Plasma mediated ablation of biological tissues with nanosecond-to-femtosecond laser pulses: relative role of linear and nonlinear absorption

Abstract

Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range of 1 ns-300 fs at 1053-nm wavelength. It was found that pulsed laser ablation of transparent and weakly absorbing gels is always mediated by plasma. On the other hand, ablation of strongly absorbing tissues is mediated by plasma in the ultrashort-pulse range only. Ablation threshold along with plasma optical breakdown threshold decreases with increasing tissue absorbance for subnanosecond pulses. In contrast, the ablation threshold was found to be practically independent of tissue linear absorption for femtosecond laser pulses. The mechanism of optical breakdown at the tissue surface was theoretically investigated. In the nanosecond range of laser pulse duration, optical breakdown proceeds via avalanche ionization initiated by heating of electrons contributed by strongly absorbing impurities at the tissue surface. In the ultrashortpulse range, optical breakdown is initiated by multiphoton ionization of the irradiated medium (six photons in case of tissue irradiated at 1053-nm wavelength), and is less sensitive to linear absorption. High-quality ablation craters with no thermal or mechanical damage to surrounding material were obtained with subpicosecond laser pulses. Experimental results suggest that subpicosecond plasma mediated ablation can be employed as a tool for precise laser microsurgery of various tissues. . His research interests are in the field of diagnostic and therapeutic applications of lasers in medicine and biology. He has published more than 70 papers and 80 conference proceedings on laser photochemistry of biomolecules, laser ablation of biological tissues, fluorescence diagnostics, and optoacoustic imaging.Dr. Oraevsky is a member of the SPIE, BIOS, LEOS, OSA, and a Fellow of the ASLMS. (M'95), for a photograph and biography, see this issue, p. 799. Luiz B. Da Silva

Surgical applications of femtosecond lasers

“…Ablation was confirmed to depend strongly on pulse duration [32], numerical aperture (NA), and pulse energy [33]. Ablated areas were probed by scanning electron microscopy (SEM) [34], atomic force microscopy (AFM) [35,36], and fluorescence microscopy to ascertain the completion and resolution of surgery.…”

Optimization of Erbium-Doped Actively Q-Switched Fiber Laser Implemented in Symmetric Configuration

“…As was expected, the minimization of the discharge time notably improved the laser performance. This suggested design for a high power actively QS-FL is a cost-effective technology that can find applications in different fields of science and engineering including laser material ablation [19], laser assisted micro-machining [20], supercontinuum generation [21], LIDAR [22] and bio-medicine [23]. We expect that the ideas presented in this article can also be applied to actively QS lasers that are based on other types of active fibers as well as to solid state and gas lasers.…”

C. elegansas a genetic model to identify novel cellular and molecular mechanisms underlying nervous system regeneration

“…It also generates more collateral damage to the surrounding tissues due to the higher pulse energy (0.5 μJ) induced by the longer pulse duration on the order of nanosecond or picosecond. [65][66][67][68] The invention of the near-infrared (NIR; 780-800 nm) femtosecond laser system brings the surgical precision of laser ablation from the cellular level (~10 μm) to the subcellular level (<1 μm) (Fig. 2).…”