Abstract
We present the results on the interaction of an all-fiber Holmium-doped laser CW radiation at a wavelength of 2100 nm with soft tissues and compare it with the other results obtained by the most used solid-state laser systems. Ex-vivo single spot experiments were carried out on the porcine longissimus muscles by varying the laser impact parameters in a wide range (average output power 0.3, 0.5 and 1.1 W; exposure time 5, 30 and 60 s). Evaluation of the laser radiation exposure was carried out by the size of coagulation and ablation zones on the morphological study. Exposure to a power of 0.3 W (1.5–18 J of applied energy) caused only reversible changes in the tissues. The highest applied energy of 66 J for 1.1 W and a 60-s exposure resulted in a maximum ablation depth of approximately 1.2 mm, with an ablation efficiency of 35%. We have shown that it is not necessary to use high powers of CW radiation, such as 5–10 W in the solid-state systems to provide the destructive effects. Similar results can be achieved at lower powers using the simple all-fiber Holmium laser based on the standard single-mode fiber, which could provide higher power densities and be more convenient to manufacture and use. The obtained results may be valuable as an additional experimental point in the field of existing results, which in the future will allow one to create a simple optimal laser system for medical purposes.
Highlights
Fiber laser sources are used in many technical and scientific fields, due to their numerous advantages in comparison with other laser systems; for example, a wide lasing wavelength range, a variety of commercially available components, the ability to obtain various operation modes, stable output power, compactness and reliability of the design, as well as high beam quality [1,2]
Based on the results obtained in [37] and the results presented in Figure 3, the following exposure times were chosen for the experiments with CW Ho-doped fiber laser radiation exposure: 5 s, 30 s and 60 s
Coagulation, carbonization and ablation zones can be attributed to irreversible damage, and the heat-affected zone is referred to as reversible damage
Summary
Fiber laser sources are used in many technical and scientific fields, due to their numerous advantages in comparison with other laser systems (solid-state or gas); for example, a wide lasing wavelength range, a variety of commercially available components, the ability to obtain various operation modes (from continuous-wave to ultrashort pulses), stable output power, compactness and reliability of the design, as well as high beam quality [1,2]. The maximum lasing wavelength in silica fibers is limited by 2200 nm, due to low luminescence quantum yield [5] and transparency losses in the short-wave infrared spectral range. Thulium and holmium laser systems, mainly the solid-state Tm:YAG, Ho:YAG lasers or fiber lasers with bulk elements such as dichroic mirrors, are widely used for these studies [10,11,12] These systems operate in a continuous-wave (CW) or in a high-energy pulsed regime with a pulse duration of 100–250 μs at a low repetition rate, and have the dependence of lasing characteristics on the active medium temperature, as well as thermal lensing in the laser crystals which could restrict the operating ranges [13]. This leads to the necessity of complex and expensive cooling systems, which increases the size and cost of the laser systems
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