Optical properties of thin films monitored in real-time at high gamma radiation doses using long period fiber gratings

• Published in: Optics and laser technology Vol. 176; p. 111019
• Main Authors: Esposito, Flavio, Burnat, Dariusz, Mihalcea, Razvan, Negut, Daniel, Srivastava, Anubhav, Campopiano, Stefania, Sansone, Lucia, Giordano, Michele, Stancalie, Andrei, Iadicicco, Agostino, Smietana, Mateusz
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01-09-2024
• Subjects: Ionizing irradiation; Long period grating; Optical fiber; Optical properties; Thin film; Ionizing irradiation; Long period grating; Optical properties; Optical fiber; Thin film
• ISSN: 0030-3992
• DOI: 10.1016/j.optlastec.2024.111019

•Optical fiber based method for real-time monitoring of thin film optical properties when exposed to gamma radiation.•Long period grating (LPG) inscribed in a radiation resistant optical fiber, which is coated with the thin film to be analyzed.•Tested for metal oxide thin films, i.e., Al2O3, TiO2 and Ta2O5, as well as a polymeric film, namely polystyrene.
In this work, we report an all-optical-fiber-based method to monitor in real-time the changes in thin film optical properties when exposed to harsh environments such as high doses of gamma radiation. The method is based on a long period grating (LPG) inscribed in a radiation resistant optical fiber, which is coated with a thin film to be analyzed. Due to impact of the environment on the film properties, the transmission spectrum of the LPG changes. To validate this methodology, we deposited oxides of various metals, i.e. aluminum (Al2O3), titanium (TiO2), and tantalum (Ta2O5), as well as a polymeric film, namely polystyrene (PS), on the LPG surface and measured the resonant wavelength shift induced by high doses of gamma exposure (dose rate of 2.3 kGy/h, up to a total dose of 46 kGy). The changes could be observed in real-time up to maximum reached dose and during the recovery period. The results are significantly dependent on thin film material. Among the oxides, TiO2 thin film demonstrated the highest susceptibility to irradiation, whereas Al2O3 exhibited the least impact. Additionally, a good recovery potential for Ta2O5 thin film was observed, hinting at its promising application in dosimetry. Conversely, the PS film exhibited a permanent effect induced by irradiation. This is the first real-time experimental study of the impact of high dose gamma radiation on thin film optical properties using a universal optical-fiber-based device. The findings pave the way for assessing radiation hardness of thin film materials or utilizing such a method to optimize material treatment involving ionizing radiation.