5 Must-Have Features in a plano concave lens

Plano-Convex Lenses are the best choice for focusing parallel rays of light to a single point, or a single line in the case of cylindrical lenses. This lens can be used to focus, collect and collimate light. It is the most economical choice for demanding applications. The asymmetry of these lenses minimizes spherical aberration in situations where the object and image are located at unequal distance from the lens. The optimum case is where the object is placed at infinity (parallel rays entering lens) and the final image is a focused point. Although infinite conjugate ratio (object distance/image distance) is optimum, plano-convex lenses will still minimize spherical aberration up to approximately 5:1 conjugate ratio. For the best performance, the curved surface should face the largest object distance or the infinite conjugate to reduce spherical aberration.

Please visit our website for more information on this topic.

Bi-Convex Lenses are the best choice where the object and image are at equal or near equal distance from the lens. When the object and image distance are equal (1:1 magnification), not only is spherical aberration minimized, but also coma, distortion, and chromatic aberration are identically canceled due to the symmetry. Bi-convex lenses function similarly to plano-convex lenses in that they have a positive focal length, and focus parallel rays of light to a point. Both surface are spherical and have the same radius of curvature, thereby minimizing spherical aberration. As a guideline, bi-convex lenses perform within minimum aberration at conjugate ratios between 5:1 and 1:5. Outside this magnification range, plano-convex lenses are usually more suitable.

Plano-Concave Lenses are the best choice where object and image are at absolute conjugate ratios greater than 5:1 and less than 1:5 to reduce spherical aberration, coma, and distortion. Plano-Concave lenses bend parallel input rays so they diverge from one another on the output side of the lens and hence have a negative focal length. The spherical aberration of the Plano-Concave lenses is negative and can be used to balance aberrations created by other lenses. Similar to the Plano-Convex lenses, the curvature surface should face the largest object distance or the infinite conjugate (except when used with high-energy lasers where this should be reversed to eliminate the possibility of a virtual focus) to minimize spherical aberration.

Bi-Concave Lenses are the best choice where object and image are at absolute conjugate ratios closer to 1:1 with converging input beam. The output rays appear to be diverging from a virtual image located on the object side of the lens; the distance from this virtual point to the lens is known as the focal length. Similar to the Plano-Concave lenses, the Bi-concave lenses have negative focal lengths, thereby causing collimated incident light to diverge. Bi-Concave lenses have equal radius of curvature on both side of the lens. They are generally used to expand light or increase focal length in existing systems, such as beam expanders and projection systems.

Positive Meniscus Lenses are designed to minimize spherical aberration and are generally used in small f/number applications (f/number less than 2.5). The Positive Meniscus Lenses have a larger radius of curvature on the convex side, and a smaller radius of curvature on the concave side. They are thicker at the center compared to the edges. Positive meniscus can maintain the same angular resolution of the optical system while decreasing the focal length of the other lens, resulting a tighter focal spot size. A positive meniscus lens can be used to shorten the focal length and increase the numerical aperture of an optical system when paired with another lens. For the best performance, the curved surface should face the largest object distance or the infinite conjugate to reduce spherical aberration.

Spherical Lens Material Options

Lens Type N-BK7 UV Fused Silica CaF2 MgF2 ZnSe Crown/Flint Plano-Convex Bi-Convex Plano-Concave Bi-Concave Achromatic Doublet Cylindrical Lenses Plano-Convex Plano-Concave

Coatings

Optical coatings are generally applied as a combination of thin film layers on optical components to achieve desired reflection/transmission ratio. Important factors that affect this ratio include the material property used to fabricate the optics, the wavelength of the incident light, the angle of incidence light, and the polarization dependence. Coating can also be used to enhance performance and extend the lifetime of optical components, and can be deposited in a single layer or multiple layers, depending on the application. Newport&#;s multilayer coatings are incredibly hard and durable, with high resistance to scratch and stains.

Hongsheng supply professional and honest service.

Anti-Reflection Coating (AR coating)

Newport offers an extensive range of antireflection coatings covering the ultraviolet, visible, near infrared, and infrared regions. For most uncoated optics, approximately 4% of incident light is reflected at each surface, resulting significant losses in transmitted light level. Utilizing a thin film anti-reflection coating can improve the overall transmission, as well as minimizing stray light and back reflections throughout the system. The AR coating can also prevent the corresponding losses in image contrast and lens resolution caused by reflected ghost images superimposed on the desired image.

Newport offers three types of AR coating designs to choose from, the Single Layer Magnesium Fluoride AR coating, the Broadband Multilayer AR coating, and Laser Line AR V-coating. A single layer Magnesium Fluoride AR coating is the most common choice that offers extremely broad wavelength range at a reasonable price. It is standard on achromats and optional on our N-BK7 plano-convex spherical lenses and cylindrical lenses. Comparing to the uncoated surface, the MgF2 provides a significant improvement by reducing the reflectance to less than 1.5%. It works extremely well over a wide range of wavelengths (400 nm to 700 nm) at angles of incidence less than 15 degrees.

Broadband Multilayer AR coating improves the transmission efficiency of any lens, prism, beam-splitter, or windows. By reducing surface reflections over a wide range of wavelengths, both transmission and contrast can be improved. Different ranges of Broadband Multilayer AR coating can be selected, offering average reflectance less than 0.5% per surface. Coatings perform efficiently for multiple wavelengths and tunable laser, thereby eliminating the need for several sets of optics.

V-coatings offer the lowest reflectance for maximum transmission. With its high durability and high damage resistance, Laser line AR V-coating can be used at almost any UV-NIR wavelength with average reflectance less than 0.25% at each surface for a single wavelength. Valuable laser energy is efficiently transmitted through complex optical systems rather than loss to surface reflection and scattering. The trade off to its superior performance is the reduction in wavelength range. AR.33 for nm is available from stock on most Newport lenses. All other V-coating can be coated on a semi-custom basis.

Coating Wavelength Range
(nm) Reflectance Cost Features AR.10
Broadband
245&#;440 Ravg <0.5% Moderate Only available on UV fused silica lenses MgF2
Broadband
Broadband
400&#;700 Ravg <1.5% Low Available on achromats, KPX series, and Cylindrical lenses AR.14
430&#;700 Ravg <0.5% Moderate Best choice for broadband visible applications AR.15
Broadband
250&#;700 Ravg <1.5% Moderate Great choice for broadband UV to visible applications AR.16
Broadband
650&#; Ravg <0.5% Moderate Excellent for NIR laser diode applications AR.18
Broadband
&#; Ravg <0.5% Moderate Ideal for telecom laser diode applications V-Coat Multilayer, AR.27 Laser Line
532 Rmax <0.25% High Highest transmission at a single wavelength V-Coat Multilayer, AR.28 Laser Line
632.8 Rmax <0.25% High Highest transmission at a single wavelength AR.33
Laser Line
Rmax <0.25% Moderate Highest transmission at a single wavelength

Click to Enlarge
A Thorlabs technician measuring the irregularity of one of our singlets using a Zygo GPI-XP/D Interferometer.

Introduction
Thorlabs has a series of quality control procedures in order to ensure our singlets meet our standards and specifications. This starts with in-process inspections of the lens&#; imaging capabilities and ends with a final inspection of surface quality and dimensions. Specifications for particular products can be found in their linked documentation by clicking the  symbol. This tab will take you through the general process used to check for quality.

Singlet Quality Practices
In-process inspection begins once the singlet has been shaped to specifications. Focal length, surface irregularity, and surface power are checked, following sampling plan Level VI given in MIL-PRF-B (see below). These three specifications are imperative for proper imaging. Surface irregularity of parts is kept to below either a quarter wavelength or a half wavelength at 633 nm, depending on the material of the singlet. Below is a graph of over 200 batches of singlets with irregularity data of both their front and back sides.

At this point, some uncoated singlets will proceed to final inspection, while others will receive an antireflective (AR) coating. The application of optical coatings has its own in-process inspections. To ensure the AR coating is applied properly, we verify both reflectance and transmission performance by scanning witness pieces using spectrophotometry; the material of these 2 mm thick witness samples matches the other parts in the run. For reflectance verification, we use at least one witness sample for each coating run. Transmitting optics receive two AR coatings, one on each surface, so for the verification of transmission, we use one witness sample that is also coated on both of its sides. Large runs use multiple witness samples to ensure the uniformity across the deposition chamber. By testing coating performance during every run, variance over time is kept low. To see how coatings vary, see the table below.

Final inspection of both uncoated and AR-coated singlets includes a batch check of diameter and thickness and a 100% visual check to ensure that the surface quality, chamfer, and clear aperture meet our published specifications. While surface quality is cosmetic to a degree, scratches, digs, and other inclusions in the surface of a part can increase the chances of damage to the singlet when used with high-power sources. These inspections are done in a clean, dark room under lighting that meets the requirements of MIL-PRF-B. Inspection under a single light source in a dark room allows for inconsistencies in the glass to be located without being obscured by glare or reflections.

MIL-PRF-B: Performance Specifications for Optical Components
MIL-PRF-B is a document created by the U.S. Army Armament Research, Development and Engineering Center's Defense Quality and Standardization Office for the specifications covering how finished optical components should be manufactured, assembled, and inspected. While primarily for use in letting the military dictate how products they use can be incorporated into their equipment, these standards have been adopted by many optics manufacturers. To download a copy of the full document, click here.

For more plano concave lensinformation, please contact us. We will provide professional answers.