ANALYSIS: ULTRAFAST LASERS


Knowledge is power in efficient ultrafast laser processing


Optimising pulse duration, energy, shape, spacing, and wavelength is key to unlocking higher throughput and quality in ultrafast laser processing, says Dariusz Świerad


Analysis and opinion section sponsored by


Figure 2: Results in glass processing show a 100fs shorter pulse duration (0.25ps versus 0.35ps) gives a higher quality result


R


ecent advances in ultrafast laser technology have created


significant improvements in materials processing outcomes. These advances are particularly beneficial for “difficult to machine” materials such as ceramics, glass, and some metals. Industries such as semiconductors, electronics, medical devices, solar photovoltaics, and batteries require high-quality and high- speed cutting and machining to meet manufacturing throughput, cost, and quality requirements. As manufacturers aim to minimise energy consumption per component produced, process optimisation has


become crucial to reducing wasted time and energy. At Fluence, we have observed


that production processes are sometimes implemented with unoptimised parameters. By focusing on key parameters such as pulse duration, energy, shape, spacing, and wavelength, changes to the process can lead to higher throughput and quality. In this article, we will explore examples of how process optimisation can enhance efficiency and quality.


Pulse duration: Unlocking higher material removal rates Ultrashort pulses – in the order of picoseconds (ps) and femtoseconds (fs) – offer a significant advantage in material


processing, as shorter pulses result in higher peak power for the same pulse energy, and a shorter interaction time with the material. This leads to “cold” processing, reducing heat input. Through application trials, it has been demonstrated that by reducing pulse duration while maintaining the same energy density (fluence), the removal rate of metals can be approximately doubled. Figure 1 depicts an example in steel, comparing 7ps pulses with 0.25ps (250fs) pulses, and similar results have been observed in titanium, with a slightly higher removal rate. Achieving high-speed cutting


with a smooth edge finish can be a challenging task when processing materials such as glass, silicon, or ceramics. However, close parameter matching to the specific material can improve the overall quality of the process. Figure 2 illustrates the impact of matching energy, spot size, and pulse duration to achieve a smoother result. While most commercial femtosecond laser sources have a pulse duration of 350 to 500fs, using 250 to 300fs can result in a dramatic improvement.


Figure 1: Ablation rate in metals is roughly doubled by reducing pulse duration from 7ps to 0.25ps (250fs)


12 Electro Optics May 2023


Pulse energy: A balancing act Traditionally, users have been more accustomed to operating at lower repetition rates and higher pulse energy, given the familiar technology of established free-


space lasers. However, having an excess of energy often leads users to waste it in their optical systems, which then forces them to operate at low repetition rates. In reality, to achieve optimum efficiency in terms of ablation rate, only a few tens of microjoules of energy at the sample are necessary. For maximum throughput efficiency, it is preferable to have 100µJ of energy at 600kHz, as opposed to 1mJ at 60kHz. One of our customers in the consumer electronics industry was accustomed to using 1mJ of energy and had not considered the possibility


“Focusing on key parameters such as pulse duration, energy, shape, spacing, and wavelength… can lead to higher throughput and quality”


of achieving the desired results with a lower energy level. As it turned out, due to the abundance of available energy, an optical beam shaping system was implemented with an efficiency of only 1%. If the optical system did not waste so much power in beam delivery, a higher repetition rate could be used to increase throughput by tenfold or more. By optimising the optical setup and process, not only can money be saved at the outset, but a lot of money can be saved in the long run by


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