A large-diameter spot size, such as 18mm, improves clinical efficiency primarily by increasing the effective depth of laser penetration and significantly reducing treatment duration. By minimizing the lateral scattering of light within the tissue, these larger spots ensure that energy reaches deep-rooted hair follicles that smaller spots often miss. Furthermore, the increased surface area per pulse allows practitioners to treat broad zones, such as thighs or underarms, with greater speed and uniformity.
Core Takeaway: An 18mm spot size solves two problems simultaneously: it overcomes photon scattering to treat deeper hair roots effectively, and it drastically reduces the number of pulses required for large body areas, optimizing both clinical results and business throughput.
The Physics of Penetration Depth
Reducing Lateral Scattering
When laser light enters the skin, photons naturally scatter in all directions.
With a small spot size, a high percentage of photons scatter "sideways" out of the target column effectively leaving the treatment area.
An 18mm spot size minimizes these lateral losses, creating a "volume effect" that forces more photons to travel vertically into the dermis.
Targeting Deep-Seated Follicles
Because lateral scattering is reduced, the laser maintains a higher energy density at greater depths.
This increased effective penetration depth is crucial for treating coarse, deep-rooted hair that resides lower in the dermis.
Without this depth, the laser might only singe the upper shaft of the hair without disabling the follicle's reproductive capability.
Operational Efficiency and Workflow
Maximizing Coverage per Pulse
Clinical efficiency is defined by the speed at which a practitioner can effectively treat a specific surface area.
A large spot size covers a significantly wider area with a single pulse compared to standard diameters.
This creates a substantial reduction in overall treatment time, particularly for large zones like the back, thighs, and underarms.
Ensuring Uniform Energy Distribution
Treating a large back with a tiny spot size requires thousands of pulses, increasing the risk of human error.
A larger diameter naturally promotes uniform energy distribution across the treatment field.
This reduces the likelihood of "skipped" areas (untreated strips) and minimizes the risk of thermal injury caused by accidental excessive overlapping.
Understanding the Trade-offs
Power Density Requirements
A larger spot size spreads the laser energy over a wider surface area.
To maintain an effective fluence (energy density) capable of destroying hair, the equipment must possess high peak power capabilities.
Using a large spot size on an under-powered machine will result in diluted energy and ineffective treatments.
Precision vs. Coverage
While 18mm is ideal for flat, broad surfaces, it lacks the agility required for small, contoured areas.
Areas such as the upper lip, ears, or toes often require a smaller spot size to ensure full contact with the skin.
Clinical efficiency drops if the operator struggles to maintain proper coupling on curved anatomical structures.
Making the Right Choice for Your Goal
To maximize the utility of your equipment, match the spot size to the specific clinical objective:
- If your primary focus is throughput speed: Utilize the 18mm spot size for large body areas (legs, back) to minimize session time and increase patient volume.
- If your primary focus is deep hair clearance: Rely on the large spot size to reduce scattering and deliver sufficient thermal damage to the deepest follicles.
- If your primary focus is facial contouring: Switch to a smaller diameter tip to ensure safety and proper contact on curved, uneven surfaces.
Leveraging a large spot size is the single most effective method for scaling treatment volume while ensuring deep-tissue efficacy.
Summary Table:
| Feature | 18mm Large Spot Size | Standard Small Spot Size |
|---|---|---|
| Penetration Depth | Deep (Minimal lateral scattering) | Shallow (High lateral scattering) |
| Treatment Speed | High (Ideal for backs & legs) | Low (Requires more pulses) |
| Energy Distribution | Uniform & consistent | Prone to overlapping/skipping |
| Best Application | Large, broad body areas | Small, contoured facial areas |
| Peak Power Need | High power required for fluence | Lower power requirements |
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References
- Erfan Bakhshi, Dorsa Rezaei. Predicting the Therapeutic Results of Unwanted Hair Growth with the Alexandrite Laser Device. DOI: 10.47760/cognizance.2024.v04i04.009
This article is also based on technical information from Belislaser Knowledge Base .
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