Laser assembly

Fig. 4. External cavity laser assembly. Laser mounts on... 

Figure B2.1.1 Femtosecond light source based on an amplified titanium-sapphire laser and an optical parametric amplifier. Symbols used P, Brewster dispersing prism X, titanium-sapphire crystal OC, output coupler B, acousto-optic pulse selector (Bragg cell) FR, Faraday rotator and polarizer assembly DG, diffraction grating BBO, p-barium borate nonlinear crystal.

Figure 7.5. Quantum-dot vertical-cavity surface-emitting semiconductor laser, svith an active layer consisting of self-assembled InojiGaAso s quantum dots (Fasor 1997),...

The 6 Nd YAG lasers pump the DM0, preamplifier and power amplifier (Fig. 19, Friedman et al., 1998). The YAG lasers are built from commercially available flashlamp/laser rod assemblies, acousto-optic Q-switches and frequency doubling crystals (LBO and KTP). Most of the mirror mounts and crystal holders are commercial. Nd YAGs are frequency doubled to 532 nm using a nonlinear crystal. The Nd YAG rod and nonlinear crystal are both in the pump laser cavity to provide efficient frequency conversion. The 532 nm light is coupled out through a dichroic and fed to multimode fibers which transport the light to the DM0 and amplifier dye cells. 

With commercially available YDFL as pumps, powers > 40 W at 1178 nm are feasible. This sets an upper limit to the conversion efficiency needed in the subsequent second harmonic generation. Numerical simulations for the amplifier and resonator Raman laser configuration indicate feasibility of the system with sufficient SBS suppression. ESO has assembled the amplifier configuration, and has demonstrated up to 4 W CW at 1178 nm. ESO s goal is to have compact and turnkey commercial fiber lasers for LGS/AO within 3 years. 

Mass spectroscopy is a useful technique for the characterization of dendrimers because it can be used to determine relative molar mass. Also, from the fragmentation pattern, the details of the monomer assembly in the branches can be confirmed. A variety of mass spectroscopic techniques have been used for this, including electron impact, fast atom bombardment and matrix-assisted laser desorption ionization (MALDI) mass spectroscopy. 

It is particularly important to study process phenomena under dynamic (rather than static) conditions. Most current analytical techniques are designed to determine the initial and final states of a material or process. Instmments must be designed for the analysis of materials processing in real time, so that the cmcial chemical reactions in materials synthesis and processing can be monitored as they occur. Recent advances in nuclear magnetic resonance and laser probes indicate valuable lines of development for new techniques and comparable instmmentation for the study of interfaces, complex hquids, microstmctures, and hierarchical assemblies of materials. Instmmentation needs for the study of microstmctured materials are discussed in Chapter 9. 

Figure 4.1.2 is a photograph of a coimterflow burner assembly. The experimental particle paths in this cold, nonreacting, counterflow stagnation flow can be visualized by the illumination of a laser sheet. The flow is seeded by submicron droplets of a silicone fluid (poly-dimethylsiloxane) with a viscosity of 50 centistokes and density of 970 kg/m, produced by a nebulizer. The well-defined stagnation-point flow is quite evident. A direct photograph of the coimterflow, premixed, twin flames established in this burner system is shown in Figure 4.1.3. It can be observed that despite the edge effects.

FIG. 7 Confocal laser scanning microscopy image of a fonr-layer polyelectrolyte/CdTe(S) nanocrystal shell assembled on 1.5-p,m-diameter ME particles. The polyelectrolyte film consists of two bUayers of PAH and PSS. (From Ref. 76.)... 

Hofkens, J., Hotta, J., Sasaki, K., Masuhara, H. and Iwai, K. (1997) Molecular assembling by the radiation pressure of a focused laser beam Poly (N-isopropylacrylamide) in aqueous solution. Langmuir, 13, 414-419. 

Spatially resolved measurements, based on the confocal laser microscope and related techniques, have recently enabled direct detection of individual molecules, single nanoparticles, and molecular assemblies, leading to elucidation of the heterogeneous nature of these systems and its dependence on the individual environments. 

Despite the frequent use of arc-discharge and laser ablation techniques, both of these two methods suffer from some drawbacks. The first is that both methods involve evaporating the carbon source, which makes it difficult to scale up production to the industrial level using these approaches. Second, vaporization methods grow CNTs in highly tangled forms, mixed with unwanted forms of carbon and/or metal species. The CNTs thus produced are difficult to purify, manipulate, and assemble for building nanotube-device architectures in practical applications. 

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