Dichroic mirrors (wavelength separators)

HR + HT | 193 nm - 12500 nm

Dichroic mirror or wavelength separator (harmonic separator) is an optical component with high reflection value at one wavelength and high transmission value at another wavelength. It is used to split one beam into two beams or combine two different laser harmonics (eg. Nd:YAG and Nd:YLF). Dichroic mirrors or wavelength separators (harmonic separators) are typically used for frequency doubling (both external and intracavity) and for alignment lasers.

This product is also widely known by other names such as harmonic filter, beam separator, beam combiner, dichroic separator.

  • Substrates
  • Applications


Most common glasses (various grades of Fused Silica, N-BK7 and equivalents) have good transmission values from ultraviolet (UV) to visible light (VIS) throughout to Infrared (IR). However, lasers can emit much longer or shorter wavelengths and these common materials must be substituted with other materials which could be supplied by 3photon, such as Magnesium Fluoride (MgF2), Calcium Fluoride (CaF2), Zinc Selenide (ZnSe), Germanium (Ge) or others.

Best material for wavelength separator (harmonic separator) must be transparent and easily polishable, for near-perfect performance, good surface quality and both reflected and transmitted wave front distortion must be controlled. 3photon best wavelength separators’ substrates are smoothly polished to 10-5 scratch-dig and both transmitted and reflected (surface) wavefront distortion is strictly controlled to <λ/10 @ 632.8 nm.


3photon engineers can design thin film coating for polarizing and non-polarizing dichroic mirrors (wavelength (harmonic) separators)

Angle of incidence (AOI)

Dichroic mirrors or wavelength separators (harmonic separators) are usually designed for 45°or 0° (normal incidence) angle, 3photon engineers can also design and manufacture custom wavelength separators (harmonic separators) to perform at 22.5° or 56° angles. Broad range of 0-22.5° or 45-56° can be produced as well.

Damage threshold

  • For low and medium power applications 3photon recommends to use electron beam evaporation (EBE) or ion assisted deposition (IAD) technique to manufacture wavelength separators (harmonic separators).
  • For medium-high power lasers 3photon engineers will pick the best thin film optical coating design and ion beam sputtering (IBS) technique will be used to manufacture laser damage resistant wavelength separator (harmonic separator)
  • For injecting pump light beam in diode pumped solid state (DPSS) lasers wavelength separator (harmonic separator) can be placed nearby laser media (laser crystal) in laser resonator as pump (rear) mirror;
  • For fluorescence microscopy dichroic mirror can be used to separate fluorescence light beam (beam with image information) from pump light;
  • Wavelength separator can separate harmonic wavelength and pumping wavelength in lasers with frequency doubling;
  • Raman spectroscopy (analysis);
  • Medical and biomedical applications;
  • Filtering out unnecessary wavelengths.

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