Energy meters and optical power meters are optical testing instruments. Power meters are optical testing instruments designed to measure the average power of a continuous light beam. The instrument is used frequently to measure the beam power of continuous wave lasers. Energy meters are optical testing instruments designed to measure the total energy of a single pulse. The instrument is used frequently to measure the beam energy of pulsed lasers. Energy meters and optical power meters can be supplied as combination test meters. Important specifications to consider include wavelength range and sensor diameter. The wavelength range is the range of wavelengths the detector is designed to test over. The sensor diameter is the diameter of the active sensor area.
Detector mechanisms for energy meters and optical power meters include pyroelectric, semiconductor, and thermal. Pyroelectric detectors are designed to measure the energy of short optical pulses that have a maximum width of 5 µs to 400 µs depending upon detector design. These detectors are made of a ferroelectric crystal that has a permanent dipole moment. When subjected to an optical pulse, the crystal is heated and causes the dipole moment to change. The changing of this dipole moment causes a current to flow. When using pyroelectrics, care must be taken not to exceed the maximum pulse width or the maximum repetition rate. Semiconductor photodiodes are ideal for making measurements of low-level light due. Thermal detectors are an array of thermocouples connected together in series in order to increase the voltage output to more easily measured levels. In use, absorption of a laser beam creates heat at the receiver area of the power probe. The power level of the laser beam determines the amount of heat and thus the temperature rise at the receiver. The number of channels and operating temperature are also important to consider.
Important performance parameters specific to power meters include power range and accuracy. The range of power the detector is designed to measure is in watts. The accuracy of the power measurement is represented as a percentage. Important parameters specific to energy meters include energy range, accuracy and maximum pulse width. The range of energy the detector is designed to measure is in Joules. The accuracy of the energy measurement is expressed as a percentage. Since energy meters measure the energy of a pulse, there is a maximum length to the pulse it can measure. Display choices include analog only, digital only , or analog and digital. The display mechanism can be LED, LCD, or a backlight mirror scale. Some energy meters and optical power meters come equipped with a handheld display.