Lasers Flashcards
Lasers
Light Amplification by Stimualted Emission of Radiation
What is collimated light
Waves are in parall
What is coherent light
Waves are all in phase and have same wavelength
When can resonance occur?
Mirrors placed at a distance apart that is a multiple of the wavelength.
Resulting light is exactly in phase and reinforces itself
Light becomes stronger and stronger while remaining in phase
Features of light from laser
Coherent (in phase)
Monochromatic (one wavelength)
Collimated (parallel rays)
How can laser damage occur?
Thermal
Ionization
Photochemical
How does thermal laser damage occur
Depends on pigment present
Melanin absorbs most of the visible spectrum of light
Xanthophyll at macula absorbs blue light and shorter wavelengths
Haemoglobin absorbs blue,green,yellow light
Photocoagulation avoids shorter wavelengthsWh
ich colour laser in the eye
Red or green longer wavelegths to avoid damage to macula pigment
How does ionizing laser damage occur
Photon energy strips electrons from molecules forming ions
IOns form a plasma that displaces tissue
NdYAG and argofluoride laserW
What are photochemical effects of laser
Pulse duration > 10secs
Free radicals formed toxic to cells
Short wavelengths cause damage at lower levels of irradiance and so more harmful
Argon laser wavelegths
Blue 488nm
Green 514nm
Blue light absorbed by xanthophylls in inner layer of macula - contraindicated
He:Ne gas laser
633nm
Visible red light
Aiming beam for lasers with invisible output
Diode laser
810nm infrared
Continuous wave mode
Absorbed by melanin\REtinal photocoagulation
Photocycloablation for glaucoma - penetrates sclera
NgYAG laser
1064nm infrared
Continuous wave laser that is Q switched and is often used to perform capsulotomy
He:Ne laser produces red aiming beam
Excimer laser
Argon-fluorine dimer laser to emin 193nm UV radiation
Absorbed by cornea and causes tissue removal
Photorefractive keratectomy, laser intrastromal keratomileusis, phototherapeutic keratectomy
What is confocal microscopy used for?
View layers of the cornea
How does OCT work
Using near infrared light
Optical beam of light directed at tissue results in most of the light scattering
Small amount of light is reflected
Scattered light does not contribute to the image but produces glare
Interferometer uses superimposition to combine separate coherent light waves together so that combination has constructive or destructive interference to distinguish scattered light from reflexted light
3D image from optical scattering media
What is class 1 laser safet
Safe, light contained in enclosure
CD player
Class 2 laser safety
Safe during normal use
Laser pointer
Class 3a
Small risk of damage within the time of the blink reflex
5mW
Class 3b
May cause severe eye damage on exposure
CD writer 500mW
Class 4
Can burn skin and cause eye damage
Industrial, scientific
Complications of Nd:YAG capsulotomy
LEns pitting, sublaxation
Iritis
Raised IOP
Retinal break
Macula oedema
Which laser for retinal photocoagulation in vitreous haemorrhage or dense cataract
Krypton Red - penetrates cataract and VH better
