Sapphire Optics
Sapphire Windows, featuring reliable mechanical/thermal/chemical robustness, large dielectric constants, and broad optical transmission from 150-5500 nm, are excellent as both optical windows and protective windows in application contexts of more stringent requirements and extreme conditions.
Sapphires' unmatched mechanical toughness and hardness are what make them stand out the most. Sapphire has a Mohs hardness of 9, making it the third hardest substance ranked after diamond and moissanite). In truth, sapphire windows can just sometimes be injured with substances other than sapphire itself due to their high resistance to scratches and abrasions. This indicates that sapphire windows are ideal for applications that will encounter splattering abrasive particles, such as drilling viewport windows, protective laser processing windows, and gun sights, as sapphire windows can ensure clear optical apertures and maintain lucid sights even under attacks from sand or grit.
Sapphire windows can sustain tremendous pressure and be formed into much thinner pieces without cracking than their dielectric equivalents because of the solid internal covalent bonding of sapphire. For instance, sapphire windows are often chosen in deepwater and navigation scenarios.
Sapphire is also heat-resistant, with a maximum working temperature of 1600°C and a maximum melting temperature of 2000°C. In comparison to other optical materials, sapphire windows have a distinct advantage in tolerating high-temperature conditions due to their high thermal conductivity. Sapphire windows are thus excellent choices for combustion chambers, high-temperature plasma chambers, etc.
Sapphire windows are resistant to most acids and alkalis, except hot caustic salts. Sapphire performs better than other materials in enduring corrosive substances and erosive environments, enabling greater use of sapphire windows in chemical, pharmaceutical, and medical facilities.
Furthermore, sapphire windows have a broad spectral transmission range of 150 nm to 5500 nm. The transmission spectra of N-BK7 and UV Fused Silica, the two most common optical glass materials, are 350 nm-2200 nm and 200 nm-2200 nm. However, sapphire outperforms N-BK7 with superior UV functions and a wider IR transmission and UV UV-fused silica with less IR absorption. Sapphire windows could be utilized in multi-spectrum optical tasks.
Shalom EO offers various kinds of Sapphire Windows. This is a list of a complete portfolio of our off-the-shelf sapphire windows. These stocked sapphire windows are uncoated, of circular or square shapes, with a wide selection of available diameters (or side lengths) up to 150mm and C-cut orientation with minimal birefringence. Most of the sapphire windows in our inventories are manufactured with 60/40 S/D surface qualities and 2λ flatness, however, advanced versions with 40/20 S/D and λ/4 flatness are also procurable as stocks.
Our single crystal sapphires are grown using the KY (Kyropoulos) method and the SAPMAC (Sapphire Growth Technique With Micro-Pulling And Shoulder Expanding At Cooled Center) method. The Kyropoulos growth method is characterized by a temperature control process to enable the gradual cooling of the single sapphire crystal, resulting in less thermal stress and mechanical shock, while the SAPMAC method is a further refined version of the KY method that excels at growing large size crystals. These two cutting-edge sapphire growth methods allow us to deliver sapphire windows of large sizes, and high purities without visible fractures, bubbles, and sub-grain.
UV-grade sapphire windows with no UV absorption peaks and high UV darkening resistance are also available in Shalom EO. During the growth process of sapphire, especially in high-purity and high-temperature conditions (such as over 2000°C), the sapphire is often grown in an environment with a reducing atmosphere. This can lead to the loss of oxygen atoms, creating F-centers where oxygen vacancies are created in the sapphire crystal, and the vacancies are filled by electrons. To address this issue, Hangzhou Shalom EO offers UV-grade sapphire windows, the sapphire is specially fabricated with eliminated oxygen defects to exhibit no absorption peak at the critical 200 nm UV wavelength. You might view the transmission curves under the technical imaging tab).
Hangzhou Shalom EO manufactures and supplies sapphire windows, our engineers are willing to arrange and supervise the entire sapphire window production procedure according to your needs. Our sapphire windows feature exceptional hardness, temperature endurance, environmental durability, and optical transmission. Each stage of production including sapphire growth, drilling, cutting, grinding, polishing, and cleaning is carried out using forward techniques and designed equipment, under stringent regulations, to ensure the superior properties of our sapphire widows. Before shipment, all the products will go through an in-house inspection. With our proficient production line, we are capable of delivering high-precision sapphire windows as well as volume production.
Besides the stocked versions, Shalom EO also supplies custom sapphire windows.
The sapphire chosen to make sapphire windows is Alpha Sapphire, manufactured in labs and factories using particular artificial methods. The produced sapphire or sapphire glass is colorless, has higher Al2O3 purities, excludes water, and has more organized, predictable micro-structures than natural sapphire, making it better equipped to meet industrial and optical-grade requirements. Keep in mind that all sapphires are single crystals, and during the growth and cutting processes, sub-grains are avoided all the time.
Alpha-Sapphire has a hexagonal structure. The lattice constant is a=b=4.758A, c=12.991A. Alpha-sapphire constitutes hexagonal-closest piled oxide floors, and the 3/2 gaps of the octahedron are filled with Al3+ ions., six floors of Al2O3 unit cells are arranged in ARAB manners.
As shown in the diagram below, sapphire windows often have the following orientations: "a," "c," "n," and "m. Sapphire is birefringent to a subtle extent and so in critical optical situations, the windows should be specified as 'zero degrees', or 'c-cut'. C-cut sapphire has the birefringence effect removed since it is cut in a direction perpendicular to the c-axis, which is parallel to the sapphire optical axis. When it comes to protecting and packaging usages such as the sight glass of wristwatches, A-cut sapphire is often utilized, which is cut in a direction perpendicular to the A-axis, exhibiting exceptional mechanical hardness and scratch resistance. If unspecified, the component will be of a 'random' cut, but it is worth noting that this is, for the most part, 60° to the optic axis as this is the 'softest' direction for the sawing. Random-cut sapphire is common because of lower costs and is acceptable if there are no stringent requirements about optical or mechanical qualities. However, as mentioned above, because the behavior of sapphire varies depending on orientations, random orientation might be subject to spontaneous variations of optical properties and other properties in the final product.
Orientation Index:
C-plane (0001) = Z-cut
A-plane (11-20) = Y-cut
M-Plane (10-10) = X-cut
R-Plane (1-102)
The Lattice Structure of Sapphire and Common Sapphire Crystal Orientations
The mechanical properties of single-crystal sapphires are relevant to their densities, the greater the densities, the better the mechanical properties. Single crystal sapphires with 100% Al2O3 composition are supposed to have theoretical densities of 3.68g/cm3. Under such presumption, the mechanical properties of sapphire are the best. Its anti-compression strength is between 1.9-24 GPa. The Young’s Modulus of sapphire is 380 Gpa, which is about twice the magnitude of iron’s 200 GPa.
The enormous hardness is another important feature of sapphire, its Mohs hardness is 9, ranking right after diamond, indicating that optical components crafted using sapphire are resistant to scratch and wear. The hardness of sapphire is also proportionate in a positive manner to the purities of sapphire.
Thermal Properties of Sapphire:
Thermal properties in main include thermal conduction coefficients, thermal diffusion coefficients, specific heat, and thermal expansion coefficients. The thermal properties of sapphire relate to the purities of sapphire. In common circumstances, the higher the purities, the higher the thermal conduction coefficients and thermal diffusion coefficients, while there is no regular pattern between Al2O3 purities and the magnitude of thermal expansion coefficients. In fact, manufacturers seem unable to agree on the thermal expansion coefficient of sapphire, Whilst there might be some variation due to the method of growth, and of course, due to the orientation, this variation is inexplicable.
Optical Transmission of Sapphire:
The optical transmission range of sapphire is wide, 225-5500mm, extending from UV to IR spectra.
No matter what the optical grades are, IR transmission is not a concern for uncoated sapphire above a wavelength of about 5000 nm. The UV range is where caution should be exercised since the transmission from 140 nm to 240 nm is susceptible to both interstitial vacancies and quite minor amounts of impurities. Although small aperture sapphire windows constructed from the aforementioned Verneuil "half-ingots" often contribute to good transmission, conventional sapphire material tends to demonstrate a poor UV performance at 160 nm to 240 nm. The major factor contributing to poor UV performance, aside from contaminants, is a wide absorption at 205 nm brought upon by interstitial vacancies.
There is also UV-grade sapphire, which is prepared to cater to UV transmission requirements. The UV sapphires will go through specific heat treatments to remove interstitial vacancies, which are reversible using heat.
In the past, the Verneuil Method was developed to fabricate synthetic sapphire. This process makes use of flame fusion. However, due to the difficulties in controlling flame heat, which results in fractures in the final product, and the substantial depletion of Al2O3 during the flame fusion process, which raises the cost of production, this approach is no longer effective in the current market. Moreover, the fact that a natural cleavage plane will be introduced down the middle of the sapphire ingot when using this approach makes it difficult to produce large-diameter sapphires.
