Wavelength and Intensity Dependence of Laser-Induced Damage in Semiconductors

Disciplines

Physical Sciences and Mathematics

Abstract (300 words maximum)

An ultrashort laser pulse is a burst of laser light lasting for time scales of a millionth of a billionth of a second, or a femtosecond. Semiconductor solids, such as silicon, have electrical properties that fall in the middle of insulators and conductors. Some semiconductors, like gallium arsenide, are used as components in light sensors, and when exposed to laser light are subject to laser-induced damage. There are two physical mechanisms that initiate ultrashort laser-induced damage in solids: photoionization and uncontrolled growth in impact ionization (known as avalanching). Photoionization also involves two mechanisms: multi-photon ionization and quantum tunneling ionization. We examine the laser-induced damage initiation dependence on laser wavelength (color) and field strength (energy). Our results suggest that multi-photon ionization alone does not sufficiently predict the onset of laser-induced damage, as is often assumed for ultrashort pulses. We include both multi-photon and quantum tunneling ionization through the unified ionization rate developed by Keldysh. This photoionization term is added to a simple impact ionization rate, making a single rate equation for the ionization yield that we solve numerically for many field strengths and wavelengths. The maximum ionization yield in each case is recorded and matched to laser-induced damage thresholds for permanent and temporary damage found in the published literature. We use these results to generate laser-damage “maps” to show experimentalists and designers of optical sensors an easy-to-use diagram of damage thresholds for different combinations of laser wavelengths and energies.

Academic department under which the project should be listed

CSM - Physics

Primary Investigator (PI) Name

Jeremy Gulley

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Wavelength and Intensity Dependence of Laser-Induced Damage in Semiconductors

An ultrashort laser pulse is a burst of laser light lasting for time scales of a millionth of a billionth of a second, or a femtosecond. Semiconductor solids, such as silicon, have electrical properties that fall in the middle of insulators and conductors. Some semiconductors, like gallium arsenide, are used as components in light sensors, and when exposed to laser light are subject to laser-induced damage. There are two physical mechanisms that initiate ultrashort laser-induced damage in solids: photoionization and uncontrolled growth in impact ionization (known as avalanching). Photoionization also involves two mechanisms: multi-photon ionization and quantum tunneling ionization. We examine the laser-induced damage initiation dependence on laser wavelength (color) and field strength (energy). Our results suggest that multi-photon ionization alone does not sufficiently predict the onset of laser-induced damage, as is often assumed for ultrashort pulses. We include both multi-photon and quantum tunneling ionization through the unified ionization rate developed by Keldysh. This photoionization term is added to a simple impact ionization rate, making a single rate equation for the ionization yield that we solve numerically for many field strengths and wavelengths. The maximum ionization yield in each case is recorded and matched to laser-induced damage thresholds for permanent and temporary damage found in the published literature. We use these results to generate laser-damage “maps” to show experimentalists and designers of optical sensors an easy-to-use diagram of damage thresholds for different combinations of laser wavelengths and energies.