Researchers have discovered a new method to improve the resolution of laser processing

Customized laser beams focused through transparent glass can generate a small dot inside the material. Researchers from Northeastern University have reported a method of using this small spot to improve laser material processing and increase processing resolution.

Their research results are published in the journal Optics Letters.

Laser processing, like drilling and cutting, is crucial in industries such as automobiles, semiconductors, and pharmaceuticals. The pulse width of an ultra short pulse laser source ranges from picoseconds to femtoseconds, and can be accurately processed in the range of micrometers to tens of micrometers. But recent progress requires smaller scales, below 100 nanometers, which is difficult to achieve with existing methods.

Researchers focus on laser beams with radial polarization, known as vector beams. The beam generates a longitudinal electric field at the focal point, resulting in a smaller spot than traditional beams.

Scientists have determined that this process has great potential in laser processing. However, one drawback is that due to the light refraction at the air material interface, the field weakens inside the material, thereby limiting its use.

"We overcame this by using oil immersion lenses to laser process glass substrates," exclaimed Yuichi Kozawa, Associate Professor at the Institute of Advanced Materials Multidisciplinary Research at Northeastern University and co-author of the paper. "Because the refractive indices of oil immersed and glass are almost the same, the light passing through them will not bend."

Further research on the behavior of radially polarized beams under circular focusing indicates that the longitudinal field is greatly enhanced. This enhancement is due to total reflection occurring at high convergence angles on the back between glass and air. By using a circularly polarized beam of light, Kozawa and his colleagues created a small focal point.

From there, they applied this method to processing glass surfaces with ultra short pulse laser beams. A single shot of the converted pulse on the back of the glass substrate will produce a hole with a diameter of 67 nanometers, approximately 1/16 of the wavelength of the laser beam.

"This breakthrough makes it possible to use enhanced longitudinal electric fields for direct material processing with higher accuracy," Kozawa added. "It provides a simple method to achieve processing scales below 100 nanometers and opens up new possibilities for laser nanoprocessing in various industries and scientific fields."

Source: Laser Net