ANALYSIS: BEAM DELIVERY
Focus-tunable lenses augment laser marking
steering in a plane (x-y control), whereas the required z-control is established using translational optics, or mechanically moving the object. These solutions work, but
Dr Branislav Timotijevic, of Optotune, shares the benefits of specialised optics in the infrared, NIR and visible wavelengths when integrated into marking applications
are not ideal in terms of size, speed, limited z-range, cost, or mechanical wear that leads to a reduced lifetime. Consequently, there has been a visible shift towards adaptive optical elements. In these cases, spatial displacement of an optical element is replaced by the change of its shape.
The demand for controlling the focus of a laser beam in all three axes is ever increasing. Traceability regulations have resulted in a higher need for laser marking in many industries, from PCB engraving in consumer electronics to the marking of medical implants. This trend is expected to
continue: according to a current report of the Japanese market research specialists, Shibuya Data Count, the laser marking market itself is on course for steady growth until 2030, with a CAGR of 4-5 per cent. One common pain point in marking applications is fast and precise focus control. The need is to focus either at specific object planes (so called 2.5D focusing), or in arbitrary volume (3D laser applications). Naturally, standard optical configurations are the first port of call for such applications: galvanometric mirrors are used to provide beam
24 LASER SYSTEMS EUROPE SUMMER 2022
Optical feedback is key Innovative developments in this field have been made by employing well-known voice coil technology – used for example, in microphones – to control the shape of a polymer lens filled with optical liquid. The first generation of Optotune’s laser focus-tunable lens EL-10- 42-OF took advantage of this technology, which has since proven to be an ideal solution in many areas of laser processing where high standards are needed in terms of laser spot size and scanning speed, especially if volumes are large. This focus- tunable lens was designed for the 1,064nm wavelength commonly used in most laser processing applications, and for low- to mid-power (50W) lasers. At these powers laser
materials processing applications are highly likely to have thermal effects that influence the stability and accuracy of a len’s optical power. For that reason, internal optical feedback was integrated into the EL-10-42-OF, which addressed this problem. This technology is constantly active during lens operation to stabilise its optical power and to allow for repeatability as low as 0.02 diopters in the whole
Figure 1: Marking field and z-ranges achievable with Optotune’s EL-10-42-OF when a 160mm f-theta lens is used
Figure 2: 3D laser marking configurations with focus tunable lenses, such as the EL-10-42-OF, remove the need for an f-theta lens
Figure 3: Inline inspection configuration using Optotune’s EL-16-40 tunable lens
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