Process
STED functions by depleting specific regions of the sample while leaving a center focal spot active to emit fluorescence. This focal area can be engineered by altering the properties of the pupil plane of the objective lens. The most common early example of this diffractive optical elements, or DOEs, is a doughnut shape used in two dimensional lateral confinement shown below. The red zone is depleted, while the green spot is left active. This DOE is generated by a circular polarization of the depletion laser, combined with a helical phase ramp. The lateral resolution of this DOE is typically between 30 and 80 nm. However, values down to 2.4 nm have been reported. Using different DOEs, axial resolution on the order of 100 nm have been demonstrated. A modified Abbe’s equation describes this sub diffraction resolution as: D=λ/(2nsinα*sqrt(1+I/Isat)). To optimize the effectiveness of STED, the destructive interference in the center of the focal spot needs to be as close to perfect as possible. That imposes certain constraints on the optics that can be used.
Read more about this topic: STED Microscopy
Famous quotes containing the word process:
“[Wellesley College] is about as meaningful to the educational process in America as a perfume factory is to the national economy.”
—Nora Ephron (b. 1941)
“I’m not suggesting that all men are beautiful, vulnerable boys, but we all started out that way. What happened to us? How did we become monsters of feminist nightmares? The answer, of course, is that we underwent a careful and deliberate process of gender training, sometimes brutal, always dehumanizing, cutting away large chunks of ourselves. Little girls went through something similarly crippling. If the gender training was successful, we each ended up being half a person.”
—Frank Pittman (20th century)
“Because her instinct has told her, or because she has been reliably informed, the faded virgin knows that the supreme joys are not for her; she knows by a process of the intellect; but she can feel her deprivation no more than the young mother can feel the hardship of the virgin’s lot.”
—Arnold Bennett (1867–1931)