Technical Note:
Achromatic Doublet Lenses

  • Superior performance to singlet lenses
  • Nearly constant focal length across the visible spectrum
  • Far superior off-axis performance
  • Multi-layer or single-layer AR coatings
  • Standard diameters and focal lengths interchange with our singlet lenses

Visible Achromatic Doublet Lenses have significantly better optical performance than singlet lenses in visible imaging and laser beam manipulation applications. Our achromats have precise specifications and tolerances for uncompromising image quality. Computer optimized designs minimize aberrations, yielding smaller focused spot sizes. Our achromats can be substituted for our singlet lenses, allowing complex experiments to be verified with simple lenses and later improved with achromats.

An achromat consists of a positive low-index crown glass lens element cemented to a negative high-index flint glass lens element. The elements are chosen so as to cancel chromatic aberration at two well separated wavelengths; usually in the blue and red region of the spectrum. Focal length is constant at those two wavelengths and focal length shifts are virtually eliminated across the visible wavelengths. All of our achromats are available with a single-layer MgF2 broadband antireflection coating to increase transmission throughout the visible spectrum. Our precision achromats are also available with a multi-layer anti-reflection coating (AR.14) for superior transmission efficiency in the broadband visible range.

These lenses are computer designed to effectively minimize spherical aberration and coma when operating at an infinite conjugate ratio. Unlike singlet lenses, this results in a constant focal length independent of aperture and far better off-axis performance. Freedom from spherical aberration and coma means that achromats are superior to singlet lenses for monochromatic applications at any visible wavelength. At 1064 nm the focal length of a typical achromat increases by approximately 0.75%. An achromat will not be diffraction limited at 1064 nm but performance will still be superior to a singlet lens.

For image relay and optical processing applications, a specially designed symmetric achromatic triplet lens optimized for 1:1 conjugate ratio is available ( PAC076 ). This lens is diffraction limited at 488, 514.5, and 632.8 nm.

Standard inch diameters allow for mounting in many Newport holders when building laboratory experiments. Our achromats can be substituted for our singlet lenses, allowing complex experiments to be verified with simple lenses and later improved with achromats.