Objective lenses

Modem EMs use electromagnetic lenses, shift devices and spectrometers. However, electrostatic devices have always been used as electron beam accelerators and are increasingly being used for other tasks, e.g. as the objective lens (LVSEM, [10]). 

After propagation into the back focal plane of tire objective lens, the scattered electron wave can be expressed in tenns of the spatial frequency coordinates k as... 

The first corrected electron-optical SEM was developed by Zach [10]. Eor low-voltage SEM (LVSEM, down to 500 eV electron energy instead of the conventional energies of up to 30 keV) the spot size is extremely large without aberration correction. Combining and correction and a electrostatic objective lens, Zach showed that a substantial improvement in spot size and resolution is possible. The achievable resolution in a LVSEM is now of the order of 1-2 mn. More recently, Krivanek and colleagues succeeded in building a corrected STEM [53,M]. 

A point light source is imaged onto the specimen by the objective and the transmitted light collected by the collector lens and detected by a broad-area detector in the case of reflection microscopy, the objective lens also serves simultaneously as a collector (see figure Bl.18.10. The resolution is solely detennined by the objective lens, because the collector has no imaging fimction and only collects the transmitted light. The... 

The specimen is immersed in the next lens encountered along the column, the objective lens. The objective lens is a magnetic lens, the design of which is the most crucial of all lenses on the instrument. Instrumental resolution is limited primarily by the spherical aberration of the objective lens. 

The final set of magnetic lenses beneath the specimen are jointly referred to as post-specimen lenses. Their primary task is to magnify the signal transferred by the objective lens. Modern instruments typically contain four post-specimen lenses diffraction, intermediate, projector 1, and projector 2 (in, order of appearance below the specimen). They provide a TEM with its tremendous magnification flexibility. 

Collectively, the post-specimen lenses serve one of two purposes they magnify either the diffraction pattern from the sample produced at the back focal plane of the objective lens or they magnify the image produced at the image plane of the objective lens. These optical planes are illustrated in the elearon ray diagram in... 

A TEM provides the means to obtain a diffraction pattern from a small specimen area. This diffraction pattern is obtained in diffraction mode, where the post-specimen lenses are set to examine the information in the transmitted signal at the back focal plane of the objective lens. 

Fig. 4.57. Example of sensitive Raman equipment. The band pass filter, BP, cleans the laser radiation. The high NA objective lens LI focuses the laser on the sample and collects the Raman scattered radiation within a large solid angle. The band-rejection filter, BR, blocks elasti-...

Objektiv, n. objective, object glass, lens. -Unse, /. objective lens, -wechsler, m. (Micros.) revolving nosepiece. 

Figure 4, Area of benzene covered gold (111). surface, for two different objective len.s defooi a.s required for unique image interpretation (see 2 ). Tri a) the gold atomic columns are black, in b) white. Moire fringes, rather than any true structural image, result from the benzene monolayer. Simulations (right) have benzene overlay on top surface only.

First we consider the electronic excitation probability Pekc for a single molecule during a single laser pulse. When a molecule has the absorption coefficient Eabs(dm mol cm ), its absorption cross section Gabs is given by 3.81 x lO Sabs cm molecule". Since the probability Peiec is proportional to the light intensity (photons s cm ) under the objective lens, it is given by... 

Hayazawa, N Inouye, Y. and Kawata, S. (1999) Evanescent field excitation and measurement of dye fluorescence using a high N.A. objective lens in a metallic probe near-field scanning optical microscopy J. Microsc., 194, 472-476. 

Figure 7.3 A schematic of a two-beam photon-force measurement system. Obj objective lens (lOOx oil immersion, N.A. 1.4), PBS polarization beam splitter, FI color filter for eliminating red illumination laser beam, F2 color filter for eliminating green illumination laser...

Laser trapping is a technique to manipulate small sized materials, which was developed by Ashkin in 1970 [20, 21]. In this experiment, a laser beam is tightly focused by an objective lens with high numerical aperture (NA), and a dielectric... 

Figure 5. Schematic arrangement for hologram formation with an electron biprism. A plane wave illuminates the specimen placed off-axis. After the object lens a wire is placed between two earthed plates. The wire is the electron optical analog of a Fresnel biprism and causes the unperturbed and perturbed waves forming the electron hologram to interfere. The object phase-shift causes a displacement in the hologram fringes, and is thus observable.

ION EXTRACTION OPTICS AND LIGHT OBJECTIVE LENS (REFLECTION MODE)... 

---