1. Distinguish filters by spectral band:
The filter is divided into ultraviolet filter, visible filter, near-infrared filter, infrared filter and far-infrared filter according to the length of the spectrum (i.e. the region where the spectrum is located).
The spectral wavelength range is as follows:
UV filter 180 ~ 400nm
Visible light filter 400 ~ 700nm
Near infrared filter 700 ~ 3000Nm
Infrared filter above 3000Nm ~ 10um
2. Distinguish filters according to spectral characteristics:
Bandpass filter, cut-off filter, spectroscopic filter, neutral density filter, reflection filter and negative filter.
What are the basic concepts and parameters of optical filters?
Bandpass type:
the light of the selected band passes through and the light outside the passband is cut off. Its optical indexes are mainly center wavelength (CWL) and half bandwidth (FWHM). It is divided into narrowband and broadband. For example, narrow band filter, nbf-808.
Short wave pass type
(also known as low wave pass): light shorter than the selected wavelength passes through and light longer than the wavelength is cut off. For example, infrared cut-off filter, ibg-650.
Long wave pass type
(also known as high wave pass): light longer than the selected wavelength passes through, and light shorter than the wavelength is cut off, such as infrared transmission filter, ipg-800.
3. Filter is distinguished by film material:
Soft film filter and hard film filter;
Soft film filter is mainly used in biochemical analyzer; Dural filter not only refers to the film hardness, but also its laser damage threshold, so it is widely used in laser system.
4. Explanation of terms related to filter:
Central wavelength (CWL):
the wavelength used by the filter in practical application. If the main peak value of the light source is 850nm LED lamp, the required central wavelength is 850nm.
Transmittance (T):
assuming that the initial value of light is 100%, there is a loss after passing through the filter, and the evaluation shows that it is only 85%, then the optical transmittance of this filter can be only 85%. In short, we all hope that the smaller the loss, the better.
Peak transmittance (TP) > 85%:
the maximum value of transmission after filter loss is more than 85%.
Half bandwidth (FWHM):
in short, it is the wavelength corresponding to 1 / 2 of the highest transmittance, and the values of the left and right wavelengths are subtracted. For example, the peak is preferably 90%, 1 / 2 is 45%, and the left and right wavelengths corresponding to 45% are 800nm and 850nm, and the half bandwidth is 50nm.
Blocked:
the transmittance corresponding to the cut-off area Because it is very difficult to achieve a transmittance of 0%, it is necessary to know that the sun can turn underground trees into carbon. It is difficult to cover everything only by this thin film. The smaller the transmittance, the better, that is, the smaller the unwanted spectral transmittance, the better.
Cut off band:
the smallest region of acceptable unwanted wavelength.
Hard coating:
oxide material plating (such as Ta2O5, SiO2, etc.).
Soft film:
in addition to oxide materials, such as fluoride (MgF2), sulfide, commonly used gold, silver, aluminum and so on.
Antireflective film (AR):
antireflective film, which increases the penetration of light and makes the most effective use of light energy.
Bbar:
back broadband antireflective film.
High reflection (HR):
light is returned or reflected more through a certain wavelength, such as a mirror used at ordinary times.
High transmittance (HT):
the loss of light passing through a certain wavelength is less. For example, the glass window used at ordinary times belongs to visible light high transmittance.
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