Influence of pulse width and speckle formation on the ablation thresholds in water by means of pulsed mid-IR laser radiation

Christoph Hansen*, Ralf Brinkmann, Reginald Birngruber

*Corresponding author for this work


The evaporation of water by means of fiber guided pulsed mid-infrared laser radiation was investigated. The influence of the pulse duration and speckle formation on the ablation threshold was determined. Optical on-line monitoring of refractive index changes at the distal fiber tip has been used to determine the cavitation threshold. Temporal and spatial speckle pattern at the distal application fiber tip were measured by imaging the fiber tip to a reference plane. An IR-CCD camera and fast IR-photodiodes were used to monitor the intensity modulation. The measured cavitation thresholds show a strong dependence on the pulse energy and the pulse duration. Overheating of water at the evaporation threshold could be calculated for the Q-switched pulse mode. Regarding speckle, spatial peak intensities up to a factor of 1.5 and 2.6 over the average intensity were evaluated for the Q-switched and the free running mode, respectively. Speckle modulation plays an important role in the free running mode to achieve the boiling point of water with the threshold radiant exposure determined. Furthermore, transient intensity fluctuations were measured across the beam profile at the fiber tip.

Original languageEnglish
JournalProceedings of SPIE - The International Society for Optical Engineering
Pages (from-to)197-202
Number of pages6
Publication statusPublished - 14.01.1997
EventProceedings of Medical Applications of Lasers in Dermatology, Ophthalmology, Dentistry and Endoscopy 1997 - San Remo, Italy
Duration: 04.09.199707.09.1997
Conference number: 59693

Research Areas and Centers

  • Academic Focus: Biomedical Engineering


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