Laser focusing

For molecules exposed to the intensity of sunlight at the earth s surface this would suggest that the molecule might be excited once in the age of the universe. However, the probability is proportional to the square of the light intensity. For a molecule exposed to a pulsed laser focused to a small spot, the probability of being excited by one pulse may be easily observable by fluorescence excitation or multiphoton ionization teclnhques. 

C. L. Tang and co-workers. Laser Focus World, 87 (Sept. 1990). 

The laser spray process uses a high power carbon dioxide laser focused onto the surface of the part to be metallized. A carrier gas such as belium blows metal particles into the path of the laser and onto the part. The laser melted particles may fuse to the surface, or may be incorporated into an aHoy in a molten surface up to 1-mm thick. The laser can be used for selective aHoying of the surface, for production of amorphous coatings, or for laser hardening. 

In Table 4.3, the Cetac product LSX-200 is the specialized system for coupling with the ICP customer s system. It includes the laser, optical viewing system for exact positioning of the laser focus on a sample surface, and the sample cell mounted on the computer controlled XYZ translation stage. The system is also provided with the appropriate gas tuhing for transport of the ablated material into an ICP-OES/MS. 

The surfaces of porous materials, e. g. catalysts, molecular sieves, or adsorbents, are much more readily accessible than smooth surfaces to Raman spectroscopy, because larger amounts of adsorbed substance can be placed within the laser focus, thus contributing to the scattering process. 

Collier, D., and Pantley, W., Deep Ultraviolet Coatings Resist Optical Damage, Laser Focus World, pp. 77-82 (Sept. 1997)... 

Because of the complexity of computer hardware and software and because of the intricacy of a risk assessment, the FDA has to all intents and purposes adopted an indirect regulatory posture. Regulated companies are informally urged to conduct independent audits of Part 11 compliance, utilizing in-house or consultant expertise. The agency can then review the details of the audit report and the credentials for experience, expertise, and independence of the auditor. Follow-up investigation of speciflc points can then be laser-focused on specific areas of concern. 

Demming et al. [17], and compared it with their experimental results. The observed increase in Raman intensity by a factor of 15 within the laser focus of about 2 pm, corresponds to a maximum local enhancement at the center of the tip apex by a factor of about 12 000 under the assumption that the tip radius is 100 nm. More precisely, about 20% of the Raman intensity is considered to originate from an area with a radius of 14 nm under the tip, which is roughly equivalent to 400 molecules out of 2 X 10 in the total focused area. 

Ren et al. reported a method to prepare a gold tip with a tip apex radius of 30 nm reproducibly [27]. They observed the TERS of a Malachite Green isothiocyanate (MGITC) monolayer on an Au(lll) surface and obtained an enhancement factor of about 1.6 X 10, by using the relation, q= /TERs/lRRs=g /l focus where q is the net increase in the signal. Iters snd rrs the signal intensities for TERS and RRS (resonance Raman scattering), respectively is the TERS enhancement (gis the field enhancement), a denotes the radius of the enhanced field, and Rfocus the radius of the laser focus. 

Figure 4. Calculation of the modulation depth using the analytic model described in the text, with the lasers focused on the axis of the molecular beam (zm = 0). The dashed curve was obtained by setting pa — pi, at zm — 0. The solid curve is the maximum possible modulation depth, obtained by setting pa — pt, at an optimum location.

Peyghambarian N, Dalton L, Jen A, Kippelen B, Marder S, Norwood R, Perry J (2006) Technological advances brighten horizons for organic nonlinear optics. Laser Focus World 42 85-94... 

Figure I. Comparative quantities for selected tensor components of second harmonic generation (left) and the linear electro-optic effect (right) (measured at 1.06 pm wavelength). (The strain free quantity, f, was measured at 0.633 pm wavelength except in the case of GaAs which was measured at - 0.9 pm). (Reproduced with permission from Ref. 8. Copyright 1982, Laser Focus.)...

J. R. Lakowicz, Fluorescence lifetime sensing, Laser Focus World May, 60-80 (1992). 

Fig. 7. Schematic diagram of forces exerted on a cell when using an inverted microscope with (A) epi-illumination (i.e., laser focused through the objective) or (B) transillumination (i.e., laser focused through the condenser). is the axial force, and Fl is the lateral trapping force. Curved arrows represent the laser beam waist and point in the direction of light propagation.

Ipor more detailed information see the book by G. W. Chantry Submillimeter spectroscopy. New York Academic Press, 1971, and the review article by K. J. Button in Laser Focus 7, 29. August 1971. 

I. Howieson, E. Normand, M.T. McCulloch, Quantum-cascade lasers smell success. Laser Focus World, 41(3) S3... 

Editorial Tunable QC laser opens up mid-IR sensing applications. Laser Focus World, PennWell Publications... 

E.J. Lerner, Infrared detectors offer high sensitivity. Laser Focus World, 32(6), 155-164 (1996). 

However, the high frequency of the laser irradiation in the visible region may lead to photochemical reactions in the laser focus. Besides, fluorescence can often cover the whole Raman spectrum. Such problems can be avoided by using an excitation wavelength in the near-infrared (NIR) region, e.g. with an Nd YAG laser operating at 1064 nm. Deficits arising from the v dependence of the Raman intensity and the lower sensitivity of NIR detectors are compensated by the Fourier-Transform (IT) technique, which is widespread in IR spectroscopy . ... 

The storage and retrieval of data by optical means, which involves the interaction of some medium with a compact laser, focused to sub-micron size, is dominated by direct bit storage onto disc media. The various types of storage media, from read only compact discs (CD-ROM) to rewritable digital versatile discs (DVD-RW), and the favoured recording materials are shown in Figure 4.5. ... 

FIGURE 8.8 A section of a single HeLa (human cervical cancer) cell stained with Phalloidin 350 (actin filaments) and MitoTracker488 (mitochondria) acquired using selective two-photon excitation, without fluorescence color filters. The image size is about 25 (xm. (From Dantus, M., Lozovoy, V. V., and Pastirk, I. Laser Focus World, 43(5) 101-104. 2007. Used with permission.)... 

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