Laser beam, experimental configuration

This paper deals with the control of weld depth penetration for cylinders in gold-nickel alloy and tantalum. After introducing the experimental set-up and the samples description, the study and the optimization of the testing are presented for single-sided measurements either in a pulse-echo configuration or when the pump and the probe laser beams are shifted (influence of a thermal phenomenon), and for different kind of laser impact (a line or a circular spot). First, the ultrasonic system is used to detect and to size a flat bottom hole in an aluminium plate. Indeed, when the width of the hole is reduced, its shape is nearly similar to the one of a slot. Then, the optimization is accomplished for... 

Experimental Setups. The experimental configurations used for CARS measurements have common features in most laboratories now. Figure 2 shows one such arrangement which is typical. A pulsed laser, in most cases a Q-switched Nd YAG, is used to generate the (o. frequency at 532 nm. In a few cases experimenters use ruby or other solid state pulsed lasers. Typically the 532 nm beam is split and the second beam is used to pump a dye laser -dye laser amplifier leg. This produces the ou probe frequency. 

Figure 2-1 of Chapter 2 shows an experimental configuration for depolarization measurements in 90° scattering geometry. In this case, the polarizer is not used because the incident laser beam is almost completely polarized in the z direction. If a premonochromator is placed in front of the laser, a polarizer must be inserted to ensure complete polarization. The scrambler (crystal quartz wedge) must always be placed after the analyzer since the monochromator gratings show different efficiencies for L and polarized light. For information on precise measurements of depolarization ratios, see Refs. 21-24. 

The absorption of two different photons also significantly increases the number of polarization variables arising in the rate equations. The ability of the experimentalist to independently vary the polarization and experimental configuration of the two laser beams allows a choice of values for these polarization parameters which significantly increases the amount of information that can be derived from the spectra. In contrast to the case of single-beam excitation, this also affords the opportunity to observe the induction of circular dichroism in a system of achiral molecules. 

Figure C3.1.13. Experimental configuration for far-UV nanosecond CD measurements using a frequeney-upconverted Ti sapphire laser as a probe source. Pj and 2 are MgF2 Roehon polarizers at eross orientations. SPj is a strained transparent plate with about 1° of linear birefringence for quasi-null ellipsometric CD deteetion. Prism PMj and the iris select the far-UV fourth harmonie of the argon laser-pumped Ti-sapphire laser s near-IR fundamental output to probe the elliptieity of the sample. A seeond laser beam at 532 nm is used to pump CD...

Fig. 4 shows the sample configuration in order to detect evanescent fields [14, 15]. A 45 -right angle prism of BK-7 glass was used in this measurement. The samples, that is, A1 thin films and C20 LB films on the A1 films were prepared as the same ones in the ATR method. The experimental system to detect the evanescent fields that was constructed in our research group is shown in Fig. 5 [14,15]. The prism was set on a rotating stage because SPs can be excited as a function of the incident angle of the laser beam similar to the ATR method. And the reflected laser beam was measured with the photodiode (PD).

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