Scanning Lens
Scanning Lens (also called scan lens or f-theta lens) is a specialized multi-element optical objective designed to focus a collimated (or near-collimated) laser beam onto a flat target plane while the beam’s direction is rapidly steered by a scanning device such as galvanometer mirrors or a rotating polygon mirror.
Key Technical Characteristics:
Unlike a simple spherical lens (which focuses onto a curved Petzval surface and produces a nonlinear relationship of the form y = f tan θ), a scanning lens is corrected for:
Flat field: The focused spots lie in a plane rather than on a curved surface, keeping the spot size nearly constant across the scan field.
f-theta (f-θ) distortion correction: Spot position on the target is made proportional to the scan angle (y ≈ f θ, with θ in radians). This allows the focused spot to move at constant linear velocity when the scanner rotates at constant angular velocity, simplifying control electronics and ensuring uniform processing speed or image fidelity.
Additional common features include:
Design for a specific laser wavelength (or narrow band), with anti-reflection coatings optimized for that wavelength (UV, visible, near-IR, or mid-IR such as 10.6 µm for CO₂ lasers).
Entrance pupil typically located near the scanner mirrors.
Options for telecentric designs (chief rays approximately perpendicular to the work surface across the field, useful for high-precision drilling or machining) versus non-telecentric designs (larger fields, lower cost).
Diffraction-limited or near-diffraction-limited performance over a defined scan field, with controlled spot size, circularity, and minimal field curvature or distortion (often <1%).
They are typically multi-element assemblies (not singlets) because of the required aberration corrections, and they have a substantial physical length relative to their focal length.
Basic Principle of Use:
A collimated laser beam is deflected by one or more scanners (pre-objective scanning is most common). The scanning lens then focuses the angularly varying beam onto a flat working plane. In two-axis systems the scanners are orthogonal, enabling 2D raster or vector scanning over a rectangular or circular field.
Main Applications:
Laser material processing: Marking, engraving, cutting, drilling, welding, and surface structuring. Consistent spot size and intensity across the field are critical.
Additive manufacturing: Selective laser sintering (SLS) or melting (SLM) of metal or polymer powders.
Laser scanning microscopy and biomedical imaging: Confocal, multiphoton, and optical coherence tomography (OCT) systems, where the scan lens forms part of the scan engine together with a tube lens and objective.
Laser displays and projection: Steering RGB beams with linear motion to avoid geometric distortion.
Barcode readers, LIDAR, and inspection systems: High-speed beam steering onto detectors or scenes.
Scanning lenses enable high-speed, high-precision laser beam delivery over a flat field with linear positioning, making them a core component in modern laser scanning systems.