High-energy pulsed Raman fiber laser for biological tissue coagulation

Abstract

Abstract:We demonstrate a high-energy pulsed Raman fiber laser (RFL) with an emission wavelength of 1.44 μm, corresponding to an absorption peak of water. Microsecond pulses with >20 mJ/pulse and >40 W peak power were generated, well above the threshold for tissue coagulation and ablation. Here, we focus on the optical characterization and optimization of high-energy and high-power RFLs excited by an ytterbium fiber laser, comparing three configurations that use different Raman gain fibers, but all of which were prepared with a one-side opened, free-run mode without output mirrors. We show that the free-run configuration can generate sufficiently high energy without requiring a closed cavity design. Experimental RFL characteristics corresponded well with numerical simulations. We discuss the Stokes beam generation process in our system and loss mechanisms mainly associated with fiber Bragg gratings.

Laser tissue coagulation and concurrent optical coherence tomography through a double-clad fiber coupler

“…Using the real-time feedback provided by OCT, it was possible to determine that the cumulative effect of 3 pulses of ~8.6 mJ each was sufficient to reach the coagulation threshold of esophageal swine tissues. It was shown previously that using single-mode delivery (beam spot size of ~37 µm), a single pulse of more than 7 mJ was sufficient to create a visible coagulation mark [6]. As expected, using the DCF inner cladding to deliver the coagulation laser requires higher energy to yield equivalent results, as the beam spot size (~220 µm) is much larger and, therefore, less spatially confined.…”

“…1(c) was smoothed to eliminate spectral features of the source. Multimode transmission of the coupler was measured using a continuous-wave modulated Raman fiber laser (RFL) built in-house, as described in [6], which provides a narrow bandwidth spectrum centered at 1436 nm corresponding to a strong absorption peak of water (main constituent of biological tissues), making it suitable for laser coagulation. The RFL light is injected at Port 3 using a lateral offset splice to excite the inner cladding modes of the injection fiber.…”

“…Laser coagulation for tissue marking was demonstrated in vivo using a continuous-wave laser source with 410 mW output power at a wavelength of 1450 nm during 2 s [3]. A pulsed Raman fiber laser was also used to demonstrate single-pulse marking using 900-µs pulses at a wavelength of 1436 nm with pulse energies greater than ~7 mJ [6], taking an advantage of the temporal confinement of the thermal energy delivery to achieve higher temperature in a shorter time in the optical zone [7]. However, the first configuration required stopping the probe's rotation to provide continuous irradiation over a few seconds, preventing real-time monitoring of the coagulation process.…”

Intravascular optical coherence tomography [Invited]

“…Recent work has suggested that direct flow measurements can be made directly from the OCT data, potentially enhancing the diagnostic information gained by intravascular imaging [113][114][115]. Other studies have suggested a potential role of OCT for monitoring atrial ablation [116][117][118]. Fig.…”

Intraoperative imaging of pediatric vocal fold lesions using optical coherence tomography

“…Earlier work focusing on combining OCT and laser therapy was performed in the field of gastroenterology, which could potentially be extended to the use of ablation laser. [37][38][39][40] The OCT handheld probe allowed extraction of features of several common benign pediatric lesion types with sufficient contrast, resolution, and penetration depth to give surgeons essential clinical insights to these lesions. Some steps are currently undertaken to further miniaturize the probe in order to allow targeting even younger patients (under 3 months).…”