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The Function of Dichroic Mirror in Fluorescence Microscopy

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In fluorescence microscopy, dichroic mirrors are used to precisely separate light beams so that certain wavelengths of light are reflected and other wavelengths of light are transmitted. It not only enhances the imaging quality of fluorescence microscopy but also greatly expands its application scope.

This article will explore the role of dichroic mirrors in fluorescence microscopy and understand how they enable efficient light path control and signals in fluorescence microscopy.

What is fluorescence microscopy?

Fluorescence microscopy is a microscopy technique that uses the principle of fluorescence to enhance the contrast of images of cells and tissues.

This microscope uses a specific light source to excite fluorescent molecules in the sample, causing them to emit light, thereby enabling the observation of the cellular structure and biochemical processes of biological samples. Fluorescence microscopes are widely used in fields such as biomedical research, disease diagnosis, and life sciences.

What filters are included in a fluorescence microscope?

Fluorescence microscopes usually contain three types of filters, and different filters play different roles in the microscope, such as:

Excitation Filter

Excitation filter are used to selectively pass specific wavelengths of light used to excite fluorescent molecules in a sample.

This filter ensures that only wavelengths of light that can cause a fluorescent reaction are illuminated on the sample, thereby improving the specificity and efficiency of fluorescent labeling.

Emission Filter

The emission filter is located on the detection path, and its main function is to allow only the wavelength of light emitted by fluorescent molecules to pass through, while blocking light of other wavelengths, including excitation light.

This allows the signal from the fluorescent label to be clearly detected instead of background or stray light, thereby enhancing the contrast and clarity of imaging.

Dichroic Mirror

A dichroic mirror is usually placed between the excitation and emission filters. Its role is to reflect the excitation light towards the sample while allowing the fluorescence emitted from the sample to pass through and further pass through the emission filter to the detector.

What is a Dichroic Mirror?

A dichroic mirror is a special type of mirror that reflects certain wavelengths of light while allowing other wavelengths to pass through.

This selective reflection and transmission is achieved through a process called thin-film interference, which involves multiple layers of dielectric material deposited on the surface of the mirror.

Dichroic mirrors play such an important role in fluorescence microscopy, as we have detailed in our previous article what is a dichroic mirror and its advantages and disadvantages, you can click to read it!

The Function of Dichroic Mirror in Fluorescence Microscopy

In fluorescence microscopy, dichroic mirrors effectively separate different wavelengths of light. This separation improves the clarity and contrast of the images obtained. The following are the functions of dichroic mirrors in fluorescence microscopy:

Excitation and emission separation

The primary function of a dichroic mirror in fluorescence microscopy is to direct excitation light to the sample and subsequently allow the emitted light to pass through the detector.

The excitation light, typically produced by a laser or other intense light source, is reflected by a dichroic mirror due to its specific wavelength-selective coating.

Once the excitation light interacts with fluorescent molecules in the sample, these molecules emit light at a different (usually longer) wavelength, which the dichroic mirror is designed to transmit.

Enhance image quality

By selectively reflecting and transmitting light, dichroic mirrors minimize the amount of excitation light reaching the detection path.

It prevents the brighter excitation light from overwhelming the weaker emission signal, resulting in clearer, higher-contrast images in which the fluorescent signal is easily distinguished from the background.

Flexibility and customization

Dichroic mirrors can be customized for different types of fluorescence microscopy applications by changing the coating to reflect and transmit specific wavelengths.

Researchers can use multiple fluorophores with different emission spectra in a single experiment, expanding the range of possible experiments and applications.

Reduce photobleaching and photodamage

Dichroic mirrors help reduce the overall sample exposure to potentially damaging high-intensity light by separating excitation and emission light.

Prolonged exposure to strong light may cause cell photobleaching (fading of fluorescent signals) and photodamage. So it is valued in live cell imaging.

In summary, dichroic mirrors contribute to more efficient, flexible, and detailed imaging in fluorescence microscopy by optimizing path and quality


In fluorescence microscopes, dichroic mirrors not only improve the clarity and contrast of imaging by precisely controlling the transmission and reflection of light but also allow researchers to conduct more complex multi-label fluorescence imaging experiments.

Separating excitation light and emission light ensures that the observed fluorescence signal is emitted by the sample rather than any background light interference, making the imaging results more realistic and reliable.

Frequently Asked Questions

Can dichroic mirrors be used with any type of light source?

Yes, dichroic mirrors can be used with a variety of light sources, common ones being mercury lamps and halogen light sources, as long as the light source emits light at a wavelength suitable for the specific dichroic mirror being used.

How do I choose the right dichroic mirror for my application?

When choosing a suitable dichroic mirror, you first need to understand the excitation and emission wavelengths of the fluorescent dye used and choose a dichroic mirror whose cutting wavelength is between these two.

At the same time, considering the light source characteristics and multi-color imaging requirements, choose mirrors that can provide high reflectivity and high transmittance to ensure the best imaging effect. Finally, seeking advice from your equipment supplier or microscopy expert can help you make a more accurate choice.

Can dichroic mirrors be used in polychromatic fluorescence microscopy?

Yes, dichroic mirrors can be used in polychromatic fluorescence microscopy. In polychromatic fluorescence microscopy, dichroic mirrors can allow simultaneous or sequential imaging of samples labeled with different fluorescence.

By using specifically designed dichroic mirrors, precise optical path control can be achieved for the specific excitation and emission wavelengths of each fluorescent dye.

If you would like to customize or purchase dichroic mirror filters, please contact us and we can customize optical filters for your application.