Wavelength dependency of laser-induced damage threshold in IT-CCD under nanosecond pulse laser irradiation

This study investigates the laser-induced damage threshold (LIDT) in IT-CCD under irradiation from 532nm and 1064nm laser pulses, both with a pulse duration of 50 ns, to explore the wavelength dependence on damage susceptibility. The LIDT values for silicon wafers and IT-CCD were measured, revealing a significantly lower LIDT under 532nm irradiation compared to 1064nm. The disparity is attributed to the differing absorption coefficients of silicon at these wavelengths, which influences the depth of light penetration. To validate this finding, a microstructural model of ITCCD pixel unit with actual physical dimensions was constructed. This model was employed to simulate the intensity distribution of the incident laser light at different wavelengths, as well as to analyze the subsequent thermal response within the pixel unit due to light absorption. The ray tracing simulations demonstrated that the light intensity distribution within a pixel unit was almost identical for both wavelengths after being focused by the microlens array. Based on the Fourier heat conduction equation, the temperature distribution within the IT-CCD pixel unit was calculated. It was found that when the damage criterion was set as the melting point of the photosensitive surface's central region, the predicted LIDT by the model closely corresponded to the experimentally obtained point damage threshold for IT-CCD. This agreement indicates that surface melting is the predominant mechanism for point damage in IT-CCD.