Energy is the ability to work and is measured in Joules. The measuring unit for most dental laser applications is the millijoule (mJ), and this is a parameter that is controlled by the operator. Power is the rate of doing work, or energy used over a period of time and is measured in Watts (W). One Watt equals one Joule per second. These are the watts displayed on the machines’ control panels. A laser beam can be emitted either as a continuous beam or in a pulsed fashion.
The pulse rate per second is measured in Hertz (Hz). The wattage displayed on the laser unit is a product of the Millijoule (energy) per pulse times the number of pulses per second (hertz). Peak Power refers to the power level in each individual laser pulse and this measurement is not visible to the operator, yet it is the most important variable dictating how the laser beam will interact with the target tissue.
Continuous wave emission mode means the laser is on the whole time it is turned on. In these lasers peak power equals the wattage output displayed. There are two basic forms of pulsed laser modes: gated wave and free running pulsed. A gated wave pulse is usually created with a shutter that blocks the laser beam from reaching the handpiece and target tissue at varying speeds. This pulse form is sometimes referred to as “chopped.” The laser is on constantly but the shutter device blocks the light from transmitting. “Superpulsed” lasers are a form of gated lasers with extremely short pulse durations. Free running pulsed lasers are not on constantly but emit photons in powerful bursts of energy measured in millionths of seconds. To better understand these concepts one can take an example of a flashlight. When a flashlight is turned on it is in continuous wave mode, moving one’s hand back and forth across the beam is gated wave mode, and turning it on and off repeatedly is free running pulsed mode. Each of these temporal emission modes has important characteristics when the laser energy interacts with tissues that need to be understood well by the practitioner. Peak power can be a difficult concept to understand but its importance cannot be overstated. Each pulse has a set amount of energy, usually the millijoules displayed on the unit. As shorter pulses are used this same energy is effectively squeezed into a smaller space, which increases the peak power of the pulse. One can think of a rubber band around a wrist as an analogy. If the rubber band is lifted three inches, it will have a fixed amount of energy in it. Now if the rubber band is slowly returned to the wrist, it will not hurt a bit. If it is let go, the energy is released in a much shorter time and it will sting and make a popping sound. Yet the actual energy expended is identical. Hard tissue dental lasers can have peak powers in the thousands of watts, and these short burst of extreme power allow for the efficient cutting of enamel, dentin and bone.