Monitoring of Femtosecond Laser Micromachining Using Ultra-high Speed Photodiodes: The Effect of Feature Depth on the Optical Process Emission
Year: 2024
Type: article
Abstract: The femtosecond (fs) pulsed laser is a versatile tool to produce microstructures down to a few microns on all kinds of materials including metals, ceramics and polymers.Generally, the topography of the fabricated structures is characterized using ex-situ measurement techniques such as confocal microscopy or white light interferometry, which significantly increases the process cycle time.Besides, it is difficult to control the laser process parameters in real-time with offline characterization methods.To closed loop the fs laser micromachining (FLµM) process, an in-process sensing strategy is required.However, unlike for laser processing with continuous and short-pulsed lasers, the process monitoring for FLµM has not been fully explored.In this work, a monitoring system based on off-axis ultra-high speed photodiodes was integrated and applied to the detection of optical process emissions during FLµM of stainless steel.Three photodiodes, whose specifications are described hereafter, were used.The reflected process radiation passes through a filter, with a specific wavelength range of visible (500-900 nm), laser beam reflection (1030 nm) and infrared (1100-1700 nm), focused onto the photodiode with an amplifier circuit.FLµM of a single line ablation at different pulse energies and scanning passes were performed to study the effect of the feature depth on the off-axis photodiode-based monitoring.In addition, a high-speed spectrometer was implemented in the FLµM working station to capture the spectral distribution of the plasma emission.The characteristics of process optical emission, temporal evolution of the spectrometer and photodiode signals, and the effects from laser machining factors were discussed.The proposed monitoring technique using optical emission-based sensor has the potential to facilitate the process control for femtosecond laser micromachining, which will ultimately result in increased productivity and quality.
Authors: Yildirim, Kerim, Nagarajan, Balasubramanian, Tjahjowidodo, Tegoeh, Castagne, Sylvie
Institution: KU Leuven
Language: English
Subfield: Computational Mechanics
Field: Engineering
Domain: Physical Sciences
Open Access status: diamond
OpenAlex ID: W4405400599