Neutral density filterIt refers to a filter with approximately constant attenuation within the basic wavelength range, which uses special optical materials and coating technology to have approximately constant attenuation effect on all wavelengths of light without changing the color of the light.

　　Neutral density filterLight attenuation is achieved through two main mechanisms:

Absorption type: The material itself (such as glass doped with special elements) or surface coating absorbs light of a specific wavelength, converting light energy into thermal energy. Absorption type filters have a simple structure, but long-term use may lead to performance degradation due to heat generation, and the damage threshold is low, making them unsuitable for high-power laser scenes.

Reflective type: using the principle of thin film interference to partially reflect light (usually not using reflected light), allowing only transmitted light to pass through. Reflective filters need to be used in conjunction with light collectors to avoid stray light interference with experimental accuracy. Its advantage lies in the absence of heat generation issues, but the reflected light may form an optical resonant cavity, requiring careful design of the optical path.

Main parameters:

1. Optical density (OD): Refers to the attenuation ability of a filter on light. The larger the OD value, the lower the transmittance and the stronger the attenuation.

2. Transmittance (T): refers to the ratio of the light intensity passing through the filter to the incident light intensity, which is logarithmically related to the optical density.

3. Wavelength range: refers to the wavelength range of light that can be uniformly attenuated by a filter. Different types of neutral density filters have different wavelength ranges.

4. Size: including the diameter, thickness, etc. of the filter, the appropriate size should be selected according to the actual application scenario.