All About Laser Frequency
Pulse frequency is the number of laser pulses emitted per second by a pulsed laser source. Pulse frequency is commonly expressed in kilohertz, but the supported frequency range and its relationship to pulse energy depend on the specific laser source.
Physical effect
When scanning speed remains fixed, increasing pulse frequency decreases the center-to-center distance between successive pulses along the scan path. When average output power remains fixed, increasing pulse frequency generally reduces the energy available to each pulse because the energy delivered each second is divided among more pulses. Actual pulse energy still depends on the laser source, pulse shape, pulse duration, and operating limits.
Pulse spacing and overlap
Pulse spacing along the scan path is approximately the scanning speed divided by the pulse frequency, using consistent units. Comparing pulse spacing with the focused spot size helps estimate whether successive pulse footprints will have gaps or overlap. The effective interaction diameter may differ from the optical spot size because it also depends on the optics, focus, beam quality, laser settings, heat accumulation, and material response.
Examples
A higher pulse frequency may produce a smoother, more continuous-looking surface interaction when the laser source still provides sufficient energy per pulse. A lower pulse frequency may provide greater energy per pulse for material removal or stronger surface texture, depending on the laser source and other settings. For a controlled diffraction experiment, keep pulse frequency fixed while varying scanning speed to test how different pulse pitches affect the engraved result.
Source differences
Laser sources and controllers do not all expose or implement frequency controls in the same way. Many engraving-oriented CO2 and diode lasers operate as continuous-wave sources whose output is rapidly modulated, rather than producing the independently shaped pulses associated with common Q-switched and MOPA fiber sources.
Safe comparison
Never command a pulse frequency outside the manufacturer's permitted range, and do not assume that equal kilohertz values produce equivalent pulses or material effects on different laser sources. When comparing pulse-frequency results, also record the laser source model, power, scanning speed, pulse duration, lens, focus method, material, and surface preparation.