Laser spot diameter

Young et al. (2002a) showed that ultraviolet laser ablation combined with MC-ICPMS (LA-MC-ICPMS) can offer advantages over other methods of spatially resolved Mg isotopic analysis of meteorite materials. They collected data for chondrules and a CAI from the Allende meteorite. Each datum in that study represents approximately 2.8 pg of material (based on a laser spot diameter of 100 pm and laser pit depth of 30 pm depths are uncertain to + 20%). 

With the laser pulse energy W = 10 5 J, the laser spot diameter d = 10X on the dielectric surface, and the light frequency v = 5x 1014 s 1, the electron velocity variation is Au = 2x 108exp(-z/zo) centimeters per second. This means that an electron beam with an energy E - 100 eV (v = 5.9 x 108 cm/s) reflects at a substantial angle of

evanescent wave produced by a femtosecond laser pulse. 

The Raman spectra on solid metal substrates were measured using a Renishaw RM2000 micro-Raman apparatus, coupled with a diode laser source emitting at 785 nm. Sample irradiation was accomplished using the 50x microscope objective of a Leica microscope DMLM. The beam power was 3 mW, the laser spot diameter was adjusted between 1 and 3 pm. Raman scattering was filtered by a double holographic notch filter system and collected by an air-cooled CCD detector. The acquisition time for each measurement was 10 s. All spectra were calibrated with respect to a silicon wafer at 520 cm. ... 

The overfilled case is illustrated in more detail in Figure 6.11 A. The image of the laser focus at the spectrometer is larger than the slit (or other entrance aperture). The AdQd is determined by the spectrometer and will not vary with /i, since Ad and Qd vary with ff and /f, respectively. The power density varies with if Pq is constant since the laser spot diameter equals [Eq. (6.2)]. For a thick sample, K increases linearly with f (since // is... 

For example, if 0 = 1 mrad and /i = 5 cm, the laser spot diameter at the focal point (often called the beam waist) is 50 pm. This minimum may define a limit in power density or spatial resolution and can affect the choice of laser. 

In laboratory with constant measurements conditions (laser intensity, laser spot diameter and so on) the line intensity (Ij) of the certain element is proportional only to its concentration (N,) in sample. Thus having number of the reference samples with known concentrations of desired elements one can cOTistruct the calibration dependence (liOcNi). For online analyses of materials on moving belt conveyer the measurement conditions are constantly changing and it is obligatory to construct the calibration dependence for each element as relation (Ij/IoOcNi) where (Iq) is the line intensity of the element, which concentration is constant during the measurements, thus (li/Io) will depends only on Ni and not on experimental conditions. 

When a laser spot (diameter, 0.5 mm) is directed on a propagating front a few seconds, the front is then broken to produce two free ends, which cringe and form a pair of counter-rotating spirals. Further on, the laser spot can be used as an artificial core to which one of the open ends is anchored. Now, by displacing the whole dish, the spiral tip follows this displacement, provided... 

Figure 8.4. Ion signals of photoionized 2,5-dihydro-xybenzoic acid molecules M as a function of laser fluence for different laser spot diameters (10, 25, 60, 125 and 200 pm). Reprinted from reference 14 with permission from Elsevier.

Laser oscillating wavelength k 940 nm Laser power 10,17,24,31W Laser scanning rate 2 mm/sec Laser spot diameter cpl. 0 mm... 

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