Einzel lens

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Implementation of an einzel lens showing the ion path. Six plates are parallel to the ion flight path with the middle plate at a particular potential. Einzel lens schematic drawing.svg
Implementation of an einzel lens showing the ion path. Six plates are parallel to the ion flight path with the middle plate at a particular potential.

An einzel lens (from German : Einzellinse – single lens [1] ), or unipotential lens, [2] is a charged particle electrostatic lens that focuses without changing the energy of the beam. It consists of three or more sets of cylindrical or rectangular apertures or tubes in series along an axis. It is used in ion optics to focus ions in flight, which is accomplished through manipulation of the electric field in the path of the ions.

German language West Germanic language

German is a West Germanic language that is mainly spoken in Central Europe. It is the most widely spoken and official or co-official language in Germany, Austria, Switzerland, South Tyrol (Italy), the German-speaking Community of Belgium, and Liechtenstein. It is also one of the three official languages of Luxembourg and a co-official language in the Opole Voivodeship in Poland. The languages which are most similar to German are the other members of the West Germanic language branch: Afrikaans, Dutch, English, the Frisian languages, Low German/Low Saxon, Luxembourgish, and Yiddish. There are also strong similarities in vocabulary with Danish, Norwegian and Swedish, although those belong to the North Germanic group. German is the second most widely spoken Germanic language, after English.

In physics, a charged particle is a particle with an electric charge. It may be an ion, such as a molecule or atom with a surplus or deficit of electrons relative to protons. It can also be an electron or a proton, or another elementary particle, which are all believed to have the same charge. Another charged particle may be an atomic nucleus devoid of electrons, such as an alpha particle.

An electrostatic lens is a device that assists in the transport of charged particles. For instance, it can guide electrons emitted from a sample to an electron analyzer, analogous to the way an optical lens assists in the transport of light in an optical instrument. Systems of electrostatic lenses can be designed in the same way as optical lenses, so electrostatic lenses easily magnify or converge the electron trajectories. An electrostatic lens can also be used to focus an ion beam, for example to make a microbeam for irradiating individual cells.

Contents

The electrostatic potential in the lens is symmetric, so the ions will regain their initial energy on exiting the lens, although the velocity of the outer particles will be altered such that they converge on to the axis. This causes the outer particles to arrive at the focus intersection slightly later than the ones that travel along a straight path, as they have to travel an extra distance.

Energy quantitative physical property transferred to objects to perform heating or work on them

In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object. Energy is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton.

Velocity rate of change of the position of an object as a function of time, and the direction of that change

The velocity of an object is the rate of change of its position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction of motion. Velocity is a fundamental concept in kinematics, the branch of classical mechanics that describes the motion of bodies.

Focus (optics) point where light rays originating from a point converge on an object

In geometrical optics, a focus, also called an image point, is the point where light rays originating from a point on the object converge. Although the focus is conceptually a point, physically the focus has a spatial extent, called the blur circle. This non-ideal focusing may be caused by aberrations of the imaging optics. In the absence of significant aberrations, the smallest possible blur circle is the Airy disc, which is caused by diffraction from the optical system's aperture. Aberrations tend to get worse as the aperture diameter increases, while the Airy circle is smallest for large apertures.

Theory

A perspective view of an einzel lens. Einzel lens 3d.png
A perspective view of an einzel lens.
Path of ions as they travel through an einzel lens. The ion mass is 200 kDa accelerated to 40 kV, the middle plate potential is at 200 V, and the plate size is 1 m (note that these values are atypical for illustrative purposes). Einzel lens ions.png
Path of ions as they travel through an einzel lens. The ion mass is 200 kDa accelerated to 40 kV, the middle plate potential is at 200 V, and the plate size is 1 m (note that these values are atypical for illustrative purposes).

The equation for the change in radial velocity for a particle as it passes between any pair of cylinders in the lens is:

with z axis passing through the middle of the lens, and r being the direction normal to z. If the lens is constructed with cylindrical electrodes, the field is symmetrical around z. is the magnitude of the electric field in the radial direction for a particle at a particular radial distance and distance across the gap, is the mass of the particle passing through the field, is the velocity of the particle and q is the charge of the particle. The integral occurs over the gap between the plates. This is also the interval where the lensing occurs.

The pair of plates is also called an electrostatic immersion lens,[ dubious – discuss ] thus an einzel lens can be described as two or more electrostatic immersion lenses. Solving the equation above twice to find the change in radial velocity for each pair of plates can be used to calculate the focal length of the lens.

Application to television tubes

The einzel lens principle in a simplified form was also used as a focusing mechanism in display and television cathode ray tubes, [3] [4] and has the advantage of providing a good sharply focused spot throughout the useful life of the tube's electron gun, with minimal or no readjustment needed (many monochrome TVs did not have or need focus controls), although in high-resolution monochrome displays and all colour CRT displays an (engineer-adjustable) focus potentiometer control is provided.

Monochrome shades of one color; describes paintings, drawings, design, or photographs in one color or values of one color, having only one colour

A monochromic image is composed of one color. The term monochrome comes from the Ancient Greek: μονόχρωμος, translit. monochromos, lit. 'having one color'.

See also

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Teltron tube

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References

  1. ↑ Liebl, Helmut (2008). Applied Charged Particle Optics. Berlin Heidelberg: Springer-Verlag. p. 39. ISBN   978-3-540-71924-3.
  2. ↑ Heddle, D W O (2000). Electrostatic Lens Systems (Second ed.). Bristol and Philadelphia: IOP Publishing. p. 63. ISBN   0 7503 0697 1.
  3. ↑ "Radio and Television" by C. A. Quarrington, 1952–1963.
  4. ↑ "Television Receiver Servicing" by E. A. W. Spreadbury, 1953.

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