Beam Expanders

Beam expanders increase the diameter of beams of collimated light and simultaneously decrease beam divergence. At Avantier we produce custom beam expanders for laser applications as well as remote sensing and interferometry.

Beam expanders
Beam expanders

Beam Expanders

Types of Beam Expanders

A beam expander may be formed of prisms, of lenses, or a combination of both.

Multi-prism beam expanders

Multi-prism beam expanders are formed from two to five prisms arranged to form an optical system with the desired properties. These prism beam expanders can be described by ray transfer matrices, and the generalized mathematical description is known as multi-prism dispersion theory.

Beam expanders that consist of two lenses are known as telescopic beam expanders. These transmissive beam expanders can be divided into two primary types: Keplerian beam expanders and Galilean beam expanders.

Keplerian and Galilean beam expanders

A Keplerian telescope consists of two plano-convex convergent lenses placed so that the distance between the lenses is equal to the sum of their focal length.  These simple beam expanders have high expansion ratios. Because the two lenses have positive focal lengths the input beam will focus at a point between the two lenses, enabling spatial filtering. However, that same property makes Keplerian beam expanders problematic for high power laser applications, as the resulting energy density and heat at the focal point can deflect light and lead to wavefront errors.

A Galilean telescope consists of one lens with a negative focal length (the objective) and another with a positive focal length (the image lens). These two lenses are also placed so the distance between them is equal to the sum of their focal lengths. As one of the lenses is negative, the objective and lens will be close together, and there will be no internal foci. This makes Galilean beam expanders a good choice of high-power laser applications, as there is no problem with high power density within the system. 

For both the Galilean and Keplerian configuration the output beam divergence can be calculated by the beam divergence of the input beam and the diameters of both output and input beams. In both cases, the ratio of input beam divergence to output beam divergence is equal to the ratio of output beam diameter to input beam diameter. This ratio is equal to the magnifying power of the beam expander system.

Beam expanders
Keplerian Telescope
Beam expanders
Galilean Telescope

Applications of Beam Expanders

Beam expanders are used whenever the diameter of a collimated beam must be increased. They can also be used to change the focus spot size for a focusing lens, or to keep a beam collimated in optical systems that have a long beam path.  

One application of beam expanders is in tunable laser resonates. Here an intracavity beam expander is used to increase the diameter of the laser beam to illuminate the width of a given diffraction grating. The beam divergence is reduced, and very narrow line widths can be emitted.

Beam expanders
Beam expanders
Beam expanders

Beam Expanders at Avantier

Our beam expanders offer a versatile range of magnification, spanning from 1.5 times to 10 times, and we specialize in crafting tailored optics and coatings to meet the precise requirements of your specific applications.

  • Precise collimation of diffraction-limited beams across a broad spectrum of input beams
  • Achieve magnifications ranging from 1.5 times to 10 times
  • Utilize an adaptable Beam Expander to enhance the divergence angle of laser beams
  • Ensure high transmittance while minimizing energy loss
  • Designed to operate effectively under high-power laser conditions
  • Customized optics and coatings tailored to meet specific application requirements

Whether you need a multi-prism beam expander, an extra cavity hybrid beam transformer, or a simple beam expander, our design and engineering team is ready to work with you to produce the exact optical component needed for your application. Please contact us today to place your custom order or schedule an initial consultation.


Contact us NOW for sales & expert advice.