BEAM SHAPING
HIGH-PERFORMANCE NIR LASER-BEAM SHAPING PROCESSING AT 350 W
SHUCHEN ZUO ET AL.*, UNIVERSITY OF MANCHESTER
A second telescope (M=x0.5) was then used to match the active area of the SLM, maximising resolution and diffraction efficiency.
The conditioned beam was directed onto the actively cooled spatial light modulator (Hamamatsu X15213-03). The device incorporates a sapphire window and active water cooling, enabling stable operation up to the kilowatt levels without overheating.
Figure 1: High-power beam-shaping optical setup with liquid-cooled spatial light modulator and scanning galvanometer.
INTRODUCTION
As recently highlighted in the government industrial strategy [1], advanced manufacturing increasingly relies on flexible, data-driven processes that maximise productivity and sustainability, using frameworks such as Industry 4.0. In an increasingly complex and competitive environment, laser systems must do more than deliver high power; they require precise control over energy distribution, using accurate beam shaping. Instead of relying on standard Gaussian profiles, structured beams such as flat- tops, multi-spot arrays, or vortex beams offer better control over laser-material interactions, leading to faster processing, higher efficiency, improved surface quality, and innovative material treatments.
Significant progress has already been made in this field. Tang et al. [2] have shown how spatial light modulators (SLMs) can create tailored beam distributions for ultrashort pulse precision laser processing. Their pioneering work established the foundations for applying SLM beam shaping in industrial contexts, but power handling has remained a critical limitation. Conventional liquid-crystal SLMs typically operate well below 200 W in continuous- wave operations, restricting their wider adoption in high-power
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manufacturing settings such as welding or additive manufacturing.
Our latest work addresses this gap by demonstrating a liquid-cooled SLM that maintains stable operation above 350 W [3]. This represents an important step towards further integrating beam shaping into high-power Industry 4.0 laser manufacturing environments.
Figure 1 shows the high-power infrared optical setup used to investigate SLM performance and for laser processing of polished stainless steel and molybdenum. A continuous wave (CW) fibre laser was directed to a liquid-cooled SLM, with a telescope-based 4f optical imaging system and scanning optics enabling us to project structured beams directly onto metal samples without losing the beam integrity.
EXPERIMENTAL METHODS
A single-mode CW laser (IPG YLS-1000-SM, 1070 nm, up to 1 kW) was used to test the high- power limits of beam shaping. The randomly polarised laser output was expanded (M=x2) and collimated before passing through a polarisation control stage (thin film polarising beamsplitter and half- wave plate). This ensured the input linear polarisation was aligned to the liquid-crystal modulator’s director.
The SLM was followed by a 4f optical system, which re- imaged the programmed phase patterns onto the entrance of a galvo-scanning head (SCANLAB hurrySCAN 20). This ensured that the shaped beams were faithfully transferred to the focusing optics. Finally, an f-theta lens (f = 320 mm) delivered the patterns onto the workpiece (polished mild steel and molybdenum).
The SLM maintained an excellent phase response, thus a high reflected degree of polarisation (DOP), DOP = 0.97 ± 0.01 up to P = 300 W, decreasing at higher powers up to 383 W. Nevertheless, the device could still deliver a complete phase control greater than 2π, the minimum required to generate reliably complex beam profiles at this level. We demonstrated that accurate phase modulation was preserved up to 383 W, almost double the ~200 W ceiling reported in earlier SLM studies, confirmed that the system was robust enough for meaningful high-power processing trials.
KEY RESULTS
The system's ability to produce parallel processing beams was initially tested by projecting a five- spot array onto polished mild steel. The programmed separations were reproduced on target (Figure 2): the maximum spot separation was 4.9 mm, with a typical adjacent spot– spot distance of ~2.2 mm. Uniformity from ablated crater volumes over 200–300 W was 0.72 ± 0.04, and a weak zero order appears from
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