Precise autofocusing microscope with rapid response

Precise and rapid focus detection is an essential operation in several manufacturing processes employing high-intensity lasers. However, the detection resolution of existing methods is notably low. This paper proposes a technique that provides a rapid-response, high-precision, and high-resolution focus inspection system on the basis of geometrical optics and advanced optical instruments. An ultrafast interface position detector and a single-slit mask are used in the system to precisely signal the focus position with high resolution. The reflected images on the image sensor are of a high quality, and this quality is maintained persistently when the target surface is shifted along the optical axis. The proposed system developed for focus inspection is simple and inexpensive, and is appropriate for practical use in the industrial production of sophisticated structures such as microcircuits and microchips.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

High-Speed Focus Inspection System Using a Position-Sensitive Detector

Cao

Hoang

Ahn

et al. 2017

“…However, the timing fluctuations of the laser source introduce noise, thereby degrading the measurement accuracy [ 32 , 33 , 34 , 35 ]. As a result, this study proposes a method to measure and compensate for fluctuations in the laser beam geometry.…”

Section: Structure Layout and Measuring Principlementioning

confidence: 99%

Design of a Measurement System for Simultaneously Measuring Six-Degree-Of-Freedom Geometric Errors of a Long Linear Stage

Liu

Chen

et al. 2018

Self Cite

This study designs and characterizes a novel precise measurement system for simultaneously measuring six-degree-of-freedom geometric motion errors of a long linear stage of a machine tool. The proposed measurement system is based on a method combined with the geometrical optics method and laser interferometer method. In contrast to conventional laser interferometers using only the interferometer method, the proposed measurement system can simultaneously measure six-degree-of-freedom geometric motion errors of a long linear stage with lower cost and faster operational time. The proposed measurement system is characterized numerically using commercial software ZEMAX and mathematical modeling established by using a skew-ray tracing method, a homogeneous transformation matrix, and a first-order Taylor series expansion. The proposed measurement system is then verified experimentally using a laboratory-built prototype. The experimental results show that, compared to conventional laser interferometers, the proposed measurement system better achieves the ability to simultaneously measure six-degree-of-freedom geometric errors of a long linear stage (a traveling range of 250 mm).

“…More importantly, some other studies have already improved the optical setup to explore the focus on a non-planar sample based on diffractive beam samplers [ 12 , 13 ] or the macro/micro dual-drive principle [ 14 ]. Furthermore, many auto-focusing devices have been developed for laser direct writing [ 14 , 15 , 16 ]; laser ablation [ 17 ]; automatic microscopy and measurement [ 18 ]; laser material processing [ 19 ]; two-photon photo-polymerization (TPP)-based micro-fabrication [ 20 ]; and several other applications [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ] in Shack-Hartmann wave-front sensor fabrication [ 21 ], parallel data processing [ 22 ], photonic force microscopy [ 23 ], controllable mirror-lens retrofocus objective [ 24 ], tunable lens focal offset measurement [ 25 ], laser micromachining [ 26 ], remote sensing [ 27 ], automated optical inspection [ 28 ], auto-focusing infinity corrected microscopes [ 29 ], and direct imaging technology [ 30 ] with detailed theoretical models. However, these focus detection systems are complicated, expensive, and inadequate for the mass production of 3D patterns [ 21 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 ].…”

Section: Introductionmentioning

confidence: 99%

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

Cao

Hoang

Ahn

et al. 2017

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.