Refraction is the blessing and the curse of microscopy.
Light travels at different speeds in different materials. It is fastest in vacuum with 299,792,458 meters per second. Slowing down when entering an optically more dense material, light gets deviated from its direction of travel. This is called refraction. The ratio n between the speed of light in vacuum (c) and that in the respective material (v) (n=c/v) is called refractive index. The refractive index is a bulk physical constant of that material. It is dependent on the temperature of the material and the energy (frequency) of the light waves traveling through.
Snell's law describes the relationship between refractive indices of two adjacent isotropic materials and angles of incidence of light traveling through the boundary between the two:
sin(a1) / sin(a2) = n2 / n1
Demonstrate how light gets refracted at the interface of two different media.
Warning: do NOT point laser towards students!
Humberto Ibarra Avila, Britta Schroth-Diez
Demonstrates how changes in refractive index change perception.
Demonstrates the essential parts of a microscope and explains the concept of conjugate planes: What are the key elements? Where is the back focal plane and what can you see there? Where is the primary image formed?
A bench with the ability to host several optical elements, in our case:
Parts can be purchased from Qioptiq (fromer Linos), Thorlabs, Newport
Then let them find the different optical planes themselves:
Warning: mind to not power up the light source too much
Kurt Anderson, Jan Peychl
Demonstrated how different wavelengths of light are scattered by differently sized objects.
- sieves ("Sortiersiebe") with two different gratings (eg. 106 and 130μm)
- dia-slides each with both a coarse and a fine grating (have them printed directly for this purpose)
Peter Evennett, Humberto Ibarra Avila, Britta Schroth-Diez
Demonstrates the effect of both objective and condenser Numerical Aperture.
Peter Evennett, Jan Peychl
Demonstrates the effect of the Numerical Aperture of an objective. Opportunity to practice some calculations around resolutiona and NA.
Humberto Ibarra Avila, Silke White