Focometry by Speckle set

Subjects discussed :
- Determination of the focal length of diverging and converging lenses
- Collimation control of a laser beam

Principles and objectives:
Speckle is linked to the scattering of a coherent source on a rough object on the scale of the wavelength of the source or to an illuminated specular object.
The size of the speckle grains depends on the wavelength of the laser, the size of the beam that illuminates and the distance between this illuminated surface and the surface on which the speckle pattern is formed.
Thus, the size of the speckle grains evolves with the section of the laser beam in the plane of the frosted screen. A large speckle pattern is observed when positioning the frosted glass in the focal plane of a converging lens. Below and beyond the focus, the size of the speckles is reduced.

Composition :
 ▪ 1 laser torch (ref.204080)
 ▪ 1 speckle telescope (ref.204708)
 ▪ 1 fine frosted slide format (ref.203296) and 1 thin blade holder on rod (ref.202448)
 ▪ 2 Clix component holders (ref.204136) and 7 Clix rings (ref.204201)
 ▪ 1 set of 4 precision converging lenses (+50, +100, +150 and +300 mm)
 ▪ 1 set of 3 precision diverging lenses (-50, -100 and -150 mm)
 ▪ 1 white, squared metal screen 20x20 cm (ref.202705)
 ▪ 1 experiment note