Noncontact photoacoustic spectroscopy during photoablation with a 193-nm excimer laser.
Photoablation with the 193-nm excimer laser in organic and inorganic material generates an audible sound wave; in a clinical context, this helps to determine when effective photoablation is taking place. We investigated whether the acoustic phenomenon would qualify as a quantitative parameter of photoablation during non-contact photoacoustic spectroscopy (NCPAS). Photoablation was performed with a 193-nm excimer laser at a fluence of 80-330 mJ/cm2 and ablation-zone diameters ranging between 1.2 and 5.13 mm. A capacitor microphone (Broel & Kjaer) emitted a time signal that was processed for Fourier transformation (FT, spectrum of frequency). The following elements of the FT-signal were studied: the integral, the amplitude, the half-value, and the location of the center frequency. The integral and the amplitude were correlated linearly with the fluence. Variation of the ablation-zone diameter between 1.2 and 5.13 mm was found to produce a squared increase of the integral and the amplitude (fluence, 180 mJ/cm2). The half-value and the center of frequency of the FT signal were constant for the same target material but varied between materials. NCPAS may qualify for the future control of various photoablation and laser parameters such as incision depth, ablation-zone diameter, fluence, and target-material identification and discrimination. Its advantage over competing optical methods is its independence from optical target properties (e.g., fluorescence, surface roughness, reflectivity).
Jean
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Sektion Experimentelle Ophthalmo-Chirurgie, Universitäts-Augenklinik, Tübingen, Germany.
Bende
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Matallana
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D000162:Acoustics; D005583:Fourier Analysis; D005780:Gelatin; D053685:Laser Therapy; D007834:Lasers; D012815:Signal Processing, Computer-Assisted
D005780:Gelatin