The pulse width controls the duration of laser energy release, acting as a primary safety valve for the skin. In a Long-pulse Alexandrite Laser system, setting the pulse width to 2 ms or longer allows energy to be delivered gradually rather than in a sudden, high-intensity spike. This gradual delivery ensures that while the hair follicle accumulates enough heat to be destroyed, the surrounding epidermis has sufficient time to dissipate that heat, preventing burns and irreversible thermal damage.
Core Takeaway The goal of pulse width modulation is to match the energy delivery to the thermal relaxation time of the target. By extending the pulse duration, you lower the instantaneous peak power, allowing surface skin to cool down while the deeper hair follicle retains the heat necessary for destruction.
The Mechanics of Thermal Relaxation
Matching the Target's Physiology
The effectiveness of the laser relies on the principle of Thermal Relaxation Time (TRT). This is the time it takes for a target tissue to lose 50% of its heat.
For effective treatment, the pulse width must be roughly equal to or slightly shorter than the hair follicle's TRT. This ensures the follicle absorbs energy faster than it can release it, leading to thermal destruction.
The Role of Gradual Energy Release
When the pulse width is set to 2 ms or longer, the laser energy is distributed over a longer period.
This avoids the delivery of excessive instantaneous power. Instead of a "hammer blow" of energy, the laser provides a sustained heating effect that is safer for the surrounding tissue structure.
Protecting the Epidermis
Allowing Heat Dissipation
The skin's surface (epidermis) contains melanin, which can absorb laser energy and lead to burns if heated too rapidly.
A longer pulse width creates a critical time window. During this window, the epidermis can transfer absorbed heat to the surrounding air or a cooling device, effectively keeping its temperature below the threshold of damage.
Preventing Melanin Cell Inhibition
High-peak power from very short pulses can cause "melanin cell inhibition," where the pigment-producing cells are damaged or destroyed.
By using a longer pulse width, the system minimizes the shock to these cells. This preserves the integrity of the skin's pigmentation and prevents complications such as hypopigmentation (white spots) or scarring.
Understanding the Trade-offs
The Risk of Short Pulse Widths
Short pulse widths (e.g., in the nanosecond range) deliver very high peak power. While efficient for vaporization or ablative tasks, they leave little time for heat conduction away from the epidermis.
In the context of hair removal, an excessively short pulse increases the risk of epidermal injury because the heat builds up faster than the skin's cooling mechanisms can handle.
The Risk of Excessively Long Pulse Widths
Conversely, if the pulse width is too long relative to the hair follicle, heat will conduct away from the follicle into the surrounding dermis before the follicle is destroyed.
This reduces treatment efficacy and can cause non-specific heating of the surrounding tissue, leading to unnecessary pain or inflammation without effectively treating the hair.
Optimizing Pulse Width for Treatment Goals
To achieve the best clinical outcomes, you must balance the need for follicle destruction against the limits of the patient's skin type.
- If your primary focus is safety on darker skin: Prioritize a longer pulse width (e.g., >10-20ms) to lower peak power and give the epidermal melanin more time to cool.
- If your primary focus is treating fine, light hair: Use a shorter pulse width (closer to the 2-3ms range) to rapidly heat the target before the energy dissipates, as fine hair holds heat poorly.
Success lies in finding the precise duration where the follicle cooks, but the skin merely warms.
Summary Table:
| Feature | Impact on Thermal Control | Clinical Benefit |
|---|---|---|
| Pulse Width (2ms+) | Delivers energy gradually rather than in a high-intensity spike. | Prevents epidermal burns and reduces shock to melanin cells. |
| TRT Matching | Synchronizes pulse duration with the hair follicle's cooling rate. | Maximizes follicle destruction while sparing surrounding tissue. |
| Extended Duration | Provides a time window for surface heat dissipation. | Enhances safety for darker skin types by lowering peak power. |
| Short Pulse Risk | Rapid heat buildup exceeds the skin's cooling capacity. | High risk of scarring, hypopigmentation, and epidermal injury. |
Elevate Your Clinic’s Safety and Precision with BELIS
At BELIS, we specialize in professional-grade medical aesthetic equipment designed exclusively for high-end clinics and premium salons. Our advanced laser systems, including Long-pulse Alexandrite, Diode Hair Removal, and Nd:YAG Pico technologies, are engineered with precise pulse width control to ensure maximum efficacy without compromising patient safety.
Whether you are looking to expand your offerings with HIFU, Microneedle RF, or specialized solutions like EMSlim and Cryolipolysis, BELIS provides the technical excellence your business deserves.
Ready to upgrade your treatment standards? Contact our experts today to discover how our tailored equipment solutions can drive your clinic's success.
References
- Gerardo A. Moreno‐Arias, Alejandro Camps‐Fresneda. Long-Lasting Hypopigmentation Induced by Long-Pulsed Alexandrite Laser Photo-Epilation. DOI: 10.1097/00042728-200304000-00020
This article is also based on technical information from Belislaser Knowledge Base .
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