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The Direction of the Filter and the Effect of Temperature on the Wavelength

1. The edge of the filter is engraved with arrows to indicate the recommended direction of the light transmission filter

Although either side of the filter facing the light source can filter light, it is better to have the coating surface facing the light source. This can minimize the thermal effect or possible thermal damage caused by the absorption of radiation outside the pass band by the dielectric substrate or the colored glass filter layer.

2. When using the filter, the collimated light should be incident on the surface of the filter perpendicularly

When uncollimated light or light non-perpendicularly incident on the surface of the optical filters, the center wavelength (the wavelength corresponding to the transmittance peak) will shift to a shorter wavelength, and the shape of the transmission band (passband) will change. By slightly changing the incident angle, the passband of the filter can be effectively adjusted in a small range. However, when the incident angle changes greatly, it will cause a large change in the center wavelength, and will significantly distort the shape of the passband, and even cause a significant drop in the passband transmittance.

The center wavelength of the bandpass filter can be fine-tuned by changing the temperature of the filter (~1 nm within the working range of the filter). This is mainly caused by slight thermal expansion or contraction of the film.

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