10.6um F-theta Lens

A standard lens focuses the laser beam on a spherical plain in contrast to an ideal flat or plane field. The use of ƒ-theta lenses provides a plane focusing surface and almost constant spot size over the entire XY image plane or scan field. The position of the spot on the image plane is directly proportional to the scan angle. Telecentric ƒ-theta lenses focus the laser beam so it is almost perpendicular (within 1 degree) to the work surface over the entire scan field. This ensures the spot is round even in the corners of the scan field and if holes or channels are machined, they are perpendicular to the work surface.

Color corrected ƒ-theta lenses are designed to accommodate multiple wavelengths. Normally each wavelength would focus to a different point on the work surface. In a color corrected lens the focal point for each wavelength coincide. This is achieved by scheduling an ideal combination of different glass types for the various lens elements in the lens. Color corrected ƒ-theta lens are primarily used for simultaneously viewing the work surface through the scan lens with a camera while laser processing. Another common application for color corrected scan lenses are for use in confocal scan microscopes which require a broad range of visible wavelengths.

We mainly provide 3 series of f-theta lenses, STY, STS and STJ.

In the following tables, the abbreviations are as follows: FL means effective focal length; EP means max. input beam diameter; SAR means scan area, AS means aperture stop; WD means working distance; OD means max. outside diameter; MT means mount thread; fs means fused silica, SA means max. full diagonal scan angle; L2 (a1) means recommended mirror separation; a2 means 2nd mirror to flange; L1 means the distance 2nd mirror and scan lens; SL means scan length; Length means the total length of the scan lens; FSD means focused spot diameter.

1. Single-element Scan Lenses (F-theta Lenses)

1) STSL Series F-theta Lenses

STSL scanner lenses specially designed and optimized for use in CO2 laser 2-axis galvo-scanner systems with full beam diameters of up to 15.0mm. Mirror sets appropriate for use with beam diameters up to 15mm require an increase in mirror separation in comparison with smaller mirrors. These changed optical conditions are catered for by the STSL series. These single-element lenses are designed to represent the best achievable compromise for on-axis and off-axis aberrations, field flatness and F-theta characteristics, obtainable using single-element spherical-surface designs of (standard) 48mm diameter. The lens materials is ZnSe.

• The lenses are meniscus form; one concave and one convex surface. The concave always faces the incident beam.
• The mirror locations are the same for every STSL lens, so any lens can replace any other in the cell and be correctly positioned. The field sizes given, assume an optical field angle of +/-20deg.
• Focused spot diameters assume a 15mm diameter full beam (approximately 12mm 1/e2) and TEM00 mode (M2 = 1). The ‘average’ is the mean of 25 field positions in a quadrant.
• For all STSL lenses, the diameter is 48.0 +0/-0.1 mm, and the edge thickness is 3.0 +/-0.1 mm.

For the above lenses, we can provide a mount as option as follows:

2) STXH Series Mounted F-theta Lenses

Ordering Information: STXH-10.6-SAR-EFL-EP-LD, where SAR is scanning area (mmxmm), EFL is focal length (mm), EP is max. entrance pupil (mm) such as 14 or 20mm and no indication is 14mm, LD is lens diameter (mm) such as 38, 48 or 65mm and no indication is 48mm.

3) STY Series 10.6um or 9.3um Mounted F-theta Lenses

STY Series 5.5um Mounted F-theta Lens

4) STH Series 10.6um Mounted F-theta Lenses

2. Mounted 2-element F-theta Lenses

1) STU2 Series Mounted 2-element F-theta Lenses

These doublet (STU2) and triplet scanning (STU3) lenses are intended to work with the same configuration of scanning mirrors and beam sizes as the STSL single-element lenses, but are offered at the shorter focal lengths where better performance is possible. The doublets have focal lengths from 75 to 300mm. Above 300mm the benefits of using a doublet are not great. The triplets are offered in two focal lengths, 75 and 100mm. These give diffraction limited performance and even further improvement over the corresponding doublet.

All the lenses are made from laser grade ZnSe. Each of the lenses comes in a black anodized aluminium mount and can also be fitted with a ZnSe protection window as an option.

Specifications:

• Material: All elements and protection window made from Laser Grade ZnSe.
• Mount details: See Figure 10.51.
• Beam diameter: Up to 15mm (12mm 1/e2)
• Optical scan field: +/-20° in X and Y.
• Focal length: Within 1%.
• Absorption: < 0.25% per element.
• Transmission: > 99.6% per element coated AR/AR for 10.6mm.
• Damage threshold: CW 3000W/mm at 10.6mm.

3. Mounted Triple-element F-theta Lenses

1) SL3 Series 3-element F-theta Lenses

2) STU3 Series Scan Lenses

• focal lengths 75 and 100mm respectively
• the 75mm focal length lens is also nearly telecentric (see below) with the focused beam less than 5° to the normal diffraction limited performance over the entire image plane
• virtually zero F-theta error
• can be fitted with a protective window

Custom designs:

The designs listed below are for a specific set of conditions that may not suit everyone’s requirement. If you need a lens for another set of conditions, such as, a larger beam, different field size or focal length, or a telecentric design, then please contact us.

Focused spot size comparison between STSL, STU2 and STU3

Dimension of STU2 and STU3

4. STG Series Telecentric F-theta Lenses

Custom-design and –made available upon request.