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ULUSAL METROLOJİ ENSTİTÜSÜ
24
ARALIK
2024
Nodular-defect induced degradation of laser damage resistance of 532 nm high reflectivity coating after exposure to gamma rays
The coupling effect of gamma-ray radiation and 532 nm nanosecond laser radiation on optical coatings and substrates was investigated. Fused silica and S-BSL7 glass with 532 nm high reflectivity (HR) coatings were irradiated using 60Co gamma-ray source at a dose rate of 1 Gy/s for a total dose of 1–500 kGy. After irradiation, the samples were subjected to raster scan testing using a laser with a pulse width of approximately 8.6 nanosecond and wavelength of 532 nm to measure their laser-induced damage threshold (LIDT). The results showed that S-BSL7 glass was significantly darkened after gamma-ray irradiation, whereas fused silica did not change color, but E’ color centers appeared at a dose of 500 kGy. All the coated samples maintained a high level of reflectivity. No significant changes are observed in the material structures of the samples. However, the LIDT of the high reflectivity film decreased significantly after 500 kGy irradiation, whereas the LIDT of all other samples showed no obvious degradation. Scanning electron microscopy of the damage pit cross-sections revealed that all the damage was initiated by nodular defects, suggesting that gamma rays affected the nodular structure. We used Monte Carlo simulations to compare the energy deposition and electron excitation conditions of the film with a nodular structure and an intact multilayer structure under gamma-ray irradiation. We found that the nodular structure slightly enhanced the effect of gamma rays on the film. Considering the small size of the nodules, this small enhancement was only apparent under high-dose gamma-ray irradiation. In general, we confirmed that gamma-ray irradiation influenced the LIDT of the 532 nm HR coating through nodular defects other than the coating stack.
1
MART
2024
Nanosecond laser damage of 532 nm thin film polarizers evaluated by different testing protocols
Different laser damage testing protocols, including 1-on-1, S-on-1, and Raster Scan, were conducted on 532 nm polarizers to evaluate the damage resistance and mechanisms. A comparison of the laser-induced damage thresholds (LIDTs) revealed different damage characteristics and major contributions to film failure for different polarizations. For P polarization, the LIDTs for the three test protocols were nearly the same because of the stabilization of two typical damage morphologies of flat-bottomed pits and mussel damage pits. For S polarization, the LIDTs for multiple pulses were lowest, where absorptive defect-induced damage was revealed. The damage characteristics of 532 nm polarizers and 1064 nm polarizers have been also compared. The mussel damage pits, which are similar to the typical damage morphologies of ultraviolet (UV) laser damage to fused silica, were observed for the first time in coatings of 532 nm polarizers. This suggests that, the polishing-induced subsurface damage of fused silica substrates may tend to be excited by a short-wavelength laser rather than the fundamental wavelength.
25
ARALIK
2023
Nodular defects induced laser damage of 532 nm thin-film polarizers
The laser damage characteristics of the thin-film polarizers for the wavelength of 532 nm and AOI of 56° were investigated using a Nd:YAG laser system with a wavelength of 532 nm and a pulse width of 9 ns. The results showed that the damage morphologies induced by nodular defects in the witnesses is significantly different compared to 1064 nm polarizers. The nodular seeds are incompletely ejected after on-shot laser and butterfly-like damage pits are formed, which gradually develop into the typical nodular ejection pits as laser irradiation. Analysis of the internal structure showed that single or two adjacent SiO2 particles formed the nodular seeds, which were mainly located in bottom layers and were tightly bound to the surrounding layers. In addition, the simulated electric field intensity (EFI) distributions and damage morphologies of nodular defects with different structures were compared, and it was found that the formation of the nodular damage is closely related with the EFI distributions in the thin films.
24
AĞUSTOS
2023
A Laser Damage Threshold for Microscope Glass Slides
However, laser-induced damage to optical components is a limitation for designing and implementing highly sensitive biosensors, necessitating the development and characterization of suitable optical components. Microscope glass slides are among the most extensively used optical units in this field. This study investigated the laser-induced damage threshold (LIDT) of high-quality microscope glass slides obtained from three different vendors. An S-on-1 protocol following the ISO 21254 series standards was adopted to ensure a meaningful comparative analysis.
19
MAYIS
2023
A Multiwavelength Vacuum Environment Laser Calorimetry System
In the current work, we describe a process of optimizing of a laser calorimeter system to characterize the thermal performance of optical glasses and thin films in a vacuum environment. The system is adapted from its predecessor, working in the atmospheric environment, and adapted for the qualification of space-based optics. The new system is capable of operating in vacuum and atmosphere environments. It can perform optical absorption measurements at five different wavelengths by uncoherent combining of five single-mode continuous-wave lasers working at 461 nm, 532 nm, 640 nm, 1064 nm, and 1070 nm wavelengths. Besides, the experimental setup includes a thermally-isolated chamber, power meter, and NTC sensors, where the sample geometry and thermometer positions can be varied by demand. The measurements are performed according to methods, regulated by ISO-11551 series standards. To control the calorimetry system and the whole measurement procedure, homemade software based on the LabVIEW programming package was developed.