Closed-loop corrective beam shaping for laser processing of curved surfaces

Abstract

Laser processing is a widely used contactless machining technique, with ultrashort pulses affording the intensity to machine almost any material. However, micro-patterning over curved surfaces can be difficult, as a fixed beam shape will necessarily be skewed when directed at a non-orthogonal sample surface. Here, we show that this aberration can be compensated via closed-loop adaptive beam shaping, via the use of a MEMS device (Texas Instruments Digital Micromirror device) acting as an intensity spatial light modulator that is used to create a beam intensity profile transformation that takes into account the local surface gradient of the sample. The patterning of 18 μm diameter circular structures over a region of a 3.00 mm diameter titanium sphere has been demonstrated. Inclinations of the surface normal of up to π/2 from the vertical were tested, and the effective range was found to be up to π/5. The MEMs device is also shown to be capable of providing a real-time and precise laser beam repositioning that compensates for the errors in the movement stages.

Deep learning for the monitoring and process control of femtosecond laser machining

“…A dichroic mirror positioned above the objective allowed for real-time observation and recording of images of the sample during machining, via a CMOS camera (Thorlabs DC1545M). The sample was positioned in three dimensions via translation stages (Thorlabs LNR50S), with automated focal position corrections used to maintain the sample surface at the image plane [37]. Figure 1(a) shows a schematic of the real-time feedback loop, showing that the machined structures are imaged by the camera and that the camera images are then processed by the neural network, which subsequently provides monitoring of the transformation of machined structures and feedback loop that is capable of halting the laser in real time.…”

Modeling adult skeletal stem cell response to laser-machined topographies through deep learning

“…Made up of a 604×684 array of square ~7.6µm mirrors (DMD pixels), the DMD is utilized to create specific spatial intensity profiles for sample ablation. The use of a Pi-shaper permitted a uniform intensity profile necessary for consistent topographical patterning of the sample, and, alongside the DMD, will allow for consistent machining over curved samples, such as bone samples and titanium implants for future expansion and increased versatility of the network model [30].…”

Analysis of the Advantages of Laser Processing of Aerospace Materials Using Diffractive Optics

“…Therefore, in parallel with the development of laser techniques, the technology of beam shaping has also progressed. For cutting, marking, engraving, and drilling, simple objectives can sometimes be used; for example, single lens objectives, one objective with two or three spherical or parabolic lenses, or a single spherical mirror [15,16]. However, that is often not sufficient to focus a beam onto a predetermined area of the workpiece.…”