Coupling laser materials

Alexandrite, the common name for Cr-doped chrysoberyl, is a laser material capable of continuously tunable laser output in the 700-800 nm region. It was established that alexandrite is an intermediate crystal field matrix, thus the non-phonon emitting state is coupled to the 72 relaxed state and behaves as a storage level for the latter. The laser-emitted light is strongly polarized due to its biaxial structure and is characterized by a decay time of 260 ps (Fabeni et al. 1991 Schepler 1984 Suchoki et al. 2002). Two pairs of sharp i -lines are detected connected with Cr " in two different structural positions the first near 680 nm with a decay time of approximately 330 ps is connected with mirror site fluorescence and the second at 690 nm with a much longer decay of approximately 44 ms is connected with inversion symmetry sites (Powell et al. 1985). The group of narrow lines between 640 and 660 nm was connected with an anti-Stokes vibronic sideband of the mirror site fluorescence. 

Fillpescu et al. [556], and Schmitschek and Schwarz [657] in 1962 were the first to point out the possibility of using the rare earth complexes as laser materials due to the low pump power necessary to excite these complexes via the IMET process and the relatively high quantum yield. The diminished lattice coupling of the rare earth ions in complexes may be very important in the liquid laser where quenching is quite serious. 

Ablation is a powerful technique that uses high-energy lasers to vaporize or ablate materials from the surface. The wavelength of the laser is tuned for the specific material to achieve maximum absorption of the energy, most often ultraviolet. The target is vaporized, creating a plume of neutral metal atoms. The plume is then cooled with a carrier gas to form clusters. It is possible to couple laser evaporation with laser pyrolysis to form alloys. 

Limitations to high-temperature materials chemistry research due to the non-availability of suitable container materials have been overcome by laser induced vaporization mass spectrometry (see e.g. Ref. 587). This technique couples laser heating of refractory materials under vacuum with the mass spectrometric analysis of the vapor plume. Hastie et al. [588] have recently investigated the vaporization of graphite by this technique. The investigations by Ohse s group on the laser induced vaporization of fast breeder oxide and carbide fuels should also be mentioned in this context (see Refs. 589, 590 and references quoted therein). 

Modem design of efficient surface emitting semiconductor lasers implies monolithic solid state stmctures with an active layer and periodic multilayer stacks comprising Distributed Bragg Reflectors (DBR). The latter provides reflection band at the emission wavelength due to multiple reflection/interference in a complex medium with periodically graded refraction index of the layers [1], The larger is the refraction index difference A n = U/ - between a couple of materials chosen to... 

As mentioned above, the irradiation conditions used in many laser materials processing applications correspond to the two-dimensional LSC wave plasma case. Therefore, plasma formation reduces the coupling of laser energy into... 

These one-dimensional array structures can be stacked on top of each other to produce a two-dimensional laser array. However, at the present stage of development, it is difiicult to achieve coupling of all of the individual stripes without the use of external optics. The highest power produced from this type of two-dimensional laser array structure has exceeded 100 W. Although the emitted energy is not totally coherent due to the inability to couple all of the individual emitters, the output power is sufficient to allow the device to be used as an optical pump to excite a solid-state laser material such as Nd YAG. This type of application is very promising for semiconductor laser array... 

A good laser material parameter is the smallest possible threshold, obtained for S=0, that is, for a veiy weidc output coupling. Then based on the denominator of eq. (118) a material Hgure of Merit M can be defined as... 

Laser based mass spectrometric methods, such as laser ionization (LIMS) and laser ablation in combination with inductively coupled plasma mass spectrometry (LA-ICP-MS) are powerful analytical techniques for survey analysis of solid substances. To realize the analytical performances methods for the direct trace analysis of synthetic and natural crystals modification of a traditional analytical technique was necessary and suitable standard reference materials (SRM) were required. Recent developments allowed extending the range of analytical applications of LIMS and LA-ICP-MS will be presented and discussed. For example ... 

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 intrinsic drawback of LIBS is a short duration (less than a few hundreds microseconds) and strongly non-stationary conditions of a laser plume. Much higher sensitivity has been realized by transport of the ablated material into secondary atomic reservoirs such as a microwave-induced plasma (MIP) or an inductively coupled plasma (ICP). Owing to the much longer residence time of ablated atoms and ions in a stationary MIP (typically several ms compared with at most a hundred microseconds in a laser plume) and because of additional excitation of the radiating upper levels in the low pressure plasma, the line intensities of atoms and ions are greatly enhanced. Because of these factors the DLs of LA-MIP have been improved by one to two orders of magnitude compared with LIBS. 

The compounds K5Nb3OFi8 and Rb5Nb3OFi8 display promising properties for their application in electronics and optics. The compounds can be used as piezoelectric and pyroelectric elements due to sufficient piezo- and pyroelectric coefficients coupled with very low dielectric permittivity. In addition, the materials can successfully be applied in optic and optoelectronic systems due to their wide transparency range. High transparency in the ultraviolet region enables use of the materials as multipliers of laser radiation frequencies up to the second, and even fourth optical harmonic generation. 

SSMS can be classified among the milliprobe techniques (Figure 8.3), i.e. it is a unique link between microprobe techniques and macroanalytical methods that are characterised by poor lateral and in-depth resolutions (as in OES), or that have no lateral resolution whatsoever (as in NAA). Also, the achievable precision and accuracy are poor, because of the irreproducible behaviour of the r.f. spark. Whereas analysis of metals, semiconductors and minerals is relatively simple and the procedures have become standardised, the analysis of nonconducting materials is more complex and generally requires addition of a conducting powder (e.g. graphite) to the sample [359]. Detection limits are affected by the dilution, and trace contamination from the added components is possible. These problems can be overcome by the use of lasers [360]. Coupled with isotope dilution, a precision of 5% can be attained for SSMS. 

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