Different Types of Mirror Substrate


A mirror substrate is the basic component of laser optics.  There are a few factors that determine the price and quality of mirror substrate like its material, a shape of substrate, size, tolerance and polishing quality.

The good quality mirror substrate has following features:

•         It should have flat and smooth surface. The flatness of mirror substrate is defined by the number of a wavelength of light that the surface can deviate from being the perfect plane. The number of the scratches and digs on substrate surface after polishing defines the smoothness of substrate. The best quality mirror substrate is the one that has a scratch specification of 20/10.


•         It should be made of a material that is free of absorption for all wavelength of high transmission.
  
•         It should have high thermal conductivity. Generally, the metal substrate is preferred for this because of the good conductance of metal over a glass. The metal commonly used to produce substrate is Copper and Aluminium. Beryllium is used when light weight, stiff mirror is used.

Some of the common materials that are used to make mirror substrate are as follow:
Soda lime (Float Glass): Mirror substrate made of this material is chemically stable, and reasonably hard.

B270 (Crown Glass): It is more transparent than soda lime glass and is resistant to solar radiation and offers high transmittance in the visible wavelength range. It has polished surface and is chemically stable.

N-BK-7: It is a successor product of lead and arsenic material. It is a clear optical glass. It is relatively hardbor-crown glass and is scratch resistant. It is a preferable choice as it has a high linear transmission in the visible range down to 350 nm.

Pyrex (Borofloat): The substrate use using Pyrex show low thermal expansion. Pyrex low expansion borosilicate is the number one choice of ideal glass equipment in most of the laboratory. They can high tolerance for temperature.

Fused Silica (Quartz): It is a glass made of amorphous silica. It does not contain any other ingredients. It has the most superior optical and thermal properties. It, therefore, has an application in semiconductors fabrication and laboratory equipment. Also, it has better UV transmission and is used to make other optics for UV spectrum. It has a low coefficient of thermal expansion that makes it a useful material for precision mirror substrate.

Location: Australia

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