Optical Properties and Design Considerations of Elliptical ...
Sep. 30, 2024
Optical Properties and Design Considerations of Elliptical ...
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When it comes to optical components, the name Hyperion Optics is synonymous with quality and innovation. With a wide range of products catering to various industries, one of their standout offerings is the elliptical flat mirror. In this blog, we will dive into the optical properties and design considerations of elliptical flat mirrors.
Understanding the basics of elliptical flat mirrors
Elliptical flat mirrors are a type of curved mirror that have a flat reflective surface. They are specially designed to have an elliptical shape rather than the traditional spherical or parabolic shape. This unique design allows for specific optical properties that make them ideal for certain applications.
Optical properties of elliptical flat mirrors
The elliptical shape of these mirrors offers distinct advantages in terms of focusing and collimating light. Due to the varying curvature across the surface, elliptical flat mirrors can achieve precise control over the reflected light. This characteristic makes them particularly useful in devices like telescopes, laser systems, and optical instruments where accurately directing and focusing light is crucial.
Another noteworthy optical property of these mirrors is their ability to correct spherical aberration. Spherical aberration is a common optical aberration that leads to blurred or distorted images. However, the design of elliptical flat mirrors can help minimize this aberration, resulting in clearer and sharper images.
Design considerations for elliptical flat mirrors
The design of elliptical flat mirrors involves several critical considerations to ensure optimal performance. One crucial factor is accurately determining the desired focal length. The focal length determines the distance at which incoming parallel light rays converge or diverge after reflection. It is essential to calculate the proper focal length to ensure the mirror meets the requirements of the intended application.
Additionally, the mirror's surface quality and reflectivity must be carefully controlled during the manufacturing process. Any imperfections or inconsistencies can impact the accuracy and efficiency of the mirror. Hyperion Optics excels in producing elliptical flat mirrors with exceptional surface quality and high reflectivity, ensuring optimal performance in various optical systems.
Applications of elliptical flat mirrors
The unique optical properties and design considerations of elliptical flat mirrors make them suitable for a wide range of applications. Here are a few notable uses:
Telescope systems
The reflectivity and accurate focusing capabilities of elliptical flat mirrors make them ideal for astronomical telescopes, enabling astronomers to observe distant objects with precision.
Laser systems
Elliptical flat mirrors play a crucial role in laser systems, helping to shape and direct laser beams for various industrial, medical, and research applications.
Optical instruments
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These mirrors are used in various optical instruments, such as cameras and microscopes, to achieve high-quality imaging and precise light control.
In conclusion, the optical properties of elliptical flat mirrors, such as their precise focusing capabilities and ability to correct optical aberrations, make them a valuable optical component for various applications. Understanding the design considerations and utilizing the expertise of companies like Hyperion Optics ensures the production of high-quality elliptical flat mirrors that meet the specific needs of different industries.
Optical mirror : a complete guide
Optical mirror : a complete guide
Magic mirror, on the wall who is the fairest one of all?.
While this guide wont provide answer to the Queens request in Disney Classic, Snow White and the seven Dwarfs, youll get a glimpse of the optical mirrors offer you can find on the market and select the best mirror that may fit your needs.
Optical mirror definition
An optical mirror is a precision optics component made of a optical polished substrate material and a high reflection coating. It can be of various shape and dimensions from less than a millimetre to several meters.
Optical mirrors are found in all the Photonics applications : in astronomy inside every telescope, in lasers by design, in vision equipment, and most of the optical assemblies systems. While their usage is quite simple : reflect the light, their range of application is wide, from UV to IR it can be used to transmit light with a change of direction, to focus light (for example in a Cassegrain telescope) or pumping light in a laser.
Types of optical mirrors
Shapes
Under the name mirror are many different types of precision optics that may be sorted as one of below type :
- Flat mirror, it is the simplest form similar to bathroon mirrors with higher precision.
- Spherical mirror, relates to mirrors with a radius of curvature either concave or convex.
- Aspherical mirror, more complex shape mirrors designed to attenuate optical aberration of reflected beam. For example : off-axis parabolic mirrors which are used to collimate a bean à 90° angle.
- Elliptical mirrors, are usually used at a 45° angle where they provide optimum circular clear aperture.
- Concave mirrors, the concave shape increase the reflection that can go more than 99% with an angle of incidence (AOI) of 0°.
- Freeform mirrors
- Prism mirrors, can be used either with outside reflection or inside reflection.
Substrate material
Mirrors substrate material are usually selected for their good shape resistance to temperatures changes, easiness of coating to bound with it and easiness of polishing to guaranty a good polishing shape. For some high power laser applications, substrate can also be the in LIDT constraint and therefore be selected carefully.
Below table shows most common substrate material for mirror blanks :
Substrate material Remarks Float Very cheap material that comes with acceptable polishing and flatness level for low requirement applications. Fused silica Resistant material with good optical machining properties, very commonly used. N-BK7 / H-K9L Most common optical glass, can be used for high requirement surface aspects. Zerodur Material almost non affected by low temperature, used mainly for space applications. Metals Polished aluminium or brass can be used for some high power laser applications, they are also easier to machined than glass type material and mechanicaly stronger. Plastics Plastic substrates are used in optical applications, but the difficulty to keep a good surface quality and the easy wearing of the parts due to outside environment limit its usage, while this remain the cheapest substrate material.Remark : for some applications where mirrors maybe of important dimensions and the part weight is an important constraint like in space industry for example, a lightening of the part can be done with a structuring of the back of the substrate.
Mirror coating
The most important part of an optical mirror is its high reflection coating, it is that coating that will be at the interface of incident beam and reflect it to an orthogonal direction.
Broadband dielectric coatings
With the improvement of vacuum deposition equipment in the last 30 years, layer of dielectric material can be deposit of substrates with a nanometric precision.
The material and the thickness used for each layer enable the trimming of a broadband of wavelengths where the incident beam will be reflected.
It has to be noted that the reflection of such mirror degrades as the AOI increases.
Metal-coated mirrors
Coating metal RefLection Indicative damage threshold Remarks Protected* silver Ravg>97.5% on the visible + NIR, Ravg>96% on MIR+FIR 3J/cm2 Very good reflection in the visible Protected* Aluminium Ravg>90% on the visible + NIR, Ravg>95% on MIR+FIR 0,3J/cm2 A MgF2 layer can be added to improve reflection in the UV (250 to 400nm) Protected* Gold Ravg>96% on the IR 2J/cm2 Without surprise the most expensive of the metal coatings.*Metal coatings are protected with SiO2 layers in order to avoid corrosion.
**An additional Chromium layer is usually added between the substrate and the metal to improve adhesion.
Laser mirrors
The critical specification for optical mirrors to be used in laser applications is their LIDT (Laser Induced Damage Threshold, or in short Damage Threshold).
This specification often measure in J/cm2 defines the energy that can be accepted by a surface area. (for reminder Watts are defining a power so values in Watts should be integrated in the time to be translated to energy).
LIDT should be defined with detail of the type of reference laser : CW or pulse laser, pulse duration, frequency and power.
Usually the coating is the contraint before the substrate, but for high power laser substrate can be wear by laser usage too. The lower the polishing and the higher of impurities in the material will bring to lower LIDT of the substrates.
Deformable mirrors
Deformable mirrors are active optics elements used in adaptative optics. They are typically made of an optical membrane, actuators and an electronic controller.
Their main usage is compensating aberrations, from example of the atmosphère in astronomy, of the eye in ophthalmology or of the cells water in biomicroscopy.
Main suppliers of deformable mirrors are ALPAO and ISP-System for high power applications.
Hot mirrors and cold mirrors
What are Hot mirrors and cold mirrors ? It is rather intuitive (while sometimes confusing) :
- Hot mirrors are reflecting the IR part of an incident beam and transmit the visible part of it.
- Cold mirrors are transmitting the IR part of an incident beam and reflect the visible part of it.
In a nutshell : Hot mirrors reflect warmth, cold mirrors reflect cold signal.
They are used to separate visible to IR parts of an optical signal.
Where to buy optical mirrors ?
Like most optical components optical mirrors are bought from precision optics manufacturers & distributors. It is rather common that the substrate and the coating are made in two different site, therefore buying mirror blank and doing the coating in-house or subcontracting it to other supplier is common practice.
Dont hesitate to contact SINOPTIX for your questions about optical mirrors or to request for a quote.
If you are looking for more details, kindly visit Optical Flat Mirror.
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