Aluminizacji mirror can not obviously be done in home conditions. It is our mirror to give to a plant specializing in the performance of optical thin films. Warn against spraying the mirrors in companies engaged in automotive headlight reflectors because the reflectivity of the layer and the uniformity of coverage may be far from the expected.
Reflecting layer in the mirrors of telescopes is mostly aluminum, vaporized in a glass vacuum napylarkach. As a source of aluminum, aluminum wire is used, cut into sections and curved in “horses” (it reminds “hacle” to sling) and suspended in the heating spirals. After connecting the voltage coil heats up , aluminum melts and dissolves in a spiral from which it gradually evaporates. Here is an image with just such a spiral of ponies.
Aluminum spiral with suspended "ponies"
This method of deposition of aluminum is used in napylarkach of oporowogrzejnym source parowania.Dużo better results are obtained in napylarkach which is the source of electron gun evaporation. They can evaporate aluminum with graphite crucible, which results in full control of the speed of evaporation and layer thickness performed. Aluminium used for the execution of the mirror has a purity 99,99%! Below the pictures sequentially: graphite crucible filled with molten aluminum and quartz-filled electron gun.
Graphite crucible filled with aluminum.
Electronic Gun
In napylarkach of oporowogrzejnym source layer thickness depends on the number of ponies established in the spiral, but it happens, after melting the aluminum can collect in a drop and fall, in consequence of which the layer is too thin. Speed of evaporation also can not be maintained as closely as things happen in the case of electron pairing. Since the speed of evaporation and temperature, depends on the structure of which will build aluminum wrap on glass. We care, that it is amorphous. In the wrong conditions can build aluminum crystalline structure and consequently can lower reflectivity. I would add, napylarkach that the evaporation source oporowogrzejnym, only possible to perform protective layer of aluminum is a layer of magnesium fluoride, while using the electron protection works can be performed with both fluoride and quartz, or quartz and titanium oxide, which gives the best mechanical properties spektralno.
Many people wonder , as large differences in thickness of the layer formed during deposition. personally heard such opinions, that does not make sense to do a super accurate mirror, layer, and so he will introduce a large distortion on the surface. In good napylarkach used in the optical industry differences in the thickness of the layers are made about 1%. If we assume, that the aluminum layer thickness is 100 nm, This distortion of the resulting amount to 1nm! Thus small differences in thickness of layers are possible by using a special planetary system, mirror placed in a cell not only rotates around an axis through the center of the chamber but also about an axis through the center of the cell. To further align the layer thickness, additionally apply a special aperture, the shape and height are chosen largely experimentally.
The interior of the apparatus of modern vacuum. Visible planetary system with five sectors and improving the uniformity of coverage of the iris.
Another, important factor that determines the quality of the coating is specular substrate surface cleanliness. It is important, of course, thorough cleaning, degreasing and removing static electricity from the surface of the mirror. Additionally, once the glass is in the apparatus, Ion cleaning is used. In older apparatus cleaning is performed fluorescent, simplifying the matter can describe it that way: inside the vacuum chamber is appropriately curved wire insulated from the housing. The application to the wire and the housing opposite poles of high voltage current ionizes the residual gas inside the chamber (possibly after obtaining a higher vacuum oxygenates to a level allowing it to ionization).This allows the surface are removed napylanej even small pollen, which may have to pick through electrostatic forces. In the modern apparatus of ion cleaning is done by running the ion. This gives much better results than the method described previously. Another advantage has equipped napylarek ion is, that the use of ion beam during the deposition process itself makes, that the aluminum layer is much better “packed”, is less “clearances” and particles, which would have had a bad stick, simply fall off. In the case of evaporation of transparent materials (Al-layer security) using ion has achieved a higher refractive index layer and a stronger.
Ion acts Gorge
Since the reflective layer applied not only depend on the mechanical properties, but also dusted the mirror spectral. Below I attach the graphic on the performance charts are reflective layers. Going from the highest sprawości are respectively: AL secured quartz and titanium oxide, then Al. Unsecured. Next , covering a large part of the graphs is the Al. magnesium fluoride protected and Al. secured by the same quartz. The apparent slight advantage in the efficiency layer of magnesium fluoride. in terms of mechanical strength of the LAYER SECURITY Quartz and Titanium oxides beats OTHER HEAD. Well situated just on the many, many years. Second in order is of course a layer of quartz. Protection of fluoride protects against oxidation, However, it is easy to draw such a layer when trying to clean.
I would add, that the spectral properties is very important to the thickness of the protective layer located. Due to the wave nature of light, to get a reflection in a row 96% krwarcu both thickness and titanium dioxide must be at least a quarter of the wavelength of light. The possibility of precise control of layer thickness of the transparent use of an optical sensor gives, while the thickness of the metallic layers is monitored by sensors, quartz. Or, to perform well with security zwierciało napylarka must have two types of sensors, the thickness and evaporation rate.
In sum, sputter the mirror in the optical apparatus to reach even 96% reflections, while not zniekształacając surface of the mirror. Evaporation of the mirror in the industrial napylarce, used for such: headlights, possible reflection about 86% With a little luck and even less, And with the outcome with great difficulty “lambda/10″ We may be “lambda/4″