MANUFACTURING with short pulse lasers FOCUS
THERMAL EFFECTS AND MATERIAL PROCESSING WITH USP LASERS In reality, the extent of the thermal effect depends on both the repetition rate( the number of pulses per second) and the thermal response of the material. The local temperature increase after a single pulse is minimal. If the interval between two consecutive pulses exceeds the material’ s thermal diffusion time, the thermal effect is negligible. However, at high repetition rates— where the time between successive pulses is shorter than the thermal diffusion time— thermal accumulation occurs( see figure 2). USP lasers can thus be considered remarkable tools for controlling temperature fields with exceptional spatial and temporal precision, even at microscopic scales.
As demonstrated, high-power USP lasers can modify any material— whether on the surface or within the volume( if transparent)— at the micrometer scale while precisely managing thermal effects. This technology enables applications as diverse as engraving your name on ultra-hard materials like diamonds or performing delicate procedures such as correcting corneal curvature in LASIK eye surgery. USP lasers are therefore invaluable tools for advanced manufacturing.
INDUSTRIAL ROBUSTNESS AND LASER TECHNOLOGIES USP lasers have been robustly integrated into industrial applications for years, including glass cutting and drilling for smartphone screen manufacturing. The two most widely used high-power USP laser technologies are:
• Ti-Sapphire( Ti: Al 2 O 3) lasers( λ = 800 nm): These lasers achieve higher peak power with shorter pulses(> 10 fs) but operate at lower repetition rates( kHz range).
• Ytterbium fiber lasers( λ = 1030 nm): These lasers offer higher repetition rates( up to 10 MHz or more) with pulse durations exceeding 100 fs. Their fiber-based design enhances robustness, making them ideal for industrial use.
For example, commercial 300 W( average optical power) femtosecond Ytterbium lasers can generate 1 million pulses per second, each delivering 300 µ J of energy in 300 fs. The first kilowatt-level average-power USP lasers are now also available. Other high-power USP laser technologies have emerged at different wavelengths, such as Erbium-doped fiber lasers( 1550 nm), Holmium femtosecond lasers( 2100 nm), etc.
Most of these lasers can be frequency-doubled or-tripled using nonlinear crystals to produce wavelengths like 515 nm or 343 nm, though this process reduces the output power.
Unlike conventional lasers, the advantage of exploring new wavelengths with USP lasers is not to enhance absorption but to exploit the material’ s transparency windows. This enables volumetric processing rather than surface-only modification. For instance, glass is transparent at 1030 nm, while silicon wafers are transparent at 1550 nm.
SURFACE FUNCTIONALIZATION One of the most studied applications of USP lasers is surface functionalization— the modification of a material’ s physical properties through micro-structuring. Micrometer-scale structuring can be achieved by etching the material
Figure 1. Peak power of a 1 mJ pulse depending on its duration, or how high peak power can be reached with low energy.
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