# On the Detection and Removal of Oxides from Laser-Treated Surfaces
## 3 Results
### Oxide Removal  
The EDS results from the W-based samples treated by annealing in a hydrogen atmosphere are shown in Table 4. For both materials, the oxygen content was significantly reduced with respect to the laser-treated surface. However, the process appeared to be more efficient for the W-Cu sample, where the content was comparable to that of a clean sample, while for the 100% W sample, it was still slightly higher. As can be seen in Figure 2, there is no marked effect on the surface morphology. The EDS results from the W-based samples treated by HF etching are presented in Table 5. Compared to the laser-treated surface (Table 1), the oxygen content is markedly reduced for all etching times, although it is still a little higher than for the hydrogen annealing treatment. There is no apparent trend with respect to etching time; thus, 20 s immersion appears sufficient to significantly reduce the content of oxides. Similarly to the previous case, there was no marked effect of this treatment on the surface morphology. The EDS results from the W-Cu samples treated by gentle ablation with various parameters are presented in Table 6. The traverse velocity was chosen to obtain the same \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Frequency (MHz)** & **No. of Passes** & **Velocity (m/s)** & \\ \hline \multirow{3}{*}{6} & & **30** & **60** & **120** \\  & **1** & 2.1,... & 2.2, 416 & 2.4, 411 \\  & **2** & 2.3, 415 & 2.1, 413 & 3.1, 412 \\  & **3** & 2.3, 413 & 2.1, 412 & 2.4, 410 \\ \hline \multirow{3}{*}{**12**} & & **60** & **120** & **240** \\  & **1** & 2.1, 391 & 2.6, 387 & 2.9, 385 \\  & **2** & 2, 385 & 2.4, 382 & 2.8, 376 \\  & **3** & 2, 380 & 2.7, 376 & 2.6, 375 \\ \hline \multirow{3}{*}{**24**} & & **120** & **240** & **480** \\  & **1** & 3.6, 365 & 4.2, 366 & 5.7, 336 \\ \cline{1-1}  & **2** & 2.9, 356 & 3.7, 353 & 5.1, 344 \\ \cline{1-1}  & **3** & 2.6, 340 & 3.8, 348 & 4.4, 321 \\ \hline As-textured & & 9–12 & \\ \hline \hline \end{tabular}
\end{table} 
Table 6: EDS results (in wt% O) on W-Cu samples treated by gentle laser ablation, along with time-resolved temperatures (in \({}^{\circ}\)C) measured during the process. A comparison of as-textured and ablation-treated surface morphology is shown in Figure 3. Since there were varying combinations of pulse frequency and traverse velocity and three parameters altogether, their values have to be presented inside the table as well. Bold numbers indicate the parameter values; regular numbers present the oxygen content from EDS (wt%) and heat accumulation temperature (\({}^{\circ}\)C) measured by LabIR Ultrashort. \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **O (wt\%)** \\ \hline W-Cu (dimples, annealed) & 0.6 \\ W (dimples, annealed) & 3.4 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: EDS results on W-based samples annealed in hydrogen atmosphere. \begin{table}
\begin{tabular}{c c} \hline \hline
**Sample** & **O (wt\%)** \\ \hline W-Cu (dimples, HF 20 s) & 1.9 \\ W-Cu (dimples, HF 40 s) & 1.8 \\ W-Cu (dimples, HF 60 s) & 2.8 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: EDS results on W-based samples treated by HF etching. overlap of laser spots on the surface in the same column of the table with changing pulse frequency. In the first column, the distance between the laser spot centers is 5 \(\upmu\)m (overlap 87%); in the second column, it is 10 \(\upmu\)m (overlap 75%); and in the last column, it is 20 \(\upmu\)m (overlap 50%). So, in each column, the material surface obtains the same number of laser pulses but with different pulse energies and over different time intervals. With increasing frequency, the pulse energy decreases (to maintain the same average power), and the length of treatment is shortened. From the obtained results, one can make several observations. The effectiveness of oxide removal generally depends on the laser treatment parameters. For high frequency and high traverse velocity ranges, the degree of oxide removal increases with the number of passes.