Jansen E D, van Leeuwen T G, Motamedi M, Borst C, Welch A J
Biomedical Engineering Program, University of Texas, Austin 78712.
Lasers Surg Med. 1994;14(3):258-68. doi: 10.1002/lsm.1900140308.
The dynamics of the water absorption peak around 1.94 microns was examined. This peak is important for the absorption of holmium and thulium laser radiation. To examine the effect of temperature on the absorption coefficient, the transmission of pulsed Ho:YAG, Ho:YAG, Ho:YSGG, and Tm:YAG laser radiation through water of 22 degrees C, 49 degrees C, and 70 degrees C was measured as a function of the thickness of the water layer. From these data the absorption coefficients were determined at the three wavelengths. We found that at all three wavelengths, the absorption coefficients decreased when increasing the temperature. Second, the absorption spectrum of water was measured from 1,850-2,150 nm with a spectrophotometer. It was found that the absorption peak at 1.94 microns (at 22 degrees C) shifts to shorter wavelengths with increasing temperatures, to 1.92 microns at 70 degrees C. A model was developed to predict the temperature distribution incorporating the dynamic change in absorption coefficient. The temperature distributions are compared to the predictions of a model assuming constant optical properties. It is shown in this study that the dynamics of the absorption coefficient has a significant influence on the expected zone of damage and ablation parameters in the 2-microns wavelength range.
研究了1.94微米附近水吸收峰的动力学特性。该峰对于钬和铥激光辐射的吸收至关重要。为了研究温度对吸收系数的影响，测量了脉冲Ho:YAG、Ho:YAG、Ho:YSGG和Tm:YAG激光辐射在22℃、49℃和70℃的水中透过率随水层厚度的变化。根据这些数据确定了三个波长处的吸收系数。我们发现，在所有三个波长下，吸收系数均随温度升高而降低。其次，用分光光度计测量了1850 - 2150纳米范围内水的吸收光谱。发现1.94微米处（22℃时）的吸收峰随温度升高向较短波长移动，在70℃时移至1.92微米。建立了一个模型来预测包含吸收系数动态变化的温度分布。将温度分布与假设光学特性恒定的模型预测结果进行了比较。本研究表明，吸收系数的动力学特性对2微米波长范围内预期的损伤区域和消融参数有显著影响。
