Laser and light source of laser hair removal machine Long pulse Nd: YAG laser pulsed light

Laser and light source of laser hair removal machine

When using the principle of “selective photopyrolysis” for laser hair removal, the laser wavelength and pulse width should ensure that the laser hits the hair follicles without damaging adjacent tissues. Clinical studies have shown that the longer the wavelength, the deeper the penetration, the smaller the scattering, but the poorer the absorption of melanin, so the energy must be enhanced, but it cannot damage the epidermis; the pulse width is smaller than the TRT (thermal relaxation of hair follicles) Time) is effective, and TRT larger than the epidermis is safe; the larger the spot size, the deeper the penetration; at the same time, active skin cooling should be used to protect the epidermis and relieve pain. When the wavelength is less than 600nm, the laser is mainly strongly absorbed by hemoglobin and protein, and when the wavelength is greater than 1100nm, the laser is mainly strongly absorbed by the water in the body tissues. When the wavelength is in the range of 600nm~1100nm, the light is transparent. Therefore, people usually choose lasers with a wavelength in the range of 600nm~1100nm for hair removal. Lasers and strong pulse light sources used for hair removal mainly include long pulse ruby ​​laser (694nm), long pulse alexandrite laser (755nm), semiconductor laser (808nm), long pulse Nd: YAG laser (1064nm), strong pulse incoherent broadband Light source (590~1200nm), etc.

1. Long pulse ruby laser

The 694nm ruby laser is strongly absorbed by melanin. This laser has 15%~20% energy to penetrate the entire dermis, and the hair with melanin in the dermis and deep layers can absorb the energy of the laser, causing the hair follicles to overheat and be damaged. The normal tissue around the hair follicle has a very low light absorption rate of 694nm. When the pulse width is constant, selective photothermal damage to the hair follicle can be achieved without damaging the surrounding normal tissue.

2. Long pulse alexandrite laser

The 755nm alexandrite laser is very similar to the ruby  laser, except that it has a slightly stronger penetrability and a lower melanin absorption rate because it has a slightly longer wavelength.

3. Semiconductor laser

The penetration depth of the semiconductor laser system in the skin tissue is more than 5mm, and the range of action can reach the deep dermis and subcutaneous fat tissue. It can effectively penetrate the epidermis to reach the hair follicle tissue of the dermis, thereby destroying hair in any part and depth of the human body. The epidermis absorbs very little laser energy, so it does not produce pigmentation.

4. Long pulse Nd: YAG laser

The long-pulse Nd:YAG laser has a wavelength of 1064nm and can penetrate 5-7mm. Due to the low affinity of melanin for the 1064nm laser, exogenous color bases (such as carbon smears) are often used for treatment. The laser spot scans the entire treatment area until the visible carbon particles are removed. The disadvantage is that sometimes the carbon particles cannot reach the hair bulb and affect the treatment effect. For example, sweat glands and sebaceous glands are easily damaged if they are contaminated with carbon particles, and the clinical effect is not ideal. Recently, it has been clinically reported to use a long pulse width laser with a wavelength of 1064nm to remove hair without using carbon smear before surgery. Because epidermal melanosomes are very sensitive to short pulse width (<1ms) lasers, and long pulse width (≤200ms) lasers, high-energy lasers can be used to effectively heat the inner and outer hair root sheaths and hair growth areas without affecting Epidermal melanosomes, so it can be safely used for the treatment of black skin.

5. Strong pulsed light

High-intensity pulsed light is not a laser light source, but a non-continuous, multi-wavelength combination light source. Its wavelength is between 550 and 1200 nm and can penetrate 1.3 mm. The treatment parameters can be adjusted according to skin color or hair color. Theoretically, the broad-spectrum wavelength light source system increases the absorption of light by non-target targets, and therefore also increases the adverse reactions

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