by IDEX Health & Science A dichroic beamsplitter is a thin-film optical filter designed to reflect certain wavelengths while transmitting others. Unlike conventional mirrors, which reflect most wavelengths equally, dichroic beamsplitters separate light based on wavelength. Most dichroic beamsplitters operate at a 45° angle of incidence and simultaneously use both the reflected and transmitted beams. IDEX Health & Science makes a wide variety of 45º dichroic beamsplitters optimized for different purposes. Every dichroic utilizes our advanced hard, ion-beam-sputtered coating technology for exceptional environmental and handling durability and no degradation even under the most intense illumination conditions. The dichroics are broadly categorized by the light source with which they are intended to be used and the spectral edge steepness and physical flatness values required for various applications. How do I choose a dichroic beamsplitter? When selecting a dichroic beamsplitter, consider: Light source type (LED, broadband lamp, or laser) and excitation wavelength(s) For a LWP dichroic, this range determines the reflection band Emission wavelength(s) For a LWP dichroic, this range determines the transmission band Edge steepness requirements Angle of incidence Application What is reflected wavefront error (RWE)? Reflected Wavefront Error (RWE) measures how much optical distortion is introduced into a reflected light beam. Low RWE values help maintain image quality, preserve focus, reduce aberrations, and improve super-resolution performance. As microscopy systems become more demanding, RWE often becomes one of the most important dichroic selection criteria. Learn more about Dichroic Beamsplitters here: Selection Guide Light Source Edge Steepness Flatter dichroic beamsplitters minimize wavefront errors that can result in defocus and imaging aberrations of the light reflected off these filters. Semrock classifies dichroic beamsplitters into four categories of flatness, as listed in the table below. NOTE: Mounting can impact flatness performance. Values below apply to unmounted parts. Which dichroic beamsplitter flatness (RWE) classification is recommended for my microscopy technique? Flatness / RWE Classification Application Specification All Classifications All curvatures Transmission: does not cause significant aberrations to a transmitted beam over the full Clear Aperture Super-resolution / TIRF ~ 1275 meters Reflection: contributes less than one Rayleigh Range of shift in focus (relative to a perfectly flat mirror) at the focal plane of a lens after reflecting a laser beam with a diameter up to 22.5 mm Super-resolution / TIRF ~ 255 meters Reflection: contributes less than one Rayleigh Range of shift in focus (relative to a perfectly flat mirror) at the focal plane of a lens after reflecting a laser beam with a diameter up to 10 mm Image-splitting ~ 1275 meters Reflection: contributes less than 1.5 x Airy Disk diameter to the RMS spot size of a focused, reflected emission beam with a diameter up to 37 mm Image-splitting ~ 100 meters Reflection: contributes less than 1.5 x Airy Disk diameter to the RMS spot size of a focused, reflected emission beam with a diameter up to 10 mm Laser ~ 30 meters Reflection: contributes less than one Rayleigh Range of shift in focus (relative to a perfectly flat mirror) at the focal plane of a lens after reflecting a laser beam with a diameter up to 2.5 mm Standard Epi-fluorescence ~ 6 meters Reflection: designed to reflect broadband excitation light that is not focused or imaged