Dr. Kester Nahen Profile

Dr. Kester Nahen

Vice President of Global Marketing at Heidelberg Engineering GmbH

SPIE Involvement:

Author

SPIE Journal Paper | 1 April 2002 Open Access

Plume dynamics and shielding by the ablation plume during Er:YAG laser ablation

Kester Nahen, Alfred Vogel

JBO, Vol. 7, Issue 02, (April 2002) https://doi.org/10.1117/12.10.1117/1.1463047

KEYWORDS: Laser ablation, Pulsed laser operation, Laser beam diagnostics, Er:YAG lasers, Mass attenuation coefficient, Skin, Photography, Particles, Tissues, Laser energy

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Proceedings Article | 9 July 2001 Paper

Interaction of laser-produced cavitation bubbles with an elastic tissue model

Alfred Vogel, Emil Brujan, Peter Schmidt, Kester Nahen

Proceedings Volume 4257, (2001) https://doi.org/10.1117/12.434701

KEYWORDS: Liquids, Laser tissue interaction, Cavitation, Laser ablation, Laser therapeutics, Cornea, Tissues, LASIK, Neck, High speed photography

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We investigated the interaction of a laser-induced cavitation bubble with an elastic tissue model by high-speed photography with up to 5 Mill. frames/sec. The elastic material consisted of a transparent polyacrylamide (PAA) gel whose elastic properties can be controlled by modifying the water content to mimic various biological tissues. The elastic modulus E of the PAA sample was varied between 0.017 and 2 MPa. The dimensionless bubble-boundary distance γ(distance between laser focus and sample boundary, scaled by the maximum bubble radius) was for each value of E varied between γ = 0 and γ = 2.2. In this parameter space, we determined the jetting behavior, jet velocity, jet penetration into the PAA sample and bubble- induced removal of PAA material. The jetting behavior varies between unidirectional jets towards or away from the boundary, and formation of an annular jet which results in bubble splitting and subsequent formation of two very fast axial jets flowing simultaneously towards the boundary and away from it. General principles of the formation of annular and axial jets are discussed which allow to interpret the complex dynamics. The liquid jet directed away form the boundary reaches a maximum velocity between 300 m/s and 600 m/s (depending on E) while the peak velocity of the jet directed towards the boundary ranges between 400 m/s and 960 m/s. The peak velocities near an elastic material are 10 times higher than close to a rigid boundary. The liquid jet penetrates PAA samples with an elastic modulus in the intermediate range 0.12 < E < 0.4 MPa. In this same range of elastic moduli and for small γ-values, PAA material is ejected into the surrounding liquid due to the elastic rebound of the sample surface that was deformed during bubble expansion. The surface of the PAA sample is, furthermore, lifted during bubble collapse when a region of low pressure develops between bubble and sample. For stiffer boundaries, only an axial liquid jet towards the boundary is formed, similar to the bubble dynamics next to a rigid wall. For softer sample, the liquid jet is directed away from the boundary, and material is torn off the PAA sample during bubble collapse, if the bubble is produced close to the boundary. These processes play an important role for the efficiency and side effects of pulsed laser surgery inside the human body.

Proceedings Article | 9 July 2001 Paper

Shielding by the ablation plume during Er:YAG laser ablation

Kester Nahen, Alfred Vogel

Proceedings Volume 4257, (2001) https://doi.org/10.1117/12.434711

KEYWORDS: Laser ablation, Pulsed laser operation, Laser beam diagnostics, Absorption, Er:YAG lasers, Photography, Skin, Particles, Laser tissue interaction, Photodiodes

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Proceedings Article | 10 May 2001 Paper

Experimental investigation of optical breakdown using nanosecond 532-nm and 1064-nm laser pulses delivered at high numerical aperture

Arnold Guerra, Vasan Venugopalan, Kester Nahen, Alfred Vogel

Proceedings Volume 4260, (2001) https://doi.org/10.1117/12.426778

KEYWORDS: Plasma, Laser damage threshold, Pulsed laser operation, Nd:YAG lasers, Wave propagation, Cavitation, Energy efficiency, Mechanical efficiency, Laser energy, Microscopes

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Proceedings Article | 13 June 2000 Paper

Acoustic signal characteristics during IR laser ablation and their consequences for acoustic tissue discrimination

Kester Nahen, Alfred Vogel

Proceedings Volume 3914, (2000) https://doi.org/10.1117/12.388042

KEYWORDS: Acoustics, Laser ablation, Picosecond phenomena, Laser tissue interaction, Pulsed laser operation, Water, Tissues, Er:YAG lasers, Photography, Signal processing

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Proceedings Article | 19 May 2000 Paper

Acoustic online monitoring of IR laser ablation of burnt skin

Kester Nahen, Werner Eisenbeiss, Alfred Vogel

Proceedings Volume 3916, (2000) https://doi.org/10.1117/12.386325

KEYWORDS: Acoustics, Laser ablation, Skin, Tissues, Pulsed laser operation, Laser tissue interaction, Er:YAG lasers, Transducers, Infrared lasers, Laser energy

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Proceedings Article | 14 June 1999 Paper

Acoustic online monitoring of IR laser ablation of burnt skin

Kester Nahen, Alfred Vogel

Proceedings Volume 3601, (1999) https://doi.org/10.1117/12.350025

KEYWORDS: Acoustics, Tissues, Laser ablation, Skin, Laser tissue interaction, Transducers, Infrared lasers, Er:YAG lasers, Pulsed laser operation, Signal detection

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Proceedings Article | 1 June 1998 Paper

Influence of optical aberrations on laser-induced plasma formation in water and their consequences for intraocular photodisruption

Alfred Vogel, Kester Nahen, Dirk Theisen, Reginald Birngruber, Robert Thomas, Benjamin Rockwell

Proceedings Volume 3246, (1998) https://doi.org/10.1117/12.309423

KEYWORDS: Plasma, Monochromatic aberrations, Laser energy, Diffraction, Microsurgery, Cavitation, Optical aberrations, Laser damage threshold, Pulsed laser operation, Laser optics

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Proceedings Article | 18 May 1998 Paper

Laser-induced breakdown in the eye at pulse durations from 80 ns to 100 fs

Alfred Vogel, Joachim Noack, Kester Nahen, Dirk Theisen, Reginald Birngruber, Daniel Hammer, Gary Noojin, Benjamin Rockwell

Proceedings Volume 3255, (1998) https://doi.org/10.1117/12.308220

KEYWORDS: Plasma, Electrons, Pulsed laser operation, Absorption, Laser damage threshold, Picosecond phenomena, Particles, Ultrafast phenomena, Free electron lasers, Eye

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Proceedings Article | 13 May 1998 Paper

Acoustic spectroscopy of Er:YAG laser ablation of skin: first results

Kester Nahen, Alfred Vogel

Proceedings Volume 3254, (1998) https://doi.org/10.1117/12.308167

KEYWORDS: Laser ablation, Pulsed laser operation, Acoustics, Skin, Laser tissue interaction, Er:YAG lasers, Transducers, Photography, Tissues, Picosecond phenomena

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Proceedings Article | 13 May 1998 Paper

Energy balance of optical breakdown in water

Alfred Vogel, Joachim Noack, Kester Nahen, Dirk Theisen, Stefan Busch, Ulrich Parlitz, Daniel Hammer, Gary Noojin, Benjamin Rockwell, Reginald Birngruber

Proceedings Volume 3254, (1998) https://doi.org/10.1117/12.308162

KEYWORDS: Plasma, Pulsed laser operation, Cavitation, Absorption, Picosecond phenomena, Energy efficiency, Laser damage threshold, Laser scattering, Scattering, Sensors

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Proceedings Article | 5 December 1996 Paper

Plasma formation in water by picosecond and nanosecond Nd:YAG laser pulses: transmission, scattering, and reflection

Kester Nahen, Joachim Noack, Alfred Vogel

Proceedings Volume 2930, (1996) https://doi.org/10.1117/12.260881

KEYWORDS: Plasma, Picosecond phenomena, Laser scattering, Scattering, Absorption, Pulsed laser operation, Laser energy, Light scattering, Sensors, Laser damage threshold

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Showing 5 of 12 publications

Conference Committee Involvement (2)

Urology: Diagnostics, Therapeutics, Robotics, and Minimally Invasive

20 January 2007 | San Jose, California, United States

Urology: Diagnostics and Therapeutics

21 January 2006 | San Jose, California, United States

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