Hybrid plastic aspheres--one of those optical-engineering essentials?

Nashua, NH--I just wanted to make a mention of a product I wish I'd had available back when I was an optical engineer fifteen years ago.

Back then, all laser diodes emitted either red or IR; any blue laser found in an optics lab would be either He-Cd or argon-ion; and the off-the-shelf simple lenses commonly available to engineers for use in the visible were usually either glass singlets or achromatic doublets.

These days, one can buy UV or blue-emitting diode lasers; small UV or blue lasers of other sorts, such as OPSL (optically pumped semiconductor); tiny green doubled YAG lasers in the form of laser pointers; and off the shelf plastic hybrid aspheric broadband lenses for under a hundred dollars. (It's the lenses I wanted to talk about.)

Diffractive-refractive plastic aspheres
The hybrid plastic aspheres, made by Edmund Optics (Barrington, NJ) and having the "TechSpec" name, are color-corrected molded aspheric-diffractive lenses that Edmund says are diffraction-limited. The refractive-asphere portion removes spherical aberration, while the diffractive surface has a negative optical dispersion, minimizing chromatic aberration. Edmund notes that the lenses are "ideally suited for imaging and ophthalmic applications, and for use with tunable laser and broadband or multispectral illumination sources."

Comparing the lenses to conventional aspherized achromats (which are also corrected for spherical, and also mostly corrected for color), Edmund says that since "the plastic hybrid aspheric lenses are an all-plastic, monolithic design, they are much lighter weight than comparable aspherized achromats. They are also available in higher numerical aperture designs than the aspherized achromats. These lenses are limited by the inherent diffraction efficiency of the aspheric surface, so they yield a lower overall transmission than comparable aspherized achromats."

The TechSpec lenses come in twenty different coated and uncoated versions: 12-mm-diameter lenses with focal lengths from 9 to 24 mm, and 25-mm-diameter lenses with focal lengths from 20 to 50 mm.

I think it's the high numerical apertures (up to 0.67 for the 12 mm lenses, and up to 0.63 for the 25 mm lenses) with high imaging quality across the visible spectrum, combined with the relatively large diameters, that would have most made my day as an optical engineer setting up experiments in the lab. But while every dog has its day, this dog is now a journalist, so there won't be any hybrid plastic aspheres for me.


--John Wallace

Laser Focus World


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