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Laser Updates in UrologyOmar Elgebaly

Lecturer of urology

Alexandria university

FEBU

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• 25 Slides

• Less Urology.

• More physics.

• I am not expert in physics.

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• The effect of the laser beam is achieved only after the absorption of the photons by water surrounding and inside the stone.

• The wavelength of the Holmium laser waves (2120 nm) are highly absorbed by water molecules.

• The laser leads to elevation of the temperature of the water molecules which will change to a vapor bubble. A mechanism referred to as Moses effect.

• Pulsed laser gives time for the bubble to disappear in between the pulses and become replaced with water molecules which will absorb the laser beam during the next pulse and makes a new vapor bubble.

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Drawbacks and Limitations

• The main draw back of the Moses effect is the inefficient energy transmission, where the initial part of the pulse is sufficient to elevate the temperature of the water molecule while the rest of the pulse is wasted.

Pulsed beam …………………

Initial part ……………………………………… Vapor bubble

Wasted part ………………… not absorbed

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Moses Technology (Lumenis)The laser pulse is modulated into two consecutive parts:

The first part separates the water by creating a small vapor bubble (“the Moses

effect”).

Then the remaining energy is transmitted via the vapor bubble toward the

target.

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Vapor Tunnel (Quanta laser)

Drawbacks and Limitations

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The laser cavity traps high energy inside, with elevation of the temperature.

Therefore, Holmium:YAG laser generators require an adequate water-cooling system, contributing significantly to the large size of these generators.

Accordingly, the maximal temperature range within the laser crystal sets a limit to the power and frequency at which a single Holmium:YAGcavity can operate

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Drawbacks and Limitations

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the Thulium fiber laser has been optimized to emit at a wavelength of 1940 nm, thus closely matching the near-infrared absorption peak of liquid water

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The emission spectrum of the diode laser used for laser pumping precisely matches Thulium ions’ absorption line.

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Summary

• Moses effect is the mechanism of all lasers to produce a vapor bubble.

• Moses technology is developed by Lumenis to increase the efficiency of energy transmission by modulating the laser pulse into two consecutive parts.

• Holmium laser wavelength does not lie at the peak of water absorption.

• Holmium ions absorb part of the light energy coming out from the flash lamp and the rest will cause heating of the system. This will limit the total energy that the machine can produce.

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Summary

• Thulium fiber laser emits wavelength at the peak of water absorption.

• Thulium fiber laser absorbs all energy coming out of the diode laser with no overheating of the system and this enhances the amount of energy that the machine can produce.

• Still Thulium fiber laser needs more studies to verify all aspects of its safety and efficacy.

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