Problems
Photobleaching can occur either from excitation into an even higher excited state, or from excitation in the triplet state. To prevent the excitation of an excited electron into another, higher excited state, the energy of the photon needed to trigger the alternative emission should not overlap the energy of the excitation from one excited state to another. This will ensure that each laser photon that contacts the fluorophores will cause stimulated emission, and not cause the electron to be excited to another, higher energy state. Triplet states are much longer lived than singlet states, and to prevent triplet states from exciting, the time between laser pulses needs to be long enough to allow the electron to relax through another quenching method, or a chemical compound should be added to quench the triplet state.
Read more about this topic: STED Microscopy
Famous quotes containing the word problems:
“The problems of society will also be the problems of the predominant language of that society. It is the carrier of its perceptions, its attitudes, and its goals, for through it, the speakers absorb entrenched attitudes. The guilt of English then must be recognized and appreciated before its continued use can be advocated.”
—Njabulo Ndebele (b. 1948)
“I have said many times, and it is literally true, that there is absolutely nothing that could keep me in business, if my job were simply business to me. The human problems which I deal with every day—concerning employees as well as customers—are the problems that fascinate me, that seem important to me.”
—Hortense Odlum (1892–?)
“If when a businessman speaks of minority employment, or air pollution, or poverty, he speaks in the language of a certified public accountant analyzing a corporate balance sheet, who is to know that he understands the human problems behind the statistical ones? If the businessman would stop talking like a computer printout or a page from the corporate annual report, other people would stop thinking he had a cash register for a heart. It is as simple as that—but that isn’t simple.”
—Louis B. Lundborg (1906–1981)