Stimulated Raman emission in the visible has been observed in glass-fiber optical waveguides. Even though the Raman cross section is quite small, relatively low threshold for Raman emission can be achieved because high optical power densities are maintained over long lengths of waveguide. The broad stimulated gain bandwidths available in glass should permit the construction of wide-band fiber amplifiers and Raman oscillators tunable over a range of 100 Å.

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once the level of the organic species has been reduced by adsorption or complexing, allowing growth of CH crystals. Since the level of silicate ions in solution will be high, the initial hydration will be rapid.However, it is difficult to see how this theory, although it explains retardation, can explain complete inhibition of hydration, since there is no evidence, even after 50 days, that hydration products form in the paste made with 0.1 c7c sodium gluconate, nor does it explain the retention of organic material in pastes with no evidence of hydration products.The SEM micrographs show a distinct change in surface features and thus the inhibition of hydration could be due to a surface phenomenon. Tadros er a1.'* showed that, in the early stages of hydration, the surface of the hydrating C,S particles carries a positive charge due to adsorption of Caz+ ions onto the silica-rich layer left as the Ca2+ ions diffuse out. It seems logical that the sugar-acid anions could adsorb onto this positively charged layer, preventing the nucleation of C-S-H aciculae. Thus the sinks for all ions in solution are poisoned and hydration is halted. This hypothesis assumes that initial hydration does occur, at least to form a small amount of hydration product. This explanation appears to be reasonable, since adsorption onto C3S in an anhydrous system is very limited.:'Because sugars are not readily ionized, the greater effect of gluconic acid at low levels can be readily explained, i.e. adsorption of the negatively charged species on the positively charged surface will be much greater. The additional stability of sugar acids in alkali h a s also been suggested as a reason for their greater effectiveness as retardersi6 and also explains why the sugar-reduced lignosulfonate fractions are as effective as the sugar-containing fractions since it is not the sugars which are responsible for most of the delay in hydration. V. Conclusions(1) The delaying action of calcium lignosulfonates in the hydration of C,S is caused by sugar acids present in the lignosulfonates. The effect is that of a delayed accelerator rather than of a slowing of the hydration rate. (2) Sugar acids are more effective as delayed accelerators of C,S hydration than sugars because of their charge and stability.(3) The delay in hydration is caused by poisoning of the Ca(OH), nuclei and complexing of Ca2+ ions, preventing a growth of Ca(OH),. (4) Inhibition of hydration occurs when the C-S-H nucleation sites on the positively charged surface are poisoned by adsorbed sugar-acid anions.