Fluorescence filters refer to various filters used in fluorescence systems, including the extraction of fluorescence energy or the acquisition of fluorescence imaging. Its main feature is good isolation to interference light and less auto-fluorescence interference. Fluorescence filters are used in various medical analysis and detection instruments such as PCR machines, fluorescence immunoassay analyzers, and fluorescence microscopes. Generally, the cut-off depth of the fluorescence filter is required to be above OD5 (optical density, OD=-lgT).
Fluorescence filters generally include three combinations, namely excitation filters, emission filters, and dichroic mirrors. Some systems do not have dichroic mirrors, which are determined by the optical path structure. There are also systems that use lasers for excitation and do not require excitation filters.
Excitation Filter: In a fluorescence microscope, only the wavelength of the excitation fluorescence can pass through the filter. In the past, short-wave pass filters were used, but now basically band-pass filters are used. Arrows are engraved on the shell to indicate the recommended light propagation direction.
Emission filter: Select and transmit the fluorescence emitted by the sample, and the light in other areas are cut off. The wavelength of the emitted light is longer than the wavelength of the excitation light (closer to red). You can choose a band-pass filter or a long-wave pass filter as the emission filter. Arrows are engraved on the shell to indicate the recommended light propagation direction.
Dichroic Mirror: also known as a dichroic filter or dichroic mirror. It is placed at an angle of 45° to the optical path of the microscope. This filter reflects one color light (excitation light) and transmits another color light (emission light). The reflectance of the excitation light is greater than 90%, and the transmittance of the emitted light is greater than 90%. The opaque part of the spectrum is reflected rather than absorbed. The color of the filter under the transmitted light and the reflected light is complementary to each other, so it is also called a dichroic filter.
