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30. Pressure wave propagation effects in the eye after photoablation.

Author

Požar, Tomaž, Horvat, Darja, Starman, Bojan, Halilovič, Miroslav, and Petkovšek, Rok

Subjects
CORNEA, LASER-assisted subepithelial keratectomy, LASER surgery, OPHTHALMOLOGISTS, LASIK
Abstract

A transient pressure wave created in photoablation-based laser corneal refractive surgery propagates along the optical axis of the eye from the cornea toward the fundus. Along its path, it is attenuated, reflected several times at tissue interfaces, focused due to the spherical shape of the cornea, and partially phase-converted to a tensile wave after passing the acoustic focus. Employing the numerical acoustic eye model, the dynamics of the acoustic focusing is described in detail. The simulated pressure waveforms are first validated against the existing measurements. Then, the calculated full pressure fields are used to obtain the extreme values of the pressure amplitude at every point within the eye over the whole timespan of interest. Over these pressure maps, various threshold contours obtained from the existing literature are superimposed to help ophthalmologists investigate the consequences of acoustic focusing within the human eye during laser keratorefractive surgery. The comparison indicates that the simulated negative peak pressure values used in the contemporary broad beam and flying spot laser-assisted in situ keratomileusis/photorefractive keratectomy treatments exceed some of the reported threshold values. The critical volume where the thresholds are surpassed is located near the lens-vitreous boundary and extends to the retina for wide beams. The photoablation-induced pressure wave focusing is, therefore, a mechanism that needs to be researched carefully and included in the list of potential risks accompanying refractive laser surgery. [ABSTRACT FROM AUTHOR]

Published
2019
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39. Pulzi na zahtevo v vlakenskih in hibridnih laserjih

Author

Petkovšek, Rok, Agrež, Vid, Petelin, Jaka, Černe, Luka, Bünting, Udo, and Podobnik, Boštjan

Subjects
gain control, poljubna ponavljalna frekvenca, pulzi na zahtevo, Physics::Optics, udc:535(045), pulse on demand, arbitrary repetition rate, vlakenski laserji, fibre lasers, nadzor ojačenja
Abstract

This paper presents an investigation of pulse-on-demand operation in fibre and hybrid lasers. Two methods for efficient gain control that enable the generation of laser pulses at arbitrary times with controlled pulse parameters are presented. The method of direct modulation of the pump power in the high-power laser oscillator is shown to generate pulses with a duration in the nanosecond range, with repetition rates varying during operation from a single shot to over 1 MHz. An advanced method using a combination of marker and idler seeding a fibre amplifier chain is investigated. Such a system can easily achieve repetition rates of several tens of MHz. The lasersʼ performances were successfully tested in a real environment on an industrial platform for laser transfer printing. Similar concepts were used for a laser source with ultrashort laser pulses (femtosecond range) on demand by using a mode-locked seed as a source and a solid-state amplifier to achieve high pulse energy and peak power.

Published
2020

47. Simulation of wave propagation inside a human eye

Author

Požar, Tomaž, Halilovič, Miroslav, Horvat, Darja, and Petkovšek, Rok

Subjects
human eye, udc:535(045), oftalmologija, wave propagation, ophtalmology, sense organs, laser medical procedures, laserski medicinski posegi, širjenje valovanja, človeško oko
Abstract

The design and development of the acoustic eye model (AEM) is reported. The model consists of a computer-based simulation that describes the propagation of mechanical disturbance inside a simplified model of a human eye. The capabilities of the model are illustrated with examples, using different laser-induced initial loading conditions in different geometrical configurations typically occurring in ophthalmic medical procedures. The potential of the AEM is to predict the mechanical response of the treated eye tissue in advance, thus complementing other preliminary procedures preceding medical treatments.

Published
2018

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