How the F2's galvanometric mirrors steer the beam at high speed, what beam divergence really means for your working area, and why the focused spot forms an hourglass that affects cut quality in thick materials.
Instead of moving the laser head on rails, the F2 deflects the beam using two tiny motorised mirrors — one per axis — to achieve speeds a mechanical carriage cannot match.
In a traditional gantry laser (diode or CO₂), the laser head moves physically along X and Y rails. Acceleration and deceleration of that mass limits speed and introduces mechanical ringing on sharp corners — visible as "ghosting" or wavy edges at high feed rates.
The F2's galvanometric system mounts two small servo-driven mirrors at a fixed point above the work surface. The beam bounces off mirror 1 (X-axis tilt) and then mirror 2 (Y-axis tilt) before passing through the f-theta focusing lens onto the material. Because a mirror weighs a fraction of a gram, direction changes happen in microseconds — enabling engraving speeds over 10,000 mm/s.
Beam steered by mirrors. No moving mass. Speeds up to 10,000 mm/s. Consistent spot quality across the field. Fixed working distance from the galvo head.
Laser head moves on rails. Speed limited by carriage mass (~500–6,000 mm/s). Works at any material height. Better for cutting thick stock over large format areas.
All laser beams spread slightly as they travel. Divergence measures that spreading rate — and determines how tightly the beam can be focused at the working surface.
The F2 specifies beam divergence at <1.5 mrad. This describes how rapidly the collimated beam expands between the galvo mirrors and the focusing lens. Lower divergence means the lens receives a tighter, more parallel beam — which translates directly into a smaller, sharper focal spot. The IR module achieves a 0.03 mm × 0.03 mm in-focus spot; the 15W diode produces a larger elliptical 0.08 mm × 0.06 mm spot.
Divergence also determines spot consistency across the working field. On a galvo system, beams aimed at the corners travel a slightly longer path than beams aimed straight down. A low-divergence beam expands so little over that extra distance that the spot quality stays effectively constant across the whole marking area.
The mrad unit makes divergence arithmetic trivial — not by coincidence, but because of how radians are fundamentally defined.
A radian is defined so that an arc of length r subtends exactly 1 radian at a circle of radius r. This means for any angle θ in radians, the arc length at radius d equals d × θ exactly (no trigonometry needed).
A milliradian (mrad) is one-thousandth of a radian. So:
The reason 1.5 mrad = 1.5 mm per metre is not a coincidence — it is built into the definition of radians. The numbers only match when you pair metres and millimetres, which happens to be the natural unit scale for laser optics. Switch to degrees and you would need tan(0.086°) × 1000 to get the same answer.
Works because tan(θ) ≈ θ for small angles. At 1.5 mrad = 0.086°, the error is less than 0.001% — negligible for any practical calculation.
1.5 mrad ≈ 0.086°. Calculating the spread in mm from degrees requires tan(0.086°) × distance — a calculator where mental arithmetic used to suffice.
| Distance | F2 beam grows by (1.5 mrad) | Poor beam grows by (5 mrad) |
|---|---|---|
| 100 mm | 0.15 mm | 0.50 mm |
| 200 mm | 0.30 mm | 1.00 mm |
| 300 mm | 0.45 mm | 1.50 mm |
| 500 mm | 0.75 mm | 2.50 mm |
| 1 metre | 1.50 mm | 5.00 mm |
The focused beam is not a point — it's an hourglass of light described by Gaussian optics. This shape determines the effective spot at different depths in your material.
Just like a magnifying glass focuses sunlight, the f-theta lens converges the beam to a minimum beam waist (radius w₀) at a specific distance — the focal plane. Above and below this point the beam expands, forming the characteristic hourglass profile.
The Rayleigh range (zR) is the distance from the waist where the beam radius has grown to √2 × w₀ — the "depth of field" boundary. Within ±zR from focus, spot area stays within 2× of its minimum, so engraving quality is consistent. Beyond zR, the beam diverges more rapidly and the mark becomes noticeably wider and weaker.
The focus position slider shows what happens when you deliberately raise or lower the focal point — a technique used in XTool software to adjust marking intensity across thick stock or to achieve different surface textures.
Normally the F2 is focused on the surface of the workpiece. But the hourglass also works as a tool — moving focus above or below the surface is a deliberate technique with several uses.
At focus the 30 µm spot produces very sharp hatch lines spaced 100 µm apart. A +1–2 mm offset grows the spot to 55–95 µm, allowing adjacent passes to blend — producing smoother, more even oxide colour across large flat panels and pendants. Reduces the "zebra stripe" hatch pattern visible in some fills.
The pinpoint intensity at focus can micro-ablate polished surfaces, introducing a texture change you didn't want. A +2–3 mm offset (spot grows to ~95–140 µm) reduces peak power density by roughly 10–20× while still reaching the oxide colour temperature — colour with no change to the mirror finish below.
The F2's depth of field is only ~1.3 mm. A ring, knife blade, or curved panel easily exceeds this — parts of the design will be defocused regardless. Focus at mid-surface to minimise the worst-case offset, or use a larger deliberate defocus to widen the effective DoF zone and reduce variation across the piece.
Defocus is creative control. The hourglass formula gives predictable diameters: +2 mm → ~95 µm, +3 mm → ~140 µm, +5 mm → ~230 µm. Use this to produce intentionally wide, soft-edged marks or to reduce energy density without touching power — giving finer colour control than the power slider alone.
| Parameter | What it means | F2 typical value |
|---|---|---|
| w₀ (waist radius) | Minimum spot radius at focus | 0.015 mm (15 µm) |
| Spot diameter | 2 × w₀ — what the spec sheet quotes | 0.03 mm × 0.03 mm (30 µm) |
| zR (Rayleigh range) | Distance at which radius = √2 × w₀ | ~0.66 mm |
| Depth of field | 2 × zR — usable focusing zone | ~1.33 mm |
| λ (wavelength) | IR laser wavelength | 1064 nm |
| F2 feature | Impact on your work |
|---|---|
| Galvo mirrors | Fill large areas extremely fast; enables consistent precision that a moving carriage cannot match at high speed |
| Low divergence <1.5 mrad | Consistent spot quality edge-to-edge across the working field; no "fuzzy corners" |
| 0.03 mm spot (IR 5W) | Extremely fine detail — 30 µm × 30 µm — finer than a human hair; jewellery and PCB-scale text are achievable |
| Rayleigh range ~0.66 mm | Depth of field ≈ 1.3 mm — any material thicker than this will have a noticeably wider spot at entry and exit surfaces |