A first-order model for computation of laser-induced breakdown thresholds in ocular and aqueous media. II. Comparison to experiment

Kennedy, Paul K.; Boppart, Stephen A.; Hammer, Daniel X.; Rockwell, Benjamin A.; Noojin, Gary D.; Roach, William P.

doi:10.1109/3.477754

Cited by 137 publications

(91 citation statements)

References 12 publications

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“…The cavitation bubble dynamics and the interaction mechanisms were examined by timeresolved photography, which is a well-established method to investigate this effect of laser-material interaction. 12,14,21,24,25 In the present study, two parameters were varied: first, the laser repetition rate and hence the temporal distance of the laser pulses, and second, the applied pulse energy. The bubble-pulse interaction features two clearly separable interaction scenarios with dependence on the investigated parameters.…”

Section: Introductionmentioning

confidence: 99%

“…[12][13][14][15][16][17][18][19][20]. Briefly, the photodisruption process can be described as follows: by tightly focusing an ultrashort laser pulse into an aqueous medium like biological tissue, nonlinear absorption processes, such as multiphoton, tunnel, and cascade ionization, are initiated within the focal volume due to the very high intensities.…”

Section: Introductionmentioning

confidence: 99%

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Effects of cavitation bubble interaction with temporally separated fs-laser pulses

et al. 2014

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Abstract. We present a time-resolved photographic analysis of the pulse-to-pulse interaction. In particular, we studied the influence of the cavitation bubble induced by a fs-pulse on the optical focusing of the consecutive pulse and its cavitation bubble dynamics in dependence on temporal pulse separation in water. As a first result, by decreasing the temporal separation of laser pulses, there is a diminishment of the laser-induced optical breakdown (LIOB) efficiency in terms of energy conversion, caused by disturbed focusing into persisting gas bubbles at the focal volume. A LIOB at the focal spot is finally suppressed by impinging the expanding or collapsing cavitation bubble of the preceding pulse. These results could be additionally confirmed in porcine gelatin solution with various concentrations. Hence, the interaction between the laser and transparent ophthalmic tissue may be accompanied by a raised central laser energy transmission, which could be observed in case of a temporal pulse overlap. In conclusion, our experimental results are of particular importance for the optimization of the prospective ophthalmic surgical process with future generation fs-lasers.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of cavitation bubble interaction with temporally separated fs-laser pulses

et al. 2014

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“…As less than a nanojoule is delivered to the tissue per pulse (at a typical average power of 10 mW and pulse repetition rate of , 80 MHz), one would not expect to observe optical breakdown. 11,12 This is substantiated by the observation that image signal intensity does not change despite repeated imaging for several minutes.…”

Section: Introduction Smentioning

confidence: 49%

Two-Photon Excitation Laser Scanning Microscopy of Human, Porcine, and Rabbit Nasal Septal Cartilage

et al. 2001

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Two-photon excitation laser scanning microscopy (TPM) was used to image human, porcine, and rabbit nasal septal cartilage. TPM provides optical sections of thick tissue specimens in situ without the use of exogenous dyes or need for tissue fixation. The cartilage tissue was imaged using near-infrared light generated by a mode-locked titanium/sapphire laser that was raster-scanned and coupled to an inverted microscope. Absorption of two photons by endogenous molecules and subsequent fluorescence was filtered to specific spectral bandwidths and detected with photomultiplier tubes. Two-photon stimulated fluorescence was detected with photomultiplier tubes optimized to specific spectral bandwidths. Signal intensity corresponds to the concentration of fluorophores, principally NADH, NADPH, and flavoproteins hence providing a means of redox imaging the cellular metabolic state. Specimens were scanned from the surface to a depth of about 150 mm. Image size was 50 3 50 mm with a diffraction limited pixel size of 0.4 mm. Cell membranes, nuclei, and matrix structures were identified in human, pig, and rabbit tissues. TPM provides a means to study three dimensional chondrocyte structure and matrix organization in situ at substantial depths, and permits longitudinal examination of cultured tissue explants without the need for exogenous dyes, tissue preparation, or fixation.

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“…The irradiance threshold for plasma formation in the femtosecond laser pulse regime in ocular media is calculated following the example of Cain et al [61] by using the first order model of Kennedy [74,75], with special attention to Kennedy, 1995 sections IV D and V F. For the ultrashort pulse regime, this model is based on the theory of multiphoton ionization in condensed media [76]. The irradiance threshold for multiphoton breakdown as derived by Kennedy is:…”

Section: C) Plasma Formationmentioning

confidence: 99%

Safety assessment in macaques of light exposures for functional two-photon ophthalmoscopy in humans

Schwarz¹,

Sharma²,

Fischer³

et al. 2016

Biomed. Opt. Express

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Two-photon ophthalmoscopy has potential for in vivo assessment of function of normal and diseased retina. However, light safety of the sub-100 fs laser typically used is a major concern and safety standards are not well established. To test the feasibility of safe in vivo two-photon excitation fluorescence (TPEF) imaging of photoreceptors in humans, we examined the effects of ultrashort pulsed light and the required light levels with a variety of clinical and high resolution imaging methods in macaques. The only measure that revealed a significant effect due to exposure to pulsed light within existing safety standards was infrared autofluorescence (IRAF) intensity. No other structural or functional alterations were detected by other imaging techniques for any of the exposures. Photoreceptors and retinal pigment epithelium appeared normal in adaptive optics images. No effect of repeated exposures on TPEF time course was detected, suggesting that visual cycle function was maintained. If IRAF reduction is hazardous, it is the only hurdle to applying two-photon retinal imaging in humans. To date, no harmful effects of IRAF reduction have been detected.

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A first-order model for computation of laser-induced breakdown thresholds in ocular and aqueous media. II. Comparison to experiment

Cited by 137 publications

References 12 publications

Effects of cavitation bubble interaction with temporally separated fs-laser pulses

Effects of cavitation bubble interaction with temporally separated fs-laser pulses

Two-Photon Excitation Laser Scanning Microscopy of Human, Porcine, and Rabbit Nasal Septal Cartilage

Safety assessment in macaques of light exposures for functional two-photon ophthalmoscopy in humans

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