Dichroic mirrors (wavelength separators)
HR + HT | 193 nm - 12500 nm
A dichroic mirror, also known as a wavelength separator or harmonic separator, is an optical component that exhibits high reflectivity at one wavelength and high transmission at another. It is commonly used to either split a single beam into two or combine two different laser harmonics (eg. Nd: YAG and Nd: YLF). Dichroic mirrors or wavelength separators (harmonic separators) are typically utilized for frequency doubling (both external and intracavity) as well as for laser alignment.
This product is also widely referred to by other names, such as harmonic filter, beam separator, beam combiner, or dichroic separator.
- Substrates
- Applications
Material
Most common glasses (various grades of fused silica, N-BK7, and equivalents) have good transmission values from ultraviolet (UV) to visible light (VIS) and through to infrared (IR). However, lasers can emit wavelengths much longer or shorter than these ranges, requiring substitution of these common materials with others, which 3photon can supply. Examples include magnesium fluoride (MgF2), calcium fluoride (CaF2), zinc selenide (ZnSe), germanium (Ge), and others.
The best material for a wavelength separator (harmonic separator) must be transparent, easily polishable, and provide near-perfect performance. This includes achieving good surface quality and controlling both reflected and transmitted wavefront distortion. 3photon’s wavelength separators are polished to a 10-5 scratch-dig finish, and both transmitted and reflected (surface) wavefront distortions are strictly controlled to <λ/10 @ 632.8 nm.
Polarization
3photon engineers can design thin film coatings for both polarizing and non-polarizing dichroic mirrors (wavelength/harmonic separators).
The Angle of Incidence (AOI)
Dichroic mirrors or wavelength separators (harmonic separators) are typically designed for angles of 45° or 0° (normal incidence). However, 3photon engineers can also design and manufacture custom wavelength separators to perform at angles of 22.5° or 56°. A broader range of 0-22.5° or 45-56° can also be produced.
Damage threshold
- For low and medium power applications, 3photon recommends the use of electron beam evaporation (EBE) or ion-assisted deposition (IAD) techniques for manufacturing wavelength separators (harmonic separators).
- For medium to high power lasers, 3photon engineers will select the best thin film optical coating design, using ion beam sputtering (IBS) to produce laser damage-resistant wavelength separators.
- For injecting pump light beam in diode-pumped solid-state (DPSS) lasers, the wavelength separator (harmonic separator) can be placed near the laser medium (laser crystal) in the laser resonator, functioning as the pump (rear) mirror
- For fluorescence microscopy, the dichroic mirror can be used to separate the fluorescence light beam (containing image information) from the pump light
- The wavelength separator can split harmonic wavelengths from pump wavelengths in lasers with frequency doubling
- Suitable for Raman spectroscopy (analysis)
- Applicable in medical and biomedical fields
- Useful for filtering out unnecessary wavelengths
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