| Apr 04, 2023 |
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(Nanowerk News) Photoexcitation, particularly photoionization, represents a vital aspect of light-matter interactions in nature, with applications spanning photosynthesis in plants, vision in biology, photography, and laser processing of materials. Conventional wisdom posits that the transformation of a substance is weaker when less light is absorbed. However, our recent findings challenge this assumption.
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In a groundbreaking paper published in Light Science & Application (“Efficient ultrafast laser writing with elliptical polarization”), a group of researchers led by Professor Peter G. Kazansky from the Optoelectronics Research Centre at the University of Southampton, United Kingdom, unveiled their discovery of efficient ultrafast laser nanostructuring with elliptical polarization in silica glass.
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| a, Birefringence images of laser patterns written in silica glass with linearly and elliptically polarized pulses. b, Scanning electron microscope (SEM) images of corresponding nanopore structures. (Image courtesy of the researchers)
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Surprisingly, despite the nonlinear absorption being approximately 2.5 times weaker, elliptically polarized pulses yield about double the birefringence compared to linearly polarized light. The team observed anisotropic nanopores with a higher concentration in elliptically polarized pulses.
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This phenomenon is attributed to the enhanced interaction of circularly polarized light with a network of randomly oriented bonds and hole polarons in silica glass, as well as the efficient tunneling ionization of defects possessing low excitation potentials by circular polarization.
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The researchers elucidated, “It is widely assumed that multiphoton ionization is the primary mechanism governing ultrafast laser writing in transparent materials, but our investigation has revealed that tunneling excitation of laser-induced defects, such as self-trapped holes, plays a crucial role in nanostructuring silica glass.”
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They further projected, “In 5D optical data storage, information can be recorded using elliptically polarized pulses with reduced energy and increased writing speed. Additionally, our demonstration enables the fabrication of large-area geometric phase optical elements and vector beam converters with ultrahigh transmittance for high-power and UV lasers.”
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