Application of filters
The application of filters across different spectral bands in the optical industry primarily leverages their wavelength selection capabilities, enabling specific functionalities by modulating the wavelength, intensity, and other optical properties. The following outlines the primary classifications and corresponding application scenarios:
Classification based on spectral characteristics:
1. Long-pass filter (λ > cut-off wavelength) This type of filter allows wavelengths longer than the cut-off wavelength to pass through while blocking shorter wavelengths. It is commonly used in biomedical imaging and medical aesthetics. For example, fluorescence microscopes utilize long-pass filters to eliminate short-wave interfering light.
2. Short-pass filter (λ < cut-off wavelength) This filter transmits wavelengths shorter than the cut-off wavelength and attenuates longer wavelengths. It finds applications in Raman spectroscopy and astronomical observation. A practical example is the IR650 short-pass filter, which is employed in security monitoring systems to suppress infrared interference during daylight hours.
3. Narrowband filter (bandwidth < 10 nm) Narrowband filters are utilized for precise detection in fields such as LiDAR and Raman spectroscopy. For instance, the BP525 narrowband filter features a central wavelength of 525 nm, a full width at half maximum (FWHM) of only 30 nm, and a peak transmittance exceeding 90%.
4. Notch filter (stopband bandwidth < 20 nm) Notch filters are specifically designed to suppress interference within a narrow spectral range. They are widely applied in laser protection and bioluminescence imaging. An example includes the use of notch filters to block 532 nm laser emissions that may pose hazards.
Classification based on functional characteristics:
- Polarizing films These components are employed to distinguish crystal anisotropy or mitigate ambient light interference. For instance, metal wire grid polarizers can withstand high-power laser irradiation and are suitable for use in autonomous driving LiDAR systems.
- Dichroic mirrors and color separators Dichroic mirrors separate specific spectral bands with steep transition edges—for example, reflecting wavelengths below 450 nm. Spectrophotometers proportionally distribute transmitted and reflected light, a functionality frequently observed in multispectral imaging systems.
Core application scenarios: - Medical equipment: Ophthalmic laser treatment and dermatological devices require the elimination of harmful spectral bands. - Optical sensing: Fluorescence microscopes employ optical filters to detect specific fluorescent proteins, such as GFP, thereby enhancing signal-to-noise ratios. - Security monitoring: IR-CUT filter sets block infrared radiation during daytime operation to ensure accurate color reproduction in captured images. - Laser technology: Notch filters are employed to suppress laser interference, with applications spanning military defense systems and precision measurement instruments.
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