The technical definition of output power related to laser products is the power level of laser beam. Expressed as less than milliwatt (< MW); a unit of power equal to one thousandth of a watt. Higher output power is brighter than the lower output power.
The main measuring equipment of laser is an optical power meter (or laser power meter). It measures the power of light in the beam (the energy transmitted per unit time). Generally, when receiving a pulse sequence with a high pulse repetition rate, it only displays the average power. Other instruments, called light energy meters, measure pulse energy.
Most power meters are based on the principle of thermal detectors: they convert optical power into thermal power through absorber structures with black coatings. They use thermopiles to measure the resulting temperature rise (or, in fact, the temperature difference between the absorber and the base). The thermal power meter is suitable for the average power of 10 MW to several kilowatts. The accuracy of the thermal power meter is moderate, the sensitivity is independent of wavelength and relatively slow.
Optical power meters can also be made from photodiodes, which are usually based on silicon, near-infrared germanium, and InGaAs, although the latter is expensive. When the laser is pointing at the photodiode detector, the current generated by the light is proportional to the light intensity and depends on the wavelength. Photodiode optical power meter can measure the power in the microwatt range, or even lower, and can use a suitable attenuator to measure higher optical power. But they are more vulnerable than thermal power meters because they are more easily damaged by high light intensity.
The most common specifications of laser power meters include average power, power density, energy, energy density, repetition rate, etc. Instrument manufacturers usually advise users to reach a stable point for the interested laser before measuring the laser power, generally between 20 and 30 minutes, because the characteristics of optical elements often change as the laser reaches balance. Other recommendations include ensuring that the beam is 40% to 60% of the optical aperture of the instrument, as too small a beam increases the possibility of damage to the detector during the measurement.
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