Noncontact photoacoustic spectroscopy (NCPAS) during photoablation: a step toward the smart laser?

Thomas Bende; Michael Matallana; Bernhard Kleffner; Manfred Ostertag; Benedikt J. Jean M.D.

doi:10.1117/12.209833

22 May 1995 Noncontact photoacoustic spectroscopy (NCPAS) during photoablation: a step toward the smart laser?

Thomas Bende, Michael Matallana, Bernhard Kleffner, Manfred Ostertag, Benedikt J. Jean M.D.

Proceedings Volume 2393, Ophthalmic Technologies V; (1995) https://doi.org/10.1117/12.209833
Event: Photonics West '95, 1995, San Jose, CA, United States

Abstract

Laser photoablation in the IR and UV is accompanied by an acoustic signal. NCPAS may be used for a non-contact monitoring of the ablation process. NCPAS was performed in combination with the 193 nm Excimer-, 2.94 micrometers Er:YAG-, and the FEL laser (< 11 micrometers ). A microphone (Bjoer & Kjaer, 20 Hz- 200kHz) was used. Gelatine, as a target material substitute for cornea was ablated. During ablation, the dependency of NCPAS as a function of fluence, ablation diameter, and target hydration was determined. NCPAS was analyzed in the time-signal and Fourier transformation (FT). The Fourier spectrum of the NCPAS signal shows two gaussian-like curves. As a function of fluence NCPAS showed a linear increase of the time dependent amplitude and the amplitude of the frequency interval, in the observed fluence range. In the FT the beam diameter leads to a square increase of amplitude. Up to the physiological value the hydration shows an increase in amplitude of the FT. NCPAS allows the discrimination of different neighboring biological materials by a typical frequency shift in the FT. On-line detection of NCPAS can be used for feed back, leading to a `smart' laser control.

Citation Download Citation

Thomas Bende, Michael Matallana, Bernhard Kleffner, Manfred Ostertag, and Benedikt J. Jean M.D. "Noncontact photoacoustic spectroscopy (NCPAS) during photoablation: a step toward the smart laser?", Proc. SPIE 2393, Ophthalmic Technologies V, (22 May 1995); https://doi.org/10.1117/12.209833

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