Power Meters FAQ's

Laser Power/Energy Sensors



All Ophir power meters, including photodiode power meters, have an air gap between the fiber tip and the sensor. Therefore they measure the power emitted by the fiber into the air and do not take into account any reflection losses there are in the fiber. Therefore, if in actual use, the fiber will be coupled with no loss to another element, then the losses should be added to the reading. These losses are usually about 4%. Thus if the reading on the Ophir meter is say 100mW, then in lossless use, the real power will be 104mW.


The spec was designed around the way such lasers are typically used. Since these lasers are normally used with focusing optics, the spec of the 120K-W does not give a maximum power density; rather, it defines the assumed focusing-lens focal length and position such that the beam will end up having a 100mm diameter at the cone, and defines the assumption of a near Gaussian beam under those conditions so we can define a baseline number. This is defined briefly in the spec, and in a bit more detail in the User Note that comes with the sensor.