a) Geometrical optics: Geometrical axis or ray optics describes

a)    Geometricaloptics:Geometricalaxis or ray optics describes the light propagation in terms of rays.

Thesimplifying assumption of geometrical optics include light rays propagate in arectilinear path as they travel in a homogeneous medium which sometimes bend orsometimes split into, at the interface between two dissimilar medium. Thisgeometrical optics does not account for certain optical effect such asdiffraction and interference.   b)   NumericalAperture:Itis the range of acceptance rotated around an axis, where the light can becoupled into a wave guide such as core of an optical fibre. In simple words, itis defined as the sine of half the angle of the acceptance cone. c)    Chromaticaberration:Theimage of the white object formed by a lens is usually coloured and blurred.This defect of the image produced by the lens is called chromatic aberration.This defect arises because of the refractive index of the material of the lensand also the focal length of lens is different for different colours of light. d)   Confocalmicroscopy:Confocalmicroscopy is an optical microscopic technique for increased resolution andcontrast by adding a spatial pinhole placed at the confocal plane of the lensto eliminate out of focus light.

We could able to perform the reconstruction of3D structures from the obtained image. e)    Schottkyemission:InSchottky emission, when high voltage is given to the sharp tip emittingmaterial, high electric field is generated at the emitting site. In order tobreak through the potential barrier, thermal energy is needed. This is alsoknown as thermal field emission. f)     MagneticLens:Magneticlens is used to focus or to deflect the moving charged particles which includeions/ electrons with the magnetic Lorentz force. Different electromagnets havedifferent field strength. It can be used as an immersion lens. It also haslower lens aberrations.

 g)    Controlloop:Controlloop in the SPM controls the Z movement of the tip and also controls thescanning motion. It also modifies the error signal in a separate control stageand supplies the modified signal to the piezo electric scanner.