Why do many laser applications require smooth shape laser beams?

What are smooth shape laser beams?

Smooth shape laser beams are characterized by uniform intensity of illumination across the beam profile or focused laser spot. Such beams do not have strong changes in uniformity, and often have a flat-top like intensity envelope. Most laser source do not have a smooth shape laser beam profile, but rather either a gaussian profile (for single mode lasers) or a complex centroid profile (for multi mode laser)

Getting smooth shape laser beams from multi-mode lasers

High laser power can be more easily and affordably achieved using multi-mode lasers, compared to single mode lasers. This makes multi-mode lasers attractive sources for integrators developing high power laser beam machines. However, due to their multi-mode nature, such laser suffers from non-uniform beam profile, that are also often unstable and change depending on the laser power level and temperature. This non uniform beam shape typically has low frequency non-homogeneity, i.e large gradual changes in intensity, that cannot be eliminated by thermal diffusion of de-speckling. To create a smooth beam profile from such laser beams, beam shaping diffusers are often employed.

Beam shaping diffusers for multimode beam smoothing

A beam shaping diffuser is a type of optical component that can generate a homogenized, pre-designed intensity distribution from any input. This is typically done by duplicating and overlaying the input beam on itself in a controlled manner, resulting in a with a smooth shape laser beam with a desired intensity distribution. Typically, beam shaping diffusers are inserted in the beam path and generate a smooth shape laser beam at the far field, or at the focus of the system. Simple smooth shape laser beam with a gaussian envelope can be achieved by low quality laser homogenizers such as ground glass diffusers. But since these diffusers do not provide any shaping functionality, the shape is not truly a smooth flat-top profile. To achieve a flat top smooth laser spot, a diffractive diffuser, or some other type of beam shaper diffuser often the best choice.

Achieving a smooth shape laser beam with single mode lasers

Single mode lasers have a a nice gaussian intensity distribution, but due to the gaussian profile, the intensity is very unequal in the beam center vs the edge. Achieving a flat top profile requires a laser beam shaper. These analytical beam shapers have a different operating principle compared to beam shaping diffusers. They change the input laser beam phase in a continuous manner that generates a smooth flat top distribution at the far field (or focus plane). Therefore, they must have a well defined input beam size and beam profile, but enable achieving smooth shape laser spots with unrivalled uniformity and edge sharpness.

Benefits of smooth shape laser spots for laser processing

Most laser applications, including laser ablation, laser grooving, laser welding and laser aesthetic treatment, require uniform illumination of the processed or treated area. Typically, a target needs to be covered by multiple exposures to the laser, each exposure treating a separate area in the target. Unmodified laser spots tend to have a centroid profile, where the illumination intensity is higher in the center of the spot compared to the edges. Such profiles tend to be inefficient and give non-uniform results when stitching multiple sub-areas, as the areas often overlap. With a smooth shape laser spot, it is possible to achieve full coverage of the treated area without overlapping. Furthermore, ablation or grooving sidewalls tend to be straight rather than sloping, and ablated area width is not strongly effected by laser pulse energy when a smooth shape laser spot is used. So if you have a laser application that needs a smooth shape laser beam, feel free to contact us at Holo/Or Ltd and we will be happy to support you with our expertise in laser shaping.