Lasers Flashcards

1
Q

Lasers

A

Light Amplification by Stimualted Emission of Radiation

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2
Q

What is collimated light

A

Waves are in parall

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3
Q

What is coherent light

A

Waves are all in phase and have same wavelength

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4
Q

When can resonance occur?

A

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

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5
Q

Features of light from laser

A

Coherent (in phase)
Monochromatic (one wavelength)
Collimated (parallel rays)

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6
Q

How can laser damage occur?

A

Thermal
Ionization
Photochemical

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7
Q

How does thermal laser damage occur

A

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

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8
Q

ich colour laser in the eye

A

Red or green longer wavelegths to avoid damage to macula pigment

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9
Q

How does ionizing laser damage occur

A

Photon energy strips electrons from molecules forming ions

IOns form a plasma that displaces tissue

NdYAG and argofluoride laserW

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10
Q

What are photochemical effects of laser

A

Pulse duration > 10secs
Free radicals formed toxic to cells

Short wavelengths cause damage at lower levels of irradiance and so more harmful

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11
Q

Argon laser wavelegths

A

Blue 488nm
Green 514nm

Blue light absorbed by xanthophylls in inner layer of macula - contraindicated

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12
Q

He:Ne gas laser

A

633nm
Visible red light
Aiming beam for lasers with invisible output

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13
Q

Diode laser

A

810nm infrared
Continuous wave mode

Absorbed by melanin\REtinal photocoagulation
Photocycloablation for glaucoma - penetrates sclera

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14
Q

NgYAG laser

A

1064nm infrared

Continuous wave laser that is Q switched and is often used to perform capsulotomy

He:Ne laser produces red aiming beam

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15
Q

Excimer laser

A

Argon-fluorine dimer laser to emin 193nm UV radiation

Absorbed by cornea and causes tissue removal

Photorefractive keratectomy, laser intrastromal keratomileusis, phototherapeutic keratectomy

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16
Q

What is confocal microscopy used for?

A

View layers of the cornea

17
Q

How does OCT work

A

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

18
Q

What is class 1 laser safet

A

Safe, light contained in enclosure

CD player

19
Q

Class 2 laser safety

A

Safe during normal use

Laser pointer

20
Q

Class 3a

A

Small risk of damage within the time of the blink reflex

5mW

21
Q

Class 3b

A

May cause severe eye damage on exposure

CD writer 500mW

22
Q

Class 4

A

Can burn skin and cause eye damage

Industrial, scientific

23
Q

Complications of Nd:YAG capsulotomy

A

LEns pitting, sublaxation
Iritis
Raised IOP
Retinal break
Macula oedema

24
Q

Which laser for retinal photocoagulation in vitreous haemorrhage or dense cataract

A

Krypton Red - penetrates cataract and VH better