论文信息 - Investigation of the photoacoustic signal dependence on laser power

Investigation of the photoacoustic signal dependence on laser power

In this study we have focused on exploring the photoacoustic signal generated by laser induced dielectric breakdown process in pure water, under normal conditions. In this case the dielectric breakdown will lead to a formation of a shock wave. We investigated the relation between pulse energy and amplitude, group velocity and power spectrum of the shock wave. Also, the threshold for dielectric breakdown is estimated. A pulsed, high power Nd:YAG laser with λ = 532 nm and a pulse duration of 12 ns was used. The laser pulse energy ranges from 0.1 mJ to 7.4 mJ. Only photoacoustic signals generated from dielectric breakdown was considered. We found that the amplitude and the average group velocity of the shock wave correlates to the laser pulse energy. The frequency contents of the photoacoustic signal changes due to both non-linear behaviour and dissipative effects. We estimated the dielectric breakdown threshold to be 0.44 × 1011Wcm-2.

[1] Reginald Birngruber,et al. Intraocular Nd:YAG laser surgery: laser-tissue interaction, damage range, and reduction of collateral effects , 1990 .

[2] Ulrich Parlitz,et al. Minimization of cavitation effects in pulsed laser ablation illustrated on laser angioplasty , 1996 .

[3] Olgert Lindau,et al. Collapse and rebound of a laser-induced cavitation bubble , 2001 .

[4] George S. K. Wong,et al. Speed of sound in pure water as a function of temperature , 1993 .

[5] D. Hammer,et al. Laser-induced breakdown in aqueous media , 1997 .

[6] A. Welch,et al. Shielding properties of laser-induced breakdown in water for pulse durations from 5 ns to 125 fs. , 1997, Applied Optics.

[7] U. Parlitz,et al. Shock wave emission and cavitation bubble generation by picosecond and nanosecond optical breakdown in water , 1996 .

[8] Malcolm J. Crocker,et al. Encyclopedia of Acoustics , 1998 .

[9] A. Grennberg,et al. Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert transform correlation , 1994, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.

[10] Dirk Theisen,et al. Plasma formation in water by picosecond and nanosecond Nd:YAG laser pulses. I. Optical breakdown at threshold and superthreshold irradiance , 1996 .