Ex Vivo Exposure to Soft Biological Tissues by the 2-μm All-Fiber Ultrafast Holmium Laser System

We present the results of ex vivo exposure by an ultrafast all-fiber Holmium laser system to porcine longissimus muscle tissues. A simple Ho-doped laser system generated ultrashort pulsed radiation with less than 1 ps pulse width and a repetition rate of 20 MHz at a central wavelength of 2.06 μm. Single-spot ex vivo experiments were performed at an average power of 0.3 W and different exposure times of 5, 30 and 60 s, varying the total applied energy in the range of 1.5–18 J. Evaluation of laser radiation exposure was performed according to the depth and diameter of coagulation zones, ablation craters and thermal damage zones during the morphological study. Exposure by ultrashort pulsed radiation with an average power of 0.3 W showed destructive changes in the muscle tissue after 5 s and nucleation of an ablative crater. The maximum ablation efficiency was about 28% at the ablation depth and diameter of 180 μm and 500 μm, respectively. The continuous-wave radiation impact at the same parameters resulted only in heating of the near-muscular tissue, without ablation and coagulation traces. Exposure to tissue with an average power at 0.3 W of ul-trashort pulsed radiation led, within 30 and 60 s, to similar results as caused by 0.5 W of continuous-wave radiation, although with less carbonization formation. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Ex-Vivo Exposure on Biological Tissues in the 2-µm Spectral Range with an All-Fiber Continuous-Wave Holmium Laser

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. © 2021 by the authors. Licensee MDPI, Basel, Switzerland