In situ 24 kHz coherent imaging of morphology change in laser percussion drilling

Abstract

We observe sample morphology changes in real time (24 kHz) during and between percussion drilling pulses by integrating a low-coherence microscope into a laser micromachining platform. Nonuniform cut speed and sidewall evolution in stainless steel are observed to strongly depend on assist gas. Interpulse morphology relaxation such as hole refill is directly imaged, showing dramatic differences in the material removal process dependent on pulse duration/peak power (micros/0.1 kW, ps/20 MW) and material (steel, lead zirconate titanate PZT). Blind hole depth precision is improved by over 1 order of magnitude using in situ feedback from the imaging system.

Coaxial real-time metrology and gas assisted laser micromachining: process development, stochastic behavior, and feedback control

“…In situ imaging permits us to correct these errors. As a demonstration, we drilled eight holes with the QCW laser with a fixed set of parameters 19 . We then drilled eight more, but tuned the pulses using information from the imaging system in order to guide the cut to a target depth.…”

“…Figure 9. Orthogonal projections of volumetric images of the air-metal interface (top: air, bottom: metal) for the two sets of holes drilled in stainless steel (A) without feedback and (B) with feedback from the imaging system as in [19]. Scale bars are 100 µm.…”

Application of self-mixing interferometry for depth monitoring in the ablation of TiN coatings

“…16 Being an offline measurement strategy, this method does not give the possibility to compensate the processing deviations. More recently, faster techniques based on Fourier domain optical coherence tomography (OCT) [17][18][19] and self-mixing interferotmetry (SMI) [20][21][22] have been proposed as solutions for ablation depth monitoring. Both of the techniques allow high speed measurement by providing data over only a single dimension, which is depth.…”

Optical coherence tomography based particle image velocimetry (OCT-PIV) of polymer flows

“…Emerging originally from the field of ophthalmology [10], OCT has found an increasing number of applications outside biomedicine in the past few years [11]. Examples range from the measurement of layer thicknesses in multilayer foils [12], the coating thickness on paper [13] or pharmaceutical tablets [14,15], the characterization of laser drilled holes [16], to the investigation of polymer solar cells [17].…”