Reflectivity of Aluminium – UV, Visible and Infrared

Aluminium has two uses in optics 1) It is often specified as a mirror substrate, as it is lightweight, easily processed and low cost, 2) It can be used as a thin film coating material. When vacuum deposited onto glass, metals, ceramics as a thin film coating of Aluminium, it means a metal or glass mirror can have the mechanical and thermal properties of the substrate, but the optical properties of Aluminium.

  

So what is the reflectivity of uncoated Aluminium ?.

It is possible to calculate this from measured values of the complex refractive index of Aluminium, and we have done this in the table below. LBP can calculate the %R, phase shift and Polarisation changes on reflection for any wavelength and angle of incidence, just call us.

REFLECTIVITY OF PURE UNCOATED ALUMINIUM AT NORMAL INCIDENCE

Wavelength            % Reflectivity
248nm                      92.6
400nm                      92.0
532nm                      91.6
633nm                      90.7
800nm                      86.8
900nm                      89.0
1um                          94.0
3um                          98.0
10.6um                     98.7
20um                        99.0
100um                      99.4

Aluminium is rarely used as an uncoated reflective surface, the mechanical and environmental properties are poor. A protective layer of MgF2 or SiO2 is needed. This can slightly reduce the above values, or restrict the coating to UV / Visible use. Aluminium does have a dip in its reflectivity in the 700nm – 900nm spectrum.

For more information about aluminium laser mirrors or protected alumnium coated mirrors see our web site