Lenses condensing

Abbe condenser. Substage two-lens condenser giving numerical aperture of 1 20-1 25. Three-lens versions give numerical aperture of 1 40. 

Photoluminescence spectra have b een measured at room temperature using a semiconductor laser as an excitation light source (10 W/cm at 980 run). Luminescence light has been collected by a lens condenser and then dispersed with a grating monochromator (MDR-23). Light detection was performed by a germanium photodiode DPD 2000 (Dilas Co.). A silicon filter was used to additionally cut off the excitation radiation. 

It is easiest to discuss the electron optics of a TEM instrument by addressing the instrument from top to bottom. Refer again to the schematic in F ure la. At the top of the TEM column is an electron source or gun. An electrostatic lens is used to accelerate electrons emitted by the filament to a h potential (typically 100-1,000 kV) and to focus the electrons to a cross-over just above the anode (the diameter of the cross-over image can be from 0.5 to 30 Mm, depending on the type of gun ). The electrons at the cross-over image of the filament are delivered to the specimen by the next set of lenses on the column, the condensers. 

Most modern TEMs use a two-stage condenser lens system that makes it possible to... 

Instruments for the measurement of fluorescence are known as fluorimeters or spectrofluorimeters. The essential parts of a simple fluorimeter are shown in Fig. 18.1. The light from a mercury-vapour lamp (or other source of ultraviolet light) is passed through a condensing lens, a primary filter (to permit the light band required for excitation to pass), a sample container, a secondary filter (selected to absorb the primary radiant energy but transmit the fluorescent... 

Set the condensing lens in position at 2 cm from the slit jaws and at the correct height. 

Heat filter glass id. Secondary condensing lens system... 

Figure 5.15 shows a ray diagram for a light-optical projection microscope. The light source is placed behind a condenser system which collects the light which is diverging from the source and illuminates the specimen. The presence of the variable aperture near to the condenser lens permits control of the area of the specimen which is... 

Figure 5.17. Illustrating the principle of STEM image formation using two pairs of scan coils between the second condenser lens and the upper objective polepiece. (Reproduced by permission of Williams and...

Fig. 2.14 The scheme of the cylindrical lens method for diffusion coefficient measurement (1) the source with the horizontal slit (2) the condenser supplying a handle of parallel beams (3) the cuvette with a refraction index gradient where the beams are deflected (4) the objective lens focusing the parallel beams to a single point (5) the optical member with an oblique slit and a cylindrical lens (6) the photosensitive material...

As the beam travels down the column, a number of electromagnetic lenses are used to guide the beam to the sample [44], The condenser lenses are part of the illumination system and are used to deliver electrons from the electron gun crossover to the sample. The condenser lenses determine the beam current reaching the sample. The objective, or final, lens determines the final spot size of the beam. A set of scanning coils are also present in the instrument column to scan the beam in a raster pattern over an area of the sample. At each point, data is collected and the points are combined to form the image. More detail on the data collection is given in the image formation section. 

Fig. 2. (a) Ray diagram in the electron microscope under imaging (microscopy) conditions. E electron source C condenser lens S sample O objective lens bfp back focal plane of O I intermediate lens P projector lens, (b) Structural imaging, diffraction and compositional functionalities of TEM. 

Dark-field illumination is classified into three types. The first one is for a microscope equipped with low numerical aperture (NA) objective lenses (see Fig. 1). To cast a shadow at the objective lens, a ring-slit as shown in Fig. IB is inserted into the light path. The second is for highNA (>0.5) objective lenses. Special, ready-made dark-field condensers or lenses are used for dark-field illumination. The third is independent... 

In order to adjust the dark-field illumination, project the illumination light onto a piece of paper placed on the microscopic stage or on the obj ective lens. Adjust the position of the slit and the height of condenser so that the transmission light illuminates the sample uniformly and brightly, and that the diameter of the shaded area produced on the surface of the objective lens is larger than that of the objective lens (see Fig 1C). 

Fig. 1. Typical locations for CAM components, showing the photometer, 1 filter wheel, 2 monochromator, 3 shutter and aperture unit, 4 beam splitter, 5 accessories for polarized light such as a rotary analyzer and a compensator, 6 beam splitter for epi-excitation fluorescence, 7 objective lens, 8 stage, 9 substage condenser, 10 condenser aperture, 11 polarizer, 12 field aperture for photometry, 13 shutter, 14 primary illuminator, 15 arc lamp, 16 shutter, 17 monochromator, 18 filter wheel, 19 and ocular, 20.

In the STEM (see Fig. Id) the electron beam is focused onto the sample by a condenser-objective lens, and the resulting electron probe can be moved across the sample by means of scan coils. Signals collected by various detectors positioned around the sample can be displayed on synchronously scanned video displays to build up images of the specimen, much in the same way as in the scanning electron microscope. 

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