The basics of lasers

Historically, polymers played a decisive role in the understanding of differences between laser treatment with nanosecond laser pulses and the fs domain [31, 32]. Another motivation for the investigation of the basics of laser-material interaction with nonabsorbing samples was the unwanted damage to optical elements (e.g., dielectric mirrors [39]) in the beam path of short-pulse lasers. The destruction of these components limits the performance of short-pulse oscillators and amplifiers. Additionally, frequency con-... 

Laser Safety Discusses the basics of lasers and safety practices and procedures and other safeguards when using lasers in the laboratory. 

Laser photons are the most important ingredients in any laser chemistry experiment. Hence, it is essential in a textbook on laser chemistry to incorporate a description of the principles of lasers and laser radiation. On the other hand, a complete discussion of laser theory and an exhaustive list of specific lasers, including their construction, operation and description of characteristics, are well beyond the scope of this short introductory part - a wealth of general laser textbooks and books on specific laser types have been written on the subject. Rather, we restrict our outline of laser sources to a summary of the principles behind laser action and to a discussion of the parameters, with which a user will very likely be confronted with in laser chemistry problems. If the reader wishes to delve deeper into the basics of laser physics, he/she is referred to general (e.g. SUfvast, 2004) or specialist texts see the Further Reading list for Part 1. 

In all of these applications, the emphasis to date has been on the use of lasers to study chemically and physically well characterized systems, that is, simple molecules in the gas phase, or in ordered phases such as molecular crystals, or in cryogenic matrices. There are exceptions to this statement, but the basic fact is that the great strides in chemical applications of lasers have been made by the chemical physics and analytical chemistry communities and largely ignored by inorganic, organic, and biological chemists. 

Dissolution Measurement. Resist solutions 1n mixtures of Isoamyl acetate/cyclohexanone/methyl Isobutyl ketone (90 5 5 by volume) were filtered through 0.45 pm disc filters, then spin-coated onto silicon wafers at about 2000 rpm. The coated wafers were prebaked 1n a convection oven at 90°C for 1 hour, then stored 1n a desiccator. The basicities of the alkaline solutions were titrated by a standard HC1 solution with a Fisher Accument pH meter, Model 805 MP. The film thickness 1s about 2 pm. Resist dissolution was measured by a He-Ne laser Interferometer 1n a thermostated bath at the desired temperatures (12.131-... 

In order to demonstrate the use of laser flash photolysis in elucidation of the MDI based polyurethane photolysis mechanism, three polyurethanes, two aryl biscarbamate models, an aryl monocarbamate model, and an aromatic amine were selected. Two of the polyurethanes are based on MDI while the third is based on TDI (mixture of 2,4 and 2,6 isomers in 80/20 ratio). The MDI based polyurethanes all have the same basic carbamate repeat unit. The MDI elastomer (MDI-PUE) is soluble in tetrahydrofuran (THF). The simple polyurethane (MDI-PU) based on MDI and 1,4-butanediol is used in the tert-butoxy abstraction reactions since it does not contain a polyether backbone. (See page 47 for structures of polymers and models.)... 

In this chapter, we review the instrumentation presently available for studying near-IR fluorescence. This includes modern semiconductor devices such as diode lasers and photodiode detectors and also more conventional devices such as discharge lamps and photomultipliers which are traditionally more usually associated with the study of UV/visible fluorescence. Throughout the chapter emphasis will be placed on the novel red/near-IR aspects of instrumentation and we will assume that the reader has a knowledge of the basics of steady-state and time-resolved techniques to the level consistent with Volume 1 of this series. 

Spengler B (2001) The basics of matrix-assisted laser desorption ionization time-of flight mass spectrometry and post source decay. In James P (ed) (2001) Proteome research Mass spectrometry. Springer, New York, p 33... 

After having established the basics of femtosecond laser pulses in microspectroscopy, we now turn to more practical aspects of possible experimental implementations laser sources and possibilities for pulse shaping. 

Fig. 7. In an effort to improve tlie performance of the basic semiconductor laser, researchers developed tlie buried-heterostructure laser. In this configuration, the p-n junction is reduced to a tube that runs the length of the semiconductor crystal. This tube is surrounded by layers of semiconductor whose wide band gap raises the electrical barrier confining charge earner s within the tube. The wide-band-gap material also confines the. photons produced at the junction. The laser beam spreads because of diffraction occurring where the beam emerges from tlie face of tire device...

The use of lasers for the excitation of Raman spectra of solids has led to the detection of many new elementary excitations of crystals and to the observation of nonlinear effects. In this review we have tried to lead the reader to a basic understanding of these elementary excitations or quasi-particles, namely, phonons, polaritons, plasmons, plasmaritons, Landau levels, and magnons. Particular emphasis was placed upon linear and stimulated Raman scattering at polaritons, because the authors are most familiar with this part of the field and because it facilitates understanding of the other quasi-particles. 

Laser Doppler velocimetry is a powerful technique for the in situ measurement of fluid velocities. The basic optical configuration for the measurement is shown in Figure 6.1. The velocity measurement is made at the intersection of two laser beams that are focused to a point in the flow. The use of laser radiation is essential since the light must be monochromatic and coherent. This is required since the intersection of the two beams must create an interference pattern within the fluid. Such a pattern is shown in Figure 6.2, where two plane waves intersect at an angle 2(J). The two waves will have the following form [55] ... 

After recalling the basics of filamentation, this chapter will briefly present the Teramobile laser system, and discuss the transmission of filaments through atmospheres perturbed by fog and clouds. 

At York University, Toronto, microwave measurements have been revived by Storry and Hessels [9,10], that could benefit of lasers to excite the 23P level, instead of the lamps used by Hughes and coworkers. Also, the detection of laser-induced fluorescence from 23P levels makes another basic difference with respect to Hughes experiments, which, together with a microwave frequency scan, eliminated the lineshape asymmetries. In this experiment, a moderate magnetic field is also used to select the transitions between the desidered Mj sublevels. The... 

Due to their large optical anisotropies, liquid crystals (LCs) have a large optical nonlinearity which is the result of molecular reorientation (Freedericksz transition) in an external field which exceeds the critical field [1], The high external field inhibits the application of LCs, and decreasing the threshold as low as possible is a difficult task [2], LCs doped with a small amount of absorbing dyes that could decrease the needed optical field intensity have been reported [3]. The basic assumption is that the anomalous reorientation of the director results from the interaction between the excited dye molecules and the host. However, this sample would easily degrade under the influence of laser radiation. 

Lasers are very powerful instruments to separate elements. Since the separation of isobars from different elements is the most difficult task in AMS, the use of lasers in connection with AMS could provide a very effective clean-up of background. The basic idea in a recent proof-of-principle experiment at the Rehovot AMS facility was to clean a negative ion beam from unwanted isobaric background ions by selective electrons detachment. S ions which have an electron affinity of 2.08 eV were effectively neutralized by interaction with 2.33 eV photons from a pulsed Nd YAg laser. The same photons did not affect Cl ions whose electron affinity is 3.62 eV. This clearly demonstrated that a laser depletion of S background in C1 measurements is feasible, opening up the possibility for sensitive C1 measurement at small AMS facilities where the ion energy is too low to perform isobar separation. However, for actual applications in AMS measurements, a substantial improvement in overall efficiency of the laser depletion process is necessary. 

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