A Guide to Choosing the Correct Mirror in Optical Systems

Mirrors are components found throughout optical systems. They can be utilized to focus and steer light, reject particular wavelengths, and combine wavelengths in imaging and additional applications. Several factors should be considered when selecting a mirror.

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Materials

Metallic Mirrors provide a combination of absorbance and reflectance (and transmittance if adequately thin).

They can be employed as neutral density filters, neutral beamsplitters, or wide wavelength-range reflectors. The kind of metal utilized defines its spectral features. The application of these mirrors is mostly outside of angle-of-incidence.

Dielectric Mirrors comprise of delicate layers of non-absorbing materials (normally fluorides and oxides), which vary in refractive index. The composition and thickness of the layers are configured to create reflectance or transmittance in wavelength ranges specified by the application or customer.

These materials absorb little to no light, so dielectric mirrors can frequently be employed as dichroic mirrors (where light of certain colors travels through while reflecting the light of different). Both the angle-of-incidence and the wavelength range must be determined at the design stage.

Function

Imaging - Needs a flatness of λ/10 or better to reduce image distortion. Beam-steering, non-imaging applications do not demand strict specifications on flatness.

Wavelength combining - Dielectric dichroic mirrors are utilized to bring together different laser beams onto one axis. This application requires a flatness of 1/4λ per inch or more.

Wavelength splitting - Desired wavelengths can also be reflected with the use of dielectric dichroic mirrors. Applications involve hot-mirrors that exclude IR and NIR light, transmitting emission light, and reflecting excitation light while identifying alternate wavelength bands with several detectors.

The reflecting and transmitting wavelengths must be thoroughly defined for this kind of application. These are normally utilized at a 45° angle of incidence.

Wavelength rejection - A researcher may want to exclude particular wavelengths from the system in some cases.

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

From a functional perspective, these are dichroic mirrors which are applied in a different respect. They are normally used at near-normal to normal incidence.

Angle of Incidence

Mirrors are mostly configured to be employed at a particular angle of incidence. Hot mirrors are normally utilized at zero or near zero degrees AOI, whereas dichroic mirrors are frequently used at 45°.

The AOI is determined by the optical design of the system. Differences in polarization should be explored when the AOI is more than around 25°. Read the article on angles of incidence to gain more information.

Physical Environment

The requirements for durability should be established according to the physical environment of which the mirror will be exposed.

Temperature cycling is critical for space applications. For applications in the outdoors, temperature and humidity cycling, abrasion resistance, condensation, and salt fog may be considerations.

Radiative flux (when the filter is put into a highly energetic or intense beam) may lead to a decline in performance over time. There are limited environmental requirements in air-conditioned laboratory spaces or a protected laboratory instrument.

Wavelength Range

UV (180-400 nm) While conventional metal mirrors perform across a wide range of wavelengths, other metals may work better over particular wavelength ranges. First-surface aluminum mirrors protected with Magnesium Fluoride are normally suggested below 430 nm.

Omega has additionally produced dielectric mirrors tailored to this range that comprise of delicate layers of transition metal oxides or silicon dioxide, magnesium fluoride, and lanthanide fluorides for the lower wavelengths.

Visible (400-700 nm) Visible mirrors are traditionally made from silver on the top side (the first-surface) or the backside of a piece of glass. They are frequently shielded with an extra layer of silicon dioxide (for the first-surface) or a plastic material that is not transmissive (for the back surface).

Dielectric mirrors comprise of non-absorbing materials in alternating layers and are produced to enhance reflectance at particular wavelengths and angles while excluding others. Enhanced metal mirrors use both dielectric and metal layers to optimize reflectivity.

NIR &#; IR (700 nm - 10 micron) In the IR and NIR, gold mirrors are commonly employed, which absorb light in certain visible wavelengths but also contain a high reflectance (greater than 95% above 1,500 nm).

A different choice is a transparent conductive oxide mirror (such as ITO) which offers transparency at shorter (visible) wavelengths with high reflectivity at longer wavelengths.

Broadband An application may sometimes need high reflectivity across a wavelength range that covers many of those mentioned earlier. These applications are astronomy, solar photothermal or photovoltaics, and hyperspectral imaging.

For the flattest and highest reflectivity response, dielectric mirrors can be produced (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.

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.

If you are looking for more details, kindly visit Optical Mirrors manufacturer.

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.

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.

For more information, please visit Optical Mirrors exporter.