F-Theta Lens - A Precision Optical Component for Laser Processing

1. Principle and Design: Solving Nonlinearity in Laser Scanning

F-Theta lenses are critical precision optical components widely used in laser processing systems such as laser marking, engraving, cutting, and micromachining. It not only enables precise focusing of the laser beam, but also ensures linearity and consistency throughout the scanning process, significantly enhancing both the efficiency and accuracy of laser operations.

The F-Theta lens—also known as an F-θ lens, flat-field focusing lens, or linear scanning lens—is specifically designed to address the nonlinearity challenges commonly found in laser scanning systems. In traditional laser scanning systems, there is a nonlinear relationship between the beam deflection angle and the scanning trajectory, which will lead to uneven scanning speed and decreased scanning accuracy.

The F-Theta lens corrects this nonlinearity through its unique optical design, establishing a linear relationship between the image height and the scan angle, expressed as:

y = f·θ

where:

y = image height (the position of the laser spot on the work surface)

f = focal length

θ= scan angle (the angle at which the laser beam is deflected by the scanning mirror)

This linear relationship allows the laser beam to move at a constant speed during scanning, ensuring both accuracy and consistency throughout the process.

2. Flat-Field Performance: Uniform Focus Across the Field

The F-Theta lens features excellent flat-field performance，meaning that the laser beam's focal point remains on the same flat plane, even as the galvo scanners deflect the beam at varying angles. This ensures consistent focus and beam quality across the entire image field, with no vignetting or distortion, thereby enhancing the overall precision and stability of laser processing.

In addition, F-Theta lens features high transmission and optimized optical design. Each lens element is coated with a high-power anti-reflective coating to maximize transmission and minimize reflection losses. The multi-element air-spaced design is optimized for flat-field focusing, allowing the laser beam to produce consistently sized focal spots across the entire scan area.

3. Applications and Selection of F-Theta lenses

F-Theta lenses are widely used in laser processing systems. They are suitable for various applications such as laser scanning, marking, engraving, cutting, and especially in laser welding system.  In these processes, the F-Theta lens precisely focuses the laser beam onto the workpiece, producing a uniform and small spot size. This not only improves processing efficiency but also ensures consistent and stable quality.

When selecting an F-Theta lens, multiple parameters must be considered to meet specific application requirements. The focal length is one of the key parameters, determining the lens's focusing ability and scan range. The scan angle affects both the scanning speed and coverage area. Additionally, factors such as the scan length (or scan field diameter), transmission rate, and damage threshold should also be taken into account. The choice of these parameters directly impacts the lens’s performance and service life.

F-Theta lenses address many challenges associated with laser scanning. Additionally, the compact design of flat-field focusing lenses allows users to reduce the number of optical components required to achieve a flat image field.These lenses enable smaller spot sizes, which in turn deliver higher scanning or printing resolution, as well as increased engraving or welding density.Most importantly, when using these lenses, the spot size (both resolution and intensity) remains nearly constant across the entire image plane.

In summary, the F-Theta lens, as a precision optical component in laser processing, features unique flat-field characteristics and linear scanning capability. Its application not only enhances the accuracy and efficiency of laser processing but also drives the continuous advancement of laser technology. When selecting and using F-Theta lenses, it is essential to consider specific application requirements and system parameters comprehensively to ensure optimal processing results and performance.

Scanner Optics has a highly experienced optical design team specializing in F-Theta lens development and custom optical solutions for a wide range of applications. Our lenses are continuously refined and optimized to deliver performance that meets or exceeds international industry standards. In addition to general laser marking applications, our products are widely used in advanced manufacturing sectors such as consumer electronics, micromachining, lithium-ion batteries, photovoltaics, and 3D printing. We manufacture four primary types of lenses: green laser F-Theta lenses,UV laser F-Theta lenses, infrared F-Theta lenses, and high- to medium-power infrared F-Theta lenses.