Using our advertising package , you can display your logo, further below your product description, and these will been seen by many photonics professionals.
If you want to learn more, please visit our website.
You are a not yet listed supplier? Get your entry!
Find more supplier details at the end of this encyclopedia article , or go to our
A mirror is an optical device which can reflect light. Usually, only those devices are meant where the reflection is of specular type and the angle of reflection equals the angle of incidence (see Figure 1). This means that reflective diffusers and diffraction gratings, for example, are not considered as mirrors, although they can also reflect light.
A somewhat more general term is reflector. While all mirrors are reflectors, there are reflectors which are somewhat more complex than a simple mirror, e.g. prisms used as retroreflectors, using more than one total internal reflection at a prism surface.
Mirror surfaces are not necessarily flat; there are mirrors with a curved (convex or concave) reflecting surface (see below).
This article deals mostly with optical mirrors as used in optics and laser technology, for example, and in other areas of photonics.
Various basic properties characterize a mirror:
Figure 1:
Reflection of light on a mirror.Additional properties can be relevant in various applications:
Ordinary mirrors as used in households are often silver mirrors on glass. These basically consist of a glass plate with a silver coating on the back side. The coating is thick enough to suppress any significant transmission from any side. Nevertheless, the reflectivity is substantially below 100%, since there are absorption losses of a few percent (for visible light) in the silver layer.
Household mirrors typically have the coating on the back side, so that one has a robust glass surface outside, which can be cleaned easily, and the coating on the back side (with an additional layer) is well protected. For other applications, one uses first surface mirrors, where the light is incident directly on the coating and does not reach the mirror substrate.
For use in laser technology and general optics, more advanced types of metal-coated mirrors have been developed. These often have additional dielectric layers on top of the metallic coating in order to improve the reflectivity and/or to protect the metallic coating against oxidation (enhanced and protected mirrors). Different metals can be used, e.g. gold, silver, aluminum, copper, beryllium and nickel/chrome alloys. Silver and aluminum mirrors are particularly popular. Others are mostly used as infrared mirrors.
The article on metal-coated mirrors gives more details.
The most important type of mirror in laser technology and general optics is the dielectric mirror. This kind of mirror contains multiple thin dielectric layers. One exploits the combined effect of reflections at the interfaces between the different layers. A frequently used design is that of a Bragg mirror (quarter-wave mirror), which is the simplest design and leads to the highest reflectivity at a particular wavelength (the Bragg wavelength).
In contrast to some metal-coated mirrors, dielectric mirrors are usually made as first surface mirrors, which means that the reflecting surface is at the front surface, so that the light does not propagate through some transparent substrate before being reflected. That way, not only possible propagation losses in the transparent medium are avoided, but most importantly additional reflections at the front surface, which could be particularly relevant for non-normal incidence.
Generally, dielectric mirrors have a limited reflection bandwidth. However, there are specially optimized broadband dielectric mirrors, where the reflection bandwidth can be hundreds of nanometers. Some of those are used in ultrafast laser and amplifier systems; they are sometimes called ultrafast mirrors, and they also need to be optimized in terms of chromatic dispersion.
Laser mirrors as used to form laser resonators, for example, are also usually dielectric mirrors, having a particularly high optical quality and often a high optical damage threshold. Some of them are used as laser line optics, i.e., only with certain laser lines. Also, there are supermirrors with a reflectivity extremely close to 100%, and dispersive mirrors with a systematically varied thin-film thickness. They can be used for high-Q optical resonators, for example.
In some cases, dielectric mirrors should also be polished on the back side &#; in particular, when some amount of light transmission is required, e.g. for output couplers of lasers.
Dielectric mirrors can be designed as cold mirrors or hot mirrors, which both can be used for removing unwanted infrared radiation &#; usually for reducing the thermal load on an optical system.
See the article on dielectric mirrors for more details.
Dichroic mirrors are mirrors which have substantially different reflection properties for two different wavelengths. They are usually dielectric mirrors with a suitable thin-film design. For example, they can be used as harmonic separators in setups for nonlinear frequency conversion.
While many mirrors have a plain reflecting surface, many others are available with a curved (convex or concave) surface, for example for focusing laser beams or for imaging applications.
Most curved mirrors have a spherical surface, characterized by some radius of curvature <$R$>. A mirror with a concave (inwards-curved) surface acts a focusing mirror, while a convex surface leads to defocusing behavior. Apart from the change of beam direction, such a mirror acts like a lens. For normal incidence, the focal length (disregarding its sign) is simply <$R / 2$>, i.e., half the curvature radius. For non-normal incidence with an angle <$\theta$> against the normal direction, the focal length is <$(R / 2) \cdot \cos \theta$> in the tangential plane and <$(R / 2) / \cos \theta$> in the sagittal plane.
There are also parabolic mirrors, having a surface with a parabolic shape. For tight focusing, one often uses off-axis parabolic mirrors, which allow one to have the focus well outside the incoming beam.
There are deformable mirrors, where the surface shape can be controlled, often with many degrees of freedom (possibly several thousands). Such mirrors are mostly used in adaptive optics for correcting wavefront distortions.
While most mirrors have a uniform reflectance across their reflecting area, there are also variable reflectivity mirrors, where the reflectance depends on the position. These are also called graded reflectivity mirrors. They are used in lasers with unstable resonators, also as variable optical attenuators.
Some types of mirrors are used for special functions:
Phase-retarding mirrors are made such that they introduce a well defined phase difference for s- and p-polarized components of a beam. For example, they can be used for converting linearly polarized light into circularly polarized light if that phase difference is <$\pi /2$>.
Absorbing thin-film reflectors are metal-coated mirrors which are designed to reflect e.g. s-polarized light at 45° angle of incidence while absorbing p-polarized light with the same direction of incidence. They work e.g. at the common CO2 laser wavelength of 10.6 μm and can be used in conjunction with a phase-retarding mirror to build a kind of polarization-based optical isolator. Such a device can e.g. be used for preventing light reflected on a workpiece from getting back to the laser. However, it can be used only for moderate power levels because otherwise the absorbed power would destroy the mirror or at least degrade its performance.
Mirror substrates in optics and laser technology often have a cylindrical form, for example with a diameter of 1 inch and a thickness of a couple of millimeters. However, there are also substrates with a rectangular, elliptical or D-shaped front surface, for example. Besides, there are prism mirrors, where a reflecting coating is placed on a prism, and retroreflectors.
For special applications, a mirror substrate with a tiny hole is used. This can be useful, for example, for combining two laser beams, one of which is sent in a focused fashion through the hole while the other beam, having a substantially larger diameter, is reflected on the mirror surface.
In fiber optics, it is also often required to reflect light &#; in most cases back into the fiber where the light came from. That can be achieved simply by butting a normal kind of mirror (e.g. a dielectric mirror] to a normally cleaved fiber end. Alternatively, one may apply a dielectric coating directly on a fiber end.
There are also completely different types of fiber reflectors, e.g. fiber loop mirrors which are strictly speaking no mirrors but another type of reflectors.
Encyclopedia articles:
Here you can submit questions and comments. As far as they get accepted by the author, they will appear above this paragraph together with the author&#;s answer. The author will decide on acceptance based on certain criteria. Essentially, the issue must be of sufficiently broad interest.
Please do not enter personal data here. (See also our privacy declaration.) If you wish to receive personal feedback or consultancy from the author, please contact him, e.g. via .
Your question or comment:
Spam check:
You will get efficient and thoughtful service from yanggu.
(Please enter the sum of thirteen and three in the form of digits!)
By submitting the information, you give your consent to the potential publication of your inputs on our website according to our rules. (If you later retract your consent, we will delete those inputs.) As your inputs are first reviewed by the author, they may be published with some delay.
-Principles of Optical Mirrors
Optical mirrors are essential components in various optical systems and devices. They work based on the principle of specular reflection, where incident light is reflected with minimal scattering or diffraction.
-Types of Optical Mirrors
There are several types of optical mirrors, each designed for specific applications:
Flat Mirrors&#;&#;have a flat reflective surface and are commonly used for directing or folding light in optical systems.
Spherical Mirrors&#;&#;can be concave or convex. Concave mirrors focus incoming light, while convex mirrors spread it out.
Parabolic Mirrors&#;&#;have a parabolic shape and are used to focus incoming parallel rays to a single point, often in telescopes and satellite dishes.
Elliptical Mirrors&#;&#;have an elliptical shape and can be used to create a point source of light.
Cylindrical Mirrors&#;&#;have a curved surface in one direction and are used for one-dimensional focusing or collimating of light.
-Performance Parameters of Optical Mirrors
To evaluate the performance of optical mirrors, consider the following parameters:
1. Reflectivity: As mentioned earlier, it measures the efficiency of light reflection and is often specified as a percentage.
2. Surface Quality: Surface quality refers to the smoothness and flatness of the mirror's surface, usually described in terms of surface irregularities, scratches, and coatings.
3. Coating: Many mirrors have coatings to enhance their reflectivity, reduce glare, or improve durability. The choice of coating depends on the application.
4. Surface Figure: Surface figure characterizes the mirror's deviation from an ideal shape, which can affect the accuracy of optical systems.
5. Diameter and Size: The size of the mirror is crucial for the intended application, as it determines the field of view and the amount of light that can be collected or directed.
-Applications of Optical Mirrors
Optical mirrors find applications in various fields, including:
1. Telescopes: Spherical and parabolic mirrors are used in telescopes to focus and magnify distant celestial objects.
2. Microscopes: Mirrors are used to direct and manipulate light in microscopes for magnification and observation of tiny structures.
3. Laser Systems: Mirrors are crucial components in laser systems for beam steering, alignment, and cavity enhancement.
4. Imaging Devices: Mirrors are used in cameras and digital imaging systems for reflecting and focusing light onto sensors.
5. Astronomy: Large reflecting mirrors in observatory telescopes capture and direct light from the cosmos for analysis.
6. Industrial Inspection: Mirrors are used for inspecting and examining objects in manufacturing and quality control.
Understanding the principles, types, and performance parameters of optical mirrors is essential for selecting the right mirror for a specific application and ensuring optimal performance in optical systems.
UNI Optics can offer the Laser Mirror with 355nm, 532nm, nm, nm, nm. Others can be available according to customers&#; requirements.
If you have any optical projects related to it, please contact us without hesitation by Linkedin or .
Thank you for your time!
If you want to learn more, please visit our website Custom Optical Mirrors.