Chapter 3 - Lasers Flashcards
What is Opthalmology?
Clinical and surgical practices related to the eye
What does laser stand for?
Light Amplification by Stimulated Emissions of Radiation
What is a mechanical wave and does it involve light?
Mechanical waves involve the periodic motion of particles in a medium. Light is NOT a mechanical wave because it can travel in both mediums and vacuums. Mechanical waves cannot travel in vacuums.
What two forces make up light?
Magnetic and Electric forces
What type of wave is light?
A transverse wave. (Two perpendicular waves that travel in the same direction)
How is the energy of light related to its wavelength
The energy of light is inversely proportional to its wavelength. (The shorter the wavelength, the more energy it is)
What is spontaneous emission?
When an electron absorbs energy through random occurrences and transitions back down to its ground state, releasing a photon.
What is stimulated emission?
When a photon that has the same energy as the energy difference between ground and excited state passes by an excited state electron and causes it to transition down to its ground state, emitting a photon.
What is population inversion?
When there is a higher amount of electrons in their excited state rather than the ground state.
What is pumping?
The process of putting electrons in a perpetually excited state
What is the active medium (aka lasing medium)?
The medium in which energy is pumped into that puts electrons in their excited state. Is often gas but could be solid or liquid.
What is the metastable state?
The state in which electrons stay in their excited energy state.
What is the optical resonating cavity?
A cavity consisting of a mirror on either side, one fully reflective, one partially. The lasing medium is placed inside.
What are the 5 most important characteristics of laser light?
- Monochromaticity
- Coherence
- Directionality
- Intensity
- Focusability
What are the three base components of a laser?
- Energy source (pump)
- Optical resonator (cavity)
- Gain medium
What is spatial coherence?
A spatially coherent laser is a laser whose light is emitted in a very well-defined beam
What is the power density of a laser (also called intensity)?
The amount of power delivered to a surface per unit area
What is fluence?
The total energy emitted by a laser beam, divided by the illuminated area. Best to be thought of as the “dose” of energy per beam.
What is coagulation?
The heat-induced disordering of proteins
What is photocoagulation?
The process of coagulation (heating tissues to cause disorder) brought on by a laser. i.e., using a laser to coagulate tissue
What is a photocoagulation burn?
When tissues surrounding a photocoagulated area die, the dead tissues develop into a burn called a photocoagulation burn
What is heat flow (heat transfer)?
The phenomenon in which heat travels from a high-temp area to a low-temp area.
What is the Thermal Relaxation Time?
It is the amount of time required for heat to flow into adjacent tissues. So if a laser is on a tissue for less time, the neighboring tissues wont be damaged.
What is photovaporization?
Water within tissue is heated to above 100 C and is hit with an extremely high power-density laser that instantly vaporizes the tissue.
What is the heat of vaporization?
The energy needed to vaporize different tissues. Different tissues all have varying levels of water content so different energy levels are needed to photovaporize different tissues
What is Photobolation?
The use of high-power lasers that use UV light to selectively break chemical bonds in tissues without causing local heating
What two modes can lasers operate in?
- CW (Continuous Wave - The laser is constantly providing power)
- Pulsed (The laser delivers an intense amount of power for an extremely short duration)
What is Q-Switching?
Using a Pockels Cell to build up energy into the laser and releasing it all in an instant to deliver extremely high amounts of power
What is the difference between average power and instantaneous power?
Average power is always smaller than instantaneous power.
What is photodisruption?
The use of pulsed lasers to create tiny explosions at the base of the laser beam which sends shockwaves that tear apart tissues and breaks up hard deposits.
What is laser lithotripsy?
Using lasers to break up gallstones in the urinary tract
How does absorption work?
DIfferent things absorb and reflect different colours. The colours that we perceive are those that are reflected off of an object, all other colours are absorbed.
How do lasers use absorption?
Since the physical colour of tissue is the colour that’s reflected, lasers must be the colour that is absorbed so that the optimal amount of energy can put into the tissue.
For example, Oxyhemoglobin appears red so a blue-green laser would be best suited for use for it.
How is photocoagulation used to treat diabetic retinopathy?
Photocoagulation covers areas damaged by leaking blood vessels, stopping the bleeding and allowing them to heal
What are some procedures done to correct myopia (near-sightedness)? Can they be done to correct hyperopia (far-sightedness)
Photorefractive Keratectomy (PRK) and Laser Assisted In-Situ Keratomileusis (LASIK). In some instances they can be done to correct far-sightedness but the vast majority of procedures correct near-sightedness.
What is Photodynamic Therapy? (PDT)
The use of light to target and destroy cells in cancer therapy and other treatments.
What are photosensitizers?
Light-activated chemicals that are injected into the bloodstream and accumulate in cells, staying longer in cancer cells. They react strongly to red-light so they are used to locate and analyze the extent of a tumour.
What are some advantages of laser surgery?
- Less blood loss
- More precise
- Targetting specific tissues (wavelength dependant)
- Versatility
- Faster recovery
- Reduced risk of infection
- Penetrating without incisions
- Cuts to arbitrary depths
What are some disadvantages of laser surgery?
- Traditional surgery may heal faster
- Accidental ignition of materials
- Additional safety training
- More expensive
- Doctors need additional training
- Damage by trial/error
- Photovaporization of gases and viruses can release them into air.
