Lasers differ from each other not only in wavelength or optical power, but also in the way in which the power is emitted. Power can be emitted continuously (continuous wave operation - CW) or in form of pulses (long pulse, giant pulse / q-switched or mode-locked).
In case of pulsed operation with a low pulse repetition rate, the peak power of each single pulse is the critical value. If the repetition rate increases, the average power needs to be taken into consideration. Please note that some lasers can be operated in different modes.
Laser safety eyewear is specified according to these operation modes. Protective eyewear for repetitively pulsed lasers must satisfy the D rating as well as the I, R or M rating appropriate to its pulse length.
Summary of Laser Operation Modes / Pulse Duration
||Typical Pulse Length
||Marking on eyewear
|Continuous Wave (CW)
||...is the continuous emission of laser radiation.
||< 0.2 s
||...is the short-term single or periodically repeated emission of laser radiation.
||> 1 µs to 0.25 s
|Giant Pulse Mode (Q-switch)
||...is like pulsed m ode, but the pulse length is very short.
||1 µs to 1 ns
||...is the emission of laser radiation with all the energy stored in the laser medium released whithin the shortest possible time.
||< 1 ns