Achromatic Doublet Lenses

An Achromatic Doublet Lens is a bulk optical element, often consisting of two cemented concave and convex single lenses made from different optical glass materials of compensating dispersion properties. Achromatic doublet lens has the distinctive feature of inducing minimizing chromatic aberration in an optical module (Chromatic aberration is the shift of focal lens resulting from different wavelengths when the incident light source consists of multi-colored radiations, the consequence is blurring of spots on the focal plane). It is also possible to correct the spherical and on-axis comatic aberration using achromatic doublet lenses through appropriate planning. And for the most part, a single achromatic doublet is optimized for infinite conjugate ratio, whilst achromatic doublet lenses in pairs work fine at finite conjugates.

In general, the construction of an achromatic doublet is simple: a lens made from materials of low refraction, high chromatic dispersion (often times Crown Glass) is cemented to another lens made from large refraction, low dispersion optical materials (often times Flint Glass). These two glasses cancel out each other dispersion to deliver a constant focal length over a certain optical spectrum. In the meantime, spherical aberrations and coma on the optical axis could also be attenuated without reducing the numerical aperture, leading to higher power throughput and smaller spot diameter. Lens shape varies with the fact of whether the doublet is positive or negative. A positive achromatic doublet lens has a positive focal length, combing one double-convex lens, and one convex-concave lens with the same radii of curvature at the interface into a biconvex lens. A negative achromatic doublet lens diverges collimated light according to its virtual focus on the object side of the lens and is composed of a double concave lens and a plano-convex lens cemented together so that its overall shape is a plano-concave diverging lens. There are also Achromatic triplet lenses which consist of three cemented elements and are shaped like a biconvex lens in total.

Hangzhou Shalom EO offers various custom 1.0mm to 300mm diameter Achromatic Doublet Lenses including positive achromatic doublet, negative achromatic doublet, achromatic triplet lens, and aspheric achromatic lens. Our achromatic lenses are made from Flint glass (e.g CDGM H-ZFLA, SHOTT N-SF5, etc.) and Crown Glass (e.g. CDGM H-ZBAF52, SCHOTT N-BK7, etc.), and we accept the designation of certain glass codes from our clients. The achromatic doublet lenses provide independence of wavelength over the visible spectrum, and are excellent for uses of multi-color white light imaging/illumination (e.g. image inversion, image magnification), laser light modulation, and NA conversion, while other working wavelength ranges could also be customized. For high precision visible uses, we recommend our aspheric achromatic lens, manufacturing using the single point diamond turning technique (SPDT) that combines the advantage of ultra-low spherical aberration from its aspherical front profile and the advantage of high chromatic resolution from its achromatic design. Custom coating options include uncoated substrates, Broadband Anti-reflection (BBAR) coatings that cut to a significant extent the reflection (average reflection below 0.5%) over a certain wavelength range, and V-coating which provides higher transmission (average reflection below 0.25%) at a narrower range, and low-cost MgF2 AR coatings (average reflection below 1.5%). The different transmission wavelength ranges of the coatings could be selected according to your requirements.