Selecting a Power or Energy Measurement Solution

Measuring power or energy can be done in many different ways and with the purpose of obtaining. In the majority of applications it is done by the commonly known power/energy meters, by laser probes or OEM sensors. In each case the finality may the same (e.g. knowing the laser power) but real, final needs may be very different, as well as their consequent economical aspects.

A Power/Energy Meter is made of a detector linked to a monitor via a special connector, storing all relevant data concerning the head. The monitor can work as a stand alone unit displaying the power/energy values and other information and can be connected to computers or chart recorders.

Power/energy meters are high end instruments whose performances may vary with the number of features or complexity of the overall setup. Prices will follow accordingly . They are measurement instruments, the which thing means that they have to undergo to classes of precision, must have tight values of repeatability, need to be periodically re-calibrated (at least once a year) to trace their performance.

For powers exceeding 100W the heads need an internal cooling system which could be a fan extracting heat from dissipating fins or water running through channels carved into the head.

This is because power/energy meters must work continuously for long periods of time facing the laser beams, even many KWs, without problems. Their reliability and capacity to work indefinitely at the maximum powers or energies makes them the ideal instrument for applications like:

• Measurement of laser or laser system stability
• Alignment of laser cavity
• Alignment of optical setups
• Measurement of losses
• Derive statistical information on laser behavior

Measure the power/energy ratio between 2 optical paths.

Doing all this is only possible by the association of a properly cooled detector with a complex electronics which reads the row data and elaborates/displays the measurements. Once the measurement session is over, the equipment can be easily removed and used elsewhere, with another laser or system.

This is not so with OEM detectors. OEM detectors use the same sensors of power/energy meters embedded in simplified housings; they respond to the need of laser manufactures (in the majority of cases) to have a continuous monitoring of their sources and are permanently fixed into the laser head or the laser machine. But we are now talking of monitoring and not fine measurement: the associated electronics is in general very simple and limited to convert the sensor output into a signal manageable by the laser control unit.

The power/energy value is displayed, maybe after basic signal treatment (e.g. the speed-up of response time) but no significant elaboration is made. Measurements are accurate and repeatable but the display of information is used to preset the power/energy levels necessary for an application, verify that set levels remain as fixed and no problems occur on the machine.

Laser Probes only read power. They make a measurement in a fixed time period and are used to make time-to-time controls at the source exit, at the working area or before/after an optical component to check its losses.

Probes simply tell which is the power level at the time of measurement, like a photo camera provides the picture of a shot taken at a certain instant; on the contrary power/energy meters can be imagined as movie or video cameras that show a real time and continuous evolution.

For the above reasons probes cannot be used for alignments, monitoring of stability or provide statistical information which all require a continuous use.

They are low cost devices and, until the introduction of LaserPoint’s Cronos and FIT series with their patented measurement and acquisition techniques, the market was only offering poorly repeatable and precise instruments.

FIT and Cronos have been the real breakthrough in this kind of measurement with the reduction of reading time (lowered from 20 sec or more to 4sec and 8sec), the possibility of making several measurements without cooling and the complete automatism of measurement which makes them independent from errors generated by wrong timings.

All these innovations have now brought those probes to have performances comparable to power meters (e.g. the FIT instruments have the same capacity of a power meter to repeat measurements with a ±1% error bar).