The optical parameters of special-shaped window pieces usually include the following aspects: 

Size and Shape

The contour dimensions of the specific shape need to be clearly defined. For polygons, parameters such as the lengths of each side and angles should be marked. For irregular shapes, the dimensions of key parts need to be determined. These parameters determine the installation position and coverage area of the window piece in the optical system. 

Thickness and Uniformity

The thickness affects the refraction and dispersion of light passing through the window piece, as well as its mechanical strength. Meanwhile, thickness uniformity is also crucial. Non - uniformity may lead to irregular changes in the light propagation path. Generally, the thickness deviation is required to be controlled within a certain range, for example, ±0.05 mm. 

Angle Parameters

For special - shaped window pieces with specific angle requirements, such as wedge angles, they will affect the propagation direction and angular deviation of light. These angles need to be accurately measured and controlled, usually in radians or degrees, with an accuracy that can reach ±0.01°. 

Clear Aperture

This refers to the size of the area through which light can effectively pass. It needs to be determined according to the requirements of the optical system to ensure that light can pass through without obstruction. Generally, its diameter or the maximum available range is marked. 

Material Refractive Index

Different materials have different refractive indices. For example, the refractive index of fused silica is approximately 1.46, and that of BK7 glass is approximately 1.506. This determines the propagation speed and path change of light in the window piece, which in turn affects the imaging quality and performance of the optical system. 

Parallelism

If the special - shaped window piece has parallel planes, the parallelism error should be controlled within a small range to ensure the accuracy of the light propagation direction when passing through. It is usually represented by the beam deviation, such as less than λ/10 (where λ is the laser wavelength).

Surface Figure Accuracy

It reflects the flatness and optical quality of the surface. Usually, it is given in the form of power (λ/p). For example, λ/4@633 nm indicates that the surface figure accuracy at a wavelength of 633 nm is one - quarter of the wavelength. The smaller the value, the higher the surface flatness.

Center Thickness Error

The deviation between the actual center thickness and the nominal center thickness should be as small as possible. Generally, it is required to be controlled within a small range, such as ±0.1 mm, to ensure the stability of the optical performance.

Surface Finish

It describes the smoothness of the surface and is usually divided into different grades. The number and size of defects such as scratches and pits are clearly defined to ensure good optical performance and appearance. For example, it should meet the M - grade or higher standard.

Chamfer

The size of the edge chamfer is generally 0 - 0.2 mm, which plays a protective role and prevents edge damage. At the same time, it may also affect the light propagation characteristics, especially in the edge area.