Laser spot size

It was found, that at standard gas-chromatograph sampling of 1 pL of analyte solution the limit of detection for different amines was measured as 0.1-3 ng/ml, or of about 1 femtomole of analyte in the probe. This detection limit is better of published data, obtained by conventional GC-MS technique. Evidently, that both the increasing of the laser spot size and the optimization of GC-capillary position can strongly improve the detection limit. 

A Q-switched, frequency-quadrupled Nd—YAG laser (X, = 266 nm) and its accompanying optical components produce and focus the laser pulse onto the sample surface. The typical laser spot size in this instrument is approximately 2 pm. A He-Ne pilot laser, coaxial with the UV laser, enables the desired area to be located. A calibrated photodiode for the measurement of laser energy levels is also present... 

The laser spot sizes were kept the same and the EL was normalised to this area. 

The application of LA-ICP-ToF-MS and LA-ICP-QMS for depth profiling of various titanium based coatings on steel and tungsten carbide and Ti based single layers is discussed in references respectively. Thickness determination was performed by LA-ICP-QMS with 5% RSD, a laser ablation rate of < 100 nm per laser shot (Nd-YAG laser at wavelength 266 nm using a laser energy of 1.5 ml at 120 p,m laser spot size), and a depth resolution of 2.5 p-m was observed. ... 

Unfortunately, any discussion of Raman signal dependence on spectrometer variables is complicated by the many different ways experiments can be performed. Laser spot size, spectrometer slit area, depth of field, and several other variables affect the magnitude of C, and, in some cases, the way it... 

An important qualifier is required for the statement that etendue remains constant through the system. The usable etendue is determined by the minimum AS2 product for the system. This minimum could be determined by the laser spot size, the entrance slit, or the detector area and is often related to the limiting aperture applied to the definition of //. For many Raman applications, the etendue is determined by the spectrometer/detector combination (e g., the // of a spectrograph and the area of a CCD pixel). Increasing the Af2 product has provided much of the motivation for building Raman spectrometers with lower // and maximum etendue. 

The spatial resolution is determined by either the laser spot size or the collection optics, both of which are ultimately limited by diffraction. The laser beam diameter at the focal spot (twice the beam waist, wq) was discussed in Chapter 6, and is given by Eq. (6.2) ... 

For single-point microscopy, the laser spot size often defines the spatial resolution, and the spectrometer is designed to collect light from an area... 

Laser spot size and its effects on power density and depth of focus... 

Recall that Pq is laser power (photons per second) not power density. Note that the Raman signal no longer depends on laser spot size or spectrometer Ad [since Ai = Ad in Eq. (3.7)], nor does it vary with incidence angle (8). 

Fig. 87 Normalized fluorescence intensity of the V pyrene peak at 393 nm from an implanted PBMA surface and ratio of pyrene spread radius R to laser spot size radius R0 as a function of laser fluence. Number of laser pulses 10. REPRINTED WITH PERMISSION OF [Ref. 360], COPYRIGHT (1998) Elsevier Science...

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