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  • Measuring Laser Power

Photonics Spectra
May 2004
Where laser precision is imperative, testing the laser power is a necessity.

Whether in industrial, medical or environmental applications, ensuring that the power level falls within certain guidelines improves quality control and reduces downtime or liabilities resulting from error or safety hazards.

Choosing a laser power meter requires much consideration, beginning with the type of laser under test. The meters fall into two main categories: thermal and semiconductor. For continuous-wave laser testing, for example, a thermopile may be the best solution. For measuring pulsed power, a pyroelectric thermal detector is used. A third type, the integrating sphere detector, may be the best choice if repeatability of measurement is important.

Intro-Power-Meter_BS34007.jpgA major consideration in laser diode testing is calibration. Power meters should be traceable to an internationally recognized standards organization, such as the National Institute of Standards and Technology. This organization has long used electrically calibrated laser calorimeters to provide traceability, but it has recently improved accuracy with a laser-optimized cryogenic radiometer.

Power meters calibrated to the strictest standards are necessary for critical applications. And calibration shouldn’t stop after the initial test. Accuracy should be maintained by having the meter recalibrated at least annually.

To some users, a power meter is like the screwdriver in the laser toolbox. It’s necessary, but not necessarily exciting. What is exciting, though, are the incremental changes made. Many meters can now be connected to a computer through a USB or an RS-232 interface, which is great for producing printed readouts in graph form. Some power meters enable use of a computer display as the monitor, which has several advantages, including the ability to control the tests remotely or to run many simultaneously.

As applications and lasers change, so will power meters. New ways of integrating meters are being developed so that testing can be done easily and quickly. For example, laser-based surgery being conducted in doctors’ offices is increasing the need for easy-to-use meters. Another example is the miniaturization of electronic components, which requires extremely precise drilling or etching. Customized power meter solutions are building the test modules into the laser setup so that repeated testing is part of the process.

The following series of articles by leaders in the industry presents an overview of the ways in which power meters continue to evolve to meet ever-changing needs.

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