ULO Optics’ multi-element f-Theta lenses are designed for superior performance for working distances between 75 and 300 mm and field sizes up to 210 x 210 mm, for high power laser applications like marking, welding and structuring. The ZnSe lenses are highly transmissive and are mounted in an aluminum housing for easy handling. A protective window can be included and is recommended for short working distances. Our lenses are available with different coatings as needed.

 Doublets, the ZSD-15-Series

The ZSD-15 series doublets contain ZnSe elements made from the same laser grade ZnSe and fully coated with low absorption anti-reflection coatings. They are capable of handling high powers while focusing down to smaller spots.

 The ZnSe-Triplets, ZST-15-75 and ZST-15-100

  • focal lengths 75 and 100mm respectively, where higher performance than the doublets is required
  • 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
  • can be fitted with a protective window


Part NumberField SizeFocal LengthSpot Diameter (s.d.)*
ZSD-15-7550 mm75 mm118 (25) micron
ZSD-15-10070 mm100 mm139 (22) micron
ZSD-15-150105 mm150 mm171 (0)
ZSD-15-200140 mm200 mm225 (0) micron
ZSD-15-250175 mm250 mm282 (0) micron
ZSD-15-300210 mm300 mm338 (0) micron
ZST-15-7550 mm75 mm89 (4) micron
ZST-15-10070 mm100 mm113 (1) micron

s.d.* = Standard deviation

Spot diameter is determined from optical computation and are not measured values from marking or engraving. The width of an engraved line is affected by laser power, material, scan speed, etc and is normally less than the values listed here.

Please note that this page is only a representation of our most commonly used replacement f-Theta multi-element lenses and is not our entire product line. If there is an item not listed or you have questions, please feel free to contact us and we will be more than happy to assist you.


ULO Optics is an ISO certified company and quality is at the heart of everything we do.  With a host of industrial affiliations you can rely on ULO to deliver.

Diversification into 1 micron optics

ULO Collaborate on the LaserSnake2 project, developing laser cutting optics for safe, remote cutting in air and in water, focused on nuclear decommissioning.