Power and Energy Meters: From Sensors to Displays

By Burt Mooney, Ophir-Spiricon Inc.

From the time the first laser was built, physicists probably thought, “That’s great!  Now how do we measure it?” Thus laser power and energy meters were born.

Since lasers are good sources of concentrated heat, it was probably assumed that heat sensing methods would best be employed for measurement. The simplest device to measure heat is a thermocouple. A simple device to measure light is a photodiode. So, some enterprising engineer designed and built such a device. Then they needed an instrument to display the results and give rapid feedback in order to tweak, align, or adjust the laser for maximum output. Early displays were basically analog meters that had a needle on a dial that went from left to right as the laser power went up.

Ophir Power/Energy Meter Calibration Procedure and Traceability/Error Analysis

By Dr. Ephraim Greenfield, VP of Engineering, Ophir-Spiricon

This document discusses the interpretation and basis for stated measurement accuracy of Ophir Laser Power/Energy meters.
1. General Discussion
2. Combination of Errors and Total Error
3. Analysis of Power and Energy Calibration Errors
4. Detailed Analysis of Power and Energy Calibration Errors

Laser Power and Energy Measurement

Ophir standard power and energy measuring heads and displays all use smart head technology. This means that all the configuration and calibration information is stored in a small memory chip inside the smart head plug, so that when the head is plugged into the display the correct power and energy are read. Except for some OEM heads, this technology is used in all Ophir heads: pyroelectric, photodiode, scanned beams, medical heads, etc.

Calibration Capability at Ophir

Calibration is perhaps the most important of our products. We have a complete line of calibration lasers so that we can always calibrate at or near the customer’s wavelength. These lasers include powers up to 400W and both CW and pulsed lasers. In addition, we have a number of heads calibrated at NIST used as calibration standards. Below is a list of the calibration wavelengths used at Ophir in calibrating our standard catalog heads. Usually the calibration is done at representative wavelengths within a band of wavelengths where the head is spectrally flat. The calibration then applies to any wavelength in this band. The specifications note the maximum additional error in each wavelength band due to variations incalibration between the wavelength of calibration and the wavelength of measurement.