Dye laser for medicine
A liquid laser(dye laser) is a laser with a liquid active element. The active element (AE), also called the working fluid, is the most important part of the laser, because it is in it, under the influence of the “pumping element”, that the inversion of electron populations occurs – the physical effect underlying the operation of any laser (Another feature of a liquid laser is the use of AE is not a halogen lamp, but another solid-state laser (usually Nd: YAG laser plays this role.). In cosmetic liquid lasers, the AE is a solution of an organic dye in ethanol, methanol, or ethylene glycol. This provides him with a number of significant advantages over solid-state or diode counterparts.
Dye laser advantages
AE of a liquid laser – a solution of dyes circulating in a closed loop, is easy to replace. The ability to manufacture a solution with the required physical and optical characteristics provides the ability to operate at any length in the range of 400-800 nm. This is an important advantage over solid-state or diode lasers, whose wavelength range is limited to just a few values. 
Separately, it is worth noting the wavelength of 585-595 nm, (yellow visible light) corresponding to the absorption peaks of hemoglobin and melatonin. Selective action on these substances allows many complex cosmetic procedures with minimal side effects, and therefore the “yellow laser” will always be in demand in the beauty industry.
However, this is not the only advantage of a liquid laser. The circulation of the AE solution makes it possible to use powerful cooling equipment. Efficient removal of excess heat allows a wide variation of the pulse length and radiation power, which in turn is another significant advantage over solid-state lasers.
Disadvantages of dye laser
In view of the above, the laser invented in the 60s was already at the peak of its popularity by the early 80s, but this state of affairs did not last long. Soon the liquid laser again gave way to solid-state competitors, and there were reasons for that.
The unusual design of the AE did not allow precise tuning of the cavity (a system of 2 mirrors providing the AE conditions necessary for lasing), because of which the radiation of such a laser was insufficiently focused. To eliminate this drawback, it was necessary to introduce a focusing lens system, which complicated an already complex design.
The structural complexity of a liquid laser is the reason for its high cost and low wear resistance, and the most expensive and unreliable part of the apparatus was its unique AE. A solution of organic dyes, although relatively cheaper than a solid-state laser crystal, has a much shorter resource, has a limited storage time, and degrades quickly with use.
Application area
Although the high cost and complexity of operation caused the end of the “golden age” of the liquid AE laser, they do not detract from its advantages. Due to its unique operating wavelength and wide range of powers and pulse durations, it is still used in cosmetology.
The most widely used liquid medical laser is found in vascular surgery. From the 80s of the 20th century to the present day, it has been used to treat a number of vascular pathologies. It also makes sense to use it against skin hyperpigmentation. A certain therapeutic effect can be achieved in the treatment of scars and scars, since the destruction of the vessels feeding them leads to a gradual resorption of the scar tissue.
Pathologies against which the liquid laser is most often used:
- Telangiectasia
- Capillary hemangioma
- Lentigo
- Weakly pigmented spots of various origins
- Freckles
Thus, although the liquid laser is not an absolute leader among those used in modern cosmetology, due to its unique advantages, it firmly holds its position in the market, still being used in cosmetology clinics.