Scientists have discovered a new method of increasing the resolution of laser processing

Focusing a special laser beam into clear glass can create a tiny spot inside the material. Researchers at Tohoku University have reported a way to use this tiny dot to improve laser processing of materials by increasing processing resolution.

Laser processing, such as drilling and cutting, is vital in industries such as automotive, semiconductor and medical. Ultrashort pulse laser sources with pulse widths from picosecond to femtosecond enable precision machining at scales from microns to tens of microns. However, recent advances require smaller scales, below 100 nanometers, and this is very difficult to achieve with current methods.

The researchers focused a radially polarized laser beam, known as a vector beam. This beam creates a longitudinal electric field at the focus, creating a smaller spot than conventional beams.

Scientists have determined that this process is promising for laser processing. However, a disadvantage is that light is refracted at the air-material interface, which weakens this field within the material, limiting its use.

“We overcame this by using an oil-immersion objective lens commonly found in biological microscopes to laser machine glass surfaces,” says co-author Yuichi Kozawa, associate professor at the Institute for Multidisciplinary Research in Advanced Materials (IMRAM) at Tohoku University. paper. document. “Immersion oil and glass have almost the same refractive index, so light passing through them does not distort.”

Further examination of the behavior of a radially polarized beam when focused in a circular manner showed that the longitudinal field increased significantly. This amplification occurs due to total reflection at wide angles of incidence at the back surface between the glass and the air. Kozawa and his colleagues created a small focal point using the annular shape of the radially polarized beam.

From there, they applied this method to laser machining of a glass surface with an ultrashort-pulse laser beam. A single pulse of the converted pulse on the back surface of the glass substrate created a hole 67 nanometers in diameter, approximately 1/16 the wavelength of the laser beam.

“This groundbreaking development allows direct processing of material with increased precision using an enhanced longitudinal electric field,” adds Kozawa. “It offers a simple approach to realize sub-100 nm processing scales and opens new opportunities for laser nanomachining in various industrial and scientific fields.”