Session: 02-11-02: Session #2: Laser-Based Advanced Manufacturing and Materials Processing

Paper Number: 99212

99212 - Metrology of Laser Ablation Using Optical Emission Spectroscopy 

Additive manufacturing has proven to be a useful and powerful tool in fabricating intricate designs that could not be accomplished using traditional manufacturing methods. Although the prints that are created have the ability to replace traditionally manufactured parts, the mechanical properties of the part can vary due to the impurities such as porosity that can occur during the manufacturing process. To mitigate this, researchers have incorporated optical instruments in the laser sintering systems to determine if there is any useful information that can be extracted from monitoring the emitted light during the writing process. This can be achieved through in-situ optical emission spectroscopy (OES) [1] or pyrometry [2]. Although the data from these two methods are useful, the laser-matter interactions in additive manufacturing have proven to be complex and there lacks metrology techniques to monitor the process in real-time.

In this work, we aim to determine a method for spectral metrology using subtractive manufacturing procedures, which can then be adopted for additive manufacturing purposes. Our experiments are focused on using a UV-vis-NIR spectrometer to examine the optical emission during laser ablation, a useful subtractive manufacturing method for patterning designs in glass, metal, ceramics, etc. To determine the best position to monitor the spectral emissions, an optical fiber was carefully positioned to ensure that the fiber intercepted the emitted light without being saturated by the intensity of the laser. The laser in this experiment was an ultrafast Ti: sapphire laser (wavelength of 780 nm, pulse duration of 40 fs) which operated nominally at a power of 6 mW and at a speed of 200 µm/s. The pattern that was tested was a set of lines that were all at a length of 5 mm and spaced apart by 950 µm to ensure that the ablation lines did not overlap. Three glass samples were ablated at varying attenuated power, using separate lines for each power change, which increased in 5% increments. The first sample had a power range from 50-100% power, the second sample ranged from 30-100%, and the third sample ranged from 5% to 100%. The width of each line was measured for each sample to determine the dosing of the laser and compare that to the spectral data gathered using the OES.

The results show a clear correlation between the laser power and its ablation width, where the width and dosing of the laser are directly proportional and increase in a consistent fashion. The spectral data showed a correlation between the scattering of the laser and the width of the ablations, where the spectra that were recorded were near that of the laser’s output (with a peak of approximately 750 nm). The results of the experiment show that the use of an optical fiber in the position at or similar to the setup in this experiment would provide meaningful data in real-time for the assessment of laser ablation. We will present detailed results of the system configuration, experimental data, and analysis results. In the future, this OES setup can potentially be used to help prevent the impurities seen in laser additive manufacturing.

[1] Lough, C. et al. In-situ optical emission spectroscopy of selective laser melting.  Manufacturing Processes 53 (2020) 336–341. https://doi.org/10.1016/j.jmapro.2020.02.016.

[2]   Zouhri, W. et al. Optical process monitoring for Laser-Powder Bed Fusion (L-PBF).

CIRP Manufacturing Science and Technology 31 (2020) 607-617. https://doi.org/10.1016/j.cirpj.2020.09.001.

Presenting Author: Briana Cuero The University of Texas at Austin

Presenting Author Biography: Briana Cuero is a senior mechanical engineering student at the University of Texas at Austin. She has worked in many engineering research endeavors, including materials science, optics, and nanofabrication. In fall of 2020, Briana Cuero began on working at NASA Goddard Space Flight Center in the Cryogenics and Fluids Branch, establishing testing structures for mass-spectroscopy systems. At the university, Briana Cuero is currently researching nanofabrication and its correlation with additive manufacturing.

Authors:

Briana Cuero The University of Texas at Austin
Kun-Chieh Chen The University of Texas at Austin
Chih-Hao Chang The University of Texas at Austin