Are High Power Laser Diode Hair Removal More Effective?

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, which provides a guiding principle for using light to achieve medical beauty effects.

Among the many applications of the selective photothermal theory, the use of lasers 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 lasers with appropriate wavelengths, 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 upgrading of diode hair removal series beauty equipment, the laser power is also getting larger and larger, from 500W to 1000W, and then to 2000W. People are increasingly pursuing high power laser diode hair removal machines, but the energy density has not increased significantly. This Why?

Diode laser hair removal technology trends.

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 relationship between energy density and power, pulse width and spot area to develop products, and this formula is also the design guideline for photoelectric 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 treatment effect. Peak power is related to cost. The higher the peak power, the higher the cost of the corresponding laser. Spot area is related to treatment efficiency. For smaller treatment areas such as armpits and lips, outputting a smaller spot area will not lead to low treatment efficiency. However, for large treatment areas such as legs and back, the larger the spot area, the higher the treatment efficiency. Pulse width is related to comfort and effect. The shorter the pulse width, the more comfortable the treatment process. At the same time, when the pulse width is within 10~30ms, the treatment effect will be better.

It is this increasingly high demand for terminal experience that has promoted the transformation of beauty equipment manufacturers’ design concepts for instruments, and also formed a new trend in laser hair removal technology.

High peak power + narrow pulse width diode laser.

In recent years, the mainstream power of diode lasers used for laser hair removal has increased from 300W to 600W, and is rapidly shifting to more than 1200W, which is one of the recognized trends in the industry. Why is there such a change? The root cause is the demand of end users for more effective and comfortable treatment experience.

According to the 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 dissipate heat 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 dissipate heat, the pulse width must be less than the thermal relaxation time of the hair follicles, so 10~30ms is ultimately defined as the best pulse width. In order to complete the 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 dissipate heat, the energy will not be excessively accumulated, and the treatment process will be more comfortable.

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

Pursuit of high effective energy diode lasers.

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 temperature of the hair follicles 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 Feiton, the treatment method of laser hair removal has changed. In order to make the treatment process more efficient and comfortable, Feiton 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, it is necessary to take into account the number of pulses per unit time. 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.

The effective energy of diode laser hair removal equipment 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 equipment is usually 1200W or more, the pulse width needs to be able to reach the upper limit of 30ms in the optimal parameters, and the frequency needs to meet the 10Hz requirement required for sliding hair removal.

Analysis of core parameters of diode laser hair removal machine.

The hair removal effect of diode laser equipment is closely related to the parameters of the machine. So in addition to power, cooling and wavelength, what are these common core parameters, frequency, pulse width and energy density?

(1) Frequency (Hz): the number of times light is emitted per second;
(2) Pulse width (ms): the duration of each light emission;
(3) Energy density (J/cm²): the energy per unit area;

List of key technical parameters of diode laser hair removal series machines

So, the question is, why does the energy density not increase when the laser power increases?

The main reason is that as the laser power increases, the heat generated per unit time will increase sharply (E = P×t). In order to prevent the laser from burning out, laser manufacturers have strictly limited the laser parameters (laser power and duty cycle, etc.).

Therefore, when designing, semiconductor instrument manufacturers cannot rely entirely on their own performance, but must design according to the parameters specified by the laser; otherwise, the laser life will be shortened or burned out, which is not covered by the laser manufacturer’s warranty.

What are the limiting parameters of the laser bar?

From the above figure, we can see that:
When the frequency is 1Hz (period T=1000ms), the maximum pulse width is 200ms;

When the frequency is 2Hz (period T=500ms), the maximum pulse width is 100ms;

… …

What parameters specified by the laser manufacturer limit the energy?

From “Energy = Power x Pulse Width (E = P×t)”, it can be seen that when the laser power increases, the parameter that limits the increase in energy is the pulse width, and the maximum pulse width of the laser is determined by the maximum duty cycle of the laser.

What is duty cycle?
Duty cycle refers to the proportion of the light emission time to the total time in a pulse cycle. For example: the frequency is set to 1Hz, that is, the light is emitted once per second, 1 second = 1000ms;

(1) For a 500W laser, the manufacturer specifies that the maximum light emission duty cycle is 40%, which means that the maximum pulse width is 400ms;
(2) For a 1200W laser, the manufacturer specifies that the maximum light emission duty cycle is 20%, which means that the maximum pulse width is 200ms;
(3) For a 2000W laser, the manufacturer specifies that the maximum light emission duty cycle is 12%, which means that the maximum pulse width is 120ms;

In summary, according to “Energy = Power x Pulse Width (E = P×t)”, although the laser power has increased, the maximum pulse width has decreased, and the overall energy has not increased significantly.

Since the energy density has not increased, why do we still pursue higher power?

We know that hair removal is a process of energy accumulation. That is, at the appropriate energy density, when the energy accumulates to a certain extent, the hair follicles will be destroyed and the hair will lose its regeneration ability, thus achieving the effect of permanent hair removal.

Higher laser power and narrower pulse width can effectively reduce the pain of hair removal, improve the comfort experience, and further improve the hair removal effect.

Some people say that the more hair you remove, the more it will fall out, and the thicker it will become. Is this true?

If you use laser hair removal, it may be that the laser energy density is too low or the accumulated energy is insufficient, and the hair follicles and hair follicle growth stem cells are not destroyed. Instead, the heat accelerates blood circulation, causing the hair to absorb more nutrients and fall out more. As long as you choose the right energy or accumulate enough energy, the hair will gradually decrease.

Finally, you will find that if the energy density of the instrument you see is adjusted to the maximum and the pulse width can be adjusted arbitrarily without restrictions, then the parameters of this machine are probably fake, because this is not scientific.

Trend towards higher beam quality for high power laser diodes.

The common laser hair removal handpiece solution adopts a waveguide design. The purpose of choosing this design is to homogenize and shrink the rapidly diverging semiconductor laser beam through an optical waveguide. This design is relatively simple, but it will bring problems such as shallow penetration depth, large energy loss, and large and heavy handpieces, which will greatly reduce the clinical effect and increase the difficulty of operation for the operator.

To solve the above problems, light field homogenization technology that can achieve high beam quality has been introduced into the field of laser hair removal – waveguide-free technology came into being. Waveguide-free technology has the following characteristics:

Greater penetration depth.

In the traditional optical waveguide method, the rapid contraction of the waveguide light outlet will greatly increase the divergence of the light beam. When the light beam enters the skin, it will rapidly diverge and attenuate laterally, resulting in a decrease in penetration depth, which significantly reduces the energy that finally reaches the hair follicles, thus affecting the hair removal effect.

The laser module used in the waveguide-free technology adopts the light field homogenization technology. The core of this technology is to collimate and homogenize the light beam emitted by the diode laser through a non-spherical light field homogenizer, so that the output light beam has a deeper penetration depth, so that more energy reaches the hair follicles directly, and the hair removal effect is better.

Lower energy loss.

Traditional optical waveguide technology causes about 10% of the energy to be lost during the entire transmission process due to light leakage loss and end face loss of the optical waveguide itself. This energy loss will reduce the treatment effect of the device on the one hand, and greatly reduce the cost-effectiveness of the device on the other hand.

However, the waveguide-free technology avoids this part of energy loss by eliminating the optical waveguide, and the entire transmission process is almost zero-loss, which greatly improves the energy utilization rate of the product and effectively improves the treatment effect.

Smaller handpiece size/lighter handpiece weight.

In order to minimize light leakage loss and ensure uniformity, the length of the traditional optical waveguide technology is usually between 40 and 100 mm. This rigid size requirement will inevitably increase the size and weight of the overall handpiece. However, since the waveguide-free technology eliminates the optical waveguide, the size of the overall diode hair removal laser handpiece is greatly reduced, and the weight is also reduced.

At the same time, as end users continue to increase their requirements for equipment diversity and treatment effects, the waveguide-free technology also makes variable spot hair removal and vacuum adsorption hair removal possible.

FAQ about high power laser diode hair removal machine.

Q: Is the hair removal effect of high power laser diode obvious?
A: The power of diode laser is a very important indicator. High power does not mean high energy. Because the power is increased, the pulse width needs to be reduced and the spot area needs to be increased. Therefore, the energy density has not changed, and the hair removal effect has not improved. However, for the comfort of hair removal, high power also means stronger comfort.

Q: How much power can be called a high power laser diode?
A: High power diode lasers usually require more than 1200 W.

Q: What is the wavelength of the high power laser diode machine?
A: For better laser hair removal treatment, the high power diode laser hair removal machine will choose a combination of multiple wavelengths, 755 + 808 + 940 + 1064 nm 4 wavelengths, which can be used by people of all skin colors.

Summary of high power laser diode.

High-power diode lasers often require smaller pulse widths, and the spot area also needs to increase accordingly, but there is no obvious improvement in energy density. Therefore, for hair removal effects, the higher the power, the better the hair removal effect.

However, if the comfort of hair removal and customer experience are considered, high-power short-pulse diode lasers will bring a better hair removal feeling.

If you need to buy high-quality FDA-approved high power laser diode equipment, then you can choose LitonLaser, a medical equipment manufacturer with 20 years of experience, and welcome your inquiries at any time.