New development trend of semiconductor hair removal

Dr. R. Rox Anderson and Dr. John A. Parrish from the United States proposed the selective photothermal theory in the early 1980s: According to the biological characteristics of different tissues, as long as the appropriate laser parameters (wavelength, pulse duration, energy) are selected, it can ensure that the lesion is treated most effectively while minimizing damage to the surrounding normal tissues. At the same time, based on this theory, Dr. Anderson and Dr. Parrish led the industry to draw a target tissue wavelength absorption spectrum (see Figure 1), which provides a guiding principle for using light to achieve medical beauty effects.

Figure 1 Photothermal theory-biological tissue absorption curve

Among the many applications of selective photothermal theory, the use of laser for hair removal is undoubtedly one of the most effective applications. The wavelength of the laser is precise and has stronger energy scalability. Doctors can use the laser with the appropriate wavelength, energy density, pulse width and other parameters to achieve hair removal according to the patient's skin color, hair color, pain perception, etc.

With the continuous advancement of laser hair removal technology and people's pursuit of beauty and experience, people are no longer satisfied with the basic demand of hair removal, but have turned to the pursuit of a safer, more comfortable, more effective and more efficient hair removal experience. This puts higher demands on laser hair removal technology and also promotes the new development of this technology.

How to transform the more comfortable, more effective and more efficient treatment experience pursued by end users into requirements for equipment, and how to transform these requirements into design language and integrate them into product design requires product development and design personnel to refer to the following formula for product development, and this formula is also the design guideline for optoelectronic medical beauty equipment. At the same time, how to balance the selection of various indicators in the following formula so that the developed equipment can better meet the needs of future end users and be more in line with the development trend of the terminal market has also become one of the core competitiveness of medical beauty equipment manufacturers.

For laser hair removal applications, energy density means effect. In theory, higher energy density will bring better therapeutic effects; and peak power is related to cost. The higher the peak power, the higher the cost of the corresponding laser. ;The spot area is related to the treatment efficiency. For smaller treatment areas such as armpits and lips, a smaller output spot area will not bring about low treatment efficiency, but for large treatment areas such as legs and back, In other words, the larger the spot area, the treatment efficiency will be significantly improved; the pulse width is related to comfort and effect. The shorter the pulse width, the more comfortable the treatment process will be. At the same time, when the pulse width is within 10~30ms, the treatment effect will be better. will be better.

It is this increasingly higher requirement for terminal experience that has promoted the change of instrument design concepts among beauty equipment manufacturers, and has also formed a new trend in laser hair removal technology.

"High peak power + narrow pulse width" trend

In recent years, the mainstream power of semiconductor lasers used for laser hair removal has experienced an increase from 300W to 600W, and is rapidly shifting to a power of more than 1200W. This is one of the recognized trends in the industry. Why is there such a change? The root cause is still reflected in the end-user's demand for a more effective and comfortable treatment experience.

According to the above energy density formula, under the premise of ensuring that the energy density (effect) and the spot area (efficiency) remain unchanged, the higher the peak power, the narrower the pulse width can be compressed. And the narrow pulse width brings better clinical effects and more comfortable clinical experience.

During the entire treatment process of laser hair removal, the laser will first pass through the epidermis, dermis, etc., and finally reach the hair follicles and destroy the hair follicles. In this process, we hope that the hair follicles will be destroyed more effectively, but at the same time, we need to avoid skin damage. Here the pulse width is particularly important.

Generally speaking, 10~30ms is recognized as the best pulse width for hair removal. This is because the thermal relaxation time of human skin tissue is generally less than 10ms, while the thermal relaxation time of melanin-rich hair follicles generally ranges from 30ms to 100ms.

During laser hair removal, the laser needs to pass through human skin tissue before reaching the hair follicles. In order to avoid skin burns, the corresponding pulse width must be greater than the thermal relaxation time of the skin tissue, so that the skin has sufficient time to cool down to avoid heat accumulation and burns. At the same time, in order to destroy the hair follicles, but do not want to give them sufficient time to cool down, the pulse width must be less than the thermal relaxation time of the hair follicles, so 10~30ms is ultimately defined as the optimal pulse width. In order to complete hair removal treatment under such a narrow pulse width condition, the traditional 300~600W peak power laser can no longer achieve the desired treatment effect. Therefore, "high peak power + narrow pulse width" has become the future development trend. At the same time, during narrow pulse width treatment, the skin has sufficient time to cool down, the energy will not be excessively accumulated, and the treatment process will be more comfortable.

The laser power required for new laser hair removal equipment is usually 1200W and above. Because within this power range, whether using a 10*10mm or 10*20mm spot output, within the optimal pulse width range of 10~30ms, the device can easily achieve the energy density output required for hair removal of more than 10J/cm².

"High effective energy" trend

For laser hair removal applications, the core is whether there is enough effective energy injected into the skin and reaches the hair follicles during the treatment process, thereby increasing the temperature of the hair follicles and damaging the hair follicles. As the hair removal treatment method evolves, the definition of effective hair removal is also changing.

Before 2010, laser hair removal used a stamping hair removal method. The effectiveness of this treatment method depends entirely on the energy value of a single pulse under the premise that the area of the handpiece light outlet is determined; the higher the energy value, the higher the hair follicle temperature in the corresponding stamping area will be raised, and the corresponding treatment effect will be better.

After 2010, under the leadership of the medical beauty equipment leader Alden, the treatment method of laser hair removal has changed. In order to make the treatment process more efficient and comfortable, Alden innovatively introduced a sliding treatment method, and the treatment frequency is often set at 10Hz. When using this sliding treatment method, it is not enough to only consider the energy of a single pulse. In order to ensure that the area scanned by the laser is not missed, the number of pulses per unit time must also be taken into account. The more energy injected into the skin per unit time, the more energy will reach the hair follicles, and the better the treatment effect will be.

Therefore, with the change of laser hair removal treatment methods, effective energy has become a new standard for measuring whether laser hair removal is effective, and high effective energy has also become a new industry trend.

Effective energy = peak power × pulse width × frequency

The higher the effective energy, the better the hair removal effect

The effective energy of new laser hair removal devices is usually 300J or more per second. This is determined by three factors: peak power, pulse width and frequency. The peak power of new laser hair removal devices is usually 1200W or more, the pulse width needs to be able to reach the upper limit of the optimal parameters of 30ms, and the frequency needs to meet the 10Hz requirement for sliding hair removal.