Solid state laser is the most widely used and mature medical laser tube. The typical solid-state medical laser is Nd: YAG laser, that is, Nd: YAG laser. The primary operating wavelength is 1064 nm. As a scalpel, the output power is about dozens of watts; as the treatment of pigmented diseases in dermatology, Q-switched output is often used, with energy up to 1 J per pulse, and the pulse width can be narrowed to several nanoseconds. It can also be used for intraocular surgery such as membranous cataract, lens capsule incision, iridotomy, lens and vitreous cord cutting in anterior chamber. This kind of laser can also be used to remove hair when it is used as long pulse output, and the pulse width can be as long as 200 ms; as a free oscillation mode, it can be used for the treatment of ophthalmic slow lacrimal duct obstruction diseases. In addition, the 532 nm wavelength Nd: YAG laser after frequency doubling has important applications in many medical fields, such as ophthalmology, dentistry, dermatology, prostatectomy and so on. It can also be used in the treatment of skin wrinkles, hair loss and fundus diseases. The other wavelength of Nd: YAG laser is 1320 nm, which can be used for the treatment of large and small saphenous varices and nonfunctional superficial varicose veins caused by blood reflux. The 1.3 μ m laser output from Nd: YAP (neodymium doped yttrium aluminate) laser tube is close to this wavelength. Because of the relatively safe characteristics of human eyes, this wavelength laser has been widely used in medical surgery, and can be used for the removal of dental caries, preparation of cavities in dental pulp cavity, dentin hypersensitivity, resection of gingival tumor and hemangioma, and in vitro irradiation of oral ulcer. In recent years, the emergence and development of mid infrared solid-state lasers with wavelengths of more than 2 mm provide a large number of new ideal choices for laser medicine, such as typical YAG laser tubes doped with Ho, TM and ER. Most of these lasers are operated by pulse operation, and the wavelength of hyag laser tube is 2.1 μ m, suitable for soft and hard arrangement of touch and non touch incision, resection and coagulation, such as for urolithiasis; dermatology treatment of pyogenic granuloma, senile warts, senile keratosis; Obstetrics and Gynecology treatment of cervical erosion; otorhinolaryngology treatment of nasal polyps, throat papilloma; lumbar intervertebral disc percutaneous surgery, etc.; the laser system is used in percutaneous myocardial revascularization, as blood vessels The ideal appliance for angioplasty is known as the fourth milestone in the treatment of coronary heart disease.
Tm: YAG (thulium doped yttrium aluminum garnet) laser output wavelength of 2.0 μ m is close to the hyag laser, and can be used for soft and hard arrangement of touch and non touch cutting, cutting and solidification. The output wavelength of the other Er: YAG laser tube is 2.9 μ M. because of the intense absorption of water to this wavelength, it is mainly used in shallow laser treatment, such as drilling blood collection, eye treatment, skin rejuvenation surgery, etc. in addition, it is also used in Otolaryngology, tumor treatment and other fields, and its treatment principle can be attributed to laser scalpel. Similarly, there is the so-called "water laser" (ER, Cr: YSGG laser, named after the use of water to guide light), with a wavelength of 2780 nm, which is used in dentistry. Some early solid-state laser tubes, such as ruby laser tube with wavelength of 694.3 nm and alexandrite laser tube with wavelength of 755 nm, were used as the earliest laser medical devices in skin pigment removal, skin depilation, tattoo removal and treatment of benign skin pigment damage. In recent years, with the continuous appearance of advanced laser tubes with comprehensive performance, this kind of laser has gradually dropped out of the scope of medical laser. It is worth mentioning that the femtosecond Ti: sapphire laser tube, which is widely used in scientific research, not only has the broadband spectrum and wavelength tuning ability including the above wavelengths, but also has the pulse width less than 100 fs, showing more and more extensive application in disease diagnosis and fine surgery. For example, Oct (optical coherence imaging) based on its ultra wide spectral characteristics has higher resolution than conventional OC, and femtosecond laser as a scalpel for photodynamic therapy, myopia and eyesight presbyopia shows better effect and prospect.
Another trend of medical laser is fiber laser. As a kind of solid-state laser, fiber laser not only covers the wavelengths of 1.064 mm, 1.3 mm, 1.5 mm and 2 mm, but also develops rapidly in femtosecond ultrashort pulse and high power output. It can be predicted that fiber laser will account for more and more proportion in the future medical laser.
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