Laser results

Figure C2.16.ll. Changes in the tlireshold eurrent density of diode lasers resulting from new stRieture eoneepts. A homojunetion diode laser was first demonstrated in 1962. SH and DH stand for single and double heterostaieture, respeetively. The best laser perfonuanee is now obtained in quantum well (QW) lasers.

The time of crystallization of a lunar "granite" has also been determined by the laser method. This "granite" is the K- and Si-rich felsite that forms clasts in 73215, 73255, and Boulder 1 at Station 2. The laser results set a lower limit of 4.00 G.y. on crystallization of the parent body of this felsite, and the Rb-Sr data set an upper limit of 4.05 G.y. [6]. 

In addition to the rather trivial differences mentioned above, laser irradiation can also lead to products as a result of reexcitaion of the carbenes. Thus, excitation of 30 in isooctane with a pulse of the 249-nm line from a KrF excimer laser results in the formation of 9,10-diphenylanthrancene (103), 9,10-diphenylphenanthrene (104), and fluorene, in addition to tetraphenylethylene (Scheme 9.31). Conventional lamp irradiation of 30 results in the formation of benzophenone azine as a major product. None of the products mentioned above are detected. Moreover, the yield of both 103 and fluorene increased markedly with increased laser power. While the details of the mechanism of this reaction are not certain yet, it is clear from the dependence on laser power that some of these products arise from carbene photochemistry. " ... 

These authors report some unique laser results. In one experiment O Connor and Hargreaves studied the effect of strongly pumping in the 3- to 6-/x CeF3 absorption band while oscillation was excited. The long-wave pumping source was in this case a 3000-watt tungsten-ribbon-filament lamp. 

Figure 11-2. 1 + 1 REMPI, 1 + 1 REMPI and UV absorption spectra of 1,3-DMU [15]. The 1 + 1 REMPI spectrum was obtained by scanning the pump laser and setting the probe laser at 220 nm with a delay time of 10 ns. Neither REMPI spectrum was normalized by the laser power, and at the short wavelength side of the figure, the low output power of the OPO laser resulted in the missing S3 feature in the 1 + 1 spectrum. The absorption spectrum was taken at 140°C, the same temperature as that of the pulsed valve during the REMPI experiments. (Reproduced with permission from J. Phys. Chem. 2004, 108, 943-949. Copyright 2004 American Chemical Society.)...

Taniguchi, et al. [99] have tested the one- and two-photon excitation for [Cr(acac)3]3- for several irradiation wavelengths but found no indication of a superlinear dependence of photoracemization or photodecomposition. This seems to be in line with the experiments of Gunde and Richardson [6] on Na3[Gd(02C-CH2-0-CH2-C02)3] 2NaC104 6H20 crystals. The possibility discussed in several papers [4-6] that in high-intensity radiation fields a pure electric dipole 2-photon absorption may lead to CD effects adds a new possibility of rationalization of the high-power laser results. 

Excitation of the visible absorption band of the manganese-containing proteins of human serum transferrin and ovotransferrin with an argon laser results in resonance-enhanced Raman bands at 1603, 1501,1264, 1173, and 752 cm1 and 1600,1500, 1236, 1171, and 752 cm-1, respectively (104). These frequencies are almost identical to those enhanced in the iron analog, demonstrating that the Mn probably occupies the iron-binding sites. All of these enhanced bands were assigned to phenolic vibrational modes. Similar studies with human... 

Less sophisticated systems tend to use white light illumination, others use gas lasers or solid-state laser diodes. Laser diodes are smaller and more robust than gas lasers, resulting in smaller instruments. Their spatial properties have increased the sensitivity of particle sensors by a factor of two, enabling dynamic size ranges of 700 1 to be measured. Fast analog to... 

The olefins represent the first stable products isolated from the photoablation of substituted polysilanes, and as such, any mechanistic hypothesis must include these species. The absence of literature precedents for photochemical silicon-carbon bond cleavage suggests the possibility of a thermal route. This suggestion is further strengthened by the observation that exposure of a number of polysilanes to IR radiation from a cw CO 2 laser results in gaseous mixtures with compositions (as determined by mass spectral analyses) that closely resemble those produced by irradiation at 308 nm. 

The photooxidation rates of nylon polymers have been monitored using Fourier Transform Infra-red spectroscopy. Norrish type-II reactions of carbonyl groups were considered to be the most important process. Another group of workers have studied the photooxidations rates of a nylon 6- polypropylene glycol copolymerIn this case polyether sequences are the major source of free radical attack resulting in high levels of hydroperoxides. Irradiation of nylon and polyester fibres with an excimer laser resulted in... 

Perhaps the most likely immediate commercial application of carbonyl fluoride, however, arises from its spectroscopic properties. Irradiation of mixtures of COF, and H, (or D,), over a wide pressure range and at ambient temperature, with the multiline output of a continuous wave CO, laser, results in the generation of excited state HF (DF) which lases [1387]. Energy transfer from the R, line (970 cm" ) of CO, (which is close in energy to the c, band of COF,) causes the dissociation of the COF, to CO and two excited state fluorine atoms which subsequentiy react with the dihydrogen (or dideuterium). However, COF, itself has been found to effect rapid vibrational de-excitation of HF [239], an observation that suggests that the COF,/H, route to the HF laser may be of limited practicality. 

All of the experiments discussed thus far were performed at Fe(C0)s pressures i3 torr, where the surface coverage is on the order of a monolayer or less. At higher surface coverages, however, very different results are observed. For example, photolysis of silica-adsorbed Fe(C0)s at a pressure of 10 torr in the room temperature cell with the nitrogen laser results in formation of the usual green Fe3(CO)i2 product, but an opaque yellow deposit that is not observed in lower pressure experiments is also formed. 

Compared to hand-made perforations by means of a specially grinded needle (Fig. 27a,b), the use of a femtosecond pulse laser resulted in well-defined perforations of the polyethylene membrane (Fig. 27c,d). Obviously, the reproducibility of the laser-generated structures is higher (Fig. 27b,d). It was impossible to reach diameters smaller than 50 pm with the mechanical technique (Fig. 27a). The fs-laser structuring yields the opportunity to tune the... 

An interesting laser device to be mentioned here is the CO laser resulting from a free-burning additive CS2/O2 flame. With the burner injector having an area of 30.5 by 0.79 cm, a maximum power of 0.6 W was obtained 82). 

Sapphire substrates, for II-Vl or III-V applications, can be found through the 100 mm range. Whereas, ZnSe, ZnTe, and GaN are found in the 1 cm range in research quantities. Efforts on ZnSe and related substrates increased with the demonstration of blue lasers in this material system. However, those efforts are foreshadowed by the blue LED and laser results in GaN. Presently there are several major research efforts underway to produce large area GaN substrates. The nitride substrate development effort also is motivated by high power, temperature and frequency device applications. For superconductors, lanthanum aluminate, strontium titanate, magnesium oxide, and other related substrates are found in the few to tens of square centimeter ranges. 

The laser bums less material in thermoplastics than IR lasers resulting in a cleaner cut and runs more stable than UV excimer lasers... 

All lasers (except the fi ee-electron laser) result from electron energy changes among discrete energy levels of atomic species, including (1) individual atoms or ions,... 

GO exhibits a higher NIR light absorption property, making it a potent photothermal agent. Compared to ultrasmall GO, rGO prepared by PEGylation showed a > 6-fold increase in NIR absorbance and irradiation with an 808 nm laser resulting in a temperature rise up to 55°C in 8 min along with an increase in concentration [86]. 

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