Sapphire

Optical sapphire, also known simply as sapphire, stands as a highly esteemed material in the realm of optics and photonics, celebrated for its exceptional optical and mechanical properties.

As a single crystal form of aluminium oxide (Al2O3) with a hexagonal crystal structure, sapphire boasts transparency across a broad spectrum of wavelengths, ranging from the ultraviolet (UV) to the near-infrared (NIR) regions, typically from around 150 nm to 5 μm. This transparency, coupled with its high refractive index (approximately 1.77 in the visible spectrum), makes sapphire an ideal candidate for various optical applications.

One of its most notable characteristics is its remarkable hardness just below diamond. This exceptional hardness, combined with its scratch resistance and durability, positions sapphire as a material of choice for applications requiring resilience in harsh environments.

The utility of optical sapphire spans a wide array of industries and fields. It finds extensive use in the fabrication of optical windows and lenses for applications demanding high optical clarity and durability, such as optical instruments, cameras, sensors, and laser systems.

Moreover, sapphire's robust mechanical properties make it indispensable in environments characterized by high pressure and temperature, such as aerospace, underwater oceanography, and oil and gas industries. Here, it serves in roles ranging from pressure windows and sensor optics to viewports for high-pressure chambers.

Furthermore, sapphire's transparency in the infrared spectrum makes it invaluable for infrared optics, particularly in thermal imaging systems, infrared detectors, and spectroscopy.

In essence, optical sapphire stands as a versatile material, essential in various optical systems and devices across multiple industries, owing to its optical clarity, durability, and mechanical strength.

Optical Sapphire (Al2O3) is a very hard crystal and has the following technical properties:

Transmission Range: 0.17 to 5.5 μm

Refractive Index: No 1.75449; Ne 1.74663 at 1.06 μm

Reflection Loss: 14% at 1.06 μm (2 surfaces)

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

Density: 3.97 g/cc

Melting Point: 2040°C

Thermal Conductivity: 27.21 W m-1 K-1 at 300K

Thermal Expansion: 5.6 (para) & 5.0 (perp) x 10-6/K

Hardness Knoop: 1800 (para) 2200 (perp)

Specific Heat Capacity: 763 J Kg-1 K-1 @ 293K

Dielectric Constant: 11.5 (para) 9.4 (perp) at 1MHz

Young’s 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 (45,000psi)

Poisson Ratio: 0.25

Solubility: 98 x 10-6 g / 100g water at 20°C

Molecular Weight: 101.96

Class/Structure: Trigonal (hex), R3c

Please note that these values are typical and may vary based on the grade and manufacturing process of the material