Laser marking · 8 minute read
Laser pulse overlap explained: spacing, hatch and pulse energy
Pulse overlap describes the geometry of successive laser pulses; it is not a universal recipe for a good mark. The arithmetic is still valuable because it connects scan speed, pulse frequency and focused spot diameter before material testing begins.
Turn speed and frequency into pulse spacing
Pulse spacing along the scan direction equals scan speed divided by pulse frequency, provided the units are consistent. At 1,000 mm/s and 20,000 pulses per second, the nominal centre-to-centre spacing is 0.05 mm.
The reciprocal gives 20 pulses per millimetre. This ideal calculation does not include scanner acceleration, corner behaviour, pulse timing dynamics or focus variation.
Compare spacing with the focused spot diameter
Geometric longitudinal overlap is (1 − pulse spacing ÷ spot diameter) × 100. With 0.05 mm spacing and a 0.10 mm focused spot, the nominal overlap is 50%.
If spacing exceeds spot diameter, the result is negative and represents a physical gap rather than usable “negative overlap.” At 3,000 mm/s, 20 kHz and a 0.10 mm spot, spacing is 0.15 mm and the gap between adjacent spot edges is 0.05 mm. Confirm that the entered diameter is the focused spot for the actual optical setup—not the lens field size.
Hatch overlap is perpendicular to pulse overlap
Longitudinal overlap follows pulses along one marked line. Hatch spacing controls the distance between neighbouring scan lines. Hatch overlap can be calculated from hatch spacing and spot diameter using the same geometric comparison, but it describes a different direction.
Treating both settings as one percentage can hide an overly dense or sparse two-dimensional energy distribution.
Pulse energy is not the same as process outcome
Approximate pulse energy equals average power divided by pulse frequency. Average power of 20 W at 20 kHz corresponds to 1 mJ per pulse. With a simplified rectangular 100 ns pulse, dividing energy by duration gives a 10 kW peak estimate—but real temporal pulse shapes and frequency-dependent source behaviour can differ.
Real beam profile, wavelength, temporal pulse shape, absorption, heat accumulation and material response are outside the overlap formula. Prove any setting on representative test coupons and use manufacturer process guidance.