Several factors should be considered when selecting lenses best suited for particular laser applications. Once a lens material and coating are selected, a laser engineer decides whether the application needs a simple plano-convex, best form (see Note 1), or aspheric lens shape.
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Answering this question properly requires knowledge of the system’s laser beam parameters (wavelength, diameter, mode, or beam parameter product [BPP]); the lens parameters (diameter, thickness, surface radii); and the application’s requirements (focus diameter, power level, power density requirements, etc.). Once the laser and lens parameters are known, focused beam metrics can be calculated and used to determine if they will meet the application’s requirements.
High-speed diamond turning machines, magnetorheological finishing (MRF) machines, and CNC asphere polishing machines, along with increased competition in the industry, are making aspheric lenses more cost-effective and commonplace. But costs are still relatively high compared to simple plano-convex and best form lenses, so it’s crucial for laser engineers to choose the appropriate lens shape for the application.
Main laser beam types
To determine whether a lens is suitable for a specific laser application, it’s important to know the laser beam type and its parameters. Laser wavelength, power, and beam profile are the three key factors needed for proper analysis of a lens. Laser power and wavelength are easy parameters to identify for most laser systems, but the beam profile can be confusing to properly parameterize.
Theoretically, Gaussian profiles have an infinite diameter. It’s not realistic to use in a lens design or analysis program, so many engineers use a beam size of 1.5X the e-2 power point diameter. Some even use the Gaussian beam diameter at the e-2 power points, clipping ~13.5% of the beam’s energy. These diameters are often used to set the clear aperture of the lens system, too. To ensure best performance when designing aspheric lenses, a beam diameter of 1.7X the e-2 power point diameter should be used. During the design phase, most analysis types trace rays through the lens and analyze the rays at the image plane, so it is important that the rays cover the full beam diameter. There are exceptions to this rule, but for most cases, 1.5–1.7X the e-2 power points will provide adequate results.
Fiber tip diameter and fiber numerical aperture are very important when designing and analyzing lenses for multimode fiber laser beams. If a manufacturer claims a full beam diameter of X mm after collimation, then X is the value that should be used to analyze a focusing lens. This specification should also be verified for the same reasons when designing collimator lenses.
If you don’t know the laser beam parameters, then at a minimum, a beam size that fits the full aperture of the lens should be used. For example, if using a 30 mm lens with a usable clear aperture of 26 mm, a beam size of 26 mm should be used to analyze lens performance.
Lens and beam analysis types
Spherical aberration is traditionally one of the main methods used to analyze single lenses in monochromatic systems (lasers, in this case). There are two types of spherical aberrations: longitudinal (LSA) and transverse (TSA)—these terms are used to differentiate between a ray error that’s transverse to the central axis and measured at the image plane, and a ray that intersects the central axis at some point before or after the image plane. Figure 1 illustrates these two measurements. Typically, only one of these parameters is used to evaluate a lens. Calculating this parameter is simple with Snell’s Law for refracting a ray through the lens, as well as simple trigonometry to trace the ray to the image plane.
As demonstrated in Figure 2, the edge ray intercept (+10 mm from the center of our lens) strikes the image plane at -0.6 mm. The minus sign indicates that the ray strikes the image plane below the central axis, and rays starting at ±3 mm strike the image plane close to zero. But for input heights greater than this, the deviation at the image plane increases exponentially.
Many differences exist between brands of contact lenses which impact lens optics. The optics of the contact lens is determined by several factors including lens material1 and design2. Optics is the way in which the refraction of light is managed to maximize vision for the contact lens wearer3. Contact lenses with aspheric optics may provide enhanced vision for many wearers.
What are Aspheric Optics?
Regular spherical contact lenses have an even curvature across the entire lens surface; in contrast, aspheric lenses have varying curvatures across the surface changing from lens center to lens edge. Aspheric lenses are used to minimize optical aberrations within the human eye4. Parts of the eye including the tear film, cornea, and crystalline lens can induce aberrations. Contact lenses deliberately induce a level of aberration in the lens that is inversely equal to the amount of natural spherical aberration inherent in the eye to help give clear, crisp and sharp vision3.
If you are looking for more details, kindly visit Aspheric Lens.
Multifocal Lens Wearers
Lens design and the patient’s pupil size are key to multifocal success. The Biofinity Multifocal has a center-distance (D) lens, which transitions through an aspheric intermediate to an outer near zone for the dominant eye. A center-near (N) lens which transitions through an aspheric intermediate to a spherical peripheral distance zone, is placed on the nondominant eye7. When compared with monovision, multifocal contact lens correction provides great vision without compromising depth perception, with continuous adaptation over the first 15 days of wear8.
Computer Users
Biofinity Energys® and MyDay Energys® are designed for digital device users. DigitalBoost™ technology is an innovative single vision aspheric lens design that delivers a +0.3D digital boost, which helps reduce eye tiredness associated with digital eye strain. Study data demonstrates that devices users have a smaller change in accommodative micro-fluctuations (AMF) when wearing this DigitalBoost™ technology, suggesting reduced ciliary muscle stress when reading on a smartphone or other devices at a close distance9.
Which CooperVision® Lenses are Available with Aspheric Optics?
The CooperVision® portfolio of monthly, bi-weekly, and daily lenses are designed with aspheric optics. The Aberration Neutralizing System™ utilizes aspheric optics to neutralize the aberrations from the eye in the Biofinity®, Avaira Vitality™ and MyDay® families. clariti® 1 day contact lenses also offer an aspheric optical design.
Biofinity® & Biofinity® XR
The Biofinity® family of lenses are monthly replacement lenses designed with aspheric optics and combined with Aquaform® Technology to gives incredible end of day comfort for your patients. Biofinity® is the most prescribed monthly replacement on the market10 and will fit almost every patient with over 240,000 unique prescriptions11,12.
Avaira Vitality™
Avaira Vitality™ lenses are highly breathable, bi-weekly replacement lenses designed with the same Aberration Neutralizing System™ as the Biofinity® family. The technology of a Avaira Vitality™ retains the lens surface moist all day, but also blocks transmission of 90% of UVA and 99% of UVB light*.
MyDay®
MyDay® daily disposable are designed with the same Aberration Neutralizing System™ to provide optimal vision combined with UV blocking* and incredible comfort all day long. The MyDay® daily disposable is available in sphere, toric, and multifocal options.
clariti® 1 day
clariti® 1 day contact lenses also offer aspheric optics and provide silicone hydrogel at a comparable price to some hydrogel lenses13†. In addition, clariti® 1 day contact lenses feature high water content (56%), UVA and UVB blocker*, and a low modulus of 0.5 MPa, comparable with other hydrogel lenses. The clariti family also offers sphere, toric and multifocal options and is an ideal entry-level contact lens for new wearers14.
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