Preservation of cultural legacy is essential for ensuring its availability for future generations. Long-term indoor storage can sometimes cause the papers to adhere, which can result in the transfer of ink stamps or prints from paper to paper, and subsequently, there emerges the need to remove these types of stains. Laser cleaning emerged as a promising technique for paper surface cleaning. This work presents the laser cleaning of a historical paper dated to the end of the 19th century using the Nd:YAG laser in a nanosecond pulsed regime, at two wavelengths, 532 and 1064 nm, and a semiconductor laser in a continuous regime, at a 552 nm wavelength. The cleaned areas are observed by optical microscopy, scanning electron microscopy, energy-dispersive spectroscopy, and spectrophotometry. The obtained results are discussed in terms of the laser cleaning efficiency characterized by several aspects. The results obtained by green and near-IR laser irradiation in pulsed and continuous regime are compared, showing favorable effects regardless of the laser wavelength. However, in some cases, laser cleaning at 1064 nm wavelength damaged the surface layer of the paper. Cleaning at 532 nm wavelength did not completely remove the ink, and the ink traces were visible under the microscope or spectrometer. The proposed efficient cleaning method for stain, dust, and stamp ink removal from historical papers includes a semiconductor laser at 552 nm, owing to the continuous action of its beam.

中文翻译：

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半导体连续和Nd:YAG脉冲激光加工在历史纸无损清洗中的应用

保护文化遗产对于确保其为子孙后代所用至关重要。长期在室内存放有时会导致纸张粘连，从而导致印章或印刷品从纸张转移到纸张，随后需要去除这些类型的污渍。激光清洗是一种很有前途的纸张表面清洗技术。这项工作展示了对 19 世纪末一篇历史论文的激光清洁，使用纳秒脉冲状态的 Nd:YAG 激光，两种波长，532 和 1064 nm，以及连续状态的半导体激光，在552 纳米波长。通过光学显微镜、扫描电子显微镜、能量色散光谱和分光光度法观察清洁区域。从几个方面表征的激光清洁效率方面讨论了获得的结果。比较了脉冲和连续模式下绿色和近红外激光照射获得的结果，无论激光波长如何，都显示出有利的效果。然而，在某些情况下，1064 nm 波长的激光清洁会损坏纸张的表层。在 532 nm 波长清洗并没有完全去除墨水，在显微镜或光谱仪下可以看到墨水痕迹。由于其光束的连续作用，所提出的用于去除历史纸张上的污渍、灰尘和印章墨水的有效清洁方法包括 552 nm 的半导体激光器。无论激光波长如何，都显示出良好的效果。然而，在某些情况下，1064 nm 波长的激光清洁会损坏纸张的表层。在 532 nm 波长清洗并没有完全去除墨水，在显微镜或光谱仪下可以看到墨水痕迹。由于其光束的连续作用，所提出的用于去除历史纸张上的污渍、灰尘和印章墨水的有效清洁方法包括 552 nm 的半导体激光器。无论激光波长如何，都显示出良好的效果。然而，在某些情况下，1064 nm 波长的激光清洁会损坏纸张的表层。在 532 nm 波长清洗并没有完全去除墨水，在显微镜或光谱仪下可以看到墨水痕迹。由于其光束的连续作用，所提出的用于去除历史纸张上的污渍、灰尘和印章墨水的有效清洁方法包括 552 nm 的半导体激光器。