Laser scanning speed

Short pulse irradiation of Mg alloys using XeCl excimer laser produced a wavy structure on the surface and the development of about 3-6 i.m thick amorphous layers on the surface. The corrosion resistance was reported to be enhanced (Schippman et al., 1999). Control of laser scanning speed plays... 

Cross-sections of laser-treated WE43 Mg alloy specimens at two different laser scanning speeds (a) 2mm/s (b) lOmm/s, with a constant energy density (6 J/cm ) (Guo et a ., 2005). 

From 7 to 8 levels of power were used to weld coupons with three different CB levels (Table 1). Accurately controlled artificial gaps of 5 different levels were created using metal shims placed parallel to the mechanical test direction (Table 1, Figure 1). In this power influence test, the laser scan speed was fixed at 25 mm/s. The shear strengths of the welds were evaluated on an Inshon universal testing machine at a loading speed of 5 mm/min. 

A series of laser scan speeds ranging from 10 to 100 mm/s were used to measure the SDT of visually clean PC specimens. For every laser scan speed setting, laser powers were chosen in the range of 10 to 100 W. Typically, 15 passes were made over all of the three surface finish areas for any one eombination of the laser scan speed and power. After each laser beam traversal in one direction over the specimen, surface was visually inspected and any visible damage was identified and recorded. 

Figure 7 shows the line energy at which surface damage occurs versus the laser scan speed. It is observed... 

Table 2 Surface damage probability for laser scan speeds of 10 to 100 nun/s and powers of 10 to 100 W on PC specimens...

Figure 7 SDT in terms of line energy vs. laser scan speed for PC specimens scanned with Rolin-Sinar DLxl6 chode laser...

For the detection of weak Raman lines, high laser power, high signal amplification, long pen period, and very slow scanning speed should be... 

If faster scanning rates are required for some specific applications they can easily be reached either by increasing the power output of the laser up to 5 W, or by focusing the beam down into the micron range. Table I compares the results obtained with the unfocused laser beam and with a 100 or 10 pm laser spot. With the most sharply focused beam, carbonization alrealy occured at a scanning speed of 50 cm s-1 and the exposure time dropped into the microsecond range. 

Photothermal decomposition of palladium acetate by scanned cw Ar+ laser irradiation produces metal features that exhibit pronounced periodic structure as a function of laser power, scan speed, substrate and beam diameter, as shown in Figures 3 and 4. The periodic structure is a function of the rate at which the film is heated by absorption of the incident laser radiation coupled with the rate at which the heat of the decomposition reaction is liberated. This coupling generates a reaction front that outruns the scanning laser until quenched by thermal losses, the process to be repeated when the laser catches up and reaches unreacted material. Clearly, such a thermal process is also affected by the thermal conductivity of the substrate, the optical absorption of the substrate in those cases where the overlying film is not fully absorbing,... 

Figure 3. Scanning electron micrographs of palladium features on quartz substrate as a function of laser power (measured on target) and scan speed. Palladium acetate precursor film thickness is 1.5 pm (cw Ar+ laser - 5145A line, spot size —0.8 pm FWHM).

Laser devices are the most sophisticated image-acquisition tools. They are particularly useful for gels labeled with fluorescent dyes because the lasers can be matched to the excitation wavelengths of the fluorophores. Detection is generally with photomultiplier tubes. Some instruments incorporate storage phosphor screens for detection of radiolabeled and chemiluminescent compounds (not discussed in this chapter). Resolution depends on the scanning speed of the illumination module and can be as low as 10 pm. 

Fig. 3. Explosive crystallization in a-Si by rapid argon-laser scanning, (a) At a scan speed of 85 cm sec-1 both explosive solid-phase crystallization and liquid-phase crystallization are exhibited, (b) Two different types of solid phase crystallization are Observed at a scan speed of 900 cm sec 1, (c) The situation is the same as that in (b) but an even higher scan speed of 1000 cm sec 1 is used. [From Bensahel and Auvert (1983b).]...

Figure 4.3-16 Raman spectrum of hydrogen chloride HCl at a pressure of 100 kPa. Slitwidth 2 cm, time constant 1 s,. scanning speed 50 cm /min, laser power 800 mW at 514.5 nm (recorded by Hochenbleicher, see Schrotter, 1982).

Figure 4.3-24 Part of the pure rotational Raman spectrum of CO2 at a pressure of 10 kPa. Slitwidth 0.21 cm, scanning speed 0.2 cm /min, laser power 8 W at 514.5 nm. The S-branch lines of the molecules in the vibrational ground state are off scale (Altmann et al., 1976).

Fig. 26.7. Sequence of fluorescence-excitation spectra of the narrow spectral feature recorded with the single-mode laser, (a) Stack of 23 fluorescence-excitation spectra recorded at a scan speed of 0.2cm /s (5GHz/s) and an excitation intensity of 0.5 W/cm. The fluorescence intensity is indicated by the gray scale. The averaged spectrum is shown in the lower panel and features a linewidth of 1.8cm (FWHM). (b) Individual fluorescence-excitation spectra together with Lorentzian fits (solid line). Prom top to bottom the linewidths (FWHM) are 1.8cm , 0.7cm , 0.9cm and 1.1 cm , respectively. Adapted from [61]...

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