LASER: Visible and IR Flashcards
What are the duties of the Clinical LASER Expert?
Assesses competency of operators
Oversses training of operators
What are the duties of the LASER Protection Supervisor?
Carries out LASER risk assesment
Writes local rules
Supervises training and safe working
Give some examples of Pre-Use checks.
Condition of fibres, cables, etc Safe intial power setting Door locked/controlled warning lights Windows covered Staff instructed
Give some examples of shutdown/handover checks.
Power setting to zero
Reporting of incidents
Returned to usual power settings
Return key
What are common faults resulting in reported incidents to staff involving a Medical LASERs ?
No/incorrect eye protection
Unintended off switch operation
Non-standard procedure
Incorrect replacement parts
What are common faults resulting in reported incidents to patients involving a Medical LASERs ?
Incorrect eye-protection Internal electrical fire Electrical shock Failure of fibre Non-standard parts/procedure
What two types of measurement device are used for the with a LASER power meter?
Thermopiles and photodiodes
How does a thermopile measure LASER power?
A thermopile is a bank of thermocouples that use the Seeback effect* to measure temperature that then indicates power.
The cool end must be kept at an ambient temperature.
*two dissimilar metals joined together that creates a voltage when heated or cooled. Voltage indicates temp
What are the characteristics of a thermopile?
10mm diameter aperture
low reflection (~2% as matte black)
wavelength responce of a few percent 200-20,000nm
can handle 10W max power or 10
What are the characteristics of a thermopile?
10mm diameter aperture
low reflection (~2% as matte black)
wavelength responce of a few percent 200-20,000nm
can handle 10W max power or 10kW/cm^2 max power intensity.
Damage threshold 10GW/cm^2
Responce time of 1-2s
How does a (Si) Photodiode measure LASER power?
Currents in diode proportional to LASER power
What are the characteristics of a photodiode?
Wavelength specific
Quick response time
Limited to a few mW continous pulse
What is the purpose of a spectra-radiometer?
LASER power meters are designed for single wavelength sources, and so will give inconsistent results if used with LEDs of Xenon flash lamps.
Power output is therefore measured using a spectra-radiometer
What are the essential properties of a LASER?
Monochromatic
Small Divergence
Coherent
What LASER is used in LASIK surgery and why?
EXCIMER LASER
UVC - 193nm
Penetrates to a depth of 0.1mm into the cornea, allowing the cornea to be reshaped but does not penetrate into other parts of the eye.
What LASER is used in the treatment of diabetic retinopathy surgery and why?
Green LASER (e.g. Argon 584nm) Passes through the eye but it is absorbed by the blood sealing the leaks.
What LASER is used in LASER Hair Removal and why?
Red/IR LASER (e.g. Alexandrite 700-800nm)
Passes through dermis and tissue, absorbed by hair follicle.
What LASER is used in LASER surgery (e.g. ENT or Gynae) and why?
Visible or IR (e.g. CO2 10,600nm)
Delicate excisions with minimal collateral damage.
Excision depth of 0.1mm.
What LASER is used in Endoscopic LASER surgery and why?
Ho-YAG 2080nm
Cuts and coagulates with minimal bleeding.
Can destroy urinary stones.
What are the different classes of LASER?
Class 1 - Safe: enclosed or low power (<1mW)
Class 1M - Safe: except with viewing aids.
Class 2 - Safe for accidental viewing: 1mW max in the visible spectrum.
Class 2M - Use of collimating optics may be hazardous.
Class 3R - Intentional intra-beam viewing may be hazardous (Power <5mW)
Class 3B - Eye hazard but no skin Hazard (Power <500mW)
Class 4 - Eye, Skin, and Fire Hazard
Where is data for the calculation of MPE found?
IEC 60825-1
What is the Nominal Ocular Hazard Distance (NOHD)?
The distance within which the MPR may be exceeded, including both specular and diffuse reflection.
What is the equation for NOHD from a LASER?
NOHD = 1000SQRT[Power/(piMPE)]
What is the equation for NOHD from a Fibre?
NOHD = (1/AA)*SQRT[Power/(pi*MPE)] AA = Acceptance angle (0.1-0.4 radians)
What is the equation for the Acceptance angle of a fibre?
AA= = arcsin(NA) NA = numerical aperture
What measures are required for safe working with LASERs?
Classification of the LASER Risk Assessment Designation of a controlled area Adequate Personal Protection. LASER local rules LASER protection Supervisor Contingency plans
What duty holders are required for working with class 3B and class 4 LASERs?
Responsible body (e.g. Trust) (delegates responsibility to LPA/Head of Med Phys) Laser Protection Supervisor Equipment Management (EBME)
