Laser line focused

The depth profiling of the Cu-Ag-Si samples was performed with the laser beam focused on to the sample surface to the spot of approximately 30-40 pm. To obtain the best depth resolution the laser fluence was maintained near the 1 J cm level, close to the threshold of the LIBS detection scheme. The intensity profiles of Cu and Ag emission lines are shown in Fig. 4.43. The individual layers of Cu and Ag were defi-... 

When compared to fluorescence detectors for HPLC, the design of a fluorescence detector for CE presents some technical problems. In order to obtain acceptable sensitivity, it is necessary to focus sufficient excitation light on the capillary lumen. This is difficult to achieve with a conventional light source but is easily accomplished using a laser. The most popular source for laser-induced fluorescence (LIF) detection is the argon ion laser, which is stable and relatively inexpensive. The 488-nm argon ion laser line is close to the desired excitation wavelength for several common fluorophores. The CLOD for a laser-based fluorescence detector can be as low as 10 12 M. 

Figure 2. Experimental set-up for Raman spectroscopy. The desired laser line is isolated from other plasma lines by a narrow bandpass filter or broadband prism monochromator, then focused onto a sample in a capillary tube. A collecting lens placed at a 90° angle to the incident beam focuses the scattered light onto the entrance slit of a monochromator with output to a photomultiplier tube (in the case of a scanning instrument) or a diode array detector.

The sample was placed in a quartz cell in a thermostated holder (25 + 0.5 °C). The laser line was focused by a lens and mirror system and the scattored light... 

W. Wei, G. Zue, and E. S. Yeung, One-Step Concentration of Analytes Based on Dynamic Change in pH in Capillary Zone Electrophoresis, Anal. Chem. 2002, 74, 934 P. Britz-McKibbin, K. Otsuka, and S. Terabe, On-Line Focusing of Flavin Derivatives Using Dynamic pH Junction-Sweeping Capillary Electrophoresis with Laser-Induced Fluorescence Detection, Anal. Chem. 2002, 74, 3736. 

Koren et al. (582) have used an intense focused pulse of C02 laser to photodissociate HDCO (formaldehyde). The 944.18 cm 1 laser line nearly coincides with an absorption line of HDCO, however, there is no absorption hand of H2CO in the region of the laser line. Thus, the authors found an enrichment factor of 40 (the ratio of HD to H2 after illumination to that in ihe original material). 

Raman spectroscopy Raman spectra from small SWNT pieces with typical dimensions of 100 pm were recorded in the back-scattering geometry using two different micro-Raman setups comprised of a triple monochromator DILOR XY and a CCD detector system, cooled either to liquid nitrogen temperature or -100°C. The 488 or 514.5 nm line of an Ar+ laser, as well as the 647.1 nm line of a Kr+ laser, were used for excitation, while the beam intensity on the sample was =0.5 mW. The laser line was focused on the sample by means of a lOOx objective with a spatial resolution of 1 pm. 

A CW tunable dye laser (Stilbene 3) is pumped by the ultraviolet lines of an argon ion laser. The laser is focused in a cell filled with a mixture of cesium and hydrogen. The cell (10 cm long with an inside radius of 2.6 cm) is connected to a reservoir containing liquid cesium and to a pumping system or a hydrogen gas tank. It is placed in an oven heated independently from the reservoir. The laser beam enters the cell from below through a flat window and is focused at a point 1 cm above the window. 

Figure 6.15. Schematic of point and line focus of the laser on a tablet. The right-hand drawing shows spinning combined with a line focus, with the gray region indicating the tablet area sampled by the spectrometer. Relative standard deviations (rsd) are shown for experiments on the tablet described in Figure 6.14.

Figure 11.1. Several imaging modes for Raman microscopy. Gray circle in global imaging case represents a defocused laser spot covering a large area compared to a point or line focus.

Line Imaging Based on a Line-Focused Laser... 

Figure 11.13. 200 Raman spectra of the 1332 cm feature of diamond obtained with a 600 pm-long line focus. The expansion of the middle 100 pm of the line demonstrates relatively constant laser intensity. (Adapted from Reference 14.)...

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