Physics:Optical unit
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Short description: Unit of measurement
An optical unit is a dimensionless unit of length used in optical microscopy. Because every diffraction limited system have their resolution proportional to wavelength/NA, it is convenient for comparison to use this unit. There are actually two units, one "axial" (along the optical axis of the objective) and one "radial".
Equation
[math]\displaystyle{ u_\mathrm{axial} = \frac{8 \pi n}{\lambda} \sin^2(\frac{\alpha}{2}) z }[/math]
[math]\displaystyle{ v_\mathrm{radial} = \frac{2 \pi}{\lambda} \frac{n \sin \alpha}{M_\mathrm{tot}} r }[/math]
where :
- [math]\displaystyle{ n }[/math] is the refractive index
- [math]\displaystyle{ \lambda }[/math] is the wavelength
- [math]\displaystyle{ \alpha }[/math] the beam conus angle
- [math]\displaystyle{ M_\mathrm{tot} }[/math] is the total magnification ([math]\displaystyle{ M }[/math] is 1 if you want the size in the sample)
Note : [math]\displaystyle{ n * \sin \alpha }[/math] = numerical aperture
References
- James B. Pawley in Handbook of biological confocal microscopy ; second edition; Appendix I
- http://www.ntmdt.com/spm-basics/view/classical-optical-microscopy (see equation 3 and 4)
![]() | Original source: https://en.wikipedia.org/wiki/Optical unit.
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