Pinhole aperture

Volatile or volatilizable compounds may be introduced into the spectrometer via a pinhole aperture or molecular leak which allows a steady stream of sample molecules into the ionization area. Non-volatile or thermally labile samples are introduced directly by means of an electrically heated probe inserted through a vacuum lock. Numerous methods of sample ionization are available of which the most important are electron impact (El), chemical ionization (CY), field ionization (FI), field desorption (FD), fast atom bombardment (FAB), and radio-frequency spark discharge. 

In a confocal microscope, invented in the mid-1950s, a focused spot of light scans the specimen. The fluorescence emitted by the specimen is separated from the incident beam by a dichroic mirror and is focused by the objective lens through a pinhole aperture to a photomultiplier. Fluorescence from out-of-focus planes above and below the specimen strikes the wall of the aperture and cannot pass through the pinhole (Figure 11.3). 

The vision of the shapes of objects requires the formation of an image on a photosensitive surface. In higher animals the optics of the eye make use of a lens (rather like a photographic camera), but there are some lower species which use a simple pinhole aperture (as was used, incidentally, in the early days of photography). 

The fluorescence from this volume is focused, via the dichroic mirror, onto a pinhole aperture. Focusing the laser on a small area limits the total amount... 

The optical principles of confocal microscopy can be understood by examining the CLSM optical path that has reflected illumination as illustrated in Figure 1.45. The laser beam is focused as an intense spot on a certain focal plane of the specimen by a condenser lens, which is also serves as an objective lens to collect the reflected beam. A pinhole aperture is placed at a confocal plane in front of the light detector. The reflected beam from the focal plane in a specimen becomes a focused point at the confocal plane. The pinhole aperture blocks the reflected light from the out-of-focal plane from entering the detector. Only the light signals... 

Confocal laser scanning microscopy (CLSM) is a very useful technique for the identification of suspensions. It uses a variable pinhole aperture or variable-width slit to illuminate only the focal plane by the apex of a cone of laser hght. Out-of-focus items are dark and do not distract from the contrast of the image. 

Detector MS, SCIEX API III, atmospheric pressure ionization, nebulizer probe 450°, 2.5 (juA Corona discharge needle, quadrupole mass filter, 0.002 inch pinhole aperture, SIM m/z 749 and 752... 

Acquire images using a 488-nm argon laser line and a lOx objective, with maximum pinhole aperture (800). Take 25 nonoverlapping predefined images to cover more than 65% of the total well surface. 

FIGURE 13 Holographic recording (the pinhole aperture is the point object which generates a spherical wave on the film). 

AOFS). A beamsplitter (BS) is used to combine the plane wave and the focused wave. Thus, the interference of mutually coherent spherical and plane wave fronts is formed on the pinhole aperture (or point object to be recorded), and the intensity pattern of the combined beam is given... 

FIGURE 17 Optical scanning holography recording of a point objeot (a pinhole aperture) is an electronic multiplier. 

---