Laser Pulse Calculator & Modulation Simulator
Adjust Pulse Width, Repetition Rate, and Optical Power to calculate pulse energy, peak power, average power, and duty cycle. Watch the waveforms update as you compare analog modulation with digital gating in real time.
Analog modulation vs. digital gating
| Optical output | Digital gating | Analog sine |
|---|---|---|
| Peak power | ||
| Minimum power | ||
| Average power | ||
| Energy per period |
Analog describes level control, not a waveform shape: it can use sine, square, or triangle signals. Digital gating switches between off and a preset level. The comparison shows ideal optical output, not input voltage.
Equations & model assumptions
For ideal rectangular pulses: period T = 1/f; duty cycle D = τf; pulse energy E = Ppeakτ; average power Pavg = PpeakD. Here τ is pulse width in seconds and f is repetition rate in hertz. Width cannot exceed one period. At 100% duty cycle the digital output is continuous; “pulse energy” is then energy per period.
Enable “Compare analog modulation” to add a waveform at the same repetition rate. Set its minimum L and maximum H optical powers independently. Sine: P(t) = L + (H − L)[1 + cos(2πft)]/2. Triangle: P(t) = L + (H − L)|2φ − 1|, where φ is the fractional part of ft. Both average (L + H)/2.
Square / rectangular analog output alternates between H and L. With high-state duty fraction d, average power is L + (H − L)d. At d = 0 it stays at L; at d = 1 it stays at H. Analog energy per period equals its average power divided by f and includes any nonzero baseline. Digital pulse width does not set analog square-wave duty cycle.
This is an ideal optical-output model with instantaneous digital transitions, zero digital off-state leakage, and no driver bandwidth, laser threshold, overshoot or thermal effects. Analog modulation is not synonymous with constant-power feedback. Actual electrical-input-to-optical-output behavior depends on the diode and driver. Extremely narrow pulses may be thinner than a screen pixel; numerical results retain their calculated values.
Example: 100 µs pulses at 1 kHz and 10 W peak give 10% duty cycle, 1 mJ per pulse and 1 W average power. An analog sine ranging from 0 to 10 W has 5 W average power. A rectangular analog waveform ranging from 2 to 8 W with 25% high-state duty averages 3.5 W.
Understanding Laser Pulse Energy and Power
How much energy does a laser deliver in one pulse? The answer depends on both its optical power and how long the pulse lasts. This laser pulse calculator and modulation simulator lets you adjust pulse width, repetition rate and power, then see the waveform and calculated results change together.
Use it to explore pulse timing, compare operating settings or check a calculation before planning a laser experiment. The digital waveform represents ideal rectangular optical pulses.
Pulse Width, Repetition Rate and Duty Cycle
Pulse width (τ) is the duration of each pulse. Repetition rate (f) is the number of pulses per second. Together, they determine the duty cycle: the fraction of time the digital output is on. This repetition rate describes the pulse timing, not the optical frequency of the light.
Here, T is the period between pulse starts. Use seconds for pulse width and hertz for repetition rate. At 100% duty cycle, adjacent rectangular pulses join into continuous output. A pulse width longer than one period is not valid for this model.
How to Calculate Pulse Energy and Peak Power
Peak power is the optical power during the rectangular pulse. Average power includes the off-time between pulses. Pulse energy is the energy delivered by one pulse, measured in joules.
Try 100 µs pulse width, 1 kHz repetition rate and 10 W peak power. The period is 1 ms, giving a 10% duty cycle. Each pulse delivers 1 mJ, and the average optical power is 1 W.
These peak-power equations assume rectangular pulses. Gaussian and other pulse shapes require their own shape factors when pulse duration is specified as full width at half maximum (FWHM).
What Changes When You Shorten a Laser Pulse?
- With peak power held constant: shortening the pulse reduces its energy. At the same repetition rate, average power decreases too.
- With average power held constant: shortening the pulse increases the required peak power. At the same repetition rate, pulse energy stays unchanged.
Switch between the two power settings to see why a shorter pulse does not automatically mean more energy or higher peak power. What you hold constant matters.
Analog Modulation vs. Digital Gating
Digital gating switches the modeled optical output between zero and a fixed on-state power. Analog modulation controls the output level and can use sine, square or triangle signals. Analog does not mean that the waveform must be sinusoidal.
Select Compare analog modulation to add an analog waveform to the graph. Choose its shape and set its minimum and maximum optical power. Both traces use the same repetition rate, but their power settings are independent. For square-wave analog modulation, you can also adjust the high-state duty cycle separately from the digital pulse width.
A sine or triangle waveform ranging from 0 to 10 W averages 5 W. A digital pulse train with 10 W peak power and 10% duty cycle averages just 1 W. A square analog waveform alternating between 2 and 8 W, with 25% of each period at the higher level, averages 3.5 W.
Setting the analog minimum and maximum to the same value produces constant output. The analog energy shown is energy per modulation period and includes any nonzero baseline power.
Using the Results with a Laser Diode Driver
The simulator models optical output, not the electrical response of a particular driver. Real pulse shapes depend on modulation bandwidth, rise and fall times, diode threshold, current limits and thermal conditions. Check those specifications when choosing hardware for your target pulse width and repetition rate.
For related calculations, explore our photonics calculators, or visit the interactive photonics simulators to explore beam focusing, divergence and fiber coupling.