velocity fields. The results showed that surface remelting with a high laser power such as 180 W laser can effectively eliminate pores within three deposited layers. However, such a remelting cannot reach defects in deeper regions. Alternatively, the layer-by-layer remelting with a laser power of 180 W can effectively eliminate the pores formed in the previous layer in real time. The results obtained from this work can provide useful guidance for the in situ control of printing defects supported by the real time monitoring, feedback and operation systems of the intelligent LPBF equipment.