Effects of laser ablation of olivine on chamber optical window transmission loss and its recovery

Abstract

Optical windows play a crucial role in laser ablation systems by protecting delicate components inside the chamber while allowing the transmission of laser energy. However, material buildup during the laser ablation process can lead to a significant loss of optical transmission over time. In this work, material deposition on the optical window by laser ablation of olivine using two laser systems operating at 30 kHz, 1 mJ pulse energy, and 20 Hz, 9.6 mJ pulse energy was performed and its impact on the window’s transmission properties, laser-induced breakdown spectroscopy (LIBS) signal, and window recovery is presented. Ablation at 30 kHz with 1 mJ pulses for 10 min resulted in substantial particle deposition on the window, causing a significant drop in transmission. Transmission of clean window dropped abruptly from 90% to nearly 0% (in the UV region from 200 to 300 nm) and 35% (at 600 nm) affecting the LIBS signal. In contrast, ablation at 20 Hz with 9.6 mJ pulses for 5 min showed no material deposition or transmission loss. Additionally, the study demonstrated that the same laser system used for ablation could be employed to remove the deposited material from the window, facilitating its recovery. Laser cleaning of the window at 30 kHz and 12 W average power restored the transmission values from 39% to 62% at 400 nm in the UV region, with potential for further improvement through parameter optimization. In addition, the identification of the hydroxyl group in olivine, which is relevant to NASA’s terahertz heterodyne spectrometer for in situ resource utilization project for the validation of water molecules is presented.