# 3.1 CO₂ Laser — Wavelength (10,600 nm) and Mechanism of Action --- ## 1. Wavelength (10,600 nm) - **Infrared spectrum** (far IR range). - Invisible to human eye → requires aiming beam (usually He-Ne laser, 632 nm) for targeting. - **Primary chromophore: Water (물)** - Water has strong absorption peak at **10,600 nm**. - Since all human soft tissue is ~70% water, virtually every tissue absorbs CO₂ laser energy. --- ## 2. Mechanism of Action ### A. Absorption & Thermal Effect 1. CO₂ laser beam penetrates only ~20–30 μm (superficial) because water absorbs it immediately. 2. Absorbed energy → **rapid heating of intracellular water**. 3. At ~100 °C: water vaporizes → **tissue ablation/vaporization**. 4. At >150 °C: carbonization can occur → charring, more collateral thermal damage. ### B. Selective Tissue Interaction - Because absorption depth is so shallow, the **zone of thermal injury is minimal** (~100–150 μm). - Provides **precise cutting/ablation** with hemostasis. - Can be tuned for: - **Continuous wave** → cutting, vaporization. - **Pulsed or superpulsed mode** → less collateral thermal injury, used in dermatology for cosmetic precision. ### C. Clinical Effect - **Ablative**: destroys epidermis & superficial dermis → resurfacing, lesion removal. - **Hemostatic**: coagulates small vessels (<0.5 mm) → bloodless field. - **Sterilizing effect**: kills bacteria/viruses in wound → useful in warts, infected lesions. --- ## 3. Clinical Applications (Relevant to Dermatology) - **Benign lesion removal**: intradermal nevi, seborrheic keratoses, warts. - **Skin resurfacing**: wrinkles, acne scars, photoaging. - **Oncologic use**: excision of superficial BCC or SCC in situ. - **Surgical use**: cutting with simultaneous coagulation. --- ## 4. Advantages - Precise, bloodless cutting. - Minimal penetration → reduces risk of deep injury. - High versatility (continuous, pulsed, fractional). --- ## 5. Limitations & Risks - **Thermal damage** if not pulsed properly → scarring, delayed healing. - **PIH (염증후 과색소침착)** common in Asian skin after ablative resurfacing. - Requires eye protection (corneal damage risk). - Not selective → any water-containing tissue is affected (less selective than pigment or vascular lasers). --- ## 6. Clinical Pearls 1. **10,600 nm = water absorption peak** → universal soft tissue ablation. 2. **Penetration is extremely shallow** (tens of microns) → precision tool. 3. **Pulse modulation** is key: continuous wave causes more collateral damage; pulsed/superpulsed safer for cosmetic dermatology. 4. In Asian patients, **fractional CO₂** is preferred for resurfacing to minimize PIH. --- ✅ **Summary for practice:** CO₂ laser operates at **10,600 nm**, absorbed strongly by water. Energy absorption causes **instant vaporization of intracellular water**, leading to precise tissue ablation and coagulation with minimal penetration depth. This makes CO₂ the gold standard for cutting, vaporizing, and resurfacing in dermatology. ---