Many optical systems include mirrors as a component. They are used to direct and focus light, combine wavelengths, and reject specific wavelengths in imaging and a host of other applications. Multiple factors should be evaluated when choosing a mirror.

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Materials

Metallic Mirrors offer a combination of reflectance and absorbance (along with transmittance if they are sufficiently thin).

They can be used as wide wavelength-range reflectors, neutral beamsplitters, or neutral density filters. The type of metal used determines its spectral characteristics. These mirrors are commonly applied outside of angle-of-incidence.

Dielectric Mirrors consist of intricate layers of materials that are non-absorbing (usually oxides and fluorides), which differ in their refractive index.

The thickness and composition of the layers are arranged to produce transmittance or reflectance in wavelength ranges required by the customer or application.

Little to no light is absorbed by these materials which means dielectric mirrors are often used as dichroic mirrors (where light of a specific color can pass through while different colored lights are reflected). Both the wavelength range and the angle-of-incidence should be calculated at the design stage.

Function

Imaging - Requires a flatness of λ/10 or more to decrease distortion of the image. Non-imaging, beam-steering applications do not require stringent flatness specifications.

Wavelength combining - Dielectric dichroic mirrors are used to combine various laser beams onto a single axis. A flatness of 1/4λ per inch or greater is required by this application.

Wavelength splitting - Target wavelengths can additionally be reflected by using dielectric dichroic mirrors. Applications include hot-mirrors that reject NIR and IR light, reflect excitation light, and transmit emission light while determining other wavelength bands with multiple detectors.

The transmitting and reflecting wavelengths must be well defined for this type of application. These are frequently used at a 45° angle of incidence.

Wavelength rejection &#; The exclusion of specific wavelengths from the system may be desired by researchers in some cases.

Some examples are hot mirrors (which reflect NIR or IR), cold mirrors (where shorter wavelengths are reflected while longer wavelengths are transmitted, commonly used in lamp assemblies) and order-sorting filters (where undesired wavelengths are reflected).

From an operational perspective, these are dichroic mirrors which are used for a different purpose. They are commonly employed at near-normal to normal incidence.

Angle of Incidence

The majority of mirrors are constructed to be used at a specific angle of incidence. Hot mirrors are usually employed at zero or near zero degrees AOI, whereas dichroic mirrors are often utilized at 45°.

The system&#;s optical design determines the AOI. Variations in polarization should be evaluated if the AOI is greater than approximately 25°.

Physical Environment

Durability requirements should be determined in the context of the physical surroundings in which the mirror will be used.

Temperature cycling is essential for space applications. For outdoor applications, humidity and temperature cycling, salt fog, abrasion resistance, and condensation may be factors to consider.

Radiative flux is where the filter is placed into a highly intense or energetic beam. This may result in its performance decreasing over time. In a protected laboratory instrument or air-conditioned laboratory spaces, the environmental requirements are smaller.

Wavelength Range

UV (180-400 nm) While traditional metal mirrors function throughout a broad range of wavelengths, different metals may have a superior performance over specific wavelength ranges. First-surface aluminum mirrors shielded with Magnesium Fluoride are usually recommended below 430 nm.

Omega has also created dielectric mirrors specific to this range that consist of intricate layers of transition metal oxides or lanthanide fluorides, silicon dioxide, and magnesium fluorides for the lower wavelengths.

Visible (400-700 nm) Visible mirrors are conventionally created from silver on the top side (the first surface) or the backside of a piece of glass. They are often protected with a plastic material that is not transmissive (for the back surface) or an additional layer of silicon dioxide (for the first-surface).

Dielectric mirrors consist of non-absorbing materials in alternating layers and are created to increase reflectance at specific angles and wavelengths while rejecting others. Enhanced metal mirrors utilize both metal and dielectric layers to maximize reflectivity.

NIR &#; IR (700 nm - 10 micron) In the NIR and IR, gold mirrors are frequently used. They absorb light in particular visible wavelengths but also offer a high reflectance (more than 95% above 1,500 nm).

A transparent conductive oxide mirror (for example ITO) is an alternative choice which provides high reflectivity at longer wavelengths and transparency at shorter (visible) wavelengths.

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Broadband - High reflectivity across a wavelength range that covers most of those mentioned earlier may sometimes be required by an application. These applications include hyperspectral imaging, astronomy, and solar photothermal or photovoltaics.

For the highest and flattest reflectivity response, dielectric mirrors can be created (the same as the Ultra Broadband Dielectric Mirror).

This information has been sourced, reviewed and adapted from materials provided by Omega Optical, Inc.

For more information on this source, please visit Omega Optical, Inc.

Optical Mirrors

Optical Mirrors

1. 

What is optical mirror?

The optical mirror realizes control beam and imaging by coating at least one side of optical substrates. Optical mirrors divide into plane mirrors and spherical mirrors. Flat mirrors are used for applications that deflect light as accurately as possible, especially for optical experiments. Concave mirrors as spherical mirrors are used to focus light at one point. The high reflection effect and other properties of optical mirrors depend on the wavelength, angle of incidence and polarization of light. Optical reflectors can be used in astronomy, metrology, aerospace and other optical systems, such as large space telescopes, large ground telescopes, early warning satellites, reconnaissance satellites, meteorological satellites, high-energy lasers, lidar systems, X-ray and vacuum ultraviolet telescopes, high resolution camera and other applications. CLZ Optical Co.,Ltd. can customize and produce broadband dielectric mirrors, metallic mirrors and concave mirrors according to your applications. At the same time, we also coat customized optical mirrors according to your requirements.

2.Optical mirrors sorted out according to geometrical shapes.

Plano mirrors

Plane mirrors are mirrors with a flat reflection surface. If an optical system can form a perfect image with random wide beam in any large space, namely, any concentric beam can still be kept as a concentric beam after passing through the system, then this system is an ideal optical system. Flat mirrors do not change the concentric nature of the light beam. They can improve the formation of the image, so flat mirrors are indispensable in an ideal optical system. Planar mirrors are suitable for interferometers, imaging systems, laser applications, collimators and other optical systems.

Concave mirrors are optical mirrors that bend inwards to focus light toward the inner focal point. When the parallel light shines on concave mirrors. It reflects on the focal point in front of the mirror through its reflection. The reflective surface is the concave surface. The focus is in front of optical mirrors. When the light source is in focus, the emitted light forms a parallel beam after being reflected. The imaging effect is also different, when the distance between the concave mirror and the object is different. Concave mirrors and optical lenses have many similar optical properties, especially in optical information processing, which can play an equivalent role. Concave mirrors are widely used in daily life, such as microscopes, astronomical telescopes, dentist mirrors, imaging systems, laser systems and other applications.

Aspherical mirrors(off-axis mirrors)

Off-axis parabolic mirrors are finite conjugate focusing mirrors that image at a set angle. They have fixed conjugate images and path length of the object. The light passing through a aspherical mirror can be parallel to the optical axis of the parallel light, completely converging to the focal point. The spherical aberration is zero by this time. Off-axis mirrors can ensure high resolution in the design of compact systems. They are a key element in spectrometers and astronomical optical instruments. Aspheric mirrors can be used in telescopes, astronomical telescopes and infrared spectroscopy systems.

3.How to choose the right optical mirrors?

As a manufacturer of optical mirrors, we recommend that firstly choose the right material and coating material according to the environment of optical mirrors and consider whether the adhesion between optical material and coating material is feasible. For example, the adhesion of gold and silver to optical glass is slightly worse than that of aluminum to optical glass. When selecting the coating layer, the main considerations are the reflectivity, laser damage threshold and mechanical properties (whether it is resistant to wear) of the film layer in different wavebands. Determine whether to use a flat mirror or a concave mirror according to the purpose of optical mirrors. In addition, the optical power or energy density on the mirror surface, polarization sensitivity, substrate flatness, and other related physical parameters need to be considered. CLZ Optical Co.,Ltd.  can not only provide you with custom optical mirrors that meet your applications, but also provide you with high-value suggestions based on years of production and supply experience. Welcome to consult.

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