Beam expansion - A unique system made of aspheric lenses

Conventional laser beam expander can only be adapted with great effort, are relatively large and only suitable for a certain wavelength. The world’s first use of an aspheric lens for laser beam expansion opens completely new possibilities. Spherical aberrations are corrected and an afocal system for large input beam diameters is realized. The aspheric beam expansion lens reduces the system size up to 50% compared to currently available optical components on the market. The asphericon laser beam expander system covers a wide wavelength spectrum. Design wavelengths of 355, 532, 632 and 780 to 1064 nm. An intelligent assembly concept saves time-consuming adjustments and ensures precision and flexibility. Discover the advantages of aspherical beam expansion for your application!

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Discover the world‘s first aspheric and diffraction-limited beam expander. The a|BeamExpander is a monolithic laser accessory with just one aspheric lens for the highest level of precision. Experience nearly endless possibilities with up to 32× beam magnification and optimized performance for different design wavelengths (355, 532, 632, 780, 1064 nm) - individually measured and certified. The asphericon beam expansion system works completely diffraction limited, both as a single element and in cascades with up to five additional coated elements. Three magnification levels are available (1.5, 1.75, 2.0), which can achieve up to 32x expansion.

Buy the a|BeamExpander

  • Available in five design wavelengths [355 nm / 532 nm / 632 nm / 780 nm / 1064 nm]
  • Max. input aperture 10.6 – 14.7 mm, max. output aperture 22.5 mm
  • Available with magnifications of 1.5 | 1.75 | 2.0
  • Possibility of combining up to five expander for up to 32 times beam expansion and over 230 intermediate stages
  • Completely diffraction-limited – individually measured and guaranteed by an original asphericon certificate
  • Laser induced damage threshold (Coating):  12 J/cm², 100 Hz, 6 ns, 532 nm

Want to calculate the required beam expansion of the laser first? Use the a|BeamExpander configurator and get desired results based on the expansion, number of laser beam expanders or a combination of both.

a|BeamExpander Configurator

Kepler telescope

The design of the Kepler telescope represents the simplest principle of a beam expansion system. Here, two converging lenses with different focal lengths are combined. The expansion or reduction of the beam crosssection results from the quotient of the focal length

(1) \(V = \frac{f_2}{f_1}\)

The overall length of the optical system is essentially determined by distance of the two lenses, which can be estimated over the sum of the focal length,

(2) \(e = f_1 + f_2\)

Galilean beam expander

In the Galilean telescope, the converging lens is replaced by a diverging lens, which decreases the construction lengths while maintaining the magnification level. Figure 1 shows both: Kepler telescope/Keplerian laser beam expander (a) and Galilean telescope/Galilean beam expander lens (b) with 10x magnification (V=10).

Spheric single lenses are used in classic gaussian beam expanders. Thus, spheric aberrations become visible. This can be remedied by asperization of one of the lens surfaces, particular where a high quality of wave front is required. The shape of the lens surface can be described by

(3) \(z(h) = \frac {h^2}{R(1+\sqrt{(1-(1+k) \frac{h^2}{R^2}}} + \sum_{i=2}^{n} A_{2i} h^{2i}\)

These beam expansion systems are typically optimized for one wavelength in terms of the shape of optical surface and lens distance. Spheric aberrations can be reduced to a minimum.

By adding an additional optical group, the beam expansion system receives additional flexibility with regard to the adjustable magnification levels. This can be done most easily with a symmetrical zoom system, which consists of three single optical lenses (converging lens-diverging lens-converging lens). Therby two lenses must be able to change their position so that an afocal beam path is ensured for each magnification level. Depending on requirements, such a system can become very complex, whereby the demands increas in terms of the mechanical mount.

Monolithic beam expansion systems

A slightly different approach is taken by monolithic beam expansion systems that are similar in operating principle to a Galilean telescope, but consists only of one optical element – a meniscus lens. The two optically active surfaces have a common center of curvature. The principle of this so-called zero lenses has been known for a very long time, but they show strong spherical aberration in their original design with two spherical surfaces and thus are only suitable for very small beam diameters and very low magnifications.

In Figure 2 (a) the beam path in such a spherical lens is shown schematically. If these optical elements are aspherized to one of the two surfaces, the spherical aberration can be corrected as shown in Figure 2 (b) and an afocal system for large beam diameters can be implemented.


The improvement in the optical properties can be clearly seen in comparison to Figure 1. The magnification in both cases corresponds to V = 2, whereby the beam diameter is different by the factor 2. The maximum attainable magnification of such a single element is V = 2. This is estimated by the paraxial magnification

(4) \(V = \frac {d}{r} * \frac {n-1}{n}\)

whereby n is the refractive index of the glass, r is the radius of the concave side, and d is the center thickness.

It turns out that the single element magnifications of the monolithic Galilean telescopes are comparatively low due to the overall length limitation. Since it is an afocal beam expansion systems, they can gradually increase the input beam while they are “connected in series” in succession in the beam path (Figure 3c).


Various magnification levels allow both, high magnifications with minimum space requirements (use V = 2) as well as finer increments (use V = 1.5 and V = 1.75). Due to the afocal design of the single elements, the meniscus lenses can arbitrarily oriented inside the beam path.

The use of monolithic beam expansion systems in cascade involves much more optical surfaces than the conventional optical systems (see Figure 3). Moreover, each second surface is aspheric! For such a cascade system for flexible beam expansion very high surface qualities of the single elements are required. Prerequisite for a variety of combinations during the subsequent use is that every single element over the entire clear aperture must be significantly better than the requirement “diffraction limited”, that is wavefront error RMS< λ/14.

If, at the same time, center thickness and decentering of the surfaces are very accurately manufactured, one can speak of a completely adjustment-free beam expansion system, since all degrees of freedom required for adjustment are fixed at an optimum by the manufacturing as monolithic element. Also, the introduction of further monolithic elements for changing the magnification level will be completely adjustment-free and therefore quick and easy.

Beam Expander are primary used for research in the optics laboratory, where they are used for example to amplify the laser or to improve the usability of the optical assembly. Also in the research and development departments of aerospace, biotechnology, imaging, materials research and materials processing, particularly of laser material processing, beam expander systems are used.

The quality of the BeamTuning elements is guaranteed by asphericon based on a high-resolution wavefront or beam profile measurement for selected components, also through certification.

Find the right a|BeamExpander for your application? Use our configurator to quickly and easily scan for the desired expansion and/or the number of a|BeamExpanders and match the calculated results with your own requirements.

To a|BeamExpander Configurator

Wavefront and divergence deviations as well as the influence on ultrashort laser pulses can be calculated with our BeamTooling App. The app is available for free download in the Apple and Google App Stores.

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Cross-system and intra-system a|Adapters enable individual BeamTuning products and mounted optics to be quickly fitted together. They also ensure high compatibility with other optics systems without the need for any additional adjustment.

asphericon’s intra-system adapters can be used to connect for example a|BeamExpanders to each other in both functional directions for the finer adjustment of magnification levels. The range of cross-system a|Adapters includes adapters with C-mount and SM1 threads for easy integration into existing set-ups, even non-system ones. Due to its external diameter, the 1.2" circumference adapter can be used as both intra-system and cross-system adapter.

Buy a|Adapters

Intra-system a|Adapters allow to combine all BeamTuning elements, e.g. to use a|BeamExpander in both functional directions, to expand or reduce the beam diameter. The a|Adapter tilt ensures precise alignment of all optical elements within the beam path and can be flexibly tilted in different directions (x- and y-direction).

Easy integrate all BeamTuning elements into any optical system (e.g. Qioptiq, OWIS or Edmund Optics) through a variety of mounting concepts by using the cross- system a|Adapters (C-Mount, SM1). Thanks to its outer diameter, the 1.2" circumference can be used both as intra-system and as cross-system a|Adapter.

a|BeamBox Essential

Compile asphericon's BeamExpansion products with MountedOptics and/or BeamShaping products flexibly for your individual application.
For a quick and easy overview, asphericon has already developed various standard combinations of the a|BeamBoxes. The “Essential” series includes five boxes for beam expansion at different wavelengths.

Request individual a|BeamBox

  • Combines up to eight a|BeamExpanders with an a|AspheriColl, a|Waveλdapt and matching a|Adapters
  • Optimized for wavelengths 355, 532, 632, 780 and 1064 nm
  • Quality: diffraction-limited wavefront
  • Multi element sets with attractive cost savings

Combine a|BeamExpander, a|Waveλdapt, a|TopShape, a|AiryShape and a|AspheriColl with a|Adapters (intra-system and cross-system) and MountedOptics individually to suit your requirements. Almost every combination is possible! Please contact us.

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Beam expanders and other optics with short delivery times.

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Precise beam expansion and shaping of laser beams – asphericon BeamTuning

In addition to the aspheric beam expanders (a|BeamExpander) for expanding and reducing lasers, asphericon has developed further optical modules within the BeamTuning line. The product range includes a fiber collimator for FC/PC laser patch fibers (a|AspheriColl), an element for using a|BeamExpanders outside their design wavelength (a|Waveλdapt), intra- and cross-system adapters (a|Adapters),and mounted aspherical optics (MountedOptics). Supplementary – also based on an aspheric optic – we offer beam shapers for a wide range of applications. Learn more about shaping a collimated laser beam into a Top-Hat beam and/or different focused beam profiles at the aspheric beam shaping optics site. Also discover our services such as high performance optical coatings and metrology.


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