Non-Ionising Radiation: Lasers

Question 1

Which sections of the EM spectrum are optical radiation?

Answer 1

• Infrared
• Visible light
• Ultraviolet

Question 2

What does LASER stand for?

Answer 2

Light
Amplification by
Stimulated
Emission of
Radiation

Question 3

How is laser light created?

Answer 3

Atoms in an excitation medium are excited to a higher state in a process known as ‘pumping’. When they return to ground state, photons are emitted into a lasing medium, where they excite several other photons that are released in a synchronised and amplified manner. This process occurs inside a laser resonator cavity.

Question 4

What are the 3 key properties of laser light?

Answer 4

• Monochromatic (very narrow spectral range)
• Directional (very little spread)
• Coherent (photons are in-phase)

Question 5

What are the 2 types of photon emission?

Answer 5

1) Continuous wave (CW)
2) Pulsed emission

Question 6

What are the 2 types of pulsed emission?

Answer 6

1) Free running (ms, µs)
2) Triggered pulse (ns, ps, fs)

Question 7

Describe the anatomy of a pulsed laser emission

Answer 7

Question 8

Define power

Answer 8

The rate of energy flow (i.e. energy flow per unit time).

Question 9

Give the equation for power

Answer 9

Question 10

Define irradiance (power density)

Answer 10

Power per unit area.

Question 11

Give the equation for irradiance

Answer 11

Question 12

Define radiant exposure (energy density)

Answer 12

Energy per unit area

Question 13

Give the equation for radiant exposure

Answer 13

Question 14

How does irradiance change over the area of a focused laser beam?

Answer 14

Question 15

Carbon dioxide lasers are _______ lasers.

Answer 15

Surgical

Question 16

Why are carbon dioxide lasers suitable for surgery?

Answer 16

They use pulsed modes (µs-ms) via fast electrical switching and have a wavelength well matched to water absorption, which gives rapid vapourisation with minimal charring.

Question 17

What are KTP lasers used for?

Answer 17

CW: to cut tissue
Pulsed mode: for vascular lesions and vessels
Q-switched mode: to remove red skin pigment

Question 18

What are diode lasers used for?

Answer 18

• Tissue heating/necrosis
• Coagulation
• Cutting
• Targetting hair follicules

Question 19

How are lasers delivered in general surgery?

Answer 19

Using an articulated arm or an optical fibre

Question 20

What is a chromophore?

Answer 20

A substance that absorbs light

Question 21

What are the 3 main chromophores in tissue?

Answer 21

• Haemoglobin
• Melanin
• Water

Question 22

Why are different lasers used to target differetn chromophores?

Answer 22

Because they absorb different wavelengths to varying degrees

Question 23

What eye hazards do lazers present?

Answer 23

• Photokeratitis
• Cataracts
• Retinal lesions
• Corneal burns

Question 24

What is the blink reflex aversion response?

Answer 24

The reflex that protects the eyes against visible lasers by causing the eyes to blink after ~0.25 s.

Question 25

Why do laser burns to the retina occur?

Answer 25

Because the eye can intensify laser exposures by up to 100,000 times by the time the light reaches the retina.

Question 26

What skin hazards do lazers present?

Answer 26

- Erythema - Accelerated skin aging - Increased pigmentation - Pigmentation darkening - Photosensitive reactions - Skin burn - Photochemical

Question 27

What are the 4 types of laser reflection?

Answer 27

- Diffuse target - Flat specular target - Convex specular target - Concave specular target

Question 28

State the 4 non-beam hazards of lasers

Answer 28

- Laser plume (Class 4 lasers can generate a plume of infectious tissue) - Fire and explosion (Class 4 lasers can ignite flamable materials) - Hazardous substances (lasers are often produced using toxic gases) - Laser dyes (carcinogens)

Question 29

What is a Class 1 laser?

Answer 29

A laser that is safe under all reasonably foreseeable conditions.

Question 30

What is the power of a Class 1 laser?

Answer 30

40 µW blue 400 µW red

Question 31

What is a Class 1M laser?

Answer 31

A laser that is safe under most conditions, but is possibly hazardous if viewed with optics (e.g. magnifiers or binoculars).

Question 32

What is a Class 1C laser?

Answer 32

Lasers designed for contact applications. They have engineering controls that allow them to be viewed without eye protection.

Question 33

What is a Class 2 laser?

Answer 33

A low power laser that is generally considered safe due to the natural aversion response of the eye (blink reflex).

Question 34

What is the power of a Class 2 laser?

Answer 34

1 mW (visible only)

Question 35

What is a Class 2M laser?

Answer 35

A laser that is the same as Class 2, but is unsafe if viewed with optics (magnifiers or binoculars). All Class 2M beams are visible.

Question 36

What is a Class 3R laser?

Answer 36

A laser that can be hazardous for visible beams if the intrabeam is intentionally viewed.

Question 37

What is the power of a Class 3R laser?

Answer 37

5 mW

Question 38

What is a Class 3B laser?

Answer 38

A laser that is normally hazardous if there is any kind of intrabeam viewing (including accidental viewing). This laser also has limited skin hazards. Viewing the diffuse reflections from this beam is normally safe.

Question 39

What is the power of a Class 3B laser?

Answer 39

500 mW

Question 40

What is a Class 4 laser?

Answer 40

A high power laser that has the potential for serious eye injuries, presents a fire hazard, and is a serious skin hazard.

Question 41

What is the power of a Class 4 laser?

Answer 41

No power limit

Question 42

Define accessible emission limit (AEL)

Answer 42

The maximum allowable emission for each class of laser, in either W or J.

Question 43

Define maximum permitted exposure (MPE)

Answer 43

The maximum exposure level to which a person can be exposed before adverse effects occur. The eyes and skin both have rated MPE values in W/m².

Question 44

Define nominal occular hazard distance (NOHD)

Answer 44

The distance at which beam irradiance equals the corneal MPE in metres.

Question 45

Why is a controlled area defined when lasers are used?

Answer 45

Because hazardous accidental exposures may occur closer than the nominal occular hazard distance (NOHD).

Question 46

How are laser controlled areas defined?

Answer 46

In the local rules, and by using signs, lights, and door interlocks around the controlled area.

Question 47

What is a Laser Protection Supervisor (LPS) / Laser Safety Officer?

Answer 47

The person responsible for supervising laser environment safety and ensuring that local rules are follwed. This person is closely involved with laser treatments.

Question 48

What is a Laser Protection Advisor (LPA)?

Answer 48

A person who must be appointed if departments are using Class 3B and Class 4 lasers. They are knowledgeable in the evaluation of laser hazards, provide advice on how to controls the risks, complete hazard analysis and risk assessments, and may produce/advise on Local Rules.

Question 49

The _______ certification scheme must be completed before becoming an LPA.

Answer 49

RPA2000

Question 50

Who is considered an authorised laser user?

Answer 50

Someone who has been approved by a clinical laser expert, and has suitable evidenced training in the clinical use of lasers.

Question 51

What should laser local rules contain?

Answer 51

1) Appointments 2) Potential hazards 3) Controlled and safe access 4) Authorised user's responsibilities 5) Safety checks 6) Normal operating procedures 7) PPE 8) Prevention of use by unauthorised persons 9) Adverse incident procedures 10) List of authorised users/operators

Question 52

What 5 sections should a risk assessment contain?

Answer 52

1) Evaluation of all hazards 2) Assessment of each risk 3) Establishing safety control procedures 4) Re-assess the risk 5) Determine if the laser is okay to use in accordance with established procedures