How to calculate laser energy and power

Feb. 28, 2024

How to Calculate Laser Energy and Power

The laser emitted by the pulse laser is discontinuous and is generally emitted at high repetition frequency pulse intervals. The emitted energy is measured in joules (J).

The energy emitted by a continuous laser is measured in the power unit watt (W), indicating the work is done per unit time.

The relationship between watts and joules: 1 W = 1 J/second.

For expamle, the pulse emission energy is 1 joule/time and the pulse frequency is 50Hz. Then the laser is emitted 50 times per second. The average power of work done per second is: 50X 1 joule = 50 joule. Therefore, the average power is Converted to 50 watts.

Let’s take another example to illustrate the calculation of peak power. For a green light pulse laser, the pulse energy is 0.1 4m J/time, each pulse width is 20ns, the pulse frequency is 100kHz, and the average power is: 0.1 4m J X 1 00k= 1 4J/s= 1 4W, that means the average power is 14 watts; the peak power is the ratio of each pulse energy to the pulse width, that is 0.14m J/20ns= 7000W= 7kW, the peak power is 7 kilowatts.

To know whether the pulse laser damage threshold of the lens is within the endurance limit, it is necessary to calculate both the peak power and the average power of the pulse laser.

For example, the laser damage threshold of a ZnSe lens is 500MW/cm2. When used in a pulse laser, the pulse energy of the pulse laser is 10J/cm2, the pulse width is 10ns, and the frequency is 50kHz.

First, calculate the average power: 10J/cm 2 X 50kHz = 0.5MW/cm 2

And then calculate the peak power: 10J/cm 2 / 1 0ns = 1 000MW/cm 2

Judging from the average power of the pulse laser, the lens can withstand damage without being damaged; but judging from the peak power of the pulse laser, it is greater than the laser damage threshold of the lens. Therefore, based on comprehensive judgment, the ZnSe lens is not suitable for use in this pulse laser. If possible, for pulsed laser lenses, the laser damage thresholds of average power and peak power should be tested separately.

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