Glossary
shows the main coating type categories and their sub-types:
Frequently asked questions
What are the main types of laser optics?
The main types of laser optics can be summarized in six categories:
| coating | description | used as |
|---|---|---|
| AR Anti-Reflection |
minimizes reflection, for highest transmission | window, rear side of filters |
| HR High Reflection |
for highest reflection | mirror, reflector |
| PR Partial Reflection |
for splitting or reducing the incoming light | partial reflector, output coupler, attenuator, beam splitter |
| Filter | combination of AR and HR/PR | long / short wave pass, edge filter, band pass filter, interference filter, notch / negative filter, dichroic filter, harmonic beam separator, beam sampler, combining mirror, pump mirror |
| Polarizer | separates the polarizations | thin film polarizer, cube polarizer, polarization sampler |
| Variables | changing transmission/reflection ratio with angle or beam position | variable attenuator, gradient output coupler / attenuator / filter |
Unfortunately, there are different standards for naming optical coatings and their abbreviations. In the glossary of LASEROPTIK, all main and subtypes are therefore listed to give a good overview: https://www.laseroptik.com/en/coating-guide/glossary/overview-coating-types
What is an anti-reflection (AR) coating?
An anti-reflection coating (AR) is the opposite of an HR coating; it minimizes the reflection of a surface. It is used on both sides of a window or on the rear surface of a filter or beam splitter, optimized for its HT-range.
https://www.laseroptik.com/en/coating-guide/glossary/ar-anti-reflection-coating
What is a high reflection (HR) coating?
There is no fixed reflection value above which one speaks of an HR coating. It just means that the coating has high reflection. We would normally say that an HR coating has low transmission, less than 0.1%. Therefore, for coatings with low losses due to scattering and absorption a standard HR coating will have about 99.85% reflection.
Higher reflection up to 99.999% is possible for NIR-coatings using super-polished substrates and special IBS coatings.
What is the difference between single, double and broadband coatings?
For a short overview of coating sub-types:
| type of coating | optimized for | used as |
|---|---|---|
| single | one wavelength | VAR, HR, PR |
| double | two wavelengths | DAR, DHR, DPR |
| broadband | broad wavelength range | BBAR, BBHR, BBPR |
| also available: | ||
| triple | three wavelengths | TAR |
| multiple | combinations of types | MAR, MHR |
| wide angle | wide angle of incidence | WAR, WHR |
For a better overview: https://www.laseroptik.com/en/coating-guide/glossary
What is a wide-angle AR or HR coating?
A wide-angle coating is optimized not only for a single angle of incidence (AOI) but also for a wide range, like 0 - 45° or 45° ±15°. To compensate for the spectral shift while tilting the optic, the coating must be broader compared to a simple AR/HR using only one fixed AOI.
How can I combine two different laser beams?
Two wavelengths can be combined by a dichroic beam combiner. Its coating reflects one wavelength and allows the second to pass completely. Beam combiners can also be used in the opposite way and then work as a beam splitter or beam separator.
A distinction between combiner and splitter therefore makes no sense and LASEROPTIK therefore refers to these optics as filters.
Filters can not only be optimized for two separate wavelengths, but special adaptation for several wavelengths or wavelength ranges is also possible. Areas with different splitting ratios or linear variation in coupling/separating can also be inserted. The polarization can be adjusted, too.
Examples of multiline and complex filter coatings are given here: https://www.laseroptik.com/en/coatings/multiline-and-complex-filter-coatings
Is a dichroic mirror the same as a beam splitter?
A dichroic mirror reflects one wavelength band and lets another one pass.
A beam splitter divides the light into a reflected and transmitted part,
- regardless of the wavelength, like a classic 50/50 beam splitter
- depending on the wavelength, means a combination of AR/HT and HR/PR-ranges
Therefore, a dichroic mirror can be considered a beam splitter, but a beam splitter is not always a dichroic mirror.
To make it easier, LASEROPTIK distinguishes between main and sub-types of coatings, which can be clearly identified, see:
https://www.laseroptik.com/en/coating-guide/glossary/overview-coating-types
What types of optical filters does LASEROPTIK offer?
Filter coatings can be used as separators as well as combiners. Here is a table of the possible sub types:
| type of coating | optimized for | used as |
|---|---|---|
| LP Long Wave Pass |
HR/PR plus HT-range for a longer wavelength or band | long wave pass, edge filter, dichroic filter, harmonic beam separator, beam sampler, combining mirror, pump mirror |
| SP Short Wave Pass |
HR/PR plus HT-range for a shorter wavelength or band | short wave pass, edge filter, dichroic filter, harmonic beam separator, beam sampler, combining mirror, pump mirror |
| NF Notch Filter |
HR/PR plus HT-ranges for a shorter and longer wavelength or band | notch filter, negative filter |
| MP Multi Pass |
combinations of several HR/PR and HT wavelength areas | multi pass, multiline coating, complex filter |
| BP Band Pass |
selecting a small wavelength area | band pass filter, interference filter |
For a better overview: https://www.laseroptik.com/en/coating-guide/glossary/filter
Can LASEROPTIK offer optics and coatings for combinations of the fundamental wavelength and its harmonics?
Yes, LASEROPTIK offers a wide range of different coating types for separating or combining the fundamental wavelength and its harmonics or for a combined use, especially for Nd:YAG, Nd:YVO4, Nd:YLF, Yb:YAG and Ti:Sapphire. Some examples are given here https://www.laseroptik.com/en/coatings/ranges/nir-1000-1100-nm-harmonics
The listed values can be adapted to all other wavelengths and laser types.
What is a variable attenuator and how does it work?
A Variable Attenuator (VA) is an optic that continuously reduces transmission by increasing the angle of incidence. It uses the wavelength shift of a tilted dielectric coating.
Commonly, a short-pass filter with optimized edge position is applied to the front and a wide-angle AR to the rear surface.
The reverse version, which increases the transmission with increasing AOI, is also possible and is called Inverse Variable Attenuator (IVA).
https://www.laseroptik.com/en/coatings/variables/variable-attenuators
Can LASEROPTIK offer OPO coatings?
Yes, we can offer all coating types used within an OPO, such as pump mirror, output coupler, filter and coatings directly on the OPO crystal.
With the high accuracy of our IBS coatings, we also can manage the GDD of the included optical components.
What is OPO?
OPO stands for Optical Parametric Oscillator. It transforms a pump laser wave into two different waves, called idler and signal, where signal is the one with the higher frequency.
Basically, an OPO is a nonlinear crystal working inside an optical resonator where the idler wave and/or the signal wave resonates. By modifying phase matching properties like the orientation or the temperature of the crystal you can change the frequency of the output. Another option is to modify its quasi phase matching period through periodic poling.
A variation in the optical path length of the resonator can be used for additional finetuning.
OPOs also convert radiation of femtosecond lasers and allow tunable lasing in other wavelength ranges.
