Beam Shapers

Author: the photonics expert Dr. Rüdiger Paschotta

Definition: optical devices for modifying the shapes of laser beams

Alternative term: beam converters

Category: article belongs to category photonic devices photonic devices

DOI: 10.61835/877 Cite the article: BibTex plain text HTML

In general, a beam shaper (or beam converter) is an optical device which somehow reshapes a light beam, i.e., it modifies its spatial profile. For example, there are refractive and micro-optic beam shapers which create a flat-top (top-hat) beam from a Gaussian input beam.

Another kind of beam shaper is often used in conjunction with a high-power laser diode, for example with a diode bar, in order to make both its beam radius and beam quality more symmetric with respect to two orthogonal directions. This facilitates e.g. launching the beam into an optical fiber with a circular cross-section, or pumping a solid-state gain medium. A popular type of device, which is based on two highly reflective mirrors and largely preserves the brightness, is described in Ref. [2]. Other devices are based on micro-optical structures, for example containing arrays of small prisms, to perform a similar function with a smaller device. Originally, such brightness-preserving beam shapers were applied to diode bars, but they can equally well be used with diode stacks.

beam shaper for symmetrizing diode laser beam quality — Figure 1: Setup of a two-mirror beam shaper [2]. The lower part shows how an array of beamlets from the emitters of a diode bar is rearranged so as to obtain a roughly equal beam quality in both directions.

Note that it would not be sufficient simply to use a combination of cylindrical lenses so as to achieve equal spot sizes in both directions; the beam qualities and thus the beam divergence angles in both directions would then remain very different. If a circular focus is formed in that way, the beam divergence at least in one direction is much larger than achievable with a beam shaper.

There are other devices performing essentially the same function with other means, e.g. with diffractive micro-optics or with fiber bundles. In the latter case, the outputs of individual emitters of a diode bar are coupled into separate fibers of a bundle, which are arranged in a linear array on the side of the diode bar, but as a circular array on the output end.

Other beam shapers perform different functions. For example, there are devices for correcting the “smile” of diode bars [4].

Finally, there are beam homogenizers for making its intensity distribution more uniform.

More to Learn

Encyclopedia articles:

Blog articles:

The Photonics Spotlight 2010-04-08: “Creating a Top-hat Laser Beam Focus”

Suppliers

The RP Photonics Buyer's Guide contains 37 suppliers for beam shapers. Among them:

Cailabs

Cailabs offers a wide range of beam shapers for various applications and laser types. Top-hat beam shapers with passive beam stabilization feature are available for single-mode lasers, especially ultra-short pulse lasers. We also offer beam shaping modules and laser heads with low focus shift and high depth of field for high-power multi-kW lasers. Reflective axicons are also available for high-quality Bessel beam generation.

Our beam shaping modules and laser heads for welding applications shape high-power CW lasers in symmetrical and asymmetrical ways. Their reflective design supports very high power (up to 20 kW) and minimizes focus shifts, therefore offering improved quality and efficiency in laser beam welding.

There are also the beam shaping modules for ultrashort pulse lasers, providing high-quality top-hat shapes with exceptional depth of field and sharpness at the diffraction limit. The modules include a mode-cleaning feature that passively stabilize the beam, ensuring a stable and high-quality process.

Bibliography

[1]	J. R. Leger and W. C. Goltsos, “Geometrical transformation of linear diode-laser arrays for longitudinal pumping of solid-state lasers”, IEEE J. Quantum Electron. 28 (4), 1088 (1992); https://doi.org/10.1109/3.135232
[2]	W. A. Clarkson and D. C. Hanna, “Two-mirror beam-shaping technique for high-power diode bars” (reflective beam shaper for symmetrizing the beam quality and preserving the brightness), Opt. Lett. 21 (6), 375 (1996); https://doi.org/10.1364/OL.21.000375
[3]	A. von Pfeil, “Beam shaping of broad area diode lasers: principles and benefits”, Proc. SPIE 4648, 82 (2002); https://doi.org/10.1117/12.462645
[4]	J. F. Monjardin et al., “Correction of beam errors in high-power laser diode bars and stacks”, Opt. Express 14 (18), 8178 (2006); https://doi.org/10.1364/OE.14.008178
[5]	X. Gu et al., “All-fiber laser beam shaping using a long-period grating”, IEEE Photon. Technol. Lett. 20 (13), 1130 (2008); https://doi.org/10.1109/LPT.2008.924640

(Suggest additional literature!)

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