825nm CWL,ODAvg>3@300~812nm,ODAvg>3@838~1000nm,FWHM 15nm,Narrowband Filter
825nm CWL,ODAvg>3@300~812nm,ODAvg>3@838~1000nm,FWHM 15nm,Narrowband Filter
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$125.00 USD
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$125.00 USD
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Common Specifications
Transmission Band:TAvg>95%@820~830nm、TMax-TMin<3%@825±4nmCenter Wavelength:825nm
Bandwidth:15nm
Blocking Band 1:ODAvg>3@300~812nm
Blocking Band 2:ODAvg>3@838~1000nm
Angle of Incidence:3±2 degree
Cone Half-angle:3.5 degree
What is a Longpass Filter?
- A longpass filter is a device that selectively transmits light of longer wavelengths and blocks or reflects light of shorter wavelengths.
- A longpass filter can be implemented as a glass plane or plastic device that is either dyed in the bulk or has interference coatings.
- A longpass filter is characterized by its cut-on wavelength, which is the wavelength at which the transmission reaches 50% of the maximum value.
- A longpass filter can be used for various applications, such as isolating spectral regions, enhancing contrast, blocking unwanted light, fluorescence microscopy, and multispectral imaging.
Key Specifications of Longpass Filter
- Transmission: the percentage of light that passes through the filter at a given wavelength or range of wavelengths.
- Blocking: the amount of light that is rejected by the filter at a given wavelength or range of wavelengths, usually expressed as optical density (OD).
- Cut-on slope: the steepness of the transition from blocking to transmission at the cut-on wavelength.
- Full width at half maximum (FWHM): the width of the transmission band measured between the wavelengths where the transmission is half of the maximum value.
- Center wavelength (CWL): the average of the wavelengths where the transmission is half of the maximum value.
- Bandwidth: the difference between the wavelengths where the transmission is half of the maximum value.
OD and FWHM Explanation
- OD and FWHM are two important parameters that affect the performance of a longpass filter.
- OD describes how much light is attenuated by the filter at a certain wavelength or range of wavelengths. A higher OD value means lower transmission and higher blocking. For example, an OD of 2 means that only 1% of the light is transmitted and 99% is blocked. An OD of 4 means that only 0.01% of the light is transmitted and 99.99% is blocked.
- FWHM describes how wide or narrow the transmission band of the filter is. A smaller FWHM means a narrower band and a sharper cut-on slope. A larger FWHM means a wider band and a smoother cut-on slope. For example, a FWHM of 10 nm means that the filter transmits light within 10 nm around the CWL. A FWHM of 100 nm means that the filter transmits light within 100 nm around the CWL.
- The choice of OD and FWHM depends on the application and the desired trade-off between transmission, blocking, and resolution. A higher OD and a smaller FWHM can provide better blocking and resolution, but may also reduce the transmission and increase the cost. A lower OD and a larger FWHM can provide higher transmission and lower cost, but may also compromise the blocking and resolution.
Example of Standard and Performance Longpass Filter
- High performance longpass filter: This filter has an OD of 4, a FWHM of 20 nm, a CWL of 600 nm, and a cut-on slope of less than 1%. It can provide high transmission (>91%) in the pass band (600-1100 nm), high blocking (OD > 4) in the stop band (200-590 nm), and sharp transition at the cut-on wavelength. This filter is ideal for applications that require high contrast, high resolution, and low background noise, such as fluorescence microscopy or Raman spectroscopy.
- Standard longpass filter: This filter has an OD of 2, a FWHM of 100 nm, a CWL of 600 nm, and a cut-on slope of about 10%. It can provide moderate transmission (>85%) in the pass band (550-1100 nm), moderate blocking (OD > 2) in the stop band (200-540 nm), and smooth transition at the cut-on wavelength. This filter is suitable for applications that do not require very high contrast, resolution, or blocking, such as general photography or color separation.