Researchers at Tohoku University have developed a new method to improve laser material processing by focusing a tailored laser beam through transparent glass to create a tiny spot inside the material. Published in the journal Optics Letters on March 1, 2024, their findings have the potential to boost processing resolution in industries such as automotive, semiconductors, and medicine. Laser machining, like drilling and cutting, is crucial in various applications, and ultra-short pulse laser sources allow for precise processing at micro to tens of microns scales. However, advancements in recent years have called for even smaller scales below 100 nanometers, which existing methods struggle to achieve.
The researchers focused on a laser beam with radial polarization, also known as a vector beam, which generates a longitudinal electric field at the focus, resulting in a smaller spot than conventional beams. One drawback of this process is the weakening of the field inside the material due to light refraction at the air-material interface, limiting its effectiveness. To overcome this limitation, the team utilized an oil immersion objective lens typically found in biological microscopes for laser processing glass substrates. The use of immersion oil with nearly identical refractive indices to glass allows light passing through them to not bend, enhancing the effectiveness of the laser beam.
By examining the behavior of the radially polarized beam when focused with an annular shape, the researchers discovered that the longitudinal field could be greatly enhanced due to total reflection at high converging angles on the back surface between the glass and air. This enhancement led to the creation of a small focal spot by using an annular-shaped radially polarized beam. Applying this method to laser process a glass surface with an ultra-short pulse laser beam, the researchers were able to create a hole with a diameter of 67 nanometers, significantly smaller than the laser beam’s wavelength.
This breakthrough in laser material processing allows for direct material processing with enhanced precision using the enhanced longitudinal electric field. It presents a simple approach to achieve processing scales below 100 nanometers and opens up new possibilities for laser nano-processing in various industries and scientific fields. The research conducted by the team at Tohoku University demonstrates the potential of tailored laser beams focused through transparent glass to improve processing resolution and enable more precise laser machining at extremely small scales, benefiting a wide range of applications.
By utilizing unique laser beam properties and overcoming limitations related to light refraction in materials, the researchers have developed a method that could revolutionize laser material processing. The ability to create a small focal spot inside transparent glass using a radial polarized beam with an annular shape opens up opportunities for enhanced precision in laser processing, enabling the creation of holes with diameters below 100 nanometers. This advancement has the potential to advance laser machining techniques in industries such as automotive, semiconductors, and medicine, where high precision and small scales are critical for successful manufacturing processes.
The application of this method to laser processing of glass substrates with ultra-short pulse laser beams showcases the potential for improved processing resolution and precision in material processing. The ability to create holes with diameters as small as 67 nanometers demonstrates the effectiveness of this technique in achieving extremely small scales. This breakthrough offers a straightforward approach to achieving processing scales below 100 nanometers, providing new possibilities for laser nano-processing in various industries and scientific fields. The research conducted by the team at Tohoku University represents a significant advancement in laser material processing and has the potential to drive innovation in precision machining techniques.
