Time-resolved study of the mechanical response of tissue phantoms to nanosecond laser pulses.

We present a time-resolved study of the interaction of nanosecond laser pulses with tissue phantoms. When a laser pulse interacts with a material, optical energy is absorbed by a combination of linear (heat generation and thermoelastic expansion) and nonlinear absorption (expanding plasma), according to both the laser light irradiance and material properties. The objective is to elucidate the contribution of linear and nonlinear optical absorption to bubble formation. Depending on the local temperatures and pressures reached, both interactions may lead to the formation of bubbles. We discuss three experimental approaches: piezoelectric sensors, time-resolved shadowgraphy, and time-resolved interferometry, to follow the formation of bubbles and measure the pressure originated by 6 ns laser pulses interacting with tissue phantoms. We studied the bubble formation and pressure transients for varying linear optical absorption and for radiant exposures above and below threshold for bubble formation. We report a rapid decay (of 2 orders of magnitude) of the laser-induced mechanical pressure measured (by time-resolved shadowgraphy) very close to the irradiation spot and beyond 1 mm from the irradiation site (by the piezoelectric sensor). Through time-resolved interferometry measurements, we determined that bubble formation can occur at marginal temperature increments as low as 3°C.

[1]  A. Vogel,et al.  Stress wave emission and cavitation bubble dynamics by nanosecond optical breakdown in a tissue phantom , 2006, Journal of Fluid Mechanics.

[2]  Emil-Alexandru Brujan Dynamics of shock waves and cavitation bubbles in bilinear elastic-plastic media, and the implications to short-pulsed laser surgery , 2005 .

[3]  Werner Lauterborn,et al.  Acoustic transient generation by laser‐produced cavitation bubbles near solid boundaries , 1988 .

[4]  Yi Chun Wang,et al.  Application of piezoelectric PVDF film to the measurement of impulsive forces generated by cavitation bubble collapse near a solid boundary , 2007 .

[5]  J. Ocaña,et al.  Optical observation of shock waves and cavitation bubbles in high intensity laser-induced shock processes. , 2009, Applied optics.

[6]  A. Oraevsky LASER-INDUCED ACOUSTIC AND SHOCK WAVES IN OCULAR TISSUES , 1995 .

[7]  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 .

[8]  Medizinisches Laserzentrum Lu ̈ beck,et al.  Shock wave emission and cavitation bubble generation by picosecond and nanosecond optical breakdown in water , 1996 .

[9]  I. Thormählen,et al.  Refractive Index of Water and Its Dependence on Wavelength, Temperature, and Density , 1985 .

[10]  Frank K. Tittel,et al.  Pulsed laser ablation of soft tissues, gels, and aqueous solutions at temperatures below 100°C , 1996 .

[11]  R. Riva,et al.  PVDF sensor in laser ablation experiments , 2004 .

[12]  Guillermo Aguilar,et al.  Short and ultrashort laser pulse induced bubbles on transparent and scattering tissue models , 2007, SPIE BiOS.

[13]  Werner Lauterborn,et al.  Optical and acoustic investigations of the dynamics of laser-produced cavitation bubbles near a solid boundary , 1989, Journal of Fluid Mechanics.

[14]  A. Vogel,et al.  Mechanisms of pulsed laser ablation of biological tissues. , 2003, Chemical reviews.

[15]  Yi Chun Wang,et al.  Development of a PVDF sensor array for measurement of the impulsive pressure generated by cavitation bubble collapse , 2006 .

[16]  B. Hooper Optical-thermal response of laser-irradiated tissue , 1996 .

[17]  Steven L. Jacques,et al.  Depth profiling of absorbing soft materials using photoacoustic methods , 1999 .

[18]  Frank K. Tittel,et al.  Mechanism of laser ablation for aqueous media irradiated under confined‐stress conditions , 1995 .

[19]  R Evans,et al.  Pump-probe imaging of nanosecond laser-induced bubbles in agar gel. , 2008, Optics express.

[20]  A M Rubenchik,et al.  Influence of pulse duration on ultrashort laser pulse ablation of biological tissues. , 2001, Journal of biomedical optics.

[21]  Peter E. Dyer,et al.  Photomechanical Processes and Effects in Ablation , 2003 .