Diode-pumped fiber lasers: a new clinical tool?

Thulium: YAG vs continuous-wave thulium fiber laser enucleation of the prostate: do potential advantages of thulium fiber lasers translate into relevant clinical differences?

PURPOSE

To compare endoscopic enucleation of the prostate using a thulium: yttrium-aluminum-garnet (Tm:YAG) laser and a super-pulsed thulium fiber laser set in continuous-wave (CW) mode, and to evaluate whether theoretical advantages of thulium fiber lasers, related to their shorter wavelength, translate into relevant clinical differences.

METHODS

In total, 110 patients suffering from lower urinary tract symptoms (LUTS) due to benign prostatic hyperplasia were randomized to undergo either thulium:YAG laser enucleation of the prostate (ThuLEP) or CW thulium fiber laser enucleation of the prostate (CW-ThuFLEP). Intraoperative and postoperative variables and complications were compared. Micturition improvement was assessed at 3-month follow-up using the International Prostate Symptom Score (IPSS), post-void residual urine (PVR) and maximum flow rate (Qmax). Erectile function was evaluated using the International Index of Erectile Function-5 (IIEF-5).

RESULTS

No significant differences between the ThuLEP and CW-ThuFLEP groups were found in terms of operative time (70.69 vs 72.41 min), enucleation time (50.23 vs 53.33 min), enucleated tissue weight (40.2 vs 41.9 g), enucleation efficiency (0.80 vs 0.79 g/min), catheterization time (2.45 vs 2.57 days), hospital stay (2.82 vs 2.95 days) and hemoglobin drop (1.05 vs 1.27 g/dl). At 3-month follow-up, no significant differences were found in IPSS (5.09 vs 5.81), Qmax (26.51 vs 27.13 ml/s), PVR (25.22 vs 23.81 ml) and IIEF-5 (14.01 vs 14.54).

CONCLUSION

ThuLEP and CW-ThuFLEP were equivalent in relieving patients from LUTS and improving micturition. Theoretical advantages of the TFL, such as shallower penetration depth and improved vaporization capacity, did not translate into relevant perioperative outcomes or clinical differences.

Recent developments in lanthanide-doped mid-infrared fluoride fiber lasers [Invited]

Mid-infrared fiber sources, emitting between 2.5 µm and 5.0 µm, are interesting for their great potential in several application fields such as material processing, biomedicine, remote sensing and infrared countermeasures due to their high-power, their diffraction-limited beam quality as well as their robust monolithic architecture. In this review, we will focus on the recent progress in continuous wave and pulsed mid-infrared fiber lasers and the components that bring these laser sources closer to a field deployment as well as in industrial systems. Accordingly, we will briefly illustrate the potential of such mid-infrared fiber lasers through a few selected applications.

Thulium fiber laser in urology: physics made simple

PURPOSE OF REVIEW

In this narrative review, we will focus on a novel thulium fiber laser's physical properties in terms of its clinical applicability.

RECENT FINDINGS

TFL has successfully moved forward from the preclinical trials into clinical practice and now is being widely used in clinics around the world. The available data suggest that the device effectively operates in soft tissues - benign prostate hyperplasia (BPH) and bladder tumors, as well as in lithotripsy. Also, the first promising results were obtained from laparoscopic surgery showing its possible applicability in the management of renal cell carcinoma. The constructional changes in fiber laser's design, lead to alteration of laser-tissue interactions, which resulted in clinical advantages of the device. Yet, the exact mechanism often is considered complex for understanding. With this work, we are aiming to build a bridge between biophysics and clinical practice and give a simple explanation of how the devices is working and why the knowledge of it is important for a clinician.

SUMMARY

The more effective wavelength (closer to the water absorption peak), favorable beam profile, different modes of action allowing to decrease carbonization on one hand and retropulsion on the other, all this makes TFL an evolution in urologic surgery. Further trials investigating on the possible pros and cons of the device are awaited.

Controllable structural tailoring for enhanced ∼2 µm emission in heavily Tm3+-doped germanate glasses

Heavily Tm³⁺-doped glass fibers are urgently desired for ∼2µm single-frequency fiber lasers and high-repetition-rate mode-locked fiber lasers. Here the structure of glass networks was tuned through controlling the numbers of non-bridging oxygens and bridging oxygens by adjusting the composition of the glasses, hence increasing the Tm³⁺ doping concentration of germanate glasses. The increased flexibility of the glass networks favors the distribution of Tm³⁺ ions to decrease fluorescence quenching, which was confirmed by the experimental and theoretical results. A heavily Tm³⁺ (9.8×10²⁰ions/cm³)-doped germanate glass was successfully fabricated without quenching by tuning the components of the glass. To the best of our knowledge, the Tm³⁺ ion doping concentration is the highest reported level in Tm³⁺-doped glasses and fibers. The results suggest that the heavily Tm³⁺-doped germanate glass is highly promising for fabricating ∼2µm glass fibers with high gain per unit length.

Thulium fiber laser utilization in urological surgery: A narrative review

The thulium fiber laser (TFL) is a novel technology under active investigation as an conceivable alternative to the Holmium:yttrium-aluminum-garnet (Ho:YAG) laser, which is currently the gold standard for an array of urologic procedures. The purpose of this review is to discuss the existing literature on the functionality and effectiveness of TFL in urological practice. We conducted a search of the PubMed, Medline, Web of Science Core Collection, SCOPUS, Embase (OVID), and Cochrane Databases for all full articles and systematic reviews on the TFL. We found a total of 35 relevant pieces of literature. The early research findings pertaining to the TFL exhibit numerous potential advantages over the Ho:YAG laser. In vitro and ex vivo studies have highlighted the TFL's ability to utilize smaller laser fibers, obtain faster stone ablation rates, and achieve less retropulsion when tested against the Ho:YAG laser in lithotripsy. Currently, there is limited in vivo research that investigates the utilization of the TFL. The in vivo results that are available, however, look promising both for laser lithotripsy and soft tissue ablation. Indeed, the existing literature suggests that the TFL has great potential and may possess numerous technological advantages over the Ho:YAG laser, especially in laser lithotripsy. Although these early studies are promising, randomized control trials are needed to assess the full applicability of the TFL in urology.

Thulium fiber laser: The new kid on the block

OBJECTIVE

Laser technology in urology is currently used for both stone lithotripsy and prostate enucleation. Thulium fiber laser (TFL) is a novel laser, with initial studies showing potential benefits over other lasers both in terms of its effectiveness and safety profile.

MATERIAL AND METHODS

In the first part of this review, a descriptive analysis of the theoretical concepts behind TFL was performed. This part focused on the physics and laser parameters as applied to the clinical practice. These were interpreted in the context of other lasers, namely, the Holmium:YAG laser to highlight the theoretical advantages as well as potential pitfalls offered by the TFL. In the second part of the review, a narrative synthesis of in-vitro studies regarding TFL and its modifications is performed assessing stone-related parameters, namely, ablation rate, operative time retropulsion, and safety.

RESULTS

TFL achieved high ablation rates in most studies and performed better than Holmium:YAG laser across a range of different settings and ablation modes when the two lasers were compared. Moreover, its ability to use low pulse energy ensures minimal stone retropulsion with the retropulsion threshold estimated to be 2-4 times higher than that of Holmium:YAG laser. From a safety viewpoint, TFL poses no additional risks than other lasers, although it does potentially lead to slightly higher temperatures in the surrounding tissues during lithotripsy.

CONCLUSION

The unique properties of TFL have made it an attractive alternative to conventional laser techniques currently used in urology. Clinical studies are required before its application can become more widespread.

Thulium-fiber laser for lithotripsy: first clinical experience in percutaneous nephrolithotomy

PURPOSE

To evaluate the efficacy and safety of thulium-fiber laser (TFL) in laser lithotripsy during percutaneous nephrolithotomy (PCNL).

METHODS

Patients with stones < 30 mm were prospectively recruited to undergo PCNL using TFL "FiberLase" (NTO IRE-Polus, Russia). Stone size, stone density, operative time, and "laser on" time (LOT) were recorded. Study included only cases managed with fragmentation. Stone-free rate and residual fragments were determined on postoperative computer tomography. Complications were classified using the Clavien-Dindo grade. Stone retropulsion and endoscopic visibility were assessed based on surgeons' feedback using a questionnaire.

RESULTS

A total of 120 patients were included in the study with a mean age of 52 (± 1.8) years; of these 77 (56%) were males. Mean stone size was 12.5 (± 8.8) mm with a mean density of 1019 (± 375) HU. Mean operative time was 23.4 (± 17.9) min and mean LOT was 5.0 (± 5.7) min. Most used settings were of 0.8 J/25-30 W/31-38 Hz (fragmentation). The mean total energy for stone ablation was 3.6 (± 4.3) kJ. Overall stone-free rate was 85%. The overall complication rate was 17%. Surgeons reported stone retropulsion that interfered with surgery in 2 (1.7%) cases insignificant retropulsion was noted in 16 (10.8%) cases. Poor visualization was reported in three (2.5%) cases and minor difficulties with visibility in four (3.3%) cases.

CONCLUSIONS

TFL is a safe and effective modality for lithotripsy during PCNL and results in minimal retropulsion.

Thulium fiber laser: the new player for kidney stone treatment? A comparison with Holmium:YAG laser

PURPOSE

To compare the operating modes of the Holmium:YAG laser and Thulium fiber laser. Additionally, currently available literature on Thulium fiber laser lithotripsy is reviewed.

MATERIALS AND METHODS

Medline, Scopus, Embase, and Web of Science databases were searched for articles relating to the operating modes of Holmium:YAG and Thulium fiber lasers, including systematic review of articles on Thulium fiber laser lithotripsy.

RESULTS

The laser beam emerging from the Holmium:YAG laser involves fundamental architectural design constraints compared to the Thulium fiber laser. These differences translate into multiple potential advantages in favor of the Thulium fiber laser: four-fold higher absorption coefficient in water, smaller operating laser fibers (50-150 µm core diameter), lower energy per pulse (as low as 0.025 J), and higher maximal pulse repetition rate (up to 2000 Hz). Multiple comparative in vitro studies suggest a 1.5-4 times faster stone ablation rate in favor of the Thulium fiber laser.

CONCLUSIONS

The Thulium fiber laser overcomes the main limitations reported with the Holmium:YAG laser relating to lithotripsy, based on preliminary in vitro studies. This innovative laser technology seems particularly advantageous for ureteroscopy and may become an important milestone for kidney stone treatment.

Advances in laser technology and fibre-optic delivery systems in lithotripsy

The flashlamp-pumped, solid-state holmium:yttrium-aluminium-garnet (YAG) laser has been the laser of choice for use in ureteroscopic lithotripsy for the past 20 years. However, although the holmium laser works well on all stone compositions and is cost-effective, this technology still has several fundamental limitations. Newer laser technologies, including the frequency-doubled, double-pulse YAG (FREDDY), erbium:YAG, femtosecond, and thulium fibre lasers, have all been explored as potential alternatives to the holmium:YAG laser for lithotripsy. Each of these laser technologies is associated with technical advantages and disadvantages, and the search continues for the next generation of laser lithotripsy systems that can provide rapid, safe, and efficient stone ablation. New fibre-optic approaches for safer and more efficient delivery of the laser energy inside the urinary tract include the use of smaller-core fibres and fibres that are tapered, spherical, detachable or hollow steel, or have muzzle brake distal fibre-optic tips. These specialty fibres might provide advantages, including improved flexibility for maximal ureteroscope deflection, reduced cross section for increased saline irrigation rates through the working channel of the ureteroscope, reduced stone retropulsion for improved stone ablation efficiency, and reduced fibre degradation and burnback for longer fibre life.

The laser of the future: reality and expectations about the new thulium fiber laser-a systematic review

The Holmium:yttrium-aluminum-garnet (Ho:YAG) laser has been the gold-standard for laser lithotripsy over the last 20 years. However, recent reports about a new prototype thulium fiber laser (TFL) lithotripter have revealed impressive levels of performance. We therefore decided to systematically review the reality and expectations for this new TFL technology. This review was registered in the PROSPERO registry (CRD42019128695). A PubMed search was performed for papers including specific terms relevant to this systematic review published between the years 2015 and 2019, including already accepted but not yet published papers. Additionally, the medical sections of ScienceDirect, Wiley, SpringerLink, Mary Ann Liebert publishers, and Google Scholar were also searched for peer-reviewed abstract presentations. All relevant studies and data identified in the bibliographic search were selected, categorized, and summarized. The authors adhered to PRISMA guidelines for this review. The TFL emits laser radiation at a wavelength of 1,940 nm, and has an optical penetration depth in water about four-times shorter than the Ho:YAG laser. This results in four-times lower stone ablation thresholds, as well as lower tissue ablation thresholds. As the TFL uses electronically-modulated laser diodes, it offers the most comprehensive and flexible range of laser parameters among laser lithotripters, with pulse frequencies up to 2,200 Hz, very low to very high pulse energies (0.005-6 J), short to very long-pulse durations (200 µs up to 12 ms), and a total power level up to 55 W. The stone ablation efficiency is up to four-times that of the Ho:YAG laser for similar laser parameters, with associated implications for speed and operating time. When using dusting settings, the TFL outperforms the Ho:YAG laser in dust quantity and quality, producing much finer particles. Retropulsion is also significantly reduced and sometimes even absent with the TFL. The TFL can use small laser fibers (as small as 50 µm core), with resulting advantages in irrigation, scope deflection, retropulsion reduction, and (in)direct effects on accessibility, visibility, efficiency, and surgical time, as well as offering future miniaturization possibilities. Similar to the Ho:YAG laser, the TFL can also be used for soft tissue applications such as prostate enucleation (ThuFLEP). The TFL machine itself is seven times smaller and eight times lighter than a high-power Ho:YAG laser system, and consumes nine times less energy. Maintenance is expected to be very low due to the durability of its components. The safety profile is also better in many aspects, i.e., for patients, instruments, and surgeons. The advantages of the TFL over the Ho:YAG laser are simply too extensive to be ignored. The TFL appears to be a real alternative to the Ho:YAG laser and become a true game-changer in laser lithotripsy. Due to its novelty, further studies are needed to broaden our understanding of the TFL, and comprehend the full implications and benefits of this new technology, as well its limitations.

Efficacy and safety of diode laser during circumvestibular incision for Le Fort I osteotomy in orthognathic surgery: a triple-blind randomized clinical trial

The aim of this triple-blind randomized clinical trial was to evaluate the efficacy and safety of diode laser during circumvestibular incisions for Le Fort I osteotomy in orthognathic surgeries in comparison with conventional techniques using electrocautery and scalpel. Patients were randomly allocated to one of three groups based on the technique employed to perform incisions: diode laser, electrocautery, and scalpel. The parameters used to evaluate the efficacy and safety of diode laser were incision velocity, duration of surgery, bleeding rate, alterations in postoperative functions, pain, edema, wound clinical healing, and infection. Thirty patients were enrolled in the study (10 per group). Regarding bleeding, the incisions performed with diode laser promoted a lower bleeding rate compared with scalpel and electrocautery (p = 0.00). The diode surgical laser was effective during the incision procedure, but required a longer time to perform the incisions compared with the other techniques evaluated (p < 0.05). No statistically significant difference was detected between groups regarding total surgical time or other safety parameters (p > 0.05). Thus, diode laser proved to be effective and safer during circumvestibular incisions for Le Fort I osteotomy than conventional devices.

Preclinical comparison of superpulse thulium fiber laser and a holmium:YAG laser for lithotripsy

PURPOSE

A superpulse (500 W peak power) thulium fiber laser operating at a 1940 nm wavelength, suitable for lithotripsy, has recently been developed. The goal of this study was to compare stone fragmentation and dusting performance of the prototype superpulse thulium fiber laser with leading commercially available, high-power holmium:YAG lithotripters (wavelength 2100 nm) in a controlled in vitro environment.

METHODS

Two experimental setups were designed for investigating stone ablation rates and retropulsion effects, respectively. In addition, the ablation setup enabled water temperature measurements during stone fragmentation in the laser-stone interaction zone. Human uric acid (UA) and calcium oxalate monohydrate (COM) stones were used for ablation experiments, whereas standard BegoStone phantoms were utilized in retropulsion experiments. The laser settings were matched in terms of pulse energy, pulse repetition rate, and average power.

RESULTS

At equivalent settings, thulium fiber laser ablation rates were higher than those for holmium:YAG laser in both dusting mode (threefold for COM stones and 2.5-fold for UA stones) and fragmentation mode (twofold for UA stones). For single-pulse retropulsion experiments, the threshold for onset of stone retropulsion was two to four times higher for thulium fiber laser. The holmium:YAG laser generated significantly stronger retropulsion effects at equal pulse energies. The water temperature elevation near the laser-illuminated volume did not differ between the two lasers.

CONCLUSIONS

Distinctive features of the thulium fiber laser (optimal wavelength and long pulse duration) resulted in faster stone ablation and lower retropulsion in comparison to the holmium:YAG laser.

Recent advances in infrared laser lithotripsy [Invited]

The flashlamp-pumped, solid-state, pulsed, mid-infrared, holmium:YAG laser (λ = 2120 nm) has been the clinical gold standard laser for lithotripsy for over the past two decades. However, while the holmium laser is the dominant laser technology in ureteroscopy because it efficiently ablates all urinary stone types, this mature laser technology has several fundamental limitations. Alternative, mid-IR laser technologies, including a thulium fiber laser (λ = 1908 and 1940 nm), a thulium:YAG laser (λ = 2010 nm), and an erbium:YAG laser (λ = 2940 nm) have also been explored for lithotripsy. The capabilities and limitations of these mid-IR lasers are reviewed in the context of the quest for an ideal laser lithotripsy system capable of providing both rapid and safe ablation of urinary stones.

10 W-level gain-switched all-fiber laser at 2.8 μm

We report a simply designed gain-switched all-fiber laser emitting a maximum average output power of 11.2 W at 2.826 µm. The corresponding extracted pulse energy is 80 µJ at a pulse duration of 170 ns. These performances significantly surpass previous gain-switched demonstrations and are close to the state-of-the-art Q-switched laser performances near 2.8 µm, but with a much simpler and robust all-fiber design. The spliceless laser cavity is made of a heavily erbium-doped fluoride glass fiber and is bounded by fiber Bragg gratings written directly in the gain fiber through the protective polymer coating.

Tm3+-doped lead silicate glass sensitized by Er3+ for efficient ~2μm mid-infrared laser material

Er³⁺/Tm³⁺ co-doped lead silicate glasses with low phonon (953cm^-1) and good thermal stability were synthesized. The ~2μm mid-infrared emission resulting from the ³F₄→³H₆ transition of Tm³⁺ sensitized by Er³⁺ has been observed by 808nm LD pumping. The optimal luminescence intensity was obtained in the sample with 1Tm₂O₃/2.5Er₂O₃ co-doped. Moreover, the energy transfer mechanism from Er³⁺ to Tm³⁺ ion was analyzed. Absorption and emission cross section have been calculated. The calculated maximum emission cross section of Tm³⁺ is 2.689×10^-21cm² at 1863nm. Microparameters of energy transfer between Er³⁺ and Tm³⁺ ions have also been analyzed. These results ensure that the prepared Er³⁺/Tm³⁺ co-doped lead silicate glasses have excellent spectroscopic properties in mid-infrared region and provide a beneficial guide for mid-infrared laser material.

High-power diode laser in the circumvestibular incision for Le Fort I osteotomy in orthognathic surgery: a prospective case series study

The incisions during orthognathic surgery are classically performed with conventional scalpel or electrocautery. Considering that the high-power diode laser surgery may provide advantages when compared to conventional incision techniques, the current study aimed to present a prospective case series of patients submitted to circumvestibular incision for Le Fort I osteotomy. Ten patients with dentofacial deformities who underwent to rapid assisted maxillary expansion or bimaxillary orthognathic surgery were enrolled in the study. All incisions were performed by a single surgeon using an 808-nm diode laser, with an optical fiber of 600 μm, at a power of 2.5 W, in a continuous-wave mode. The performance of the incision was evaluated by incision velocity, bleeding, edema, secondary infection, clinical healing, and pain. The velocity of the incision ranged from 0.10 to 0.20 mm/s (mean 0.13 ± 0.03 mm/s). Considering bleeding during the soft tissue incision, all surgeries were classified as absent bleeding. All patients presented a clinical healing of the surgical wound in a period that range from 3 to 5 weeks and experienced swelling during the follow-up period. On average, approximately 50% of the swelling had resolved after the third postoperative week, and 28.8% of swelling remained after 2 months after the surgery. The pain decreased after 2 and 3 days, and 90.0% of the patients reported no pain after 7 postoperative days. High-power diode laser is effective and safety during circumvestibular incisions for Le Fort I osteotomy in orthognathic surgery decreasing bleeding, surgery time, pain, and edema after orthognathic surgery.

2 μm laser oscillation of Ho3+:Tm3+-codoped silica microspheres

2 μm laser oscillation with a low threshold has been achieved in Ho³⁺:Tm³⁺-codoped silica microspheres (HTCSMs). Ho³⁺:Tm³⁺-codoped solgel functionalization film is applied to the surface of a silica microsphere, and an optical tapered fiber is adopted to couple an 808 nm continuous-wave laser to serve as the pump light source. Multimode and single-mode laser oscillations around 2 μm within the eye-safe wave band are observed due to the I₇5→I₈5 transitions of Ho³⁺ ions sensitized by Tm³⁺. The morphology characteristics of microspheres determine the multimode laser oscillation spectrum. The free spectral range is in good accordance with the calculated value based on Mie scattering theory. The HTCSM laser oscillation shows characteristics of good capability, simple process, high flexibility, and low cost.

High-power widely tunable all-fiber thulium-assisted optical parametric oscillator at SWIR band

A novel short-wave infrared (SWIR) all-fiber thulium-assisted optical parametric oscillator (TAOPO) that exploits jointly optical parametric conversion and thulium amplification in a highly nonlinear fiber (HNLF) and thulium-doped fiber (TDF) is demonstrated. This is implemented through constructing a joint fiber line by directly fusion splicing 50 m HNLF with 1.5 m TDF. Incorporating a bidirectional-pumping scheme, i.e., forward-pumped by a step-tuned C-band pulsed laser, and simultaneously backward-pumped by an L-band continuous-wave laser, this TAOPO produces a pulsed SWIR laser at output power higher than 200 mW, signal-to-noise ratio over 40 dB, and wavelength tuning range beyond 150 nm from 1815 to 1968 nm. Via separate characterization of the HNLF and TDF joint fiber line, the tunability of the current TAOPO to shorter wavelength is only limited by the employed fiber components, while higher power could be realized by increasing the backward pump power. This TAOPO could be a promising platform for the generation of a highly functional SWIR source that facilitates applications such as bond-selective imaging of deep tissue.

Enhanced 2.7 μm mid-infrared emissions of Er3+ via Pr3+ deactivation and Yb3+ sensitization in LiNbO3 crystal

The use of Pr³⁺ codoping for enhancement of the transition of Er³⁺: ⁴I_11/2 → ⁴I_13/2 2.7 μm emissions was investigated in the Er/Yb codoped LiNbO₃ crystal for the first time. It is found that the codoped of Pr³⁺ ion in Er³⁺, Yb³⁺ and Pr³⁺ triply doped LiNbO₃ crystal (Er/Yb/Pr: LN) greatly enhances Er³⁺: 2.7 μm emission under excitation of a common 970 nm laser diode, depopulates the lower laser level of Er³⁺:⁴I_13/2, and has little influence on the higher laser level of Er³⁺:⁴I_11/2 at the same time for population inversion. The 2.7 μm emission characteristics and energy transfer were investigated in detail. The energy transition efficiency from lower laser level of Er³⁺:⁴I_13/2 to Pr³⁺:³F₄ level is as high as 0.42, indicating that the Pr³⁺ ion is an effective deactivation ion for Er³⁺ ion in LiNbO₃ crystal. These results suggest that Er/Yb/Pr: LiNbO₃ crystal may become an attractive host for developing solid state lasers at around 2.7 μm under a conventional 970 nm LD pump.

Gamma radiation induced darkening in barium gallo-germanate glass

Barium gallo-germanate (BGG) glass is an important glass matrix material used for mid-infrared transmission and mid-infrared fiber laser. In this study, we investigated the γ-ray irradiation induced darkening effect of BGG glass. Optical transmittance spectra, electron paramagnetic resonance (EPR) and thermoluminescence (TL) spectra were employed to investigate the γ-ray irradiation induced defects. Two kinds of Ge-related defects in the irradiated BGG glass, named Ge-related non-bridging oxygen hole center (Ge-NBOHC) and Ge-related electron centers (GEC), were verified. In addition, the absorption bands of the two defects have been separated and the peak absorptivity of Ge-NBOHC and GEC defects is at 375 nm and 315 nm, respectively.

Short pulse-width gain-switched Ho:YAG ceramic laser at ∼2.09 μm

This paper presents a short pulse-width gain-switched Ho:YAG ceramic laser at 2089 nm resonantly pumped by a homemade Q-switched Tm:fiber laser at ∼1908  nm. We generated stable pulses of 44-103 ns duration and 0.13-2 kW peak power at 20 kHz of pulse repetition frequency when the incident pump pulse energy increased from ∼0.1 to 0.3 mJ. We also obtained an average output power of 1.76 W under an incident pump power of 6 W, corresponding to a slope efficiency of 41.8%. Finally, this paper discusses the prospects to further improve the results with even a shorter pulse-width and higher peak power.

Tm³⁺ doped barium gallo-germanate glass single-mode fibers for 2.0 μm laser

Tm³⁺ doped barium gallo-germanate (BGG) glass has emerged as a promising 2.0 μm laser material offering excellent optical property. Unfortunately, low anti-crystallization ability and high OH⁻ content of the glass have hindered the fabrication of high-quality optical fibers. In this paper, La₂O₃ and Y₂O₃ were added into BGG glass to enhance the glass anti-crystallization ability. Additionally, the optimized Reaction Atmosphere Procedure (RAP) was utilized to minimize OH⁻ content. Continuous Tm³⁺ doped BGG glass single-mode (SM) fibers were successfully obtained by the rod-in-tube technique for the first time to our best knowledge. A 140 mW all-fiber laser at 1.95 μm was demonstrated using a 9.7-cm-long as-drawn Tm³⁺ doped BGG glass SM fiber upon excitation of a home-made 1568 nm fiber laser.

High-efficiency ytterbium-free erbium-doped all-glass double cladding silicate glass fiber for resonantly-pumped fiber lasers

A highly efficient ytterbium-free erbium-doped silicate glass fiber has been developed for high-power fiber laser applications at an eye-safe wavelength near 1.55 μm. Our preliminary experiments show that high laser efficiency can be obtained from a relatively short length of the gain fiber when resonantly pumped at 1535 nm in both core- and cladding-pumping configurations. With a core-pumping configuration as high as 75%, optical-to-optical efficiency and 4 W output power were obtained at 1560 nm from a 1 m long gain fiber. When using a cladding-pumping configuration, approximately 13 W output power with 67.7% slope efficiency was demonstrated from a piece of 2 m long fiber. The lengths of silicate-based gain fiber are much shorter than their silica-based counterparts used in other experiments, which is significantly important for high-power narrow-band and/or pulsed laser applications.

2.7 μm emission of high thermally and chemically durable glasses based on AlF3

AlF₃-based glasses (AlF₃-YF₃-CaF₂-BaF₂-SrF₂-MgF₂) with enhanced thermal and chemical stability were synthesized and compared with the well-known fluorozirconate glass (ZBLAN). The 2.7 μm mid-infrared emission in the AlF₃-based glasses was also investigated through the absorption and emission spectra. Both the temperature of glass transition and the characteristic temperatures (ΔT, H_r, k_gl) of the fluoroaluminate glasses were much larger than those of the ZBLAN glasses. The corrosion phenomenon can be observed by naked-eye, and the transmittance dropped dramatically (0% at 3 μm) when the ZBLAN glass was placed into distilled water. However, the AlF₃-based glass was relatively stable. The fluoroaluminate glasses possessed large branching ratio (20%) along with the emission cross section (9.4×10⁻²¹ cm⁻²) of the Er³⁺:⁴I_11/2→⁴I_13/2 transition. Meanwhile, the enhanced 2.7 μm emission in highly Er³⁺-doped AYF glass was obtained. Therefore, these results showed that this kind of fluoride glass has a promising application for solid state lasers at 3 μm.

Nanowatt threshold, alumina sensitized neodymium laser integrated on silicon

Low threshold lasers based on rare-earth elements have enabled numerous scientific discoveries and innovations in industry. However, pushing the threshold into the sub-microwatt regime has been stymied by a fundamental material phenomenon. Specifically, rare earth dopants form clusters which quench emission and reduce efficiency. Here, we fabricate resonant cavity lasers from neodymium-doped silica films containing alumina. The alumina prevents the clustering of the Neodymium, enabling the lasers to achieve thresholds of 530 nanoWatts at room temperature.

Mid-infrared spectroscopic properties and energy transfer of Er3+/Yb3+ co-doped bismuth germanate glass

An Er3+/Yb3+ co-doped bismuth germanate glass is synthesized and analyzed. The radiative characteristics and mid-infrared spectroscopic properties are investigated under excitation of a conventional 980 nm laser diode. The prepared glass possesses higher spontaneous transition probability (68.82 s(-1)) and larger calculated emission cross-section (7.73×10(-21) cm2) corresponding to the 4I11/2→4I13/2 transition. The calculated energy migration coefficient (CDD) among Yb3+ ions is larger than the energy transfer coefficient (CDA) from Yb3+ to Er3+, indicating the energy transfer process assisted with energy migration. The excellent spectroscopic properties along with the outstanding thermal stability suggest that this glass may become an attractive host for developing solid state lasers operating in the mid-infrared range.

All-fiber Q-switched operation of thulium-doped silica fiber laser by piezoelectric microbending

We demonstrate an all-fiber Q-switched laser operation in the 2 µm region on the basis of a dynamic periodic microbend and pulsed-pump configuration. A single-mode thulium-doped silica fiber is pumped by 1.6 µm-band laser diodes, and the dynamic loss is introduced in the fiber ring resonator by the periodic microbend that is electrically controlled with a piezoelectric actuator. When the voltage-off period of the piezoelectric actuator is set at 20 µs for the pump power of 120 mW, the output pulse power is measured by 420 mW with a pulse width of 1.3 µs.

Skin burns after laser exposure: histological analysis and predictive simulation

Thermal effects of laser irradiation on skin are investigated in this paper. The main purpose is to determine the damage level induced by a laser exposure. Potential burns induced by two lasers (wavelength 808nm and 1940nm) are studied and animal experimentations are performed. Several exposure durations and laser powers are tested. Based on previous works, a mathematical model dedicated to temperature prediction is proposed and finite-element method is implemented. This numerical predictive tool based on the bioheat equation takes into account heat losses due to the convection on skin surface, blood circulatory and also evaporation. Thermal behavior of each skin layer is also described considering distinct thermal and optical properties. Since the mathematical model is able to estimate damage levels, histological analyses were also carried through. It is confirmed that the mathematical model is an efficient predictive tool for estimation of damage caused by lasers and that thermal effects sharply depend on laser wavelength.

Novel approach towards cross-relaxation energy transfer calculation applied on highly thulium doped tellurite glasses

In this paper we calculated, for the first time to the best of our knowledge, the cross relaxation parameter of Tm(3+) ions in tellurite glasses over a wide range of concentrations: from 0.36 mol% up to 10 mol%. A new measurement approach based on emission spectra monitoring is proposed. This method is very simple and allows to measure even very highly doped samples. The obtained values of cross-relaxation parameter show a linear dependence with respect to dopant concentration over the full investigated interval, suggesting a dipole-dipole interaction process. The measured slope is 1.81x10(-17) cm(3) s(-1) mol%(-1).

Enhanced emission of 2.7 μm pumped by laser diode from Er3+/Pr(3+)-codoped germanate glasses

A novel Er(3+)/Pr(3+) codoped germanate glass was fabricated and analyzed. Efficient emission at 2.7 μm from the glass was observed upon excitation of a conventional 980 nm laser diode. The 2.7 μm emission characteristics and energy transfer (ET) were investigated. Population inversions between ⁴I(13/2) and ⁴I(11/2) levels have been achieved, and an enhanced emission from 2550 to 2800 nm was obtained. Large ET efficiency of 95% indicates that the ET process from Er(3+) to Pr(3+) (⁴I(13/2), ³H₄)→(⁴I(15/2), ³F₃) is efficient and that Pr(3+) can enhance the emission of 2.7 μm by quenching the lower laser level of Er(3+) via ET.

Millijoule-level Yb-doped photonic crystal fiber laser passively Q-switched with AlGaInAs quantum wells

We report on a millijoule-level Yb-doped photonic crystal fiber (PCF) laser passively Q-switched with AlGaInAs quantum wells (QWs). Three types of AlGaInAs devices with different QW numbers are fabricated to investigate the performance. With 50 groups of three AlGaInAs QWs as a saturable absorber (SA), the PCF laser generates an average power of 7.1 W with a pulse repetition rate of 6.5 kHz at a pump power of 16 W, corresponding to the pulse energy of 1.1 mJ. The maximum peak power is up to 110 kW.

Highly stable and efficient erbium-doped 2.8 microm all fiber laser

We demonstrate the efficient and stable CW laser operation at 2.824 microm of a diode-pumped erbium-doped fluoride fiber laser employing an intracore fiber Bragg grating high reflector. An output power of 5 W and an optical-to-optical conversion efficiency of 32% are reported. The temporal and spectral stability of the laser represent a significant improvement over previous work. This report paves the way to the commercialization of compact and stable fiber lasers for spectroscopic and medical applications.

Compact 2 W wavelength-tunable Er:ZBLAN mid-infrared fiber laser

We report a high-power diode-pumped wavelength-tunable (2.7-2.83 mum) erbium-doped ZBLAN mid-infrared fiber laser. Continuous-wave output of >2 W with a spectral linewidth of 1.27 GHz was obtained. Nevertheless, the wavelength-tunable range was found to shrink with increasing pump power. The gain bandwidth narrowing under strong pumping may be ascribed to the enhanced reabsorption process and the weakened population inversion associated with shorter-wavelength emissions.

Stable high-power continuous-wave Yb(3+)-doped silica fiber laser utilizing a point-by-point inscribed fiber Bragg grating

We report on a narrowband 5 W cw fiber laser incorporating a point-by-point fiber Bragg grating inscribed into the core of a Yb(3+)-doped double-clad fiber. The laser featured excellent long-term wavelength and power stability (0.3%), as well as a very narrow (15 pm) linewidth, when passive temperature stabilization of the grating was implemented.

10-W-level diode-pumped compact 2.78 microm ZBLAN fiber laser

We report on >9W transverse-fundamental-mode CW output near 3 mum from a 4m heavily erbium-doped ZBLAN double-clad fiber laser pumped by a collimated 100 W 975 nm laser diode array. The pump threshold of the fiber laser was about 1W, and the slope efficiency was 21.3%. The peak wavelength of free running was about 2708 nm at low pump power and moved to around 2785 nm at high pump power. Output of 9W was obtained when the launched pump power was 42.8W. The output, however, fluctuated intensively like a pulsed laser, and the operation broke down with optical damage of the pumping end facet when the pump was increased beyond 42.8 W. Therefore, alleviation of the operation fluctuation, heat management, and strengthening the pumping fiber are crucial considerations for the stable operation of 10-W-level mid-IR ZBLAN fiber lasers.

Numerical analysis and experimental results of high-power Er/Pr:ZBLAN 2.7 microm fiber lasers with different pumping designs

Gain factor and output performance of erbium-praseodymium codoped ZBLAN double-clad fiber lasers at 2.7 microm with different pumping designs were calculated and analyzed. Single-end backward pumping with a highly reflective mirror butted against one fiber end and dual-end pumping with Fresnel reflections from both fiber ends were found to be the most efficient pumping designs. Ten-watt-level Er/Pr:ZBLAN fiber lasers proved to be achievable with recent diode laser and ZBLAN fiber technologies. Their corresponding optimum fiber lengths for different pumping configurations were determined. It was also found that fiber lasers with a flat evolution of gain factor can obtain the largest output power. Experimental results of 4 m and 12 m fiber lasers showed very good agreement with simulation results.

High-power laser vaporization of the canine prostate using a 110 W Thulium fiber laser at 1.91 microm

INTRODUCTION

The Thulium fiber laser may have several advantages over current urology lasers, including smaller size, more efficient operation, improved spatial beam quality, more precise tissue incision, and operation in pulsed or continuous-wave modes. Previous laser-tissue interaction studies utilizing the Thulium fiber laser have been limited to laser powers of less than 5 W, restricting potential medical applications. This study describes the preliminary testing of a high-power Thulium fiber laser for vaporization of the canine prostate, ex vivo.

STUDY DESIGN/MATERIALS AND METHODS

A continuous-wave, 110-W Thulium fiber laser operating at a wavelength of 1.91 microm, delivered 88.5+/-2.3 W of power through a 600-microm-core silica fiber for non-contact vaporization of canine prostates (n = 6).

RESULTS

The Thulium fiber laser vaporized prostate tissue at a rate of 0.83+/-0.11 g/minute. The thermal coagulation zone measured 500-2,000 microm, demonstrating the potential for hemostasis.

CONCLUSIONS

The high-power Thulium fiber laser is capable of rapid vaporization and coagulation of the prostate. In vivo animal studies are currently being planned for evaluation of the Thulium fiber laser for potential treatment of benign prostate hyperplasia (BPH).

Thulium fiber laser lithotripsy: An in vitro analysis of stone fragmentation using a modulated 110-watt Thulium fiber laser at 1.94 µm

BACKGROUND AND OBJECTIVES

The high-power Thulium fiber laser has previously been shown to rapidly vaporize and coagulate soft urinary tissues (e.g., prostate). This is the first preliminary study of a high-power Thulium fiber laser for fragmentation of urinary stones.

STUDY DESIGN/MATERIALS AND METHODS

A continuous-wave, high-power Thulium fiber laser operating at a wavelength of 1.94 microm, was modulated to operate in pulsed mode with an output pulse energy of 1 J through a 300-microm-core silica fiber at a 20 milliseconds pulse length and repetition rate of 10 Hz. The fragmentation time to reduce uric acid (UA) (n = 13) and calcium oxalate monohydrate (COM) (n = 6) stones into particles < 2 mm was measured.

RESULTS

Mean initial mass of the UA and COM stones measured 860+/-211 and 763 +/- 204 mg. Fragmentation rates measured 388 +/- 49 and 25 +/- 2 mg/minute. Average time needed to fragment the UA and COM stones into particles < 2 mm was 2.25 +/- 0.63 and 30.7 +/- 8.4 minutes, respectively.

CONCLUSIONS

The high-power Thulium fiber laser, when operated in pulsed mode, is capable of fragmenting both soft (UA) and hard (COM) urinary stones. The Thulium fiber laser may be useful as a single laser system for use in multiple soft and hard tissue laser ablation applications in urology.