Page 112 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Hence, the minimum allowable optical density for this laser output is 6.4 – in practice we tend to ‘over-compensate’ OD values, to add extra protection. Hence, for Q-switched (and picosecond) lasers an LPA will usually recommend a minimum OD of 7 at 1064nm.
Note – for a picosecond laser of 100 ps pulse duration, the minimum OD would be 7.1 for a maximum laser energy density of 12.5 J/cm2. Commercial systems in the skin-laser arena cannot generate such high fluences in useable spot diameters with such short pulsewidths.
 You must NEVER use a Class 4 laser without protective glasses.
And, NEVER look directly into the beam of a Class 4 – even with safety glasses!!!
Ocular Protective Equipment
If you are working with Class 3B or Class 4 lasers and the laser beam is not totally enclosed then you will need to wear laser safety goggles. These may also be considered necessary for work with some Class 3R lasers (invisible wavelengths). It is important that ones with the correct optical density for the laser you are using are worn.
 As a general rule alignment goggles, that still allow the user to see where the beam is, are recommended for visible lasers whereas high optical density goggles should always be worn when working with invisible lasers, such as the Nd:YAG. The goggles chosen need to conform with the appropriate standard: EN 207:2017 for total eye protection, and EN 208:2017 for alignment goggles (ANSI Z136.1 – Z136.9, in America).
All Class 4 lasers must be used with the appropriate safety goggles. These must be chosen according to the wavelength(s) emitted by the laser. For a Q-switched Nd:YAG laser this means that the goggles must protect against both 1064 nm and 532 nm.
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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Figure 61: Typical laser warning signs

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