Lithium Fluoride(LiF) Meniscus Lenses

Lithium fluoride crystals have a wide transmission band (110 to 6,600 nm) and a high transmittance, especially in the vacuum UV band, which is the highest among known materials. Therefore, it is used as an optical material in the ultraviolet band. Lithium fluoride meniscus lenses are popular in many UV and IR applications.

Our company offer lithium fluoride meniscus lenses in various sizes and focal lengths.

Meniscus Lenses are concave-convex lenses that contain both positive and negative meniscus lenses. The Positive meniscus lenses are thicker in the middle than at the edges, allowing light to converge, and are designed to reduce tertiary spherical aberration. When they are used to converge a collimated beam, the convex side should face the light source to reduce spherical aberration.

The negative meniscus lenses are thinner in the middle than at the edges and are designed to reduce tertiary spherical aberration. When used to diffuse the beam, the convex side should face the beam to reduce spherical aberration.

The important parameters of meniscus lenses are: size, focal length, design wavelength, finish, face accuracy, eccentricity, substrate material and other attributes. Suitable parameters of meniscus lenses can be selected according to specific applications.

Lithium Fluoride (LiF) crystal is an excellent optical crystal material with a wide transmission band (110 to 6,600 nm) and high transmittance, especially Lithium Fluoride( LiF) crystal has the highest transmittance in the vacuum ultraviolet band among known materials, so it is used as a window material in the ultraviolet band. Lithium Fluoride( LiF ) crystals are also indispensable spectroscopic crystal components in electronic probes, fluorescence analyzers and large optical instruments.Lithium Fluoride( LiF) crystal has the highest transmittance in the vacuum ultraviolet band among known materials, so it is used as a window material in the ultraviolet band. In the infrared band,Lithium Fluoride( LiF )crystals have the lowest refractive index and are often used as window materials for infrared lasers and infrared night vision devices.

 Lithium fluoride is sensitive to thermal shock and is attacked by atmospheric moisture at temperatures above 400°C.

Coating refers to coating a transparent electrolyte film or metal film on the surface of the substrate material by physical or chemical methods. The purpose is to change the reflection and transmission characteristics of the material surface to reduce or increase the reflection, beam splitting, color separation, light filtering, polarization and other requirements.We can provide various optical coatings such as anti-reflective films, high-reflective films, spectral films, and metallic films. Broadband anti-reflective films are available for UV, visible, NIR and mid-infrared wavelengths.

DUV Grade

●Typical Size：φ50mm、φ100mm

●Maximum size：φ120mm

●Application Wavelength：110nm - 6.0μm

●Tansmittance：>70%@140nm; >90%@280nm; >90%@5μm

●Crystal Structure：Monocrystalline

●Internal transmittance：>99.0% @ 280nm（10mm thick sample）

●Average stress birefringence：≤10nm/cm@633nm

●25-125mW green light test without naked eye visible light column, bubbles, scattered particles, etc.

Transmittance test

●Inspection equipment

UV-Visible Spectrophotometer

  Strain gauges

  Laser pointer (green light, power 25-125mW)       

●Samples

  Lithium fluoride crystals, diameter not less than 20 ~ 50mm, thickness 10 ± 0.5 mm，through the polished surface finish to 80/50

●Test band

 190nm~1100nm，2.5μm~12μm

●Qualification requirements

  T>92%@280nm

Monocrystalline

●There are no visible grain boundaries or wicker-like stripes on the crystal surface when examined under naked eye daylight. 

Sub-crystal

●When examined under naked-eye daylight, there are willow stripes on the surface of the crystal with an area < 1/6 (end diameter), and the willow stripes are not visible after polishing . 

Polycrystalline

●When examined under naked-eye daylight, there are penetrating crystal boundary lines on the surface of the crystal, and the difference in the degree of light and darkness between the two sides of the crystal boundary lines is obvious. 

●N-BK7

    N-BK7 is the most commonly used optical glass for processing high quality optical components,, with excellent transmittance from visible to near-infrared wavelengths(350-2000nm), and has a wide range of applications in telescopes, lasers and other fields. N-BK7 is generally chosen when the additional benefits of UV fused silica (very good transmittance and low coefficient of thermal expansion in the UV band) are not required.

●UV fused silica

     UV fused silica has a high transmission from the UV to NIR  (185-2100nm).  In addition, UV fused silica has better uniformity and lower coefficient of thermal expansion than H-K9L (N-BK7), making it particularly suitable for high power laser and imaging applications.

●Calcium fluoride

    Due to its high transmittance and low refractive index within a wavelength of 180nm-8um, calcium fluoride is often used as windows and lenses in spectrometers and thermal imaging systems. In addition, it has good applications in excimer lasers because of its high laser damage threshold.

●Barium fluoride

    Barium fluoride have high transmittance from the 200nm-11um and they are resistant to stronger high-energy radiation. At the same time, barium fluoride has excellent scintillation properties and can be made into various infrared and ultraviolet optical components. However, the disadvantage of barium fluoride is that it is less resistant to water. When exposed to water, the performance degrades significantly at 500℃, but it can be used for applications up to 800℃ in a dry environment. At the same time, barium fluoride has excellent scintillation properties and can be made into various infrared and ultraviolet optical components.It should be noted that when handling barium fluoride material, gloves must be worn at all times and hands must be washed thoroughly after handling.

●Magnesium fluoride 

    Magnesium fluoride is ideal for applications in the wavelength range of 200nm-6um. Compared to other materials, magnesium fluoride is particularly durable in the deep UV and far IR wavelength ranges. Magnesium fluoride is a powerful material for resistance to chemical corrosion, laser damage, mechanical shock and thermal shock. It is harder than calcium fluoride crystals, but relatively soft compared to fused silica, and has a slight hydrolysis. It has a Nucleus hardness of 415 and a refractive index of 1.38.

●Zinc selenide 

    Zinc selenide has high transmittance in the 600nm-16um and is commonly used in thermal imaging, infrared imaging, and medical systems. Also, due to its low absorption, zinc selenide is particularly suitable for use in high-power CO2 lasers. It should be noted that zinc selenide is a relatively soft material (Nucleus hardness 120) and is easily scratched, so it is not recommended for use in harsh environments. Extra care should be taken when holding, and cleaning, pinching or wiping with even force, and it is best to wear gloves or rubber finger covers to prevent tarnishing. Cannot be held with tweezers or other tools.

●Silicon 

    Silicon is suitable for use in the NIR band from 1.2-8um.Because of its low 

    density, silicon is particularly suitable in applications where weight

    requirements are sensitive, especially in the 3-5um . Silicon has a Nucleus 

    hardness of 1150, which is harder than germanium and not as fragile as 

    germanium.It is not suitable for transmission applications in CO2 lasers 

    because of its strong absorption band at 9um.

●Germanium 

    Germanium is suitable for use in the near-infrared band of 2-16um and is well 

    suited for infrared lasers. Due to its high refractive index, minimal surface 

    curvature and low chromatic aberration, germanium does not usually require 

    correction in low power imaging systems. However, germanium is more 

    severely affected by temperature, and the transmittance decreases with

    increasing temperature; therefore, it can only be applied below 100°C. The 

    density of germanium (5.33 g/cm³) is taken into account when designing 

    systems with strict weight requirements. Germanium lenses feature a

    precision diamond lathe turned surface, a feature that makes them well suited

    for a variety of infrared applications, including thermal imaging systems, 

    infrared beam splitters, telemetry, and in the forward-looking infrared (FLIR)

    field.

●CVD ZnS 

    CVD ZnS is the only infrared optical material, other than diamond, that covers visible to long-wave infrared (LWIR), full wavelength and even microwave wavelengths, and is currently the most important LWIR window material. It can be used as windows and lenses for high-resolution thermal imaging systems, as well as for advanced military applications such as "tri-optical" windows and near-infrared laser/dual-color infrared composite windows.