Common Lenses

Plano Convex Lenses

The Plano Convex lens is the standard focusing optical elements. It is the most cost efficient choice in large f-number systems (f#>10) which are diffraction limited and in smaller f-number systems where less than optimal spot size and spherical aberration can be tolerated.

Plano Concave Lenses

The Plano Concave lens is the simplest negative lens. This shape is commonly used for low index materials (n<2) to expand light beams or to increase system focal lengths. The curved surface facing the collimated beam or the longest conjugate distance produces minimal spherical aberration.

Bi-Convex Lenses

The Bi-Convex lens is used as a focusing element in low f-number systems (f#< 2.5) and in intermediate f-number systems (2.5>f#<10) where minimizing aberrations and /or material path length (i.e. absorption) make it preferable to the Plano Convex design. Because of the symmetry of the surfaces (R1=R2) in this lens, image distortion effects of each surface tend to cancel each other at equal or near equal conjugate distances.

Bi-Concave Lenses

The Bi-Concave negative lens is used to expand light beams or to increase focal lengths particularly where minimal material path length to reduce absorption is desirable.

Positive Meniscus Lenses

These lenses are designed to minimize spherical aberration and are usually used in small f-number applications (f#<2.5). For 2.5<f#10, meniscus lenses can also improve image quality and reduce spot size and are recommended if these are critical.

Negative Meniscus Lenses

Negative Meniscus lenses are offered as an alternative to other negative lenses and are particularly appropriate for the high index IR materials. They are commonly used in beam expanding applications where minimal spherical aberration is desired.

Plane Parallel Windows

Circular windows of a wide variety of transmissive materials are used in numerous optical applications. The optical faces of these windows are parallel to each other. The “parallelism” specification listed is a maximum angular deviation between the two surfaces. In other words, a window listed with a parallelism of minutes will have an angular deviation between the two optical surfaces of 3 arc minutes or less.

Plano Mirrors

Plano Mirrors are total reflectors used in laser cavities and in beam steering and path-folding applications. A plane mirror has one flat, highly polished surface which is coated either with a broadband coating such as chromium-gold, protected silver or protected aluminum (aluminum with a silicon monoxide overcoat) or with a silver dielectric multi-layer coating enhanced at some wavelength. The second side of a plano mirror is fine ground.

Plano Concave Mirrors

Plano Concave mirrors are used as total reflectors in laser cavities and in a variety of other precision optical applications. Standard substrates are single crystal silicon (highest thermal conductivity), and Pyrex (low co-efficient of thermal expansion).

Brewster Angle Window

A window positioned at Brewster’s angle with respect to incoming radiation does not reflect radiation polarized parallel to the plane of incidence (p-polarized) but it will reflect come of the s-polarized radiation. The reflected radiation is entirely s-polarized (polarized perpendicular to the plane of incidence).

Brewster angle windows are used in laser cavities to produce polarized output. The output is polarized in the plane formed by the cavity axis and the direction normal to the window. The window is used uncoated which increases its life in contact with a laser medium discharge.

These windows are also used as polarizers either in reflection or transmission. In refection, some of the useful energy is lost but output is 100% polarized by one surface. In transmission, 100% of the energy in the desired polarization is retained (neglecting absorption of the material) but a series of window surfaces are needed to produce a highly polarized output.

Wedged Windows

Wedge windows offer a simple solution to some common problems encountered in certain applications with plane parallel windows. Rather than specify a parallelism value as a maximum angular deviation between the two surfaces of the window, wedged windows specify both a maximum and a minimum value for wedge angle. In addition, the nominal angular values are larger, because the purpose of these windows is to deliberately provide a noticeable angular deviation between the first and second surfaces of the window. In applications where fringing between parallel surfaces or coaxial reflections from the first and second surfaces are a problem, wedged windows offer a simple solution. They are also useful in transmission as wedge prisms.

Plano Partial Reflectors

Partial Reflectors are used in numerous laser and other optical applications in the UV, VIS, and IR regions of the spectrum. Partial reflectors utilize one surface is most often coated to produce the desired performance but may be uncoated. In this case the reflectivity is determined by the substrate index of refraction. The other surface is always anti-reflection coated for high index materials (ZnSe, Ge, ZnS) and is often AR coated even for low index materials (Fused Silica, CaF2).

A partial reflector (or output coupler) becomes a beamsplitter when used in non-normal incidence.