Shown in the flash diagrams are two scan lens designs. The multi-lens design is a telecentric lens. Notice how the focused laser beam always strikes the working field normal to its surface. Telecentric lenses typically have multiple lens elements and cost more than non-telecentric or single element lens designs. The primary benefit of a telecentric lens is to keep all of the focused “rays” of the laser beam at an angle close to normal from the working field. Telecentric lenses can have up to 5 degrees of incidence angle off of the 90 degree normal angle.

Having parallel or near parallel beams has several advantages. One advantage of lowering the angle of incidences at the working field is found in cutting or drilling applications. Unless the beams are near or close to normal from the material to be cut or drilled, one would end up with slanted holes or chamfered cut edges.

Another benefit is found when trying to penetrate a material such as crystal. If the incident beam strikes at an angle too far from normal, the beam may reflect off of the surface and fail to penetrate. Another benefit is that the focused spot will not elongate and become elliptical as a result of increasing scan angles as found in non-telecentric lenses.

Notice how in the non-telecentric lens, the focused spot strikes the working field at greater and greater angles of incidence as the beam travels farther and farther from the center of the field. This results in a spot with lower and lower energy density as the spot elongates and becomes more elliptical. This can result in less penetration or ablation and greater line thickness in the corners of a marking field.

The decision to use a telecentric lens or not is based on the application requirement and system budget. Basic marking applications typically do not require telecentric lenses, but often cutting and drilling applications do require a telecentric lens. Contact a NTI applications specialist to find out what lens is suitable for your application.

For more detailed information about Scan Lenses, click on this link: Scan Lens Theory