2.6 Photodisruption
Definition
- disruption of tissues due to the rapid ionization of molecules caused by exposure to laser light.
Type of Lasers
Q-switch neodymium (Nd:YAG) laser
picosecond or femtosecond laser
Process
- the electric field strength of focused radiation is high enough to pull electrons out of the atoms, forming a plasma and producing an optical breakdown with shock waves disrupting the tissue
- the shorter the pulse, the smaller the energy to get an optical breakdown
- the cavitation bubble is also smaller and the side effects will be reduced
Example
- the reaction of a picosecond laser pulse on a gallstone
Titanium (Ti) sapphire laser
- the bubble has its maximum dimension after about 300 µs, then it collapses and normally a multiple rebound effect occurs.
Plasma Formation
Definition
- 4th state of matter including solids, gases and liquids.
- It is an ionized gas mixture consisting of ions, electrons and neutral atoms.
- Typically at low pressures and high temperatures.
Formation
- When more heat is provided to atoms or molecules, they will be ionized.
- Electron will gain enough energy to escape its atoms. Then, atoms become ions.
- In sufficiently heated gas, ionization happens many times creating clouds of free electrons and ions.
Types of Plasma
- Natural Plasma: stars, space between planets, intergalactic medium
- Artificial Plasma: TV screens, neon signs, plasma ball
- Terrestrial: lightning, polar aurora
Reference
References: