Diode Laser Research Articles

Effective mitigation of photodarkening-induced transverse mode instability in a monolithic fiber laser oscillator by 450 nm laser irradiation.

The photodarkening (PD) and transverse mode instability (TMI) effects are two main factors limiting the power increase and long-term stability of high-power fiber lasers. A prolonged burn-in test for an all-fiber laser oscillator below the TMI threshold was carried out. We observed the PD-induced TMI effects, which manifested as a sudden decrease in the output power due to higher-order mode leakage. After several minutes of exposure to a high-power density 450 nm laser diode (LD), the output power returned to its initial state, significantly enhancing the oscillator's stability. The 450 nm LD probably mitigates the accumulation of thermal effects by inhibiting the photodarkening effect, thus preventing the occurrence of the TMI effects and improving the stability of the oscillator's output power. Our work provides useful guidance for the development of high-stability fiber laser oscillators.

Transient opto-thermal simulation analysis and experimental validation of LERP systems

Abstract Solid-state technology has revolutionized the lighting industry. However, efficiency-droop-limited LEDs introduce constraints to the luminances achieved, and as a result, laser diodes (LDs) are replacing them in the remote phosphor setup. This introduces a new family of lighting solutions, laser-excited remote phosphor (LERP) systems, which can outperform cutting-edge LEDs. LERP systems however have not yet reached their full potential as the high intensity laser beam induces high temperatures within the phosphor material whose emission characteristics heavily depend on temperature. For this reason, a simulation framework has been developed that combines optical and thermal analysis in order to study and optimize these systems and derive their temperature thresholds for sustainable long-term usage. The focus here is on transient analysis, where the interplay between optical and thermal effects can be accounted for and the time dynamics of the system can be investigated. This enables the study of operation points near or at the thermal quenching regime. Furthermore, advanced material models have been developed in order to incorporate the temperature-dependence. The experimental validation of the model has shown that experimental and simulated results are in good agreement.

Growth, spectroscopy properties, and laser operation of single crystal fiber: Nd3+-doped CNGG

Nd3+-doped calcium niobium gallium garnet single crystal fibers (Nd:CNGG SCFs) with varying Nd3+ concentrations were successfully grown using the laser-heated pedestal growth (LHPG) method. The study thoroughly examines the fundamental physical structure, optical properties, and laser characteristics of the as-grown Nd:CNGG SCFs. Results indicate that the Nd:CNGG SCF exhibits broader absorption and emission full width at half maximum (FWHM) compared to bulk single crystals. Moreover, pumped by a commercial 808 nm laser diode, continuous-wave laser operation at 1061 nm with a half-height width of 1.86 nm was achieved. The laser output power reached 1.04 W at an absorbed power of 7.46 W, with a slope efficiency of 25.4% relative to the absorbed pump power. These findings suggest that Nd:CNGG SCF holds promise as a practical and potent candidate for laser gain medium, offering significant research potential in the field of lasers.

Luminescent and magnetic Y2O3: Er3+-Yb3+@γ-Fe2O3 bifunctional broadband emitting nanocomposites

The development of novel nanocomposites containing upconverting luminescent materials and magnetic nanoparticles have shown their potential applications in the hyperthermia and bio-imaging. In this regards, the search for new class of nanocomposites, which is responsive to magnetic and optical guiding in medical fields are in demand. To resolve the problem, bifunctional upconverting Y2O3: Er3+-Yb3+@γ-Fe2O3 nanocomposites have been synthesized through ball milling approach. Nanocomposites are able to upconvert NIR photons into overall yellowish-white colour broadband visible emission in 400–900 nm wavelength range at room temperature under 980 nm CW laser diode excitation. Thermal conductivity study shows an improved phonon scattering process in the Y2O3: Er3+-Yb3+@γ-Fe2O3 (∼ 0.0681 W/mK) nanocomposites as compared to Y2O3: Er3+-Yb3+ (∼ 0.0750 W/mK) phosphors due to grain boundary expansion. Broadband UC emission is originated via Yb-Yb dimer formation and heat associated continuum emission is reported due to photon avalanche (∼ 6 NIR photons) phenomenon. Besides, it also exhibits the attraction ability towards the magnet. Therefore, the developed nanocomposites can be used in converting the NIR radiation into broadband upconversion emission and luminescence imaging applications.

Optical Characteristics of the Black Seed Oil: Fluorescence and Adulteration Detection.

Understanding the optical characteristics, especially the fluorescence properties of vegetable oils, particularly black seed oil (BSO), is an essential prerequisite for the development of the future applications in both medicinal and nutritional fields. In this way, it is essential to identify the roles played by the components such as unsaturated fatty acids, carotenoids, flavonoids, vitamin E, and chlorophylls in the BSO fluorescence spectra. In the current landscape, challenges arise from the adulteration of BSO with impurities such as sunflower oil (SO), complicating efforts to obtain pure BSO. Here, dependence of the BSO fluorescence on excitation wavelength has been examined using UV- visible diode lasers (λ = 355, 405, 440, 532 and 660nm) as excitation sources. Though conjugated unsaturated fatty acids, flavonoids and chlorophylls are mainly contributed to the fluorescence due to UV excitation, wavelengths in the visible range specifically excite carotenoids, vitamin E, and chlorophylls. By utilizing the laser-induced fluorescence (LIF) technique, we explored the effects of inner filters and setup geometry to gain deeper insights into the BSO fluorescence dynamics. Differential spectral analysis (DSA) revealed that adulteration of BSO with SO alters its fluorescence features. As a result, a novel approach is proposed for adulteration detection, based on the simultaneous excitation of BSO and SO by a 405nm laser, benefit to indirect excitation of the carotenoids of BSO by fluorescence emission of SO within the spectral range of 400-500nm, which results in the enhancement of BSO fluorescence in the region of 500-600nm.

Efficacy and Safety of Non-Ablative Dual Wavelength Diode Laser Therapy for Genitourinary Syndrome of Menopause: A Single-Center Prospective Study.

This study evaluates the efficacy and safety of non-ablative diode laser therapy for genitourinary syndrome of menopause (GSM) in post-menopausal women unable to use hormonal therapies. A pilot prospective study was conducted from September 2023 to April 2024, involving 22 post-menopausal women aged 45-73years. Participants underwent three sessions of diode laser treatment with the Leonardo® dual-wavelength Diode laser. Assessments were made at baseline, 3months, and 6months post-treatment. Main outcome measures included Visual Analog Scale (VAS) scores for GSM symptoms, Vaginal Health Index Score (VHIS), and sexual function evaluated using the Female Sexual Function Index (FSFI-6), Pelvic Organ Prolapse/Urinary Incontinence Sexual Questionnaire (PISQ-12), and Sexual Quality of Life-Female (SQOL-F) questionnaire. Significant improvements were observed in VHIS, increasing from 12 to 19.27 at 6months (p<0.001). GSM symptoms improved significantly: vaginal dryness scores decreased from 7.72±2.37 to 3.72±2.53, burning sensation scores dropped from 6.00±3.22 to 1.90±1.81, and dyspareunia scores reduced from 8.09±2.11 to 3.90±2.58 (all p<0.016). Sexual function improved, indicated by FSFI-6 scores increasing from 12.27±7.29 to 19.30±6.24 (p<0.016) and SQOL-F scores rising from 63.18±22.93 to 71.45±23.31. No adverse events were reported. Non-ablative diode laser therapy is effective and safe for managing GSM symptoms in post-menopausal women, offering significant symptom relief and enhancing sexual health without serious side effects. Further research with a larger cohort and extended follow-up is needed to confirm these findings. Clinical Trials ID NCT06503003.

Laser diode self-injection locking to an integrated high-Q Fabry-Perot microresonator.

Self-injection locking (SIL) of laser diodes to microresonators is a powerful technique that enables compact narrow-linewidth lasers. Here, we extend this technique to chip-integrated Fabry-Perot (FP) microresonators, which offer high-quality factors and large mode volumes in a compact footprint, reducing fundamental thermorefractive noise (TRN). The resonators consist of a silicon nitride waveguide terminated by two photonic crystal reflectors fabricated via scalable ultraviolet lithography. Evanescent side-coupling allows precise tuning of the SIL feedback mechanism. We present a theoretical model and experimentally demonstrate SIL, resulting in a fundamental thermorefractive-noise-limited laser. The experiments and the theoretical model are in excellent agreement. These results complement current SIL techniques and are relevant to chip-scale low-noise laser systems.

Simultaneous detection of soot, temperature, and C2H2 in laminar premixed flames using a multi-pass diode laser absorption spectrometer

We report the development of a multi-pass diode laser absorption spectroscopy system for simultaneous measurements of soot volume fraction (SVF), temperature, and C2H2 concentration using a single diode laser near 1.543 µm. A line-shaped beam spot pattern is chosen for the open-path Herriott multi-pass cavity, enabling sensitive detection at various heights above the burner with an effective optical absorption path length of approximately 1.2 m in a 6 cm diameter flame region. The gas parameters (temperature and C2H2 concentration) and the SVF are determined from the absorption spectra of the target C2H2 line pair and the laser extinction of the soot, which can be extracted from the detected signal, respectively. The performance of the system was confirmed in laminar premixed ethylene and air (C2H4/air) sooting flames produced by a standard bronze plug McKenna burner at four representative equivalence ratios. All the measurement results were compared with the two-dimensional (2D) computational fluid dynamics (CFD) simulations using a skeletal mechanism with the Moss−Brookes model. The good quantitative and qualitative agreement between the TDLAS measurements and 2D CFD simulations confirms the powerful capability of the developed system.

The efficacy of infrared diode laser in enhancing the regenerative potential of human periodontal ligament stem cells (hPDLSCs)

BackgroundThe present study aimed to investigate the effects of infrared diode laser irradiation on the proliferation and differentiation capacity of periodontal ligament stem cells (hPDLSCs), which are optimal cell sources for periodontal regeneration.MethodshPDLSCs were isolated and characterized by flow cytometric analysis of mesenchymal stem cell markers, and their trilineage differentiation capacity was tested. hPDLSCs were then cultured and irradiated with infrared diode laser (970 nm) at a power of 200 mW and a fluence of 4 J/cm2 for 3 s. MTT assay was performed to assess cellular proliferation. Cell cycle analysis was performed, and the impact of infrared diode laser irradiation on the stemness and osteogenic differentiation potential of hPDLSCs was evaluated via RT‒PCR.ResultsInfrared diode laser application enhanced the stemness, viability, proliferation, and differentiation of PDLSCs. Stem cell markers (OCT4, SOX2, and NANOG) were significantly upregulated in hPDLSCs exposed to laser irradiation. There was significant overexpression of RUNX2, ALP, OPN, and OCN on day 14 after laser application.ConclusionsThese findings provide valuable insights into the specific applications of infrared diode lasers to effectively regenerate periodontal tissues. The results can aid in the development of precise clinical protocols aimed at enhancing osseointegration and promoting tissue regeneration. Ultimately, the combination of infrared diode laser with hPDLSCs is promising for stimulating periodontal regeneration.

Design of electron blocking layer and its influence on the radial hole transport in GaN-based vertical cavity surface emitting laser diodes

Design of electron blocking layer and its influence on the radial hole transport in GaN-based vertical cavity surface emitting laser diodes

679/339.5 nm radiation generation of pr: YLF laser pumped by fiber coupled blue laser diode module

679/339.5 nm radiation generation of pr: YLF laser pumped by fiber coupled blue laser diode module

Laser Application in Surgical Treatment of Benign Prostatic Hyperplasia

Benign prostatic hyperplasia (BPH) is a prevalent condition among middle-aged and elderly men, often causing lower urinary tract symptoms (LUTS). Current treatment options encompass watchful waiting, pharmacological therapy, and surgical intervention. Among these, surgical treatment rapidly alleviates LUTS and enhances quality of life, making it the most effective approach for moderate to severe BPH. In recent years, with the rapid development and clinical application of various laser technologies, transurethral resection of the prostate (TURP), once considered the "gold standard," has faced controversies due to its higher surgical morbidity and limitations in treating large prostate volumes. Laser technologies, with their remarkable surgical efficacy, safety, and reduced morbidity, have increasingly gained favor among clinicians. This article primarily delves into the clinical advancements of diode laser minimally invasive technology in BPH treatment, aiming to provide a theoretical basis for clinicians in addressing clinical challenges.

Comparative Effectiveness of Diode Laser Therapy and Topical Turmeric Extract Ointment in Promoting Healing of Wounds in a Murine Model.

The intricate biological process of wound healing is influenced by a wide range of therapeutic techniques. In this work, the effects of topical turmeric extract ointment and diode laser therapy on wound healing in a mouse model were investigated. Out of the sixty mice, three groups of twenty male mice each were created. Three groups received treatment: the first was a control group that got no treatment; the second group received topical application of 5% curcumin twice a day; and the third group received diode laser therapy, which involved direct laser beam therapy for five minutes a day at an output power of 100 mW at an 810 nm wavelength. Over the course of two weeks, the study examined histological changes and wound closure rates. On days 0 through 14, the wound area was measured with digital calipers to provide quantifiable statistics about the process of healing. In histological analyses, epithelializations, and collagen deposition, in addition to inflammatory cells, were investigated using hematoxylin and eosin staining. It was demonstrated by comparing the outcomes to those of a control group that diode laser therapy and turmeric extract ointment are both successful therapeutic options. The results demonstrate that different therapies, while with differing degrees of effectiveness, greatly quicken the healing process of wounds. According to these results, topical turmeric extract ointment could be used as an additional or supporting therapy to aid in the healing of wounds during medical treatments.

Spectrally narrowband simultaneous dual-wavelength emission from Y-branch DBR diode lasers at 785 nm

Y-branch distributed Bragg reflector (DBR) diode lasers with a stable narrowband emission in simultaneous dual-wavelength operation with spectral distances below 3.2 nm are presented. The Y-branch laser consists of two laser branches with different DBR gratings serving as wavelength-selective rear-side mirrors. Therefore, two emission wavelengths with a spectral distance defined by the DBR grating periods can be generated simultaneously. A Y-coupler combines the two ridge waveguide (RW) branches into a single straight output RW. Devices with a spectral distance of 0.6 nm and 2.0 nm emitting around 785 nm are manufactured. Selecting the operation parameters carefully, stable narrowband emission for both wavelengths is obtained. Resistors serving as heaters implemented next to the DBR gratings allow for wavelength adjustment and a tuning of the spectral distance. At an optical output power of 100 mW, the spectral distance can be shifted from 0 to 1.55 nm (0–0.76 THz) for the former device or from 1.00 to 3.15 nm (0.49–1.54 THz) for the latter device, respectively. This makes the Y-branch DBR diode laser particularly interesting for the generation of THz beat-note signals, needed to generate THz radiation via photo-mixing.

808nm diode laser in the treatment of Hidradenitis Suppurativa: a retrospective study.

Hidradenitis suppurativa (HS) is a chronic, recurrent inflammatory disease characterized by painful lesions such as nodules, abscesses, and sinus tracts, primarily affecting intertriginous areas. Traditional treatments range from antibiotics and hormonal therapies to biologics and surgical options. Recently, lasers and light-based treatments has gained attention as a non-systemic treatment for HS, targeting hair follicles to potentially alleviate symptoms and improve quality of life. This study evaluated the efficacy of 808nm Diode laser therapy in managing HS by retrospectively reviewing data from 16 patients (13 men, 3 women) aged 23-61 who underwent between two and four sessions. Patients had not received systemic treatment in the three months preceding or during the therapy. Key outcome measures included the Modified Hidradenitis Suppurativa Score (MHSS), Hidradenitis Suppurativa Physician's Global Assessment (HS-PGA), Hidradenitis Suppurativa Clinical Response (HiSCR), and Dermatology Life Quality Index (DLQI). Results indicated a significant reduction in MHSS from a median of 20.0 before treatment to 9.0 at six months (p = 0.001). The HS-PGA score also significantly decreased from a median of 3.0 to 2.0 (p = 0.012). Of the 10 patients evaluated for HiSCR, 8 showed a positive response. DLQI scores improved from a median of 4.5 to 1.0 (p = 0.002). The treatment was well-tolerated, with only mild pain reported and no severe adverse effects. In conclusion, 808nm Diode laser therapy appears to be an effective modality for reducing disease severity and enhancing quality of life in HS patients, likely due to its anti-inflammatory effects. These findings suggest that Diode laser therapy could be a valuable addition to current HS management strategies, with further research needed to explore its long-term efficacy.

Initial experience of 980‐nm diode laser treatment for recurrent non‐muscle‐invasive bladder cancer

IntroductionLaser ablation using a 980‐nm wavelength diode laser, which is a new‐generation laser, for recurrent bladder cancer is known to have a lower incidence of complications and recurrence than conventional transurethral resection of bladder tumor surgery. This is the first study to report the use of 980‐nm diode laser ablation for recurrent non‐muscle‐invasive bladder cancer in Japan.Case presentationA 73‐year‐old man underwent transurethral laser ablation for the treatment of recurrent non‐muscle‐invasive bladder cancer. Laser irradiation was performed using LEONARDO DUAL (diode laser/980‐nm wavelength) and a 400‐μm BARE laser fiber. Pathological evaluation indicated low‐grade urothelial carcinoma, pTa. The patient was discharged on the second postoperative day with no perioperative or postoperative complications.ConclusionThis case suggests the potential of transurethral laser ablation for treating recurrent non‐muscle‐invasive bladder cancer.

Ultra‐Thin Strain‐Relieving Si1−xGex Layers Enabling III‐V Epitaxy on Si

AbstractThe explosion of artificial intelligence, the possible end of Moore's law, dawn of quantum computing, and the continued exponential growth of data communications traffic have brought new urgency to the need for laser integration on the diversified Si platform. While diode lasers on group III‐V platforms have long‐powered internet data communications and other optoelectronic technologies, direct integration with Si remains problematic. A paradigm‐shifting solution requires exploring new and unconventional materials and integration approaches. In this work, it is shown that a sub‐10‐nm ultra‐thin Si1−xGex buffer layer fabricated by an oxidative solid‐phase epitaxy process can facilitate extraordinarily efficient strain relaxation. The Si1−xGex layer is formed by ion implanting Ge into Si(111) and selectively oxidizing Si atoms in the resulting ion‐damaged layer, precipitating a fully strain‐relaxed Ge‐rich layer between the Si substrate and surface oxide. The efficient strain relaxation results from the high oxidation temperature, producing a periodic network of dislocations at the substrate interface, coinciding with modulations of the Ge content in the Si1−xGex layer and indicating the presence of defect‐mediated diffusion of Si through the layer. The epitaxial growth of high‐quality GaAs is demonstrated on this ultra‐thin Si1−xGex layer, demonstrating a promising new pathway for integrating III‐V lasers directly on the Si platform.

High-speed 3D measurement using the kinoform array and light source shift.

A new, to the best of our knowledge, fringe projector using the kinoform is proposed in this Letter. The kinoform array makes the hologram easy to manufacture, and the phase shift is realized by light source shift. The fringes can be shifted at a high speed due to the high-speed switch of the light source. An active binocular 3D measurement system using the proposed projector is demonstrated, and a binocular matching algorithm from coarse to fine using a laser speckle and fringe phase is proposed. Three laser diodes are adopted as light sources, and the three-step phase-shifting is achieved. The dimension of the projector is 30 mm × 26 mm × 12 mm and the switching speed is up to 1.5 kHz. The 3D measurement speed reaches 70 fps in the experiment.

Absorber-Free Mode-Locking of a Hybrid Integrated Diode Laser at Sub-GHz Repetition Rate

We demonstrate absorber-free passive and hybrid mode-locking at sub-GHz repetition rates, using a hybrid integrated extended cavity diode laser operating near 1550 nm. The laser is based on InP as a gain medium and a Si3N4 waveguide feedback circuit. Absorber-free Fourier domain mode-locking with ≈15 comb lines at around 0.2 mW total power is achieved with repetition rates around 500 MHz, using three highly frequency-selective micro-ring resonators that extend the on-chip cavity length to 0.6 m. To stabilize the repetition rate, hybrid mode-locking is demonstrated by weak RF modulation of the diode current. The RF injection reduces the Lorentzian linewidth component from 8.9 kHz to a detection-limited value of around 300 mHz. To measure the locking range of the repetition rate, the injected RF frequency is tuned with regard to the passive mode-locking frequency and the injected RF power is varied. The locking range increases approximately as a square-root function of the injected RF power. At 1 mW injection, a wide locking range of about 80 MHz is obtained. We also observe the laser maintaining stable mode-locking when the DC diode pump current is increased from 40 mA to 190 mA, provided that the cavity length is maintained constant with thermo-refractive tuning.

Solid-to-gas phase transition kinetics of diverse potassium occurrence forms during biomass pellet combustion: Time-resolved detection and multi-step modeling

The solid-to-gas phase transition of potassium during biomass combustion significantly impacts ash-related issues in bioenergy systems, affecting operational efficiency and equipment longevity. However, the specific mechanisms and kinetics of this transition process remain inadequately understood. This work investigates the time-resolved transition of solid-phase potassium to the gas phase during the combustion of rice husk and wheat straw pellets, combining experimental measurements with theoretical modeling. Tunable diode laser absorption spectroscopy (TDLAS) was employed to measure atomic potassium concentrations 15 mm above burning pellets tray, where gas-phase equilibrium is approached. Key combustion characteristics including thermogravimetric profiles, spectral radiation, and temperature were simultaneously monitored. A novel multi-step model was developed to describe the transition of different forms of solid-phase potassium (organic, exchangeable, and inorganic) to the gas phase. This model integrates TDLAS measurements, observed combustion characteristics, and biomass physicochemical properties. Thermodynamic equilibrium calculations were used to estimate the atomic potassium fraction from total gaseous potassium. The results showed that the solid-to-gas phase transition of organic potassium synchronizes with volatiles release. In contrast, the maximum emission rates of inorganic and exchangeable potassium occurred at the onset of char combustion. The developed model agrees well with the online detection experiments and were further validated by offline ICP analysis of residual ash. While not directly simulating gas-solid interface reactions near the particle surface, this work lays groundwork for future multi-scale modeling of particle-laden flows and reactor-scale phenomena in biomass combustion systems.