Abstract

The paper presents a new method for characterization of Erbium laser ablation processes widely employed in various medical applications. The method is based on detection of shock waves propagating in air above the irradiated surface by means of a wideband piezoelectric sensor and analysis of the acquired signal waveforms. This sensor set-up offers the possibility for integration into the Er laser hand-piece which opens the way to the on-line process monitoring. A new model of the sensor is developed in order to take into account the relative position and orientation of the sensor and its mechanical and electrical properties. The model is verified by comparing the signal waveforms acquired at different sensor distances and orientations relative to the ablated spot with the theoretical waveforms calculated on the basis of numerical solutions of the Taylor-Sedov point explosion model and the developed sensor model. Excellent agreement is observed between the acquired and theoretical waveforms and serves a basis for a novel method that employs shock-wave energy released during the ablation process as a process characteristic that can be determined from the acquired signal waveforms. It is shown that shock-wave energy exhibits significantly less dependence on the position and orientation of the sensor than other waveform characteristics (time of fight, amplitude…) that are currently used for the ablation process characterization.

Highlights

  • The Er:YAG laser, with a wavelength of 2.94 μm [1], is a well-established tool in medicine and surgery, in dentistry [2] and dermatology [3]

  • Observing excellent agreement between the theoretical and experimental waveforms, we propose a novel method that employs shock-wave energy released during the ablation process as a process characteristic that is almost independent of the exact geometrical properties of the detection set-up

  • We describe a method and a set-up that opens the possibilities for on-line process monitoring in Er:YAG laser ablation

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Summary

Introduction

The Er:YAG laser, with a wavelength of 2.94 μm [1], is a well-established tool in medicine and surgery, in dentistry [2] and dermatology [3]. Various set-ups have been examined for this purpose: spatially resolved techniques, such as schlieren [9] and [10], shadowgraphy [11] to [14] or holography [15], as well as the temporally resolved ones: laser interferometer [16] to [18], laser beam deflection probe [19] and [20] and capacitive or piezoelectric acoustic sensors [7], [8] and [21] While most of these techniques represent useful research tools within controlled laboratory experiments, only a few of them exhibit the potential to be used for on-line process monitoring in real medical applications. Additional technical factors come into prominence: e.g. compactness, affordability, insensitivity to environmental influences, speed of response, etc

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