A sufficiently powerful pulsed-laser beam can be used to `drill' a hole in a stainless-steel workpiece. Here we present a real-time method for determining the depth of such a hole produced by ...multi-pulse laser drilling with a Q-switched Nd:YAG laser. The developed experimental setup allowed us to detect the laser-induced ultrasonic waves in the surrounding air and in the workpiece simultaneously by means of a probe-beam-deflection method and a piezoelectric transducer. Our optodynamic approach involved an analysis of these ultrasonic waves in order to determine the depth of the hole at any stage of the process. The increasing depth of the hole and its maximum extent were estimated from changes in the propagation time of the ultrasonic waves traveling from the bottom of the hole to both detectors. Measurements of the maximum hole depth were compared with the predictions of a theoretical model and they were found to be in a good agreement.
Laser induced breakdown in water represents an abrupt high intensity photoacoustic phenomenon. The pressure front that appears at its site represents an ultrasonic shock wave spreading into ...surrounding water. At the same time the cavitation bubble develops. The effect of both is particularly important in ocular microsurgery, where Q-switched lasers are used to vaporize the tissue in procedures such as posterior capsulotomy. Formation of the cavitation bubble and the propagation of the sound wave were analyzed by an optodynamic experimental set-up. It is based on two-dimensional scanning technique using a beam deflection probe. From the beam deflection probe signals the time of flights for both the sound wave and the cavitation bubble were determined. By using Hugoniot curves and the two-dimensional time of flight data field the pressure amplitude in the front was estimated. Simultaneously the expansion of the cavitation bubble was also analyzed and its energy was determined.
We propose a method for evaluating the size of the laser-induced breakdown region in water based on the detection and analysis of optodynamic waves. The breakdown region is an optodynamic source of ...pressure waves that propagate into the surrounding liquid as an ultrasonic pulse. In the experiment the optical breakdown was generated by a standard ophthalmic Nd:YAG laser with a pulse duration of 10
ns and a maximum energy per pulse of 10 mJ. The pulses were detected inside the liquid with a laser-beam deflection probe. The waveforms were captured in the far-field and analyzed. The analysis provides information about the apparent size of the optodynamic source, which is directly related to the size of the breakdown region. The proposed method can be adapted for online monitoring.
Conversion of light to thermal and mechanical energy in the vicinity of the water–air interface was studied experimentally. The focus of an IR pulsed laser was moved in steps in vertical direction ...from the position inside the water upwards to the position slightly above the surface, in the air. The generated optodynamic waves were detected by probe beam deflection. Two probe beams were used simultaneously, both laying parallel to the surface, one inside the water and the other one in the air. The analysis and comparison of the waveforms captured in the two media provide information about the position and size of the optodynamic source relative to the interface, indicating the relative efficiency of thermal energy conversion that takes place in the vicinity of the interface both in the air and inside the water. Three positions of the optodynamic source can be determined from the waveforms: in the air, at the interface and inside the water.
Measurements of laser drilling rate of different woods were performed. Using an Er:YAG laser, very long and narrow holes with depth-to-diameter ratio above 100 were achieved. This indicates the ...occurrence of laser beam trapping. The process has been investigated as a typical optodynamic process. Optoacoustic waves were detected by microphone and analysed to monitor the hole depth produced by consecutive laser pulse exposure of the same spot. The results may have relevance to Er:YAG laser applications in the wood industry.
