Abstract
Minimally invasive laser surgeries that require the use of a flexible endoscope (flexiscope) could benefit from high-energy nanosecond laser pulses delivered through fibers for real-time tissue characterization and phenotyping. The damage threshold of the fiber's glass material limits the maximum amount of deliverable peak power. To transmit high-energy pulses without damaging the fiber material, large-diameter fibers are typically used, leading to a limited bending radius. Moreover, in a large-core fiber, self-focusing can damage the fiber even if the tip remains intact. In this work, we tested a fused-end fiber bundle combined with a beam shaper capable of delivering more than 20 MW (>100 mJ/5 ns). The fiber bundle was tested over more than eight hours of operation, with different bending radiuses down to 15 mm. The results demonstrate, to the best of our knowledge, the highest peak power delivered through a flexible fiber, for a frequency-doubled Q-switched Nd:YAG laser.
Highlights
IntroductionQ-switched Nd:YAG lasers have been used in industry and medicine for a wide array of applications, including hard and soft tissue ablation [1,2,3,4], laser-based diagnosis [5,6], laserinduced breakdown spectroscopy (LIBS) [7,8,9], laser-induced shockwave measurement [10,11,12], photoacoustic imaging/tomography [13,14], particle image velocimetry (PIV) [15], nanoparticle synthesis [16,17,18], laser shock processing [19], spark generation (laser ignition) [20,21] as a feedback mechanism for tissue-specific laser surgery [22,23,24]
Q-switched Nd:YAG lasers have been used in industry and medicine for a wide array of applications, including hard and soft tissue ablation [1,2,3,4], laser-based diagnosis [5,6], laserinduced breakdown spectroscopy (LIBS) [7,8,9], laser-induced shockwave measurement [10,11,12], photoacoustic imaging/tomography [13,14], particle image velocimetry (PIV) [15], nanoparticle synthesis [16,17,18], laser shock processing [19], spark generation [20,21] as a feedback mechanism for tissue-specific laser surgery [22,23,24]
We report on the use of a fiber bundle in combination with a top-hat beam shaper for flexible delivery of second harmonic pulses of a Q-switched Nd:YAG laser beam
Summary
Q-switched Nd:YAG lasers have been used in industry and medicine for a wide array of applications, including hard and soft tissue ablation [1,2,3,4], laser-based diagnosis [5,6], laserinduced breakdown spectroscopy (LIBS) [7,8,9], laser-induced shockwave measurement [10,11,12], photoacoustic imaging/tomography [13,14], particle image velocimetry (PIV) [15], nanoparticle synthesis [16,17,18], laser shock processing [19], spark generation (laser ignition) [20,21] as a feedback mechanism for tissue-specific laser surgery [22,23,24]. Considering the high peak power of Q-switched lasers (mJ/ns = MW) and the small diameter (cross-section) of optical fibers (10−3–10−6 cm2), the fiber optic often faces a peak power density (GW/cm2–TW/cm2) that exceeds the laser-induced damage threshold (LIDT) of the glass material. To overcome these challenges, a number of alternatives have been proposed. Other limiting factors of hollow-core fibers include a dramatic increase in attenuation (loss) as it bends [27,28,29] and optical breakdown (air plasma creation) inside the capillary (bore) To overcome the latter, researchers have experimented with blowing an inert gas with a higher plasma generation threshold into the capillary, and reducing the air pressure by creating a vacuum [29]. While the results showed an improved LIDT, the setup was highly complex (requiring a rotary pump and pressure gage) and bulky, especially at the tip of the fibers, making the technique unsuitable for endoscopic applications
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