Laser Output Measurement
A laser is a device that emits an optical beam. A laser beam carries a certain amount of optical power. Lasers emit beams in two different ways: continuous wave (CW) or pulsed. A CW laser emits a steady power as shown in Figure 52.1. CW laser power is measured in terms of watts. The power of commonly used CW lasers ranges from a fraction of milliwatts for a small helium–neon (He–Ne) laser to tens of kilowatts for a carbon dioxide (CO2) laser. A pulsed laser emits a pulsed power as shown in Figure 52.2. The pulse can be repeated. The pulse duration and repetition rate vary for lasers of different types and are adjustable for some types of lasers. Pulsed laser power is more easily measured in terms of energy per pulse such as joules per pulse. The term “per pulse” is usually omitted. The energy of commonly used pulsed lasers ranges from a few picojoules for a semiconductor laser to tens of megajoules for a semiconductor laser array. The pulse repetition rate ranges from a single pulse for an excimer laser or an x-ray laser to hundreds of megahertz for a neodymium/YLF laser. The pulse duration ranges from tens of femtoseconds for a Ti/sapphire laser up to CW for a CO2 or He–Ne laser.