Laser intensity (Intensity) is crucial in the field of medical cosmetology, which directly affects the effect and safety of treatment. Laser intensity refers to the energy intensity of the laser beam per unit time and per unit area, which is another way of saying power density. It is related to the power and spot diameter of the laser, usually in watts per square centimeter (W/cm²), indicating the energy transmitted by the laser per unit area and per unit time.

Related concepts closely related to laser intensity include laser power (Power), power density and energy density. These three concepts will be explained in detail in subsequent articles.

In short, power represents the speed of energy transfer, measured in watts (W), and is the most important parameter after the wavelength of the laser relay, because power determines the response of the tissue. If the power is too high or too low, the expected effect may not occur in the desired way.

Laser intensity and laser power can be used to derive the concepts of power density and energy density. Among them, energy density (or energy density per unit area) is the energy per unit area, measured in joules per square centimeter (J/cm²); power density is the energy density per second, measured in watts per square centimeter (W/cm²). As can be seen from the formula, power density is actually another expression of laser intensity.

Use mathematical formulas to help understand the relationship between these concepts:

First, let's clarify the relationship between the units of joule, watt, area, and time:

The total energy in all time and all area is joule (J);

The energy per unit time and all area is "joule/time", that is, power, the unit is "watt (W)", 1 watt (W) = 1 joule (J)/ 1 second (s);

The total energy per unit area over all time is "Joule/area", that is, energy density, and the unit is "Joule/square centimeter (J/cm²)";

The energy per unit time and per unit area is "Joule/(time*area)", that is, power density, "J/(s* cm²)", and the aforementioned power unit "Watt (W) = Joule (J)/time (s)" is substituted to obtain "Watt (W)/square centimeter (cm²)".

In summary, the formula relationship of the four concepts is as follows:

Applying the above four concepts to lasers, we can get the following results:

The total laser energy refers to the total energy delivered by the laser beam during the pulse duration and the total spot area, and the unit is joule (J).

The laser energy density refers to the total energy delivered by the laser beam during the pulse duration and per unit area, and the unit is joule/square centimeter (J/cm²).

The laser power refers to the energy delivered by the laser beam per unit time and the total spot area, representing the energy transfer rate, and the unit is watt (indicated by capital "W"). 1 watt = 1 joule/1 second.

Laser intensity refers to the energy transmitted by the laser beam per unit time and per unit area. It represents energy intensity and is related to the power and spot diameter of the laser beam. It is usually measured in watts per square centimeter (W/cm²).

Laser power density refers to the energy transmitted by the laser beam per unit time and per unit area. The calculation formula is "power density = energy density ÷ pulse duration". Since the unit obtained by joule/time is watt, the unit of power density is watt/square centimeter (W/cm²). It can be seen that power density is actually another expression of laser intensity.

In summary, laser intensity (also known as power density, as mentioned above) is the ratio of power to the area illuminated by the laser beam, which is determined by both the power of the laser and the size of the spot. Power density combines the three basic elements of laser: energy, time, and spot size. Power density = energy ÷ spot size area ÷ pulse duration. Since optical devices deliver light energy to a specific spot area within a specific time, laser intensity (power density) is a good indicator for comparing different systems.

Laser intensity (power density) is a key factor in determining the type of tissue reaction. While energy density determines whether there will be a reaction, laser intensity (power density) determines the specific nature of the reaction.

A common misconception is that a device with a higher energy density, such as IPL, is better because it may reach 20J/cm², while a laser may only be 5J/cm². But this comparison ignores the importance of laser intensity (power density). For example, an IPL device may release energy in 10 milliseconds, while a Q-switched laser may release it in 10nm.

Take IPL and laser as examples. The power density of IPL is 2000W/cm² (20J/cm² / 10ms), while the power density of Q-switched laser is as high as 500,000,000W/cm² (5J/cm² / 10ns). This means that the laser intensity (power density) of the laser is 250,000 times that of the IPL. Figuratively speaking, if the power density of IPL is represented as 1 cm on the graph, then the power density of the laser needs to be represented as 2.5 km.

Therefore, understanding the power density is crucial to evaluating the treatment effect, and knowing the energy density alone is not enough.

If a high-power laser is irradiated on a small area, it will produce high intensity; conversely, if the same power is dispersed over a larger area, the laser intensity will be reduced.

High-intensity lasers mean that a large amount of energy is concentrated in a small spot area, and this energy density can produce deep thermal effects or photochemical reactions. In contrast, low-intensity lasers have a more uniform energy distribution and are suitable for gentler treatments. In other words, if a high-energy beam is delivered for a long time, it may cause excessive tissue damage. But the same high-energy beam delivered in a very short time may produce a desired treatment effect, such as in tattoo removal.

Similarly, low-energy beams delivered over a longer period of time may stimulate tissue reactions at low energy levels, such as in LED systems and skin regeneration therapies.

Therefore, in medical aesthetics, it is very important to control both the power and intensity of the laser to ensure the safety and effectiveness of the treatment.

1. Skin treatment

In medical cosmetology, laser intensity determines the depth and effect of treatment. For example, in the treatment of pigmentation, such as freckles or spots, the intensity of the laser needs to be high enough to effectively destroy the pigment particles, but not too high to avoid damaging the surrounding healthy skin. The laser heats and breaks up the pigment particles through selective photothermal action, allowing them to be cleared by the body's immune system. High-intensity lasers can achieve this process in a shorter time, but they need to be strictly controlled to prevent excessive heat from causing skin burns or uneven pigmentation.

2. Tattoo Removal

Laser tattoo removal relies on precise control of laser intensity. Tattoo ink particles are large in size, and higher intensity laser pulses are usually required to break these particles small enough to be removed from the body. During treatment, too high an intensity may cause excessive heating of the skin and scarring, while insufficient intensity may not effectively remove the ink. Therefore, the physician must adjust the laser intensity according to the color and depth of the tattoo and the patient's skin type.

3. Skin Tightening and Wrinkle Removal

Laser skin tightening treatment stimulates collagen production in the skin through high-intensity lasers, thereby improving the firmness of the skin. Such treatments usually use medium to high intensity lasers to ensure sufficient heat penetration into the dermis to promote collagen production. However, intensity control is crucial. Too high an intensity may cause excessive damage to the skin, while too low an intensity may not be effective. Therefore, the laser intensity during treatment needs to be precisely adjusted to balance the effect and safety.

Laser Intensity Control and Safety

Accurate control of laser intensity has a direct impact on the effect and safety of treatment. Too high laser intensity may cause skin burns, pigmentation or long-term skin damage. On the other hand, too low laser intensity may lead to insignificant treatment effects, and multiple treatments are required to achieve the desired effect. Therefore, laser equipment in medical cosmetology needs to have precise intensity adjustment functions and be operated by experienced physicians to ensure the safety and effectiveness of treatment.

· Summary ·

In the field of medical cosmetology, the adjustment and control of laser intensity is crucial to the treatment effect. It not only determines the distribution and depth of laser energy, but also directly affects the safety of treatment. Whether it is treating skin pigmentation, tattoo removal, skin tightening or photorejuvenation, appropriate laser intensity can ensure the best treatment effect while reducing the risk of side effects. Through scientific and reasonable intensity control, laser treatment in medical cosmetology can achieve efficient and precise beauty effects.