How to Easily Calculate the Peak Power of Your Pulsed Laser

If you want to have the peak power calculated easily and quickly: Click on this laser peak power calculator. If you want to know how to measure the actual pulse shape of your laser and use that to calculate your laser's peak power, read on.

Developers and researchers working with pulsed laser sources are often interested in the maximum power of their laser. With pulsed lasers, however, most measuring devices only indicate the total energy of a pulse or, alternatively, the average laser power. How to measure the peak power of a pulsed laser beam with Ophir Spiricon instruments?

Ophir offers a fast photo sensor with a response time in the nanosecond range - the FPS-1 sensor. It was developed to measure the temporal behavior of a pulsed laser beam. The FPS-1 is easy to connect to an oscilloscope, which displays the power over time during the pulse. Since the oscilloscope does not show the absolute value of the power over time, but only the relative behavior and the shape of the pulse, it cannot be used directly to determine the peak power. However, a simple calculation enables the peak pulse power to be derived from this.

Figure 1. FPS-1 Fast Photodiode

Three steps to peak laser power:

  1. Connect the sensor to the oscilloscope and measure the laser pulse; the total energy of the pulse must be known
  2. As an equivalent pulse, construct a rectangle in the freely selected units (AU) of the oscilloscope, the height of which corresponds to the peak power and the area of ​​which corresponds to the area shown in the oscilloscope curve. The time duration can be determined using the constructed rectangular pulse (the construction can be carried out most simply by fitting the numerical data set to the oscilloscope curve).
  3. Once the total energy of the pulse is known, the peak power and, consequently, the non-random vertical scale of the oscilloscope display can be determined. To do this, the total energy of the laser pulse is divided by the constructed time duration, which was determined using the approximation rectangle.

Let's assume in the example below a total energy of 10mJ was measured.

  1. The curve ( A1 ) shows a peak of 55 AU; the sum of the values ​​read is in AU = 268
  2. Find the approximate area under the curve by multiplying the sum by the step size: 268 * 0.1 ms = 26.8 ms ( A2 )
  3. Find the amount of time that, when multiplied by the peak power, corresponds to the area just found. This results in the replacement heart rate ( A3 )
Figure 2. Oscilloscope curve of a laser pulse; the red substitute pulse with area A3 is an approximation to the actual pulse with area A1

The equation is:

((time duration) = (approximate area under curve A2 ) / (peak power AU) ie

(duration) = (26.8 ms)/55 = 0.49 ms.

With a total pulse energy of 10 mJ, for example, this results in a peak power of 10 mJ divided by 0.49 ms, i.e. approximately 20.5 mW.

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