Athermalized plastic lens

DETAILED DESCRIPTION The invention provides an athermalized plastic lens in which optothermal changes are balanced by refractive and diffractive optics, allowing the lens to achieve thermal performance characteristics similar to those of a glass lens, while being inexpensive, lightweight, and easily shaped.
When the lens includes an axicon, the lens provides equipment such as bar code scanners with an extended working range.
Preferred implementations of the invention may include one or more of the following.
The lens may include a refractive surface and a diffractive optical element, wherein optothermal changes due to the refractive surface counter optothermal changes due to the diffractive optical element.
The optothermal changes may cancel each other and include changes affecting the focal length of the lens.
The lens may include polycarbonate.
The lens may include acrylic.
The lens may include a net positive power.
The optothermal expansion coefficient of the refractive optical apparatus may be higher than an optothermal expansion coefficient of the diffractive optical apparatus.
The lens may include a diffractive optical element that is substantially smaller than the lens.
The first surface of the lens may provide substantially all of the negative power of the lens, and the second surface of the lens may provide substantially all of the positive power of the lens.
The surface of the lens may provide substantially all of the negative power of the lens and substantially all of the positive power of the lens.
The diffractive optical apparatus may include a diffractive optical element that is substantially spherical in average.
The surface of the lens may be substantially flat.
The refractive optical apparatus may be divided unevenly between first and second surfaces of the lens.
Substantially all of the diffractive optical apparatus may be disposed on one surface of the lens.
The diffractive optical apparatus may be divided substantially evenly between first and second surfaces of the lens