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Aspheric optics may now be fabricated by a computer-controlled diamond turning process, and they are becoming more readily available than in the past. But aspherics are difficult to polish accurately, and their cost becomes very high.
![two singlet lenses in zemax file two singlet lenses in zemax file](https://www.thorlabs.com/images/xlarge/3281-xl.jpg)
The high laser irradiance can easily damage the cement.Īnother option is the use of aspheric lenses, which can give excellent performance and which theoretically may be designed to eliminate spherical aberration completely. 121 (May 1989).) Copyright © 1989ĭoublet lenses used with lasers should generally be air-spaced, rather than cemented lenses. The calculations are relevant to lenses with 2 cm clear aperture and 10 cm focal length. Comparison of the amount of laser energy contained within a focal spot of specified radius, as a function of radius, for a singlet lens and a doublet lens. The cost of doublet lenses is higher than that of singlets, but the performance advantages may often be worth the added cost.įigure 5-4.
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A properly designed doublet lens can reduce the distortion of the wavefront as it passes through the lens, and it can also substantially reduce the effect of aberrations that increase the focal diameter above the diffraction limit. The simplest case is that of a two-element spherical lens (doublet). In such cases, the focal diameter may be reduced by use of multielement lenses or lenses with specially formed surfaces that are not spherical (aspheric lenses). Here, we will describe some of the choices available for optical elements for use with lasers, and discuss how they may improve the focusing for laser applications.Īs we saw, in many cases singlet lenses yield focal spots with diameter dominated by spherical aberration, rather than by diffraction. The discussion in that chapter was limited to single-element lenses (singlets) with spherical surfaces. Chapter 2 described the focusing properties of laser light, including the minimum diffraction-limited focal spot size and the effect of spherical aberration. Many laser applications require optical elements to focus or shape the beam. Ready, in Industrial Applications of Lasers (Second Edition), 1997 B.