Stimulated emission microscope

Here, Ri f and Rf i are the rates (per moleeule) of transitions for the i ==> f and f ==> i transitions respeetively. As noted above, these rates are proportional to the intensity of the light souree (i.e., the photon intensity) at the resonant frequeney and to the square of a matrix element eonneeting the respeetive states. This matrix element square is oti fp in the former ease and otf ip in the latter. Beeause the perturbation operator whose matrix elements are ai f and af i is Hermitian (this is true through all orders of perturbation theory and for all terms in the long-wavelength expansion), these two quantities are eomplex eonjugates of one another, and, henee ai fp = af ip, from whieh it follows that Ri f = Rf i. This means that the state-to-state absorption and stimulated emission rate eoeffieients (i.e., the rate per moleeule undergoing the transition) are identieal. This result is referred to as the prineiple of microscopic reversibility. 

The uncertainty principle, according to which either the position of a confined microscopic particle or its momentum, but not both, can be precisely measured, requires an increase in the carrier energy. In quantum wells having abmpt barriers (square wells) the carrier energy increases in inverse proportion to its effective mass (the mass of a carrier in a semiconductor is not the same as that of the free carrier) and the square of the well width. The confined carriers are allowed only a few discrete energy levels (confined states), each described by a quantum number, as is illustrated in Eigure 5. Stimulated emission is allowed to occur only as transitions between the confined electron and hole states described by the same quantum number. 

Several far-field light microscopy methods have recently been developed to break the diffraction limit. These methods can be largely divided into two categories (1) techniques that employ spatially patterned illumination to sharpen the point-spread function of the microscope, such as stimulated emission depletion (STED) microscopy and related methods using other reversibly saturable optically linear fluorescent transitions (RESOLFT) [1,2], and saturated structured-illumination microscopy (SSIM) [3], and (2) a technique that is based on the localization of individual fluorescent molecules, termed Stochastic Optical Reconstruction Microscopy (STORM [4], Photo-Activated Localization Microscopy (PALM) [5], or Fluorescence Photo-Activation Localization Microscopy (FPALM) [6]. In this paper, we describe the concept of STORM microscopy and recent advances in the imaging capabilities of STORM. 

In addition to the spontaneous emission of excited molecules, fluorescence and phosphorescence (Section 2.1.1), the interaction of electromagnetic radiation with excited molecules gives rise to stimulated emission, the microscopic counterpart of (stimulated) absorption. Albert Einstein derived the existence of a close relationship between the rates of absorption and emission in 1917, before the advent of quantum mechanics (see Special Topic 2.1). 

The probability of stimulated emission by an excited molecule, Bpv, is the same as that of the reverse process, absorption by the ground-state molecule. This is a consequence of the law of microscopic reversibility if the number of excited molecules Nm is equal to the number of ground-state molecules N , then the rates of stimulated absorption and emission must be equal. If by some means a population inversion can be produced, Nm > Nn, the net effect of interaction with electromagnetic radiation of frequency v will be stimulated emission (Figure 2.4). This is the operating principle of the loser. LASER is an acronym for light amplification by stimulated emission of radiation (Section 3.1). 

Figure 11.21 StimuLated emission depletion (STED) microscopy. The sample is excited using single-photon excitation (PUMP pulse) in a confocal microscope arrangement. A time-delayed DUMP pulse selectively depletes close to 100% of the exdted state population in a region around the focus of the PUMP pulse. Using this approach. Hell and co-workers were able to obtain a 5-fold reduction in the fluorescent spot size in the vertical (Z-direction) and a greater than a 2-fold reduction in the horizontal Y/X) direction, leading to a final image size of 97 by 104 nm...

To realize the observation/detection on nanofluidics, the LIF with high resolution is a vital factor. With the release of stimulated emission depletion (STED) fluorescence microscope, the super-resolution LIF microscope on confocal manner, the high resolution at the order of nanometer was obtained [7, 8]. It was utilized to measure the velocity of fluorescent probes in nanofluidics and to observe the ion... 

This is termed stimulated emission, and is responsible for lasing (see Sect. 14.4.2.4). According to microscopic reversibility ... 

Figure 2.8. The process of electron-stimulated x-ray emission in the electron microscope.

X-ray spectroscopy is also a useful tool when used in combination with a SEM. The SEM uses very short-wavelength, high-energy electrons, commonly exceeding 15,000 V, to stimulate X-ray emission much as an incident X-ray beam would. When an X-ray detector is coupled to an electron microscope, a compositional analysis of very small areas, only a few microns wide, is possible. One application is the identification of the mineral grains that are found in complex materials such as prehistoric pottery, which is particularly useful for identifying small mineral grains in complex matrices such as tempered pottery. 

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