Plasma mediated ablation of biological tissues with ultrashort laser pulses

Technical Report · Wed Mar 08 04:00:00 EST 1995

DOI:https://doi.org/10.2172/71373· OSTI ID:71373

Oraevsky, A A ^[1]; DaSilva, L B; Feit, M D ^[2]

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1. Lawrence Livermore National Lab., CA (United States)
2. Lawrence Livermore National Lab., CA (United States); and others

Plasma mediated ablation of collagen gels and porcine cornea was studied at various laser pulse durations in the range from 350 fs to 1 ns at 1,053 nm wavelength. A time resolved stress detection technique was employed to measure transient stress profiles and amplitudes. Optical microscopy was used to characterize ablation craters qualitatively, while a wide band acoustic transducer helped to quantify tissue mechanical response and the ablation threshold. The ablation threshold was measured as a function of laser pulse duration and linear absorption coefficient. For nanosecond pulses the ablation threshold was found to have a strong dependence on the linear absorption coefficient of the material. As the pulse length decreased into the subpicosecond regime the ablation threshold became insensitive to the linear absorption coefficient. The ablation efficiency was found to be insensitive to both the laser pulse duration and the linear absorption coefficient. High quality ablation craters with no thermal or mechanical damage to surrounding material were obtained with 350 fs laser pulses. The mechanism of optical breakdown at the tissue surface was theoretically investigated. In the nanosecond regime, optical breakdown proceeds as an electron collisional avalanche ionization initiated by thermal seed electrons. These seed electrons are created by heating of the tissue by linear absorption. In the ultrashort pulse range, optical breakdown is initiated by the multiphoton ionization of the irradiated medium (6 photons in case of tissue irradiated at 1,053 nm wavelength), and becomes less sensitive to the linear absorption coefficient. The energy deposition profile is insensitive to both the laser pulse duration and the linear absorption coefficient.

• Research Organization: Lawrence Livermore National Lab., CA (United States)
• Sponsoring Organization: USDOE, Washington, DC (United States); Whitaker Foundation (United States)
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 71373
• Report Number(s): UCRL-JC--120215; CONF-950226--39; ON: DE95011748
• Country of Publication: United States
• Language: English

Related Subjects

56 BIOLOGY AND MEDICINE
APPLIED STUDIES
BIOLOGICAL EFFECTS
COLLAGEN
CORNEA
ENERGY DEPOSITION
EXPERIMENTAL DATA
IRRADIATION
LASER RADIATION
PATHOLOGICAL CHANGES
SOLID STATE LASERS
SWINE
THEORETICAL DATA
ULTRASTRUCTURAL CHANGES