Overview of the laser: Laser (Laer) is the English “excited radiation amplification of light (lightamplicationbystimulatedemissionofradia-tion)” of the word acronym, the light emitted is light energy. Electromagnetic radiation is a fundamental form of energy, combining the properties of waves and particles. A certain amount of electromagnetic energy, called a photon, can excite an excited atom and cause the latter to emit another photon with the same energy as the excited photon. The resulting photon has the same energy and wavelength and is coordinated in its periphery (direction, time and space). In 1960, Maiman observed an excited release of red light in a ruby crystal excited by a flashlamp. 1983 saw the introduction of the theory of selective photothermolysis, and pulsed lasers targeting specific skin structures such as blood vessels, melanosomes and hair follicles began to make their way into the history books. With the continuous innovation of laser technology, the application of lasers in cosmetic dermatology has become more and more extensive, including soft tissue grinding and vascular lesions tattoos, pigmented lesions hirsutism and photoaging skin treatment. Lasers have several properties (monochromaticity, coherence, parallelism and high energy) that distinguish them from other light sources. Monochromaticity refers to the release of light for only a single wavelength or a narrow band of wavelengths, while determining the wavelength of the radiated light. Coherence describes light waves traveling in the same direction, time and space, like a squad of soldiers marching in step. Coherence allows the laser to be focused into a spot size as narrow as the wavelength itself. Parallelism refers to the characteristic of coherent light waves that can be emitted over long distances with no or minimal dispersion, allowing the laser beam to travel long distances without significant energy loss. Lasers can be transmitted in either continuous or pulsed mode. In the continuous mode, the laser produces a continuous beam. Argon lasers are representative of this type of laser. These lasers usually have a limited peak power; however, the peak power can be obtained by releasing the laser in pulses over a short period of time.Q-switched lasers release very short pulses at very high peak power levels. The term “Q” refers to the mass switching of energy stored in the laser emitting medium, whereby the latter is abruptly changed to produce short, intense pulses of light. Pulsed laser repetition frequency is expressed in hertz (Hz). Certain lasers can emit a series of rapid, low-energy pulses that behave as continuous lasers in surgical procedures, which are referred to as quasi-continuous modes. Skin Q-switched lasers are designed to emit pulses with pulse widths of 10 to 100 ms and energy densities typically in the range of 2 to 10 J/cm2. These short pulse widths and high energy pulses are effective for selective removal of tattoos and pigmented lesions. Tips: We occasionally see the so-called punching laser, pixel laser and so on in the medical aesthetic institutions, in fact, all belong to the range of fractional laser, but different regions, different equipment manufacturers named differently. Some medical beauty organizations use this as a selling point, publicizing that it is the world’s leading technology, and the online information is relatively small, and even all the soft articles produced by the machine manufacturers, resulting in some of the candidates being deceived.