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:
“You can read the best experts on child care. You can listen to those who have been there. You can take a whole childbirth and child-care course without missing a lesson. But you won’t really know a thing about yourselves and each other as parents, or your baby as a child, until you have her in your arms. That’s the moment when the lifelong process of bringing up a child into the fold of the family begins.”
—Stella Chess (20th century)
“The moralist and the revolutionary are constantly undermining one another. Marx exploded a hundred tons of dynamite beneath the moralist position, and we are still living in the echo of that tremendous crash. But already, somewhere or other, the sappers are at work and fresh dynamite is being tamped in place to blow Marx at the moon. Then Marx, or somebody like him, will come back with yet more dynamite, and so the process continues, to an end we cannot foresee.”
—George Orwell (1903–1950)
“A designer who is not also a couturier, who hasn’t learned the most refined mysteries of physically creating his models, is like a sculptor who gives his drawings to another man, an artisan, to accomplish. For him the truncated process of creating will always be an interrupted act of love, and his style will bear the shame of it, the impoverishment.”
—Yves Saint Laurent (b. 1936)