Mirrors
Optical Mirrors are used in optical instruments for light reflection. They have a smooth, highly polished surface to reflect light. The reflecting surfaces is usually treated with reflective optical coating materials.
The reflective coatings will vary depending on the application and the required wavelength range. Coatings include aluminium, silver, gold and dielectric. Optical mirrors can be made from a variety of materials depending on the application.
Some materials include borosilicate glass (BK7); copper, used in high-power applications because of its high thermal conductivity; fused silica is suitable for use with moderately-powered lasers or changing environmental conditions; nickel for applications where resistance to both thermal and physical damage is required.
Flat Mirror
A plane mirror is a mirror with a flat (planar) reflective surface. For light rays striking a plane mirror, the angle of reflection equals the angle of incidence. The angle of the incidence is the angle between the incident ray and the surface normal (an imaginary line perpendicular to the surface). Therefore, the angle of reflection is the angle between the reflected ray and the normal and a collimated beam of light does not spread out after reflection from a plane mirror, except for diffraction effects.
Convex
A convex mirror is a spherical reflecting surface in which its bulging side faces the light source. There are numerous uses of the convex mirror which is also referred to as the fish-eye mirror by automobile enthusiasts and diverging mirror by physicists. The term ‘diverging mirror’ is based on its behaviour of making rays diverge upon reflection. This means that when a parallel light ray hits a convex mirror, it reflects outwards and travels directly away from an imaginary focal point.
Silver Mirror
Silver coated mirrors offer the highest reflectance in the visible-NIR spectrum of any metallic mirror, while also offering high reflectance in the IR. In order to protect them from oxidation, these mirrors have a durable SiO2 overcoat with an approximate thickness of 100 nm. Though the overcoat helps to protect silver from tarnishing, high humidity environments should be avoided.
Concave Mirror
A concave mirror is a mirror that is curved inward in the middle. It might help you to remember this if you think that when you look in a concave mirror, it looks like you are looking into a cave. The equation we use when dealing with concave mirrors is called the mirror equation. This equation is used to determine how far away an object is from the mirror (image distance) and how large or small the object is (object size.)
The law of reflection is still true for concave mirrors but because the mirror's surface is curved, the angle at which the light hits the surface, also known as the incident angle, is different depending on which part of the mirror the light hits.
Aluminum Mirrors
Aluminium and aluminium alloys can easily replace most glass mirrors, and are popular for making lightweight scanning mirrors and galvo mirrors or where overall weight is an issue such as in aerospace, defence and medical optical systems. Customers working to optimise SWaP (size, weight and power) should be aware of aluminium mirrors.
Aluminium based mirrors are a good alternative to Silicon mirrors in moving mirror or flying optics applications as aluminium is far easier to engineer into complex shapes. Further weight saving is possible by using ribbed and pocketed designs on the rear of the mirrors.
Gold Mirror
Gold coatings have excellent and consistent reflectivity in the infrared and good reflectivity in the visible regions. Protected gold coatings offer a durable finish that provide 96% reflectivity. Protected gold helps to protect the mirror from damage and makes it easier to clean.
Unprotected gold coatings provide a higher reflectance than protected gold but they are much more delicate. These mirrors can be used in applications where the polarization state needs to be strictly maintained or to prevent dispersion due to the overcoat of protected gold mirrors.