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Lowered threshold energy for femtosecond laser induced optical breakdown in a water based eye model by aberration correction with adaptive optics.

Hansen A, Géneaux R, Günther A, Krüger A, Ripken T - Biomed Opt Express (2013)

Bottom Line: We found that for initial aberrations with a root-mean-square wave front error of only one third of the wavelength the threshold energy can still be reduced by a factor of three if the aberrations are corrected to the diffraction limit by adaptive optics.The transmitted pulse energy is reduced by 17% at twice the threshold.Furthermore, the gas bubble motions after breakdown for pulse trains at 5 kilohertz repetition rate show a more transverse direction in the corrected case compared to the more spherical distribution without correction.

View Article: PubMed Central - PubMed

Affiliation: Laser Zentrum Hannover e.V., Hollerithallee 8, 30419 Hannover, Germany.

ABSTRACT
In femtosecond laser ophthalmic surgery tissue dissection is achieved by photodisruption based on laser induced optical breakdown. In order to minimize collateral damage to the eye laser surgery systems should be optimized towards the lowest possible energy threshold for photodisruption. However, optical aberrations of the eye and the laser system distort the irradiance distribution from an ideal profile which causes a rise in breakdown threshold energy even if great care is taken to minimize the aberrations of the system during design and alignment. In this study we used a water chamber with an achromatic focusing lens and a scattering sample as eye model and determined breakdown threshold in single pulse plasma transmission loss measurements. Due to aberrations, the precise lower limit for breakdown threshold irradiance in water is still unknown. Here we show that the threshold energy can be substantially reduced when using adaptive optics to improve the irradiance distribution by spatial beam shaping. We found that for initial aberrations with a root-mean-square wave front error of only one third of the wavelength the threshold energy can still be reduced by a factor of three if the aberrations are corrected to the diffraction limit by adaptive optics. The transmitted pulse energy is reduced by 17% at twice the threshold. Furthermore, the gas bubble motions after breakdown for pulse trains at 5 kilohertz repetition rate show a more transverse direction in the corrected case compared to the more spherical distribution without correction. Our results demonstrate how both applied and transmitted pulse energy could be reduced during ophthalmic surgery when correcting for aberrations. As a consequence, the risk of retinal damage by transmitted energy and the extent of collateral damage to the focal volume could be minimized accordingly when using adaptive optics in fs-laser surgery.

No MeSH data available.


Related in: MedlinePlus

Aberration correction of model eye to diffraction limited wave front: eye model aberrations with 0.263 µm rms wave front error (left), wave front after adaptive optics closed-loop correction with 0.030 µm rms error (right).
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g004: Aberration correction of model eye to diffraction limited wave front: eye model aberrations with 0.263 µm rms wave front error (left), wave front after adaptive optics closed-loop correction with 0.030 µm rms error (right).

Mentions: The adaptive optics system performance was analyzed for the model eye with the PTFE sample as a reflector. The result of the wave front measurement with the Hartmann-Shack-sensor and closed-loop aberration correction is given in Fig. 4Fig. 4


Lowered threshold energy for femtosecond laser induced optical breakdown in a water based eye model by aberration correction with adaptive optics.

Hansen A, Géneaux R, Günther A, Krüger A, Ripken T - Biomed Opt Express (2013)

Aberration correction of model eye to diffraction limited wave front: eye model aberrations with 0.263 µm rms wave front error (left), wave front after adaptive optics closed-loop correction with 0.030 µm rms error (right).
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3675865&req=5

g004: Aberration correction of model eye to diffraction limited wave front: eye model aberrations with 0.263 µm rms wave front error (left), wave front after adaptive optics closed-loop correction with 0.030 µm rms error (right).
Mentions: The adaptive optics system performance was analyzed for the model eye with the PTFE sample as a reflector. The result of the wave front measurement with the Hartmann-Shack-sensor and closed-loop aberration correction is given in Fig. 4Fig. 4

Bottom Line: We found that for initial aberrations with a root-mean-square wave front error of only one third of the wavelength the threshold energy can still be reduced by a factor of three if the aberrations are corrected to the diffraction limit by adaptive optics.The transmitted pulse energy is reduced by 17% at twice the threshold.Furthermore, the gas bubble motions after breakdown for pulse trains at 5 kilohertz repetition rate show a more transverse direction in the corrected case compared to the more spherical distribution without correction.

View Article: PubMed Central - PubMed

Affiliation: Laser Zentrum Hannover e.V., Hollerithallee 8, 30419 Hannover, Germany.

ABSTRACT
In femtosecond laser ophthalmic surgery tissue dissection is achieved by photodisruption based on laser induced optical breakdown. In order to minimize collateral damage to the eye laser surgery systems should be optimized towards the lowest possible energy threshold for photodisruption. However, optical aberrations of the eye and the laser system distort the irradiance distribution from an ideal profile which causes a rise in breakdown threshold energy even if great care is taken to minimize the aberrations of the system during design and alignment. In this study we used a water chamber with an achromatic focusing lens and a scattering sample as eye model and determined breakdown threshold in single pulse plasma transmission loss measurements. Due to aberrations, the precise lower limit for breakdown threshold irradiance in water is still unknown. Here we show that the threshold energy can be substantially reduced when using adaptive optics to improve the irradiance distribution by spatial beam shaping. We found that for initial aberrations with a root-mean-square wave front error of only one third of the wavelength the threshold energy can still be reduced by a factor of three if the aberrations are corrected to the diffraction limit by adaptive optics. The transmitted pulse energy is reduced by 17% at twice the threshold. Furthermore, the gas bubble motions after breakdown for pulse trains at 5 kilohertz repetition rate show a more transverse direction in the corrected case compared to the more spherical distribution without correction. Our results demonstrate how both applied and transmitted pulse energy could be reduced during ophthalmic surgery when correcting for aberrations. As a consequence, the risk of retinal damage by transmitted energy and the extent of collateral damage to the focal volume could be minimized accordingly when using adaptive optics in fs-laser surgery.

No MeSH data available.


Related in: MedlinePlus