The selection of the 755 nm wavelength in Alexandrite laser systems is driven by the principle of selective photothermolysis, designed to exploit the high absorption rate of melanin. This specific wavelength is engineered to be aggressively absorbed by the pigment found in hair follicles, rapidly converting light energy into the thermal energy necessary to dissolve the target tissue. This mechanism ensures high-precision destruction of the follicle while striving to leave the surrounding non-pigmented skin unharmed.
The 755 nm wavelength functions by maximizing energy absorption within the melanin spectrum, allowing for the precise thermal dissolution of hair follicles. While this results in high-efficiency treatment for specific hair types, the intense absorption by pigment necessitates strict protocols to prevent damage to other melanin-rich areas, such as the eyes.
The Physics of Selective Photothermolysis
Targeting the Chromophore
The core technical foundation of the Alexandrite laser is its interaction with melanin, the primary chromophore (light-absorbing molecule) in hair. The 755 nm wavelength is positioned within a peak absorption range for melanin. This allows the laser to distinguish between the hair follicle and the surrounding tissue based on pigment concentration.
Energy Conversion and Dissolution
Once the 755 nm light strikes the melanin, it is immediately converted into thermal energy (heat). This heat is conducted into the hair follicle and its germinative center. The temperature rises sufficiently to dissolve the regenerative cells responsible for hair growth, effectively disabling the follicle.
Pulse Duration and Thermal Control
Matching Thermal Relaxation Time
Effective treatment relies on more than just wavelength; the timing of the energy delivery is critical. The laser's pulse width is calibrated to sit between the thermal relaxation times of the epidermis (skin surface) and the hair follicle. This ensures the follicle retains enough heat to be destroyed, while the skin cools down fast enough to avoid injury.
Controlled Energy Release
To prevent "explosive" damage to the skin surface, these systems often utilize a long pulse duration (typically 10 to 15 ms). This allows thermal energy to act slowly and continuously on the germinal cells. This controlled release is vital for safety, minimizing non-specific thermal damage to the surrounding dermis.
Understanding the Trade-offs
High Absorption Risks
The very feature that makes 755 nm effective—its high affinity for melanin—creates specific risks. Because the wavelength is so efficiently absorbed by pigment, it poses a danger to melanin-containing ocular tissues, specifically the retinal pigment epithelium. Strict safety protocols and eye protection are non-negotiable to prevent permanent thermal damage to the eyes.
Skin Tone Limitations
While 755 nm is highly effective for fine, dark hair on light skin, its high absorption rate can be problematic for darker skin tones. In darker skin, the epidermal melanin competes for the laser energy, increasing the risk of surface burns. Other wavelengths, such as 1064 nm, are typically preferred for darker complexions as they bypass the surface pigment more effectively.
Making the Right Choice for Your Goal
When evaluating the utility of the 755 nm Alexandrite laser, consider the specific patient profile and safety requirements.
- If your primary focus is treating fine, dark hair on light skin: The 755 nm wavelength offers superior efficiency due to its peak melanin absorption capabilities.
- If your primary focus is safety on darker skin tones: You should likely avoid 755 nm in favor of longer wavelengths (like 1064 nm) to prevent epidermal thermal damage.
- If your primary focus is operational safety: You must implement rigorous ocular safety protocols, as the 755 nm wavelength poses a specific thermal threat to retinal pigment.
The 755 nm Alexandrite laser represents a high-precision tool that trades broad versatility for exceptional efficacy on specific, pigment-rich targets.
Summary Table:
| Feature | Alexandrite 755 nm Specification |
|---|---|
| Core Principle | Selective Photothermolysis |
| Primary Target | Melanin (Chromophore) |
| Energy Conversion | Light to Thermal (Heat) |
| Pulse Duration | 10 to 15 ms (Typical) |
| Best Suitability | Fine, dark hair on light skin tones |
| Safety Focus | High ocular protection & epidermal cooling |
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References
- Roberto Anaya-Alaminos, María V. Ramírez-Garrido. Accidental Foveal Photocoagulation Secondary to Alexandrite Laser. DOI: 10.5301/ejo.5000474
This article is also based on technical information from Belislaser Knowledge Base .
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