Fused Silica(UVFS)Double-Concave Lenses - UM OPTICS

Fused silica is typically used for applications from the ultraviolet (UV) to the near infrared (NIR). Its high transmittance, good heat resistance, and excellent environmental durability make it suitable for use in laser equipment, emission and detection protection equipment, and imaging systems in the UV spectrum.

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Our company offer fused silica biconcave lenses in various sizes and focal lengths.

Biconcave lenses have a negative focal length and consist of two concave surfaces of equal curvature, which can disperse a parallel incident beam outward and are commonly used for beam spreading, collimation, projection and focal length expansion of optical systems. Biconcave lenses disperse a collimated beam to an imaginary focal point and are commonly used in Galilean beam expanders.

The important parameters of biconcave lenses are: size, focal length, design wavelength, finish, face accuracy, eccentricity, substrate material and other attributes. Suitable parameters of biconcave lenses can be selected according to specific applications. Natural quartz, also called quartz glass, which is synthesized by a number of processes to form fused silica, is the most common and most important material for optical components. Compared to natural quartz, synthesized fused silica has a higher radiometric hardness and higher absolute transmittance. This enables it to have excellent optical properties in the ultraviolet, visible, near-infrared, and infrared bands, as well as in the terahertz band.

Compared to K9 and bk7 materials, fused silica offers higher thermal properties and purity, as well as excellent environmental durability, making it more suitable for use in harsh applications.

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.

Natural quartz, also called quartz glass, is synthesized by a number of processes to form fused silica (Fused silica). It is the most common and most important material for optical components. Compared to natural quartz, synthetic fused silica has a higher radiometric hardness and higher absolute transmittance. Therefore, it is able to have good optical properties in the UV, visible, near IR, IR bands, and terahertz bands.

According to the transmittance of different bands, quartz transmittance is classified as follows.

JGS1  Far Ultraviolet Optical Quartz Glass 185- nm 

JGS2  Ultraviolet Optical Quartz Glass 220- nm 

JGS3  Infrared Optical Quartz Glass 260- nm

Transmission spectroscopy:

These two images show the transmittance of fused silica and natural quartz respectively.

The above graph shows the transmission spectra of several commercial fused silica models, and it can be seen that they all have high transmission at 185-nm. Depending on the model, the transmission spectra vary slightly, for example, some models still have more than 80% transmission in the deep UV band at 165nm, some models have an absorption peak near nm, and some models can maintain more than 80% transmission until nm.

The chart below shows the transmission spectrum of natural quartz, which is only guaranteed to have high transmission from 270nm to nm and much lower transmission in the UV band than fused silica. The reflectance of natural and fused quartz is basically the same, both are less than <10%. In the near UV band it is close to 10%, and at any time the wavelength increases, the quartz reflectance slowly decreases to approximately 6% in the near IR band.

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-nm), 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-nm).  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 

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    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 , 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 applications such as "tri-optical" windows and near-infrared laser/dual-color infrared composite windows.

Lenses are integral to optics, shaping how we perceive and engage with the world. Achromatic lenses, a longstanding fixture in optical technology, address chromatic aberration, a common optical flaw causing color fringing. Among these, color-corrected achromatic lenses specialize in enhancing this correction. This article delves into the advantages and drawbacks of employing color-corrected achromatic lenses.

Production Process of Achromatic Lenses

Achromatic lenses, crucial for color correction, are crafted by combining concave and convex lens elements of different dispersions. This results in an achromatic doublet, the most common type, although triplet lenses are also used. Leading manufacturers like Shanghai Optics follow a methodical process:

• Component Lens Formation: Different optical glasses are melted, stirred, and poured into molds to form lenses based on the desired correction.
• Achromat Assembly: Individual lenses are aligned and cemented to create an achromat capable of effectively correcting chromatic aberration.
• Lens Integration: The achromat is incorporated into lens assemblies for various applications, such as microscope objectives and telescopes.

Manufacturers may tailor the lens design, sometimes adding aspheric properties to address spherical aberration along with chromatic aberration. Shanghai Optics, adhering to ISO standards, utilizes advanced metrology equipment to ensure precise achromatic lens performance, meeting clients’ specifications reliably.

Advantages of Color-Corrected Achromatic Lenses

• Compact and Lightweight: Ideal for portable devices, these lenses are more compact and lighter than comparable designs, meeting size and weight constraints.
• Versatility: Applicable in various optical systems, including cameras, microscopes, telescopes, and eyeglasses, these lenses are valuable across photography, astronomy, and microscopy.
• Enhanced Image Quality: Meticulously combining different lens elements, these lenses significantly improve image quality by eliminating distracting color fringing associated with chromatic aberration.
• Cost-Effective Production: While not eliminating chromatic aberration entirely, these lenses are often more cost-effective than specialized designs like apochromatic lenses, making them accessible to a broader user base.
• Wider Aperture: Beneficial in low-light conditions or for achieving a shallow depth of field, color-corrected achromatic lenses often allow wider apertures. The absence of chromatic aberration ensures sharp, distortion-free images at these wider apertures.

Disadvantages of Color-Corrected Achromatic Lenses

• Weight and Size Trade-offs: Despite being more compact and lighter than some lenses, color-corrected achromatic lenses may still be bulkier and heavier than basic single-element lenses, posing challenges in situations prioritizing minimized equipment size and weight.
• Limited Correction: Despite their proficiency in reducing chromatic aberration, color-corrected achromatic lenses may exhibit residual aberration, particularly at the image field edges.
• Limited Aperture Control: While offering wider apertures, these lenses may lack the same aperture control as specialized lenses, impacting creative options for photographers and cinematographers.
• Reduced Light Transmission: Achromatic lenses, including color-corrected versions, may slightly diminish light transmission compared to simpler designs, a consideration in applications where maximizing light throughput is crucial.
• Complex Design: Achieving effective color correction demands intricate and precise optical designs, leading to more challenging and expensive manufacturing and maintenance processes.

Color-corrected achromatic lenses significantly advance optics by effectively combating chromatic aberration. Their advantages, including improved image quality, wider apertures, versatility, and cost-effectiveness, make them popular in various optical systems. However, it’s vital to consider their limitations—limited correction, complex design, reduced light transmission, aperture control, and weight/size trade-offs—when selecting lenses for specific applications. Ultimately, lens choice depends on the optical system’s needs and acceptable trade-offs in cost, size, and performance. While color-corrected achromatic lenses are valuable, careful consideration of their pros and cons is essential for informed decisions and desired optical outcomes.

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