VEGA Wide Field Optics^TM Scanning / Imaging Modes

Resolution Mode

In the Resolution mode the condenser lenses are controlled as a zoom condenser, the intermediate lens is off, and the objective lens projects the focused electron beam onto the specimen surface with the minimum spot size.

Two computer automated algorithms can be used:

	OptiSpot allows fast and reproducible set up of the maximum probe current for each selected spot size (i.e. optimum angular aperture and, therefore, resolution).
	OptiMag automatically provides the optimum spot size for the chosen magnification.

In practical terms, the end results are consistent, reproducible, high resolution and high S/N images, which can be achieved quickly and easily - whether you're an expert microscopist or just a novice.

Focus on your work - not the machine.

Depth Mode

Depth mode provides enhanced depth of focus.

The depth of focus is inversely proportional to the angular aperture of the incident beam. In this mode, the intermediate lens works effectively as an "aperture changer" - its excitation changes will influence the beam so that the angular aperture of the incident beam can be set considerably lower than optimum. This means that the microscope does not work at the ultimate resolution, however in the range of lower and medium magnifications the difference in resolution cannot be seen. On the other hand, the difference in acquired depth of focus is clearly remarkable even at short working distances and often very useful, especially when investigating specimens with high topography.

Field Mode

Field mode provides an enhanced field of view, as well as very high depth of focus.

The electron beam is focused on the specimen surface by means of the intermediate lens IML, while the objective lens is off. The final angular aperture of the incident beam is so small and the depth of focus so large that the image is focused in all accessible positions of the specimen stage. Because the objective lens is off, it does not affect the electron beam, which can pass through the lens without being restricted to the paraxial (center) area. The position of the scanning pivot point is optimized in order to reach the maximum field of view, which is limited only by the bore of the final lens. The field of view is substantially larger than in Resolution or Depth modes.

Field mode can also be used to produce a well-collimated beam, which can be useful in lithographic and electron channeling applications.

Fish-Eye Mode

Fish-Eye mode provides an extremely large field of view and depth of focus.

The final lens is operated at maximum excitation and the scan coils are adjusted so as utilize the whole area of the final lens bore. In this way, a very high deflection angle - and an extra large field of view - is obtained. Since the objective lens is operated at maximum excitation, the intermediate lens IML is used for focusing. As in the Field mode, the angular aperture is therefore very small, providing exceptionally high depth of focus.

Fish-Eye mode provides a very useful "macro" view of the specimen stage, and is very convenient when navigating large or multiple samples.