Making the invisible visible – It is all about wavelength discrimination

Fluorescence microscopy is a widely used imaging technique in biological, medical research and many other fields of work. It relies on the detection of fluorescence signals that are 1000 times weaker than scattered light, which in turn is 1000 times weaker than the light that the sample is illuminated with. Alas, the task in fluorescence microscopy is to detect a signal that is a million times weaker than the illumination light. This fact explains the high requirements to the filters and dichroic beam splitters that are used in fluorescence microscopes. For a detailed description of fluorescence and fluorescence microscopy please refer to Carl Zeiss' excellent Microscopy Online Campus website or Nikon's equally valuable resource MicroscopyU.


Measured blocking of a High Performance Fluorescence Filter Set.

Separating absorption and emission spectra

Absorption and emission spectra of most fluorophores (fluorescent dyes) are closely located and often even overlap. This requires that excitation and emission filters have very steep edges to effectively separate absorption and emission peaks from each other. High out-of-band rejection is essential to make the the weak fluorescence signal detectable among the strong illumination light. Located at the heart of an epi-fluorescent set-up is the dichroic beamsplitter that mirrors the illumination light into the microscope lens and onto the sample and at the same time lets pass the fluorescence light into the eyepiece or onto the CCD or CMOS camera attached to the microscope. Well designed dichroic beamsplitters have broad reflection and transmission wavelength ranges with a sharp transition in between. They help suppressing the excitation light by at least two orders of magnitude and allow contrast rich imaging of cells and other specimens.

Decades of experience with fluorescence filters

Did you know that Delta Optical Thin Film was the first to suggest the use of interference filters to Carl Zeiss and Leica in the late 1960s? We started volume manufacturing of fluorescence filters in the early 1970s and were the first to implement computer controlled deposition in the early 1990s. Using our own synthesis and deposition control software allows us to offer coatings made with plasma assisted e-beam evaporation technology with a quality equal to that achievable by IBS and similar technologies. With our decades of experience we are today the biggest supplier of high performance fluorescence custom optical filter sets to the market leading manufactures of fluorescence microscopes.

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