Paltauf G, Schmidt-Kloiber H
Institut für Experimentalphysik, Karl-Franzens Universität Graz, Austria.
Lasers Surg Med. 1995;16(3):277-87. doi: 10.1002/lsm.1900160310.
Absorption of a short laser pulse produces high thermoelastic stress in the irradiated volume. The relaxation of this stress at a free (tissue-air) surface leads to tensile loading, resulting in mechanical spallation. Using model substances, we investigated the role of this effect in tissue ablation.
STUDY DESIGN/MATERIALS AND METHODS: Stained water and gelatine were irradiated with short pulses (8 ns duration) from a Nd:YAG laser at 1,064 nm wavelength. The dynamics of the induced effects were observed with laser-flash photography and stress wave detection.
Spallation is indicated by the formation of cavitation bubbles below the irradiated surface and is strongly influenced by impurities serving as nucleation sites. Material ejection due to spallation was observed in the liquid sample at a fluence leading to a temperature below the boiling point but needed a temperature in excess of 100 degrees C in gelatine, owing to the small mechanical energy available for this process, estimated to be < 1%.
The mechanical action of thermoelastic stress waves is characterized by high stress amplitudes but low energetic efficiency. A model combining spallation and vaporization is therefore proposed for efficient tissue ablation.
短激光脉冲的吸收会在照射区域产生高热弹性应力。这种应力在自由（组织 - 空气）表面的松弛会导致拉伸载荷，从而引发机械性剥落。我们使用模型物质研究了这种效应在组织消融中的作用。
研究设计/材料与方法：用波长为1064nm的Nd:YAG激光的短脉冲（持续时间8ns）照射染色水和明胶。通过激光闪光摄影和应力波检测观察诱导效应的动态过程。
在照射表面下方形成空化气泡表明发生了剥落，并且剥落受到作为成核位点的杂质的强烈影响。在液体样品中，当能量密度导致温度低于沸点时，观察到由于剥落引起的物质喷射，但在明胶中这需要温度超过100℃，因为该过程可用的机械能较小，估计小于1%。
热弹性应力波的机械作用具有高应力幅度但能量效率低的特点。因此，提出了一种结合剥落和汽化的模型用于有效的组织消融。
