In-Situ Real-Time Focus Detection during Laser Processing Using Double-Hole Masks and Advanced Image Sensor Software.

Binh Cao,Phuong Hoang,Jeng-O Kim,Heeshin Kang,Jiwhan Noh,Sanghoon Ahn

doi:10.3390/s17071540

Abstract

In modern high-intensity ultrafast laser processing, detecting the focal position of the working laser beam, at which the intensity is the highest and the beam diameter is the lowest, and immediately locating the target sample at that point are challenging tasks. A system that allows in-situ real-time focus determination and fabrication using a high-power laser has been in high demand among both engineers and scientists. Conventional techniques require the complicated mathematical theory of wave optics, employing interference as well as diffraction phenomena to detect the focal position; however, these methods are ineffective and expensive for industrial application. Moreover, these techniques could not perform detection and fabrication simultaneously. In this paper, we propose an optical design capable of detecting the focal point and fabricating complex patterns on a planar sample surface simultaneously. In-situ real-time focus detection is performed using a bandpass filter, which only allows for the detection of laser transmission. The technique enables rapid, non-destructive, and precise detection of the focal point. Furthermore, it is sufficiently simple for application in both science and industry for mass production, and it is expected to contribute to the next generation of laser equipment, which can be used to fabricate micro-patterns with high complexity.

Highlights

Ultrafast laser processing has become increasingly significant in academic research and engineering
We propose a new system for in-situ real-time exploration of focal position during laser processing with double-hole masks
S-type, SPI Lasers) with a wavelength of 1064 nm for fabrication, a laser diode with a wavelength of 655 nm for focus detection, an objective lens (M Plan Apo NIR 5x, Mitoyo, Japan), a specimen, a bandpass filter (FB780-10, CWL = 780 nm, FWHM = 10 nm, Thorlabs) that allows the transmission of 655 nm wavelength beams, prevents the transmission of 1064 nm wavelength beams, and allows adjustment of the beam spot on the image sensor by removing the speckle patterns induced by the roughness of the target surface, an achromatic tube lens with a focal length of 100 mm, and two beam splitters

Summary

Introduction

Ultrafast laser processing has become increasingly significant in academic research and engineering. Most of them employ the leading technologies and advanced principles of optics, such as confocal microscopy [1,2]; investigation of the optical characteristics of a working laser beam [3,4,5,6,7,8,9], in which the analysis of chromatic aberration of the fabrication beam during laser drilling [3] and laser welding [4,5], the construction of digital holograms [6], reflected-light microscopy [7], integral sliding mode control [8], and confocal point sensor [9] was performed; Fourier fringe analysis [10]; and utilization of the printed focus pattern [11] Those methods are all brilliant, but they seem to be expensive and not reproducible when applied in the industry with an enormous number of target samples. We draw conclusions on the proposed technique of real-time focus detection

Working Principle of of the the Focus

Optical Design for Focus Detection and Fabrication

Calibration for Focus Detection

Experimental andof

Conclusions