Sapphire Windows

Exceptional hardness and chemical resistance
High thermal durabilities excellent for harsh environments
Maximum diameter 300mm
Various dimensions, shapes, orientations, and precision standards
Broad wavelength range from 150-5500nm
Blank substrates, AR-coated windows, and precision windows are available
Check out our Sapphire Window Stock List here

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Specifications:

Materials	Sapphire crystals	Diameter Range	Max. 300mm
Aperture	>90%	Dimension Tolerance	+0.0/-0.2mm
Thickness Tolerance	+/-0.1mm	Surface Quality	Optional: 60/40, 40/20 or 20/10 S/D
Parallelism	30 arc sec	Chamfer	0.3-0.5mmx45°
Coating	No coating, or single layer MgF2 and other custom coating options

Basic Properties:

Transmission Range	0.15 to 5.5 μm	Refractive Index	No 1.75449; Ne 1.74663 at 1.06 μm
Reflection Loss	14% at 1.06 μm	Absorption Coefficient	0.3 x 10^-3 cm-1 at 2.4 μm
Reststrahlen Peak	13.5 μm	dn/dT	13.1 x 10^-6 at 0.546 μm
dn/dμ = 0	1.5 μm	Density	3.97 g/cc
Melting Point	2040°C	Thermal Conductivity	27.21 W m-1 K-1 at 300K
Hardness	Knoop 2000 with 2000g indenter	Specific Heat Capacity	763 J Kg-1 K-1 at 293K (4)
Dielectric Constant	11.5 (para) 9.4 (perp)at 1MHz	Youngs Modulus (E)	335 GPa
Shear Modulus (G)	148.1 GPa	Bulk Modulus (K)	240 GPa
Elastic Coefficients	C11=496 C12=164 C13=115 C33=498 C44=148	Apparent Elastic Limit	300 MPa (45,000 psi)
Poisson Ratio	0.25	Solubility	98 x 10^-6 g/100g water
Molecular Weight	101.96	Class/Structure	Trigonal (hex), R3c

Infrared Sapphire (Al2O3) Windows, featuring broad optical transmission from 150-5500nm spanning from UV to MWIR spectrum, and robust mechanical/thermal properties, high chemical resistance, are suitable for applications in harsh and variant environments or requiring a broad transparent wavelength range (e.g. infrared imaging, infrared spectroscopes, etc.).

Sapphire exhibits favorable transmission properties in the infrared region, in particular in the near-infrared (NIR) and mid-infrared (MWIR) wavelengths. Sapphire's most distinguishing attribute is its unequaled surface hardness, which imparts excellent scratch resistance and durability to sapphire windows. Another remarkable virtue of sapphire windows is their chemical inertness which makes them resistant to corrosion. Sapphire windows can have a large length-to-thickness ratio without fracturing because of the tight internal covalent bonding of single-crystal sapphire while demonstrating good thermal stability due to its high thermal conduction.

Shalom EO offers various forms of Infrared Optical Sapphire Windows including flat windows with parallel faces, circular/rectangular windows, wedge windows, and other custom specifications. Large aperture sapphire windows with diameters up to 300mm are available, and surface qualities of 60/40, 40/20, and 20/10 Scratch/Dig are optional according to the precision requirements of your interest.

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. (switch to the resource tab for a more detailed introduction to the KY and SAPMAC method.)

Our blank sapphire substrates feature high transmission in the wavelength range between 2.5-4.5µm with an average transmission rate above 85%. Single-layer MgF2 coatings and other AR coatings could be deposited to increase transmission. With state-of-the-art technologies, you can experience optical excellence with a diverse range of sapphire window products: optical sapphire windows (flat circular, flat rectangular, sapphire wedge windows, sapphire step windows), protective sapphire laser windows, sapphire windows for sight glass and packages of machine, sapphire windows metalized with nickel, chrome, and gold films on the window edges. Typically, our sapphire windows are z-cut to prevent birefringence. Besides, we also provide a large selection of Stocked Sapphire Windows.

Application Notes:

Note: If you are interested in more knowledge about sapphire windows, click here to visit our resource sector to learn more about:

C-cut, A-cut, and Random-cut Sapphire Windows:

The orientation of a crystal is a vector describing a random line connecting two nodes on the lattice. Due to the anisotropic nature of crystals, the distribution and the arrangement manner of the atoms change along different directions or upon different lattice planes. The result of this is that the properties and behaviors, even of the same crystals, but with different orientations will differ to a significant extent. This is the reason of choosing the proper orientations and cutting planes of crystals is critical when using crystals to produce various components and elements.

The Sapphire crystals utilized to produce sapphire windows of different functions will be grown and cut/sliced with an engineered orientation, and the orientation is often determined because it will optimize the crystal’s performance to achieve the intentions of interest.

The lattices within the sapphire are arranged in a hexagonal structure. When a sapphire element is produced, the direction of its inner structure affects the functionalities of the element.

sapphire structure sapphire window orientation

Figure 4.The Lattice Structure of Sapphire and Common Sapphire Crystal Orientations

C-Cut Sapphire Windows has an orientation index of (0001). The sapphire is cut in a direction perpendicular to the c-axis. The c-axis is the optical axis of sapphire. Light projected along the direction of the optical axis minimizes birefringence. In practice, the light will be incident with a perpendicular angle to the apertures of the sapphire windows, which means the light will travel inside the sapphire windows parallel to the optical axis, eliminating the birefringence effect. C-cut sapphire windows are often chosen for critical optical applications (e.g. laser windows). C-cut sapphire is sometimes called zero-degree sapphire, or z-cut sapphire.

A-cut Sapphire Windows are selected when scratch resistance and hardness are important.

There are also Random-cut Sapphire Windows. Random-cut implies the sapphire ingots are cut or sliced with no specific regard to directions. Random cut sapphire window orientation is when the instrinsic birefringence of the sapphire window is acceptable if and when 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.

Before the cutting or slicing procedure, sometimes the manufacturer would grow the bulk sapphire crystal of a specific orientation. For example, the bulk sapphire designated to produce a c-cut sapphire window will be grown with an orientation that maximizes the utilization efficiencies of the c-planes.

Curves:

Transmission of Sapphire Windows without Coating from 2.5μm to 8.0μm

Sapphire Windows-optical transmission

Sapphire Growth Technique-The Kyropoulos Method and The SAPMAC Method

Kyropoulos Sapphire Growth:

The Kyropoulos method or the KY technique is a modification of the Czochralski method, compared with the CZ sapphire growth method, the crystals are formed inside the crucible and the KY method is characterized by a temperature control process to enable the gradual cooling of the single crystal, resulting in less thermal stress and mechanical shock. The procedure is explained below:

First, Aluminum oxide (Al2O3) or other appropriate raw materials are heated to their melting point, forming a molten metal bath in the crucible. The seed crystal is pulled upward (at a controlled rate). The molten material solidifies at the solid-liquid interface as the seed crystal is pulled upwards. The solidification rate is controlled through cooling, which allows the sapphire crystal to form from the top down. The result KY growth method is a pear-shaped single sapphire crystal with a controlled solidification process, minimizing defects and yielding high-quality material suitable for advanced optical and industrial applications.

Figure 1. Kyropoulos Sapphire Growth Process

SAMPAC Sapphire Growth:

The SAMPAC (sapphire growth technique with micro-pulling and shoulder expanding at the cooled center) method is a novel sapphire crystal growth method invented for growing large size sapphire crystals.

At present, only a limited number of methods such as HEM, Temperature Gradient Technique (TGT), and Kyropoulos are capable of growing optical-grade large-size sapphire crystals.

However, The sapphire crystals grown using the heat exchange method can indeed reach large sizes and are good in quality but require a large amount of helium as a coolant, which is expensive.

The quality of sapphire crystals grown using the TGT method is comparable to that of products produced by the heat exchange method, but the crystal blanks need to be annealed in high-temperature oxidation and reduction atmospheres, and the subsequent processing of the blanks is complicated.

The SAPMAC method is a method for growing large-sized sapphire crystals developed based on the improvement of the KY and CZ methods. When growing sapphire crystals using the SAPMAC method, the entire crystal growth process can be divided into four stages: seeding, shoulder reduction, constant diameter, and annealing and cooling.

The main advantages of the SAPMAC method are:

1. access to large-size crystals is guaranteed, and the crystal orientation inheritance is good during the entire crystallization process;

2. only a minute of pulling up introduces the process, which reduces the temperature field disturbance and makes the temperature field more uniform;

3. the crystal can grow without contacting the crucible wall, and the crystal is not pulled out of the crucible during the entire growth process

4. the temperature difference in the crystal is small, which can effectively reduce thermal stress; water is used as the working fluid in the heat exchanger, and the crystal can be annealed in situ.