Lasers stoichiometric materials

Because of the absence of 5qq quenching by simple ion pair interactions, high Eu concentrations and stoichiometric materials should be usable for laser action. 

Ho3+ is the second most extensively exploited lanthanide laser ion in terms of different transition lased, it is the most exploited. Stimulated emission is observed for 12 transitions with wavelengths ranging from 0.55 to 3.91 ym and in hosts including crystals, three stoichiometric materials (HoF3-LiHoF4, H03AI5O-12) (19, 2lj, thin films (52), and silicate glass (75). 

In contrast to other lasers where the active ion is dispersed in a crystalline or glassy host, stoichiometric materials are pure chemical compounds of rare earths. Therefore, there is no question of rare earth ion size, charge, or coordination to be considered as in other laser materials. Also, since the rare earth is not a dilute substitutional impurity, the inhomogeneous broadening is very small and there is no statistical distribution of ion-ion separations. Other spectroscopic properties, including intensities and cross sections, are similar to those in other crystalline hosts. 

The product was identihed by a number of spectroscopic methods. Dioxygen uptake was measured by spectrophotometric titration. MALDI-TOF-MS (matrix-assisted laser desorption/ionization-time of flight-mass spectrometry), an MS method particularly suited to determining molecular masses of biopolymers and synthetic materials with relative masses up to several hundred kilodaltons, determined that the product contained stoichiometric amounts of the heme starting material, the copper complex, and dioxygen in a 1 1 1 ratio. 

It is characteristic of such a laser ion source that the experimental conditions for LIMS can be optimized with respect to a stoichiometric evaporation and effective ionization of solid sample material by varying the laser power density as demonstrated in Figure 2.20. Under certain experimental conditions fractionation effects can be avoided. Stoichiometric laser evaporation and ionization of analyzed material is found at a laser power density between 109Wcm 2 and 1010Wcm-2. In this laser power density range, the relative sensitivity coefficients of the chemical elements (RSC = measured element concentration/true element concentration) are nearly one for all the... 

Pressure effects on the energy transfer between f elements of the same kind were studied by Merkle et al. (1981) for the case of Nd3+-Nd3+ pairs in Ndx Y xP50i4 (x = 1,0.1). This material was studied in detail because of its potential use as a stoichiometric laser material. An outstanding property is a very weak concentration quenching of the luminescence. The total luminescence decay rate of the 4F3/2 multiplet in Ndx Y xP50i4 (x = 1,0.1) underpressure is shown in fig. 17. Obviously the stoichiometric compound shows a much larger increase of the decay rate than the doped compound. 

In analogy to the observed behaviour in LIMS, in LA-ICP-MS increasing fractionation effects are observed with decreasing laser power density for <10 Wcm . These fractionation effects increase significantly if the laser power density is lower than lO Wcm. A stoichiometric laser ablation of sample material is observed at a laser power density between 10 Wcm and 10 °Wcm in the author s laboratory. 

PLD of crystalline and stoichiometric ferroelectric materials has been successful for a number of materials. For example, crystaUine PbTiOs thin films have been deposited at only 350 °C using a KrF excimer laser (A. = 248 mn). The low deposition temperature makes this a potentially attractive method for directly fabricating ferroelectric/semiconductor hybrid devices. A related solid that is more difficult to prepare in thin film form is PbZri- ThOs. To maintain the Pb stoichiometry and ensure random mixing of Ti and Zr requires careful control of film synthesis conditions. ... 

Zinc selenide (yellow) and telluride (brown) have similar stractures to those of the sulfide, both existing in both wurtzite and zinc blende modifications. The selenide is used with zinc sulfide as a phosphor. It has the interesting property that it can act as a bine-green solid state laser bine-green laser action in solids is rare (most solid-state lasers function towards the red end, 635 nm or more, of the spectrum). At room temperature, laser action with the selenide at a wavelength of 525 nm (green) is observed and at -196°C at 495 nm (bine). Unfortunately the laser is relatively short-lived. Zinc telluride is a wide band gap semicondnctor whose electron transport properties in the form of thin films of stoichiometric and nonstoichiometric forms have been mnch studied. Its applications in optoelectronics, for example, as an optical recording material, have been reviewed. ... 

If the laser radiation is not absorbed by the sample (e.g., with transparent materials), a substance performing the function of absorption centres (such as powdered carbon or nickel) is introduced into the sample for the latter to be pyrolysed. For example, in ref. 93 it was proposed to decompose transparent polymers (e.g., polyethylene, polystyrene) exposed to a laser beam by placing the samples made in the form of a thin film on the flat surface of a blue cobalt glass rod. The light products are formed primarily in the plasma torch - the rapidly frozen plasma induced by the laser radiation. These products are essentially low-molecular-weight gases whose analysis permits the sample composition to be determined. Such an analysis is known as plasma-stoichiometric analysis [94]. 

The technique consists of firing a pulsed excimer laser at a stoichiometric pellet of the material to be deposited and under suitable conditions of laser energy density, oxygen partial pressure, substrate tenperature and deposition angle, high quality films are deposited. What is remarkable about the process is the stoichiometric deposition of films adhieved by this technique. The composition of the pellet is closely reproduced in the films. A schematic of the deposition system is shown in fig. 4. The deposition and annealing parameters are shewn in table 3. 

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