Laser operating parameters

In recent reports (2-7), it has been shown that it is important to consider the effect of such laser operating parameters as pulse repetition rate on the polymerization kinetics. It was clearly demonstrated that pulsing the laser at narrow time intervals on the order of the lifetime of growing polymer radical chains resulted in a premature chain termination due to injection of small molecule "terminator" radicals into the system. In this paper we focus on the effect of pulse repetition rate on the polymerization of multifunctional acrylates, in particular 1,6-hexanediol diacrylate (HDODA) and trimethylolpropane triacrylate (TMPTA). 

As we will see the use of saturated laser induced fluorescence spectroscopy will allow us to ignore some of these effects. we can infer the importance of others and for the time being the remainder have to be evaluated on a case by case basis for each molecular system and for the operating parameters of the experiments. 

The parameter gv depends on the shape of the laser pulse and the duty cycle. Pulses with a Gaussian temporal profile result in gv = 0.664 while gv = 0.588 is found for hyperbolic-secant square (sech2) pulses. Combination of Eqs. (40) and (41) results in Eq. (42), showing that pulsed lasers are more efficient excitation sources compared to lasers operating in cw mode. 

The key operational parameters of exciplex and excimer lasers used in optical lithographic applications include exposure-dose-related parameters comprising average power, pulse energy, repetition rate, and pulse width temporal coherence spatial coherence including beam dimensions, beam divergence, and beam uniformity and maintenance and reliability. Table 13.2 lists some of the key operational parameters of KrF, ArF, and F2 laser systems used in optical lithography. 

Figure 3. Light output as a function of current of the injection laser operating at 1.51 pm (at 20 °C). Insert shows quantum-well parameters. (Adapted from Ref. 39.)...

A more suitable approach for on-line analysis is to view atomic emission directly from the small plasma formed above the sample surface when the sample is ablated using the laser. This approach, which is shown schematically in Fig. 20.12 has been applied to analyses of a variety of materials (e.g. [58-74]) and is known under a variety of names such as laser induced plasma spectrometry (LIPS), laser induced breakdown spectrometry (LIBS) and laser spark emission spectrometry (LASS). The laser used is typically a Nd YAG laser operating either at its fundamental, doubled or quadrupled frequency, although excimer and CO2 lasers have also been used. The important parameter of the laser is that it must be capable... 

There are several versions of the experimental realizations of mode-locked or synchronously pumped lasers. Table 6.1 gives a short summary of typical operation parameters of the different techniques. More detailed representations of this subject can be found in [663-670]. 

The quality of the beam from a present ASE-type X-ray laser is considered poor by usual laser standards, again because of the lack of high quality cavities. It is hoped that this will improve with further development, fital operating parameters, present values, and crystal-ball projections for the near future are discussed in the following paragraphs. 

The laser intensities required to exploit gaseous nonllnearltles in a short time period dictate employment of pulsed lasers. These are typically frequency-doubled neodymiumrYAG lasers at 532 nm which are ideally spectrally situated for CARS work from both a dye laser pumping and optical detection standpoint. These lasers operate at repetition rates in the 20-50 Hz range. The combustion medium cannot be followed in real time, but is statistically sampled by an ensemble of single shot measurements which form a probability distribution function (pdf). From the pdf, the parameter time average can be ascertained as well as the magnitude of the turbulent fluctuations. 

The schematic layout of IPUC-LIDAR, a transversely excited atmospheric (TEA) CO2 laser-DIAL system, is shown in Figure 28.20, and its operating parameters are summarized in Tablele 28.3. 

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