Growing Laser Crystals

As we have shown, crystal growth from a liquid melt is accomplished by establishing an equilibrium between the solid crystal and the liquid melt. By displacing the equilibrium in slight favor of the solid, the crystal will grow. The crystal growth rate is determined by two factors  

We have already shown how stirring of the melt affects heat flow. The rate of crystallization, i.e.- the growth rate, is the major crucial factor in the growth of laser crystals. Although most crystals can be pulled at a rate of several millimeters per hour, the laser crystal can only be pulled at a rate of 0.4 mm./hr. or less. What this means is that if we wish to have a laser crystal of about 4.0 centimeters, it would take about 100 hours to grow it. The costs of growing even larger crystals increases exponentially. 

The crystal most studied has been the YAG, i.e.- YgAlgOu, activated by Nd . As we said, cubic YAG, grows very slowly from a melt, especially from a 1,0,0 plane. If growth is Induced from a 1,1,1 plane, the growth of the single crystal is accelerated by more than ten times. The reason is 

Measuring particle size and growing single crystals 

On the right, we have shown a stylized version of the phase diagram between the two aluminates. There is limited solid state solubility at high 

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Use Electronic and optical applications, starting materials for growing single crystal solid-state lasers, high-temperature dry film lubricants in the form of ceramic-bonded coatings. 

If the sides of the crystal are kept straight during growth, the lattice planes remain intact. However, if the crystal is necked-in" or "pulled-in" during growth, line-defects appear in the lattice structure. If this is a laser-crystal that we are growing, the line defects have a localized effect upon the refractive index of the crystal, making it useless as a laser crystal. 

Moreover, the typical tools of supramolecular chemistry, such as NMR spectrometry, require concentrations usually in excess of 10 " mol/1. and other favorite methods such as mass spectroscopy [fast-atom bombardment (FAB), electrospray ionization (ESI), matrix-assisted laser desorption ionization (MALDI)], and vapor-pressure os-moinetry do not directly provide information about supramolecular behavior in solution. The most favorite method, x-ray analysis, suffers from the limitation posed by the ultimate requirement of being able to grow single crystals. While this is. in numerous instances, possible in the case of pure molecular entities, supramolecules, being mixed molecular objects by nature, are usually difficult to grow in the form of a single crystal. 

The raby laser, the first laser discovered, is produced by implanting chromium ions into an aluminum oxide crystal host and then irradiating the crystal with a flash lamp to excite the laser levels. Although raby lasers were frequently used during the early days of the laser, the difficulties associated with growing the crystals, compared with the ease of making neodymium lasers, has led to their being used much less often in recent times. 

Fig. 10 shows a sequence of laser microscopy images taken during the nucleation and growth of misfit dislocations. The starting time, to, for the observations was 14 h after the addition of a dose of particle to grow the crystal from its critical thickness of 22-30 pm. A number of dislocations are marked and their length as a function of time is plotted in Fig. 11(a). Note that dislocations 3 and 4 are not present at the beginning and hence their nucleation is observed. 

The flame-fusion process allows the dopant concentration of the growing crystals to be changed during growth by means of a double-feeder system shown in Fig. 16.13. This allows growth of, for example, ruby laser crystals with sapphire ends for high-power laser crystals with reduced surface damage. 

The performance of 2,5-DHB as a matrix for MALDI of proteins (chicken egg albumin, horse heart cytochrome c) at 337-nm-wavelength laser radiation was described by Strupat et al." Samples from protein-matrix mixtures with mass ratios between 1.5 X 10 and 1 X 10 were prepared by drying solutions onto metal substrates as well as by growing single crystals. The detection limit was found to 1 fmol, and good shot-to-shot reproducibility was obtained. 2,5-DHB was found to be insensitive to contaminations by inorganic salts, buffers, and detergents, even up to 10% sodium dodecylsulfate (SDS). 

Formation of a cBN film by the DC plasma CVD method has also been claimed (301). Laser-assisted plasma CVD, in which an excimer laser beam irradiated a growing film, was reported to be effective for growing cBN crystals (302,303). 

Growth of long chains (n > 102) in mixed 1 1 crystals of ethylene with chlorine or bromine at 20-70 K has been studied in detail by Wight et al. [1992a, 1993]. Active radicals were generated by pulsed laser photolysis of Cl2 or Br2. The rate constant has been found to be kc = 8-12 s-1 below Tc = 45 K. The chain grows by the radical chain mechanism... 

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