Generation of acoustic waves by cw laser radiation at the tip of an optical fiber in water

详细信息    查看全文

• 作者：V. I. Yusupov ; A. N. Konovalov ; V. A. Ul’yanov ; V. N. Bagratashvili
• 关键词：cw laser radiation ; acoustic pulses ; optical fiber ; moderate power
• 刊名：Acoustical Physics
• 出版年：2016
• 出版时间：September 2016
• 年：2016
• 卷：62
• 期：5
• 页码：537-544
• 全文大小：825 KB
• 刊物类别：Physics and Astronomy
• 刊物主题：Physics
  Acoustics
  Russian Library of Science
  
• 出版者：MAIK Nauka/Interperiodica distributed exclusively by Springer Science+Business Media LLC.
• ISSN：1562-6865
• 卷排序：62

文摘

We investigate the specific features of acoustic signals generated in water under the action of cw laser radiation with a power of 3 W at wavelengths of 0.97, 1.56, and 1.9 μm, emerging from an optical fiber. It is established that when a fiber tip without an absorbing coating is used, quasi-periodic pulse signals are generated according to the thermocavitation mechanism due to the formation and collapse of vapor–gas bubbles of millimeter size. In this case, the maximum energy of a broadband (up to 10 MHz) acoustic signal generated only at wavelengths of 1.56 and 1.9 μm is concentrated in the range of 4–20 kHz. It is shown that when there is no absorbing coating, an increase in the laser-radiation absorption coefficient in water leads to an increase in the frequency of generated acoustic pulses, while the maximum pressure amplitudes in them remain virtually constant. If there is an absorbing coating on the laser-fiber tip, a large number of small vapor–gas bubbles are generated at all laser-radiation wavelengths used. This leads to the appearance of a continuous amplitude-modulated acoustic signal, whose main energy is concentrated in the range of 8–15 kHz. It is shown that in this case, increasing the absorption coefficient of laser radiation in water leads to an increase in the power of an acoustic emission signal. The results can be used to explain the high therapeutic efficiency of moderate-power laser-fiber apparatus.