Role of dessication in pulsed laser ablation at the 2.94-um wavelength: experiments and modeling

Laurel Roxanne Jones; Steven L. Jacques

doi:10.1117/12.434716

9 July 2001 Role of dessication in pulsed laser ablation at the 2.94-μm wavelength: experiments and modeling

Proceedings Volume 4257, Laser-Tissue Interaction XII: Photochemical, Photothermal, and Photomechanical; (2001) https://doi.org/10.1117/12.434716
Event: BiOS 2001 The International Symposium on Biomedical Optics, 2001, San Jose, CA, United States

Abstract

A difficulty with using an OPO laser to reshape the cornea by ablation is the tendency for ablation to stop prematurely. We report on using an OPO laser (2.94 um wavelength, 5 ns pulse duration, 7 mJ pulse energy, approximately 0.5-mm 1/e²-radius Gaussian beam) to ablate a 20% acrylamide gel as a model for the cornea. Experiments demonstrated that ablation proceeds at an average rate of ablation of 3-4 μm/pulse then stops at about 1 mm depth. A computer model was developed to simulate the ablation and desiccation processes. Using a range of operating parameters, the model could achieve ablation rates of 2.8-3.5 μm/pulse and cessation of ablation after 0.25-2.1 mm. A key factor is the absorption coefficient of desiccated gel which was measured experimentally to be about 1700 cm^-1. In conclusion, desiccation from residual heat after an ablative pulse creates a dried layer that attenuates subsequent pulses. If the threshold energy density required for ablation is too high, then too much residual energy remains after each pulse and the consequent dried layer halts the ablation process.

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Laurel Roxanne Jones and Steven L. Jacques "Role of dessication in pulsed laser ablation at the 2.94-μm wavelength: experiments and modeling", Proc. SPIE 4257, Laser-Tissue Interaction XII: Photochemical, Photothermal, and Photomechanical, (9 July 2001); https://doi.org/10.1117/12.434716

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KEYWORDS

Laser ablation

Absorption

Pulsed laser operation

Cornea

Optical parametric oscillators

Computer simulations

Attenuators

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