Repetition rate dependency of low-density plasma effects during femtosecond-laser-based surgery of biological tissue

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 2009-11, Vol.97 (3), p.695-699
• Main Authors: Kuetemeyer, K., Baumgart, J., Lubatschowski, H., Heisterkamp, A.
• Format: Article
• Language: English
• Subjects: Biological and medical applications; Biological and medical sciences; Engineering; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; Fundamental areas of phenomenology (including applications); General aspects; Instrumentation. Materials. Reagents. Research laboratory organization; Lasers; Optical Devices; Optics; Photonics; Physical Chemistry; Physics; Physics and Astronomy; Quantum Optics; Radiation effects on optical elements, devices, and systems
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s00340-009-3746-y

Femtosecond laser based nanosurgery of biological tissue is usually done in two different regimes. Depending on the application, low kHz repetition rates above the optical breakdown threshold or high MHz repetition rates in the low-density plasma regime are used. In contrast to the well understood optical breakdown, mechanisms leading to dissection below this threshold are not well known due to the complexity of chemical effects with high numbers of interacting molecules. Furthermore, the laser repetition rate may influence their efficiency. In this paper, we present our study on low-density plasma effects in biological tissue depending on repetition rate by static exposure of porcine corneal stroma to femtosecond pulses. We observed a continuous increase of the laser-induced damage with decreasing repetition rate over two orders of magnitude at constant numbers of applied laser pulses or constant laser pulse energies. Therefore, low repetition rates in the kHz regime are advantageous to minimize the total delivered energy to biological tissue during femtosecond laser irradiation. However, due to frequent excessive damage in this regime directly above the threshold, MHz repetition rates are preferable to create nanometer-sized cuts in the low-density plasma regime.