Laser Pulse Calculator

LASERs can turn on and off at incredibly high speed (though not necessarily so), creating a train of LASER pulses: our LASER pulse calculator takes as input a few characteristic quantities and returns most fundamental features of the pulses.

Here you will learn:

• What is a laser pulse train, and what are the main quantities associated with it;
• How to calculate the laser pulse duty cycle;
• How to calculate a laser pulse energy;
• How to calculate the peak power of a pulsed laser for three different pulse shapes;
• How to calculate the intensity of a pulsed laser;

And much more!

A laser pulse is a short, relatively energetic burst of light that propagates with the properties of a Gaussian beam in a specific direction. The pulse is defined by an abrupt increase in power, followed by a similar, ideally symmetric, decrease.

Few characteristic quantities define a laser pulse:

• The pulse duration $T$, that is the full width at half-maximum (FWHM) of the pulse (in the time dimension);
• The repetition rate $f$, that is the frequency of the pulses (how many pulses in a second/unit time);
• The average power $P_{\text{avg}}$ of each pulse; and
• The spot diameter $S$, that is the diameter of the pulsed beam.

The LASER pulse's shape also has relevance in the calculations. The shape of the pulse quantifies the fashion in which the power of the beam rises and decreases. The most common shapes are:

• Rectangular pulse;
• Gaussian pulse; and
• Sech² pulse (based on the hyperbolic secant function: check our hyperbolic functions calculator to know more).

The first quantity we calculate is the duty cycle of the LASER pulse train. To do so, we need to multiply the duration of each pulse by the repetition rate, obtaining the amount of time the laser is on:

The multiplication by $100$ allows you to express the laser duty cycle as the percentage of the time unit the laseris on.

The distance from peak to peak, that is, the separation between pulses, depends on the repetition rate since it is the periodicity of the pulse. We calculate it with:

The pulse energy depends on the average power of the pulse:

We use this quantity to calculate the peak power of the pulse. At this step, the shape of the pulse becomes relevant, hence we have three possible expressions:

Now that you know how to calculate the peak power of a pulsed laser, we can also learn how to calculate the intensity of a laser pulse.

To calculate the intensities of a laser pulse, we need to consider the beam spot size: the smaller the spot, the higher the intensity since the power of the pulse is concentrated in a smaller area.

Where $A$ is the area of the circular beam spot size:

Don't mistake the laser intensity for the laser brightness. They are two different things! We talked more about the practical use of light intensities in the Beer Lambert Law Calculator if you're interested.