I. Introduction to Medical Lasers and the Necessity of Heat Dissipation
Medical lasers represent an important application of laser technology in the field of medicine. With advantages such as high precision and minimally invasive procedures, their applications have been steadily expanding. From ophthalmic vision correction and skin pigmentation treatment to surgical cutting and hemostasis, medical lasers are widely used. Below is a brief introduction to three representative types of medical lasers:
Semiconductor Lasers
Features: Use semiconductor materials as the gain medium, offering diverse wavelengths (e.g., 810 nm, 980 nm). They are compact, efficient, and long-lasting.
Applications: Rehabilitation physiotherapy (pain relief, promoting blood circulation), dermatology (hair removal using 808 nm wavelength to destroy hair follicles), dentistry (soft tissue surgery), oncology (photodynamic therapy as a light source).
Electro-optical efficiency: 30%–60%.
Er:YAG Laser
Features: Wavelength of 2940 nm (infrared). Water absorption is extremely high, resulting in superficial action with minimal damage to surrounding tissues.
Applications: Skin resurfacing (wrinkles, scars), dental whitening (removing plaque and pigments), corneal refractive surgery.
Electro-optical efficiency: 1%–5%.
CO₂ Laser
Features: Wavelength of 10.6 μm (infrared). Strongly absorbed by tissue water, generating high temperatures that vaporize and carbonize tissue. Primarily used for cutting, cauterizing, and coagulation.
Applications: Dermatology (warts, condyloma acuminatum), otolaryngology (vocal cord surgery), gynecology (cervical lesions), surgery (tumor removal).
Electro-optical efficiency: 10%–20%.
From the above, it is clear that the electro-optical efficiency of medical lasers is not high. Even high-efficiency semiconductor lasers reach only about 60%. This means a large proportion of energy is converted into heat. Without proper dissipation, the laser’s temperature will inevitably rise.
Temperature increase negatively affects medical laser performance, as shown in the table below:
| Impact | Description | Example Data |
| Wavelength Drift | Temperature changes alter the refractive index of the gain medium, causing wavelength drift and affecting treatment outcomes. | For some semiconductor lasers, each 1°C rise can cause a 0.2–0.5 nm wavelength drift. |
| Threshold Current Increase | Higher temperatures raise the threshold current. | For typical medical laser diodes, every 10°C rise may increase threshold current by 10%–20%. |
| Output Power Decrease | Excessive heat lowers the gain coefficient of the medium, reducing output power. | In dermatology treatments, unstable or reduced output power prolongs treatment. |
| Shortened Lifespan | Heat accelerates material aging, corrosion, and optical component damage. | Under high-temperature conditions, lifespan may drop to half or less compared to normal conditions. |
II. Common Heat Sink Types for Medical Lasers and Their Characteristics
Because medical lasers are used in critical clinical settings, the choice of heat sink must emphasize cooling capacity, temperature stability, noise level, and reliability. Based on these principles, the following heat sink types are commonly used:
Extrusion Heat Sink
Structure: Made from aluminum alloys (typically 6063 or 6061) via extrusion, with continuous fins to increase surface area and enhance natural convection.
Advantages: Low cost, mature processing technology, lightweight, easy installation.
Disadvantages: Limited thermal conductivity (~200 W/m·K), cooling capacity affected by ambient temperature.
Application scope: Low-power (<15 W) medical lasers such as dental treatment lasers and cost-sensitive portable devices.
Practical application:Sirona dental laser using 6063-T5 aluminum extrusion (120×80×40 mm, 280 g). At 25°C, it dissipates 12 W, keeping diode junction temperature below 65°C.
Fin Heat Sinks
Structure: Usually made of aluminum or copper, with regular heat dissipation fins, dissipating heat through natural air convection.
Advantages: Simple structure, low cost, no noise, and high reliability.
Disadvantages: Limited heat dissipation capacity, only suitable for low-power medical lasers (<10W).
Application scope: Low-power laser treatment instruments, portable laser beauty equipment.
Practical application: Cynosure Icon ruby laser system adopts a combined heat sink of copper base + aluminum fins, with a base size of 100×60×25mm, 25 fins, a spacing of 2mm, and a height of 20mm.
Heat Pipe Heat Sinks
Structure: Using the phase change principle of evaporation – condensation to quickly conduct heat to the heat sink or liquid cooling end.
Advantages: High heat transfer efficiency, light weight, and can quickly equalize temperature.
Disadvantages: Complex structure and relatively high cost.
Application scope: Portable medical laser equipment requiring miniaturized design.
Practical application: Lumenis LightSheer laser hair removal instrument adopts a copper heat pipe + aluminum fin heat dissipation scheme, using 4 Φ5mm heat pipes with a 60×60mm fin group. It can stably dissipate 40W of heat without a fan, ensuring that the laser diode temperature is ≤70°C, meeting the needs of long-term clinical use.
Liquid Cold Plate Heat Sinks
Structure: The laser module is in close contact with the metal water – cooling plate, and the cooling liquid (deionized water/ethylene glycol, etc.) takes away heat through pipeline circulation.
Advantages: High heat dissipation efficiency, suitable for high – power lasers; good temperature uniformity.
Disadvantages: Complex system, requiring water pumps, cooling liquid, and pipelines; high maintenance cost.
Application scope: Medium and high – power lasers (>50W), such as surgical lasers (CO₂, Nd:YAG), high – power semiconductor laser treatment instruments.
Practical application: Sharplan’s 400W CO₂ surgical laser adopts a dual – cycle liquid cooling system (main cycle + backup cycle), with a heat exchanger area of 0.4m² and a temperature control of ±0.5°C.
III. Recommendations for Heat Sink Selection in Medical Lasers
| Device Type | Power Range | Recommended Heat Sink | Specific Parameters |
| Ophthalmic laser indicators, small dermatology cosmetic lasers | 5–20 W | 1.Fin heat sink 2.Extrusion heat sink | 1. Copper fins with natural convection. 2. Low-cost aluminum extrusion. |
| Ophthalmic therapeutic lasers (e.g., excimer refractive lasers) | 30–80 W | Heat pipe heat sink | Heat pipe + aluminum fins; passive cooling at 30–60 W, low-speed fan assist at 60–80 W. |
| Dental therapeutic lasers | 50–100 W | 1.Liquid cold plate 2.Heat pipe | 1. Liquid cold plate with glycol solution, pump flow 5–10 L/min. 2. Copper base + 6–8 Φ8 mm heat pipes. |
| High-power Nd:YAG lasers for oncology | 200–800 W | Combined liquid cold plate + heat pipe | Heat pipes rapidly transfer heat to liquid cold plate; high-performance pumps, coolant, and heat exchanger required. |
| High-power CO₂ surgical lasers | 300–1000 W+ | High-efficiency liquid cold plate | High-flow pumps (15–30 L/min), large plate heat exchanger, full monitoring (temperature, flow, leakage alarm). |
These recommendations serve as general guidelines for selecting heat sinks in different types of medical lasers. For more precise requirements, we can provide tailored cooling system solutions to ensure optimal device performance under demanding conditions.
