What's the difference between Reflective and Absortive Filter?
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Absorptive filters
attenuate or block unwanted wavelengths by using the absorption properties of materials such as colored glass, dyes, or films. When light passes through the filter, certain wavelengths are absorbed by the material, converting their energy into heat or excited-state energy, while other wavelengths are transmitted.
Reflective filters
(usually referring to interference or dichroic filters) achieve filtering through the interference effect of multiple thin layers. Alternating high- and low-refractive-index layers are coated on a glass substrate. When light enters, different wavelengths undergo interference within the multilayer stack: wavelengths meeting constructive interference are transmitted and enhanced, while others experience destructive interference and are reflected.
Spectrum Features
Absorptive filters generally have a wide transmission band and cannot easily achieve extremely narrow bandpass or steep edge characteristics. Their peak transmittance is limited by the material itself and is usually lower than that of interference filters. Additionally, the available types of colored glass are limited, restricting the selectable wavelength range.
Reflective (interference) filters, on the other hand, can be precisely designed to provide extremely narrow bandpass or sharp cutoff spectral characteristics.
Thermal Stability and Laser Damage Threshold
Absorptive filters absorb a large amount of optical energy during operation, which can easily cause thermal effects.
Reflective filters, on the other hand, are often made using hard-coating processes (such as ion-beam sputtering), giving them a higher laser damage threshold and better thermal durability.
