@article{Noack,
   author = {Noack, J. and Vogel, A.},
   title = {Laser-induced plasma formation in water at nanosecond to femtosecond time scales: calculation of thresholds, absorption coefficients, and energy density},
   journal = {Quantum Electronics, IEEE Journal of},
   volume = {35},
   number = {8},
   pages = {1156-1167},
   keywords = {absorption coefficients
electron density
high-speed optical techniques
multiphoton processes
photoionisation
plasma density
plasma production by laser
plasma theory
water
H<sub>2</sub>O
absorption coefficient
breakdown threshold
cascade ionization
collision losses
complex pulse duration dependence
decreasing laser pulse duration
distilled water
energy density
energy threshold
femtosecond time scales
free electron density
free electrons
high-power laser pulses
laser pulse
laser-induced plasma formation
multiphoton ionization
multiphoton ionization gains
nanosecond laser pulses
nanosecond time scales
numerical solution
plasma absorption coefficient
plasma energy density
plasma generation
plasma transmission
pulse durations
quantitative agreement
rate equation
recombination losses
thresholds},
   year = {1999}
}

@article{Noack,
   author = {Noack, J. and Hammer, D.X. and Rockwell, B.A. and Vogel, A. and Noojin, G. D.},
   title = {Influence of pulse duration on mechanical effects after laser-induced breakdown in water},
   journal = {J Appl Phys},
   volume = {83},
   number = {12},
   pages = {7488-7495},
   year = {1998}
}

@article{Geerling,
   author = {Geerling, G. and Roider, J. and Schmidt-Erfurth, U. and Nahen, K. and El Hifnawi, E. S. and Laqua, H. and Vogel, A.},
   title = {Initial clinical experience with the picosecond Nd: YLF laser for intraocular therapeutic applications},
   journal = {Br J Ohthalmol},
   volume = {82},
   number = {5},
   pages = {504-509},
   year = {1998}
}

@article{Scammon,
   author = {Scammon, R.J. and Chapyak, E.J. and Godwin, R.P. and Vogel, A.},
   title = {Simulations of shock waces and cavitation bubbles produced in water by picosecond and nanosecond laser pulses},
   journal = {SPIE Proc.},
   volume = {3254},
   pages = {264-275},
   year = {1998}
}

@article{Noack,
   author = {Noack, J. and Vogel, A.},
   title = {Single-shot spatially resolved characterization of laser-induced shock waves in water},
   journal = {Appl Optics},
   volume = {37},
   number = {19},
   pages = {4092-4099},
   year = {1998}
}

@article{Vogel1997,
   author = {Vogel, A. and Gunther, T. and Asiyo-Vogel, M. and Birngruber, R.},
   title = {Investigations on the origin of refractive effects in intrastromal refractive surgery with the picosecond laser},
   journal = {Ophthalmologe},
   volume = {94},
   number = {7},
   pages = {467-474},
   note = {Yp140
Times Cited:2
Cited References Count:21},
   abstract = {Background: Picosecond laser intrastromal photorefractive keratectomy (ISPRK) aims at achieving a flattening of the central cornea by plasma-mediated tissue evaporation without affecting the anterior or posterior corneal layers. We investigated the laser-induced tissue effects to establish a functional relationship between laser parameters and tissue removal and to assess their influence on the healing process and long-term refractive changes.
Materials and methods: A modified ISL 2001 System with a cone angle of 30 degrees was used for in vitro investigations of the laser effects in water and porcine cornea. Photographic methods were used to determine the plasma volume and the thickness of the laser-generated intrastromal bubble layer as a function of the pulse energy and the number and separation in which the pulses were applied (216 eyes). Histological evaluation was done by polarization microscopy (9 eyes).
Results: Polarization microscopy revealed only minor signs of thermal tissue damage. The maximum amount of tissue that can be evaporated without damaging the outer corneal layers corresponds to a layer about 10 mu m thick. With a 6-mm optical zone, this tissue removal yields an immediate refractive effect of only 0.85 dpt. Stronger long-term refractive changes observed in animal experiments and clinical studies must thus be due to the healing response of the cornea. The healing response may be induced by mechanical distortion due to intrastromal bubble formation affecting about one third of the corneal thickness.
Conclusion: Since the refractive effects are apparently strongly influenced by corneal healing, they are poorly predictable and can probably not be used for clinical purposes.},
   keywords = {refractive surgery
intrastromal photorefractive keratectomy
picosecond laser
photodisruption
cavitation
photorefractive keratectomy
intraocular photodisruption
corneal tissue
pulses},
   ISSN = {0941-293X},
   DOI = {DOI 10.1007/s003470050141},
   url = {<Go to ISI>://WOS:000071246700001},
   year = {1997},
   type = {Journal Article}
}

@article{Vogel,
   author = {Vogel, A.},
   title = {Nonlinear absorption: intraocular microsurgery and laser lithotripsy },
   journal = {Phys. Med. Biol.},
   volume = {42},
   number = {5},
   pages = {895},
   year = {1997}
}

@article{Chapyak,
   author = {Chapyak, J. and Godwin, R.P. and Vogel, A.},
   title = {A comparison of numerical simulations and laboratory studies on shock waves and cavitation bubble growth produced by optical breakdown in water},
   journal = {SPIE Proc.},
   volume = {2975},
   pages = {335-342},
   year = {1997}
}

@article{Asiyo-Vogel1997,
   author = {Asiyo-Vogel, M and Koop, N and Brinkmann, R and Engelhardt, R and Eggers, R and Birngruber, R and Vogel, A},
   title = {Darstellung von LTK-Läsionen durch optische Kurzkohärenztomographie (OCT) und Polarisationsmikroskopie nach Sirius-Rot-Färbung},
   journal = {Ophthalmologe},
   volume = {94},
   pages = {487-491},
   year = {1997}
}

@article{Asiyo-Vogel1997,
   author = {Asiyo-Vogel, M. N. and Koop, N. and Brinkmann, R. and Engelhardt, R. and Eggers, R. and Birngruber, R. and Vogel, A.},
   title = {Evaluation of LTK lesions by optical low coherence tomography (OCT) and polarization microscopy after Sirius-Red staining},
   journal = {Ophthalmologe},
   volume = {94},
   number = {7},
   pages = {487-491},
   note = {Yp140
Times Cited:5
Cited References Count:21},
   abstract = {Background: Information on the extent and degree of the thermal effect produced is of great importance for control of the laser dosage in laser thermokeratoplasty (LTK) and for postoperative follow-up. We investigated on acute LTK effects which information images obtained by optical low coherence tomography (OCT) offer compared to those obtained by polarization microscopy.
Methods: Porcine eyes were irradiated through a 400 mu m quartz fiber using light from a laser diode emitting up to 300 mW at a wavelength of 1.86 mu m. Thermal lesions of varying strength were scanned using an experimental OCT device with about 25 mu m lateral and 20 mu m axial resolution. Histologic evaluation of the scanned areas was done by polarization microscopy after Sirius-Red staining, and similar lesions were also analyzed by TEM.
Results: Both methods differentiated three damage zones: a transition zone, a zone of moderate coagulation, and a central zone of strong coagulation. In the transition zone,increased birefringence was seen in polarization microscopy, which correlated with increased light scattering seen in the DCT images,ln the moderately coagulated zone, a decrease in birefringence was associated with an even stronger increase of the OCT signal, In the central zone,a loss of the fibrillar tissue structure was observed, which led to a complete loss of birefringence and a strong reduction of the OCT signal.
Conclusions: Although OCT does not provide the detailed information on thermal changes of tissue seen by the histologic method, it offers information on the extent and degree of tissue changes without preparation artifacts and provides a non-invasive method of immediate and follow-up control of LTK lesions, A quantitative analysis of changes in corneal thickness and curvature is much simpler than by a slit lamp. Time-resolved measurements of corneal light scattering may be used for on-line control of the laser-light dosage during LTK.},
   keywords = {refractive surgery
laser thermokeratoplasty
collagen denaturation
collagen shrinkage
optical low coherence tomography
polarization microscopy
sirius-red staining
tissue
collagen
eye},
   ISSN = {0941-293X},
   DOI = {DOI 10.1007/s003470050144},
   url = {<Go to ISI>://WOS:000071246700004},
   year = {1997},
   type = {Journal Article}
}

@article{Asiyo-Vogel,
   author = {Asiyo-Vogel, M. and Brinkmann, R and Notbohm, H. and Eggers, R. and Lubatschowski, H. and Laqua, H. and Vogel, A.},
   title = {Histologic analysis of thermal effects of laserthermokeratoplasty and corneal ablation using Sirius-Red polarization microscopy},
   journal = {J Cataract Refr Surg},
   volume = {23},
   pages = {515-526},
   year = {1997}
}

@article{Noack,
   author = {Noack, J. and Tonnies, R. and Hohla, K. and Birngruber, R. and Vogel, A.},
   title = {Influence of ablation plume dynamics on the formation of central islands in excimer laser photorefractive keratectomy},
   journal = {Ophthalmology},
   volume = {104},
   number = {5},
   pages = {823-30},
   note = {0161-6420 (Print)
Comparative Study
In Vitro
Journal Article
Research Support, Non-U.S. Gov't},
   abstract = {PURPOSE: The aim of this study was to understand the dynamics of ablation products during excimer laser photorefractive keratectomy, and their influence on the formation of central islands. METHOD: Laser flash photography was used to investigate the dynamics of ablation products during photorefractive keratectomy. The ablation plume over polymethyl methacrylate (PMMA) and porcine cornea targets ablated with different zone diameters was imaged at various times between 10 musec and 100 msec after the ablating laser pulse. On PMMA targets, the profiles of the resulting ablation craters were measured. RESULTS: In all cases, the ablation products formed a ring vortex. The plume velocities on cornea were found to be approximately twice as fast as on PMMA for all zone diameters. For both materials, the ablation plume evolves faster for smaller zone diameters. Central islands were observed for zone diameters between 1 and 7 mm on PMMA substrates. The islands became more pronounced with increasing zone diameter. CONCLUSIONS: A major cause for the formation of central islands was found to be particle redeposition at the center of the ablation zone. Because of the vortex dynamics, redeposition of particles favorably occurs at the center of the ablation zone. Additionally, the dynamics of the ablation plume lead to a concentration of airborne particles over the center of the ablation zone, which also may contribute to the creation of central islands by partial absorption of the next excimer laser pulse.},
   keywords = {Animals
Cornea/*pathology/*surgery
Image Processing, Computer-Assisted
*Keratectomy, Photorefractive, Excimer Laser
Methylmethacrylates
Models, Anatomic
Swine
Time and Motion Studies
Volatilization},
   year = {1997}
}

@article{Vogel1997,
   author = {Vogel, A. and Günther, T. and Asiyo-Vogel, M. and Birngruber, R.},
   title = {Factors determining the refractive effects of intrastromal photorefractive keratectomy with the picosecond laser},
   journal = {J Cataract Refract Surg},
   volume = {23},
   number = {9},
   pages = {1301-1310},
   abstract = {To determine the relationship between laser parameters and tissue removal with picosecond laser intrastromal photorefractive keratectomy (ISPRK) and to assess the effect of the parameters on the healing process and the long-term refractive changes.},
   keywords = {Animals
Corneal Stroma
Follow-Up Studies
Lasers, Excimer
Microscopy, Polarization
Photorefractive Keratectomy
Refraction, Ocular
Refractive Errors
Swine
Wound Healing
pathology
physiopathology
surgery
adverse effects
methods
physiology
etiology},
   year = {1997}
}

@article{Hammer,
   author = {Hammer, D.X. and Jansen, E.D. and Frenz, M. and Nojin, G.D. and Thomas, R.J. and Noack, J. and Vogel, A. and Rockwell, B.A. and Welch, A.J.},
   title = {Shielding properties of laser-induced breakdown in water from pulse durations from 5 ns to 125 fs.},
   journal = {Appl Optics},
   volume = {36},
   pages = {5630-5640},
   year = {1997}
}

@article{Zwaan,
   author = {Zwaan, M. and Behnle, U. and Engelhardt, R. and Vogel, A. and Kloess, W. and Birngruber, R. and Weiss, H. D.},
   title = {In-vitro-Untersuchungen zur gepulsten Laserangioplastie in flüssigem und gasförmigem Medium.},
   journal = {Fortschr Röntgenstr},
   volume = {164},
   number = {1},
   pages = {68-71},
   year = {1996}
}

@article{Vogel1996,
   author = {Vogel, A. and Engelhardt, R. and Behnle, U. and Parlitz, U.},
   title = {Minimization of cavitation effects in pulsed laser ablation illustrated on laser angioplasty},
   journal = {Appl Phys B},
   volume = {62},
   pages = {173-182},
   year = {1996}
}

@article{Gerling1996,
   author = {Gerling, G. and Vogel, A. and ElHifnawi, E. and Koop, N. and Droge, G. and Birngruber, R. and Brinkmann, R.},
   title = {Morphological and biomorphometrical observations on laser thermal keratoplasty - Histological and biomorphometrical examination of the relationship between refractive change and the volume of laser thermal keratoplasty lesions following Cr:Tm:Ho:YAG laser treatment},
   journal = {German Journal of Ophthalmology},
   volume = {5},
   number = {2},
   pages = {84-91},
   note = {Vf915
Times Cited:4
Cited References Count:21},
   abstract = {Laser thermal keratoplasty (LTK) is currently under clinical trial for the correction of hyperopia and hyperopic astigmatism by means of collagen coagulation in the peripheral cornea. The purpose of our study was to optimize the ratio between the volume of damaged corneal stroma and the refractive effect so as to minimize potential side effects such as endothelial damage or induction of glare phenomena. We therefore performed histological and morphometrical examinations of enucleated pig eyes to determine the relationship between the coagulated stromal volume and the refractive change after LTK using a pulsed Cr: Tm: Ho: YAG laser (wavelength 2.12 mu m) on enucleated pig eyes. The refractive change was documented with a Littman ophthalmometer. Morphometrical analysis was performed using polarized light microscopy of sirius red-stained specimens. This special stain separated the thermally changed stroma into a dark, nonbirefringent center and a birefringent peripheral zone. The volume of both zones was positively correlated with the refractive change induced. The volume was in turn influenced by the choice of laser parameters, From the ratio of the volume to the refractive change it was found that pulse energies above 30 mJ led to an enlargement of the coagulation volume without increasing the refractive change effectively. The use of high pulse energies did not improve the effect of LTK but only increased the risk of unwanted side effects. However, an increase in the laser repetition rate at a constant pulse number per spot led to refractive changes with a minimal coagulation volume. The highest relative refractive change was achieved with a dark central zone and a birefringent zone, each having a volume of about 50 - 80 x 10(-3) mm(3).},
   keywords = {laser thermal keratoplasty
hyperopic correction
biomorphometry
sirius red stain
polarization microscopy
organization
microscopy
collagen},
   ISSN = {0941-2921},
   url = {<Go to ISI>://WOS:A1996VF91500004},
   year = {1996},
   type = {Journal Article}
}

@article{Vogel1996,
   author = {Vogel, A. and Nahen, K. and Theisen, D and Noack, J.},
   title = {Plasma Formation in Water by Picosecond and Nanosecond Nd: YAG Laser Pulses - Part I: Optical Breakdown at Threshold and Superthreshold Irradiance.},
   journal = {IEEE},
   volume = {2},
   number = {4},
   pages = {847-860},
   year = {1996}
}

@article{Nahen,
   author = {Nahen, K. and Vogel, A.},
   title = {Plasma Formation in Water by Picosecond and Nanosecond Nd: YAG Laser Pulses - Part II: Transmission, Scattering, and Reflection},
   journal = {IEEE},
   volume = {2},
   number = {4},
   pages = {861-871},
   year = {1996}
}

@article{Vogel,
   author = {Vogel, A. and Busch, S.},
   title = {Shock wave emission and cavitation bubble generation by picosecond and nanosecond optical breakdown in water},
   journal = {J Acoust Soc Am},
   volume = {100},
   pages = {148-165},
   year = {1996}
}

@book{Vogel,
   author = {VOGEL, A. and ASIYO-VOGEL, M. and BIRNGRUBER, R.},
   title = {Untersuchungen zur intrastromalen refraktiven Hornhautchirurgie mit Picosekunden-Nd: YAG-Laser-Pulsen},
   publisher = {Springer},
   address = {Berlin, ALLEMAGNE},
   volume = {91},
   keywords = {Surgery
Chirurgie
Cornea
Corn&#233
e
YAG laser
Laser YAG
Neodymium
N&#233
odyme
Stroma
Laser produced plasma
Plasma produit par laser
Cavitation bubble
Bulle cavitation
Eye
Oeil
Sheep
Mouton
Animal
In vitro
Artiodactyla
Ungulata
Mammalia
Vertebrata},
   year = {1994}
}

@article{Ludwig,
   author = {Ludwig, K. and Busch, L. C. and Jungnickel, K. and Vogel, A.},
   title = {Präparation critical-point-getrockneter Mausembryonen mit einem Laserskalpell},
   journal = {Ann Anat},
   volume = {176},
   pages = {559 - 563},
   year = {1994}
}

@article{Vogel,
   author = {Vogel, A. and Capon, M. R. and Asiyo-Vogel, M. and Birngruber, R.},
   title = {Intraocular photodisruption with picosecond and nanosecond laser pulses: tissue effects in cornea, lens, and retina},
   journal = {Invest Ophthalmol Vis Sci},
   volume = {35},
   number = {7},
   pages = {3032-44},
   note = {0146-0404 (Print)
Journal Article
Research Support, Non-U.S. Gov't},
   abstract = {PURPOSE. Nd:YAG laser photodisruption with nanosecond (ns) pulses in the millijoule range is an established tool for intraocular surgery. This study investigates tissue effects in cornea, lens, and retina to assess whether picosecond (ps) pulses with energies in the microjoule range can increase the surgical precision, reduce collateral damage, and allow applications requiring more localized tissue effects than can be achieved with ns pulses. METHODS. Both ps and ns Nd:YAG laser effects on Descemet's membrane, in the corneal stroma, in the lens, and at the retina were investigated in vitro in bovine and sheep eyes and in cataractous human lens nuclei. For each tissue, the optical breakdown threshold was determined. The morphology of the tissue effects and the damage range of the laser pulses were examined by light and scanning electron microscopy. The cavitation bubble dynamics during the formation of corneal intrastromal laser effects were documented by time-resolved photography. RESULTS. The optical breakdown threshold for ps pulses in clear cornea, lens, and vitreous is, on average, 12 times lower than that for ns pulses. In cataractous lens nuclei, it is lower by a factor of 7. Using ps pulses, Descemet's membrane could be dissected with fewer disruptive side effects than with ns pulses, whereby the damage range decreased by a factor of 3. The range for retinal damage was only 0.5 mm when 200 microJ ps pulses were focused into the vitreous. Picosecond pulses could be used for corneal intrastromal tissue evaporation without damaging the corneal epithelium or endothelium, when the pulses were applied in the anterior part of the stroma. The range for endothelial damage was 150 microns at 80 microJ pulse energy. Intrastromal corneal refractive surgery is compromised by the laser-induced cavitation effects. Tissue displacement during bubble expansion is more pronounced than tissue evaporation, and irregular bubble formation creates difficulties in producing predictable refractive changes. CONCLUSIONS. The use of ps pulses improves the precision of intraocular Nd:YAG laser surgery and diminishes unwanted disruptive side effects, thereby widening the field of potential applications. Promising fields for further studies are intrastromal corneal refractive surgery, cataract fragmentation, membrane cutting, and vitreolysis close to the retina.},
   keywords = {Animals
Cattle
Cornea/injuries/surgery/*ultrastructure
Laser Surgery/adverse effects/instrumentation/*methods
Lens, Crystalline/injuries/surgery/*ultrastructure
Microscopy, Electron, Scanning
Retina/injuries/surgery/*ultrastructure
Sheep},
   year = {1994}
}

@article{Vogel1994,
   author = {Vogel, A. and Asiyovogel, M. and Birngruber, R.},
   title = {Investigations on Intrastromal Refractive Surgery with Picosecond Nd-Yag Laser-Pulses},
   journal = {Investigative Ophthalmology & Visual Science},
   volume = {35},
   number = {4},
   pages = {2155-2155},
   note = {Mz585
Times Cited:0
Cited References Count:0},
   ISSN = {0146-0404},
   url = {<Go to ISI>://WOS:A1994MZ58504161},
   year = {1994},
   type = {Journal Article}
}

@article{Vogel,
   author = {Vogel, A. and Busch, S. and Jungnickel, K. and Birngruber, R.},
   title = {Mechanisms of intraocular photodisruption with picosecond and nanosecond laser pulses},
   journal = {Lasers Surg Med},
   volume = {15},
   number = {1},
   pages = {32-43},
   note = {0196-8092 (Print)
Journal Article
Research Support, Non-U.S. Gov't},
   abstract = {Nd:YAG laser photodisruption with nanosecond (ns) pulses is an established method for intraocular surgery. In order to assess whether an increased precision can be achieved by the use of picosecond (ps) pulses, the plasma size, the shock wave characteristics, and the cavitation bubble expansion after optical breakdown with ps- and ns-laser pulses were investigated by time-resolved photography and acoustic measurements. Nd:YAG laser pulses with a duration of 30 ps and 6 ns, respectively, were focused into a water-filled glass cuvette. Frequency doubled light from the same laser pulses was optically delayed between 2 ns and 136 ns and used as illumination light source for photography. Since the individual events were well reproducible, the shock wave and bubble wall position could be determined as a function of time. From the slope of these r(t) curves, the shock wave and bubble wall velocities were determined, and the shock wave pressure was calculated from the shock velocity. The plasma size at various laser pulse energies was measured from photographs of the plasma radiation. The breakdown thresholds at 30 ps and 6 ns pulse duration were found to be 15 microJ and 200 microJ, respectively. At threshold, ps-plasmas are shorter than ns-plasmas, but at the same pulse energy they are always approximately 2.5 times longer. The initial shock pressures were 17 kbar after ps-pulses with an energy of 50 microJ, and 21 kbar after 1 mJ ns-pulses. The pressure amplitude decayed much faster after the ps-pulses. The maximum expansion velocity of the cavitation bubble was 350 m/s after a 50 microJ ps-pulse, but 1,600 m/s after a 1 mJ ns-pulse. The side effects of intraocular microsurgery associated with shock wave emission and cavitation bubble expansion can be considerably reduced by the use of ps-pulses, and new applications of photodisruption may become possible.},
   keywords = {Eye/*radiation effects
Humans
*Laser Surgery/methods
Models, Structural
Physics},
   year = {1994}
}