The material of the IR optics

Success in IR optics manufacturing relies on various factors.

Below, you will find a quick guide with some tips and tricks on how to choose the right material for your unique IR laser application

◾ IR Fused Silica [SiO₂], (0.3 – 3.5 µm): This substrate is one of the most commonly used in this spectral region. In IR-grade fused silica, it is essential to maintain a low content of hydroxyl (-OH), typically below 10 ppm. Significant absorption bands related to hydroxyl content occur around wavelengths of 2.2 μm and 2.7 μm, but other bands, such as those around 1.4 μm, are also relevant for the 1.55 μm medical wavelength band.

◾ Calcium Fluoride [CaF₂], (0.2 – 9 µm): This material possesses excellent IR spectral performance, high laser durability, low-stress birefringence, and high refractive index homogeneity. It is one of the most versatile and popular substrates for the Mid-IR spectral region.

◾ Sapphire [Al₂O₃], (0.3 – 5 µm): Sapphire is most suitable for high-power applications. It offers numerous advantages, including extreme surface hardness and scratch resistance. A high grade of sapphire exhibits minimal light scatter or lattice distortion, making it ideal for the most demanding optical applications.

◾ Germanium [Ge], (2 – 14 µm): It has good thermal conductivity and is very hard due to having the same crystal structure as diamond. It has low dispersion making it suitable for Mid-IR ultrafast lasers, OPOs and OPAs, however limited to low-power lasers due to severe refractive index dependence on temperature and high nonlinear index.

◾ Silicon [Si],  (2 – 5 µm): It has a slightly lower refractive index than Germanium and is very hard and stable over different temperatures making it suitable for extreme environments.

◾ Silicon carbide [SiC]: unique composite material mostly used in reflective optics manufacturing due to unique mechanical stability and stiffness combination. Its lightweight nature renders it suitable for applications requiring low inertia.