Dynamic behavior of photoablation products of corneal tissue in the mid-IR: a study with FELIX

• Published in: Applied physics. B, Lasers and optics Lasers and optics, 1999-01, Vol.68 (1), p.111-119
• Main Authors: Auerhammer, J.M., Walker, R., van der Meer, A.F.G., Jean, B.
• Format: Article
• Language: English
• Subjects: Free electron lasers; Infrared devices; Laser ablation; Light absorption; Particle size analysis; Proteins; Pulsed laser applications; Spectroscopic analysis; Stroboscopes
• ISSN: 0946-2171; 1432-0649
• DOI: 10.1007/s003400050595

The properties of pulsed IR-laser ablation of biological soft tissue (porcine cornea) were studied in vitro systematically and quantitatively with a free-electron laser in the wavelength range 6 less than or equal to lambda less than or equal to 20 mu m at fluences ranging from 3.1 to 9.4 J/cm super(2). Dynamic parameters such as the extension of the ablation cloud, the initial velocity and momentum of the ablated particles as well as the ablation threshold, the ablated mass, and the particle size were investigated. The ablation plume was made visible with a stroboscopic technique. For a fluence of 3.1 J/cm super(2) the average initial velocity of the ejected particles was deduced from the extension of the plume to range from 120-400 m/s. Measurements of the recoil momentum using a sensitive pendulum led to values between 0.5 and 2.0 mm g/s. All measured properties were related to the spectroscopically determined absorption coefficient of cornea alpha sub(cornea). Where absorption due to proteins is high (at lambda identical with 6.2 and 6.5 mu m), ablated mass, velocity and recoil momentum behave according to alpha sub(cornea). For the first time, variations of the ablation plume from pulse to pulse were observed. Those, as well as the particle size, not only depend on the absorption coefficient, but also on the predominant absorber.