What is a laser?
Light Amplification by Stimulated Emission of Radiation
The device produces a beam of coherent light with a specific wavelength in the infrared, visible or ultraviolet regions of the electromagnetic spectrum.
What are the properties of laser light?
- Monochromic - consisting of a single wavelength or colour
- Coherent - photons are in phase (like marching soldiers)
- Collimated - photons are almost in parallel (aligned), with little divergence from the point of origin
What are the components of a laser?
- A lasing medium or ‘gain medium’
May be solid (crystals, glasses), liquid (dyes or organic solvents), gas (helium, CO2), or semiconductors - An energy source or ‘pump’
May be a high voltage discharge, a chemical reaction, diode, flash lamp or another laser - An optical resonator or ‘optical cavity’
Consists of a cavity containing lasing medium with 2 parallel mirrors on either side, one highly reflective, the other partially reflective allowing some light to leave cavity to produce laser’s output beam (output coupler)
How is laser light produced?
Principles at atomic level
- When energy is applied to an atom, the energy is absorbed and the atom moves from low energy level (ground state) to a high energy level (excited state). This procedure is energy absorption
- One or more electrons in the atom move to higher energy orbits further from the nucleus
- Electrons then spontaneously fall back to their resting orbits, releasing the excessive energy in the form of photon (spontaneous emission)
- Photons produced are of similar wavelength
- Stimulated emission is where photons released from an atom in an excited state trigger photons to be released from neighbouring excited atoms - the released photons are identical, the same wavelength and are in phase
- Population inversion is where >50% of atoms are in their excited state
What types of laser are used in medical practice?
- CO2 laser
Uses photo-thermal effect, rapidly heating tissues.
Used for precise cutting and coagulation of soft tissue
Used in laser airway surgery - Nd-Yag laser:
Used for photo coagulation of GI bleeding lesions and bronchial carcinoma - Argon laser
Photo dissociation results in non thermal ablation
Used for corneal reshaping
Treatment of lesions such as port wine stains
What types of laser are used in medical practice?
- CO2 laser
Uses photo-thermal effect, rapidly heating tissues.
Used for precise cutting and coagulation of soft tissue
Used in laser airway surgery - Nd-Yag laser:
Used for photo coagulation of GI bleeding lesions and bronchial carcinoma - Argon laser
Photo dissociation results in non thermal ablation
Used fir corneal reshaping
Treatment of lesions such as port wine stains
How is laser produced?
Laser is produced by the energy released by electrons moving from high energy to low energy orbits, followed by the collision with excited atoms (stimulated emission) releasing 2 photons identical in wavelength, phase and in parallel
What are the main absorbing components of laser ?
Laser light has to be absorbed by the tissue in order to exert biological effect.
Main absorbing components are water, melanin, and haemoglobin
What determines the depth of penetration?
The wavelength determines depth of penetration
What are the principle dangers of lasers?
- Damage to eye
- Burns
- Flammability
What is laser wavelength?
Laser wavelength is the distance between 2 crests on a wave, and is measured in nanometers (nm)
What is a laser diode?
A laser diode, also known as a semiconductor laser, is a light-emitting diode that uses stimulated emission to form a coherent light output.
The light exits the diode in many directions and used a lens to form a collimated beam of laser light
