J. Eur. Opt. Society-Rapid Publ. 22, 24( 2026) 251
Table 4. Spot Distance, Track Distance, and Dose calculated for different exemplary combinations of dose( F1 F2) and asymmetry( F2 / F1) for a particular LIOB Threshold Energy( 50 nj) and Single pulse energy( E p = 100 nJ).
F1 F2 |
F2 / F1 |
F1 |
F2 |
Eth( nJ) |
E p( nJ) |
Bubble |
|
|
|
|
|
|
diameter( lm) |
Spot distance( lm)
Track distance( lm)
Dose( mJ / cm 2)
1.27 |
1.27 |
1.00 |
1.27 |
50 |
100 |
5.3 |
5.3 |
4.2 |
446 |
1.43 |
1.60 |
0.95 |
1.51 |
50 |
100 |
5.3 |
5.7 |
3.5 |
500 |
1.60 |
2.00 |
0.89 |
1.79 |
50 |
100 |
5.3 |
6.0 |
3.0 |
559 |
1.79 |
2.63 |
0.82 |
2.17 |
50 |
100 |
5.3 |
6.5 |
2.5 |
626 |
2.00 |
3.46 |
0.76 |
2.63 |
50 |
100 |
5.3 |
7.0 |
2.0 |
701 |
Table 5. Spot Distance, Track Distance and Dose calculated for different exemplary combinations of dose( F1 F2) and asymmetry( F2 / F1) for a series of LIOB Threshold Energy and pulse energies compatible with previous works [ 9 ].
F1 F2 |
F2 / F1 |
F1 |
F2 |
Eth( nJ) |
E p( nJ) |
Bubble |
|
|
|
|
|
|
diameter( lm) |
Spot distance( lm)
Track distance( lm)
Dose( mJ / cm 2)
1.41 |
2.62 |
0.73 |
1.92 |
35 |
50 |
3.6 |
4.9 |
1.9 |
553 |
1.41 |
2.62 |
0.73 |
1.92 |
35 |
70 |
4.7 |
6.5 |
2.5 |
440 |
1.41 |
2.62 |
0.73 |
1.92 |
35 |
100 |
5.8 |
7.9 |
3.0 |
416 |
1.41 |
2.62 |
0.73 |
1.92 |
50 |
70 |
3.9 |
5.4 |
2.0 |
639 |
1.41 |
2.62 |
0.73 |
1.92 |
50 |
100 |
5.3 |
7.3 |
2.8 |
496 |
1.41 |
2.62 |
0.73 |
1.92 |
50 |
145 |
6.6 |
9.0 |
3.4 |
468 |
1.41 |
2.62 |
0.73 |
1.92 |
70 |
100 |
4.5 |
6.1 |
2.3 |
697 |
1.41 |
2.62 |
0.73 |
1.92 |
70 |
145 |
6.1 |
8.3 |
3.2 |
548 |
1.41 |
2.62 |
0.73 |
1.92 |
70 |
200 |
7.3 |
10.0 |
3.8 |
524 |
F2( the scaling factor for track distance) remains consistently greater than one, reflecting a stronger degree of overlap between adjacent tracks.
This strategy forms the basis of asymmetric spacing patterns( Spot Distance > Track Distance). Allowing larger spot spacing and even exceeding the bubble diameter can be beneficial when paired with reduced track spacing, as this compensates for the reduced overlap along the path by increasing overlap between adjacent scan lines. By minimizing consecutive spot overlap, these configurations reduce the chance of bubble interference caused by residual cavitation activity, particularly since the interpulse interval along a path is in the sub-microsecond range, which may be too short for cavitation bubbles to fully expand or dissipate. In contrast, inter-track intervals occur over milliseconds, allowing bubbles to reach full expansion before interacting with pulses from adjacent lines [ 9 ]. Therefore, avoiding spot overlaps along the scan pathway does not only act in the spatial but simultaneously in the temporal overlap domains.
This temporal separation enhances the predictability and control of tissue response as shown in the Figure 5. It is worth noting that Dose( F1 F2) is the identical for both asymmetric spacing pattern( Figure 5B) and symmetric spacing pattern( Figure 5A), but asymmetry( F2 / F1) and phase delay differs( 1 vs. 2 3 0. 5 and0vs. 0.5, respectively). Although the total delivered fluence( dose, energy) remains the same, yet as evident in the Figure 5, the triangular gaps in Figure 5B are smaller than the diamond gap in Figure 5A. This geometric difference has two important implications. First, the total uncovered area in Figure 5B( the sum of the two triangular gaps) is smaller than that of the diamond-shaped gap in Figure 5A, indicating improved coverage( higher fill fraction) for the same number of pulses. Second, the area of each gap in Figure 5B is substantially smaller, implying reduced tissue bridge dimensions. Spatially, this suggests improved coverage and potentially easier tissue separation in the asymmetric configuration for the same pulse and treatment cumulative energy. Temporally, the reduced consecutive spot interaction combined with longer inter-track delays promotes a more gentle and efficient laser – tissue interaction. Conversely, asymmetric settings with F2 > F1( spot spacing larger than track spacing) and F1 < 1( non-overlapping consecutive spots) allow both improved coverage, laser – tissue interaction efficiency, and easier tissue separation at the same pulse and treatment cumulative energy, as well as equivalent outcomes at reduced cumulative energy, with continuous trade-offs between these regimes.
The residual gap in tissue cutting is characterized not by the nearest-neighbor spacing, but by the typical linear extent of the largest uncovered region within a unit cell. To characterize residual tissue gaps, one can introduce a characteristic void length‘ defined as a linear measure proportional to the square root of the uncovered area fraction. Specifically, given by the expression