Search Results (103)

Optimized designs of the ytterbium-doped fiber (YDF) have been effective at mitigating transverse mode instability (TMI) and enabling high-power scaling. In this study, the use of low-NA confined-doped YDFs is explored to achieve high-power nearly-single-mode continuous-wave lasers. Three types of 25/500 µm YDFs are manufactured with ~80% doping ratio and respective NAs of 0.058, 0.053, and 0.048. Experimental results indicate that the corresponding TMI thresholds increase with the descending NA in the YDFs. Based on the YDF with a NA of 0.048, the master oscillation power amplification (MOPA) fiber laser is scaled to 6.79 kW with nearly-single-mode beam quality. Full article

In this study, we present the development of a high-average-power, exceptionally stable extreme-ultraviolet (EUV) laser source based on a high-order harmonic generation (HHG) technique. The spectrum of an ytterbium-doped laser is broadened through self-phase modulation (SPM) in a gas-filled hollow fiber and compressed down to 25.3 fs for efficient harmonic generation. The high harmonics are generated in a krypton (Kr) gas cell, delivering a total power of 241 μW within the 30–60 nm spectral range, corresponding to a single harmonic output of 166 μW at a central wavelength of 46.8 nm. Notably, the system demonstrates good power stability with a root-mean-square (RMS) deviation of only 1.95% over 12 h of continuous operation. This advanced light source holds great potential for applications in nano- and quantum-material development and in semiconductor wafer defect detection. Future work aims to further enhance the output power in the 30–60 nm band to the milliwatt level, which would significantly bolster scientific research and technological development in related fields. Full article

The spectral characteristics of pump laser diodes (LDs) introduce significant ambiguity into the performance evaluation of high-power ytterbium-doped fiber lasers (YDFLs), obscuring their intrinsic efficiency and hindering reliable system design. Here, we introduce a rigorous quantitative framework that decouples these pump-induced effects by referencing laser performance to the absorbed, rather than the launched, pump power. Our analysis demonstrates that the widely reported discrepancies in conventional optical-to-optical (OO) and slope efficiencies are governed almost entirely by variations in pump absorption, while the influence of the quantum defect is negligible. This approach provides a robust metric for intrinsic laser performance that is independent of the LD’s spectral properties, proving particularly valuable for systems pumped by non-wavelength-stabilized LDs (nWS-LDs). We uncover a non-monotonic evolution of the unabsorbed residual pump power, revealing that the peak thermal load on system components occurs at an intermediate operational state, not at maximum pump power. This finding challenges conventional thermal management strategies and is critical for ensuring the long-term operational reliability of high-power YDFLs. Full article

We describe the output characteristics of a compact, passively Q-switched, diode-end-pumped (Er/Yb):Glass laser operating in a multi-pulse burst mode. Such operation enables much higher optical efficiency and larger output of total energy than possible with conventional solitary pulse emissions. The laser generated a 15-pulse burst of pulses at 1.5 μm with a combined energy of 5.8 mJ. Measurements of pulse energies, spatial mode characteristics, output beam divergence, and impact of thermal effects in the (Er/Yb):Glass are described. These results are compared to predictions of a numerical simulation using a finite-difference beam propagation method (FD-BPM) that incorporates thermal effects caused by distributed local heating in the glass. We show good agreement between the measured and simulated laser output characteristics. Full article

This study looks at the effect of surface conditioners hydrofluoric acid (HFA), Ytterbium fibre laser (YFL), and Hydroxyapatite nanoparticles (HANPs) on the surface roughness (Ra) and shear bond strength (SBS) of different viscosity resin cements to lithium disilicate glass ceramic (LDC). A total of 78 IPS Emax discs were prepared and categorized into groups based on conditioning methods. Group 1 HFA–Silane (S), Group 2: YFL-S, and Group 3: HANPs-S. A scanning electron microscope (n = 1) and profilometer (n = 5) were used on each conditioned group for the assessment of surface topography and Ra. A total of 20 LDC discs for each conditioned group were subsequently categorized into two subgroups based on the application of high- and low-viscosity dual-cured resin cement. SBS and failure mode were assessed. ANOVA and post hoc Tukey tests were employed to identify significant differences in Ra and SBS among different groups. LDC conditioned with HFA-S, HANPs-S, and YFL-S demonstrated comparable Ra scores (p > 0.05). Also, irrespective of the type of conditioning regime, the use of low-viscosity cement improves bond values when bonded to the LDC. LDC treated with YFL-S and HANPs-S can serve as an effective substitute for HFA-S in enhancing the Ra and surface characteristics of LDC. The low-viscosity resin cement demonstrated superior performance by achieving greater bond strength. Full article

In this work, we report the formation of multiple mode-locking states in an Erbium/Ytterbium co-doped fiber laser, such as domain-wall (DW) dark pulses, high-order dark harmonic pulses, dissipative soliton resonance (DSR) pulses, and dual-wavelength h-shaped pulses. By increasing the pump power and adjusting the quarter-wave retarder (QWR) plates, we experimentally achieve 310th-order harmonic dark pulses. DSR pulses emerge at a pump power of 1.01 W and remain stable up to 9.07 W, reaching a maximum pulse width of 676 ns and a pulse energy of 1.608 µJ, while Dual-wavelength h-shaped pulses have a threshold of 1.42 W and maintain stability up to 9.07 W. Using a monochromator, we confirm that these h-shaped pulses result from the superposition of a soliton-like pulse and a DSR-like pulse, emitting at different wavelengths but locked in time. The fundamental repetition rate for dark pulsing, DSR, and h-shaped pulses is 321.34 kHz. This study provides new insights into complex pulse dynamics in fiber lasers and demonstrates the versatile emission regimes achievable through precise pump and polarization control. Full article

In this paper, we report on the growth and characterization of high doping concentration (2.1 at%) ytterbium (Yb) doped lithium niobate (Yb:LiNbO₃) crystal. By using a slightly modified Czochralski method, we have successfully grown a usable size (2 mm × 2 mm × 30 mm) Yb:LiNbO₃ single crystal. We also conducted the energy-dispersive X-ray spectroscopy (EDS) and the X-ray diffraction (XRD) analyses, which experimentally confirm that the grown crystal is a Yb:LiNbO₃ single crystal. We also measured the absorption and emission spectra of the grown crystal. It was found out that there is a near-flat broad emission within a spectral range of 1004–1030 nm when excited at 980 nm for this high doping concentration Yb:LiNbO₃ crystal. Such a near-flat broad emission can be very useful for realizing high slope efficiency ultrafast (femtosecond) lasing in the Yb:LiNbO₃ crystal due to the low quantum defect of the Yb:LiNbO₃ crystal. We also investigated the electro-optic effect of the Yb:LiNbO₃. The experimental result confirms that the electro-optic (EO) effect of a highly doped (2.1 at%) lithium niobate crystal is close to the EO value of the pure lithium niobate. Thus, the highly doped Yb:LiNbO₃ crystal can still be an effective electrically tunable lasing medium. It can enable electrically tunable, high slope efficiency femtosecond lasing due to the combined features, including (1) a near flat broad emission spectrum at the spectral range of 1004–1030 nm, (2) a non-compromised electro-optic effect at high doping concentration Yb:LiNbO₃ crystal, and (3) a low quantum defect. Full article

Random lasers (RLs) based on glasses and glass-ceramics doped with rare-earth ions (REI) deserve great attention because of their specific physical properties such as large thermal stability, possibility to operate at high intensities, optical wavelength tunability, and prospects to operate Fiber-RLs, among other characteristics of interest for photonic applications. In this article, we present a brief review of experiments with RLs based on tellurite and germanate glasses and glass-ceramics doped with neodymium (Nd³⁺), erbium (Er³⁺), and ytterbium (Yb³⁺) ions. The glass samples were fabricated using the melt-quenching technique followed by controlled crystallization to achieve the glass-ceramics. Afterwards, the samples were crushed to obtain the powder samples for the RLs experiments. The experiments demonstrated RLs emissions at various wavelengths, with feedback mechanisms due to light scattering at grain/air and crystalline/glass interfaces. The phenomenon of replica symmetry breaking was verified through statistical analysis of the RLs intensity fluctuations, indicating a photonic phase-transition (corresponding to the RL threshold) analogous to the paramagnetic-to-spin glass transition in magnetic materials. The various results reported here highlight the potential of glasses and glass-ceramics for the development of RLs with improved performance in terms of reduction of laser threshold and large lifetime of the active media in comparison with organic materials. Full article

We propose and demonstrate a tunable femtosecond electro-optic optical frequency comb by shaping a continuous-wave seed laser in an all-fiber configuration. The seed laser, operating at 1.5 μm, is first cascade-phase-modulated and subsequently de-chirped to generate low-contrast pulses of approximately 8 ps at a repetition rate of 5.95 GHz. These pulses are then refined into clean, high-quality picosecond pulses using a Mamyshev regenerator. The generated source is further amplified using an erbium–ytterbium-doped fiber amplifier operating in a highly nonlinear regime, yielding output pulses compressed to around 470 fs. Tunable continuously across a 5.7~6 GHz range with a 1 MHz resolution, the picosecond pulses undergo nonlinear propagation in the final amplification stage, leading to output pulses that can be further compressed to a few hundred femtoseconds. By using a tunable bandpass filter, the center wavelength and spectral bandwidth can be flexibly tuned. This system eliminates the need for mode-locked cavities, simplifying conventional ultrafast electro-optic combs by relying solely on phase modulation, while delivering femtosecond pulses at multiple-gigahertz repetition rates. Full article

We present a reliable and all-fiberized single-polarization, high-order mode fiber laser. The experimental setup employed polarization-maintaining ytterbium-doped fibers and a combination of different fiber Bragg gratings to achieve high mode purity and stable output. The system achieved a maximum output power of 3.8 W, a polarization extinction ratio (PER) of 96.7%, and a mode purity of 95.32% for the LP₁₁ mode. Furthermore, the laser demonstrated notable stability; during a 120 min stability test, the standard deviation of the output power was measured at 0.15%, while the standard deviation of the polarization extinction ratio (PER) was 0.07%. This work offers a reliable solution for the generation of stable, high-purity LP₁₁ mode lasers. Full article

We report on the formation of homogeneous nanostructures using a two-step ablation process with square flattop beams of femtosecond (fs) laser pulses. The Gaussian beam output from a ytterbium fs laser system was converted to a square flattop beam by a refractive beam shaper and a square mask. This beam was split into two with a diffraction optical element, and then the downsized beams were spatially and temporally superimposed on a titanium surface. In the first step, the interference fringes of these two beams formed grooves with a period of 1.9 µm through ablation. Next, the surface was irradiated at normal incidence by a single beam to form a homogeneous line-like nanostructure with a period of 490 nm in a 53 μm square area. This nanostructure had a constant period and was formed over 95% of the laser-processed area, indicating that the ratio between the nanostructure and modification area was over six times larger than that for a Gaussian beam. Full article

Pulsed laser sources operating in the spectral range of 1.8 to 2.1 μm draw considerable attention due to their wide range of practical applications in many areas, including medicine, sensing, materials processing, etc. In this work, we propose a pulsed Tm-doped fiber laser scheme operating in the 2 μm spectral region with pulsed pumping at 1.57 μm. The pump source consisted of a series-connected Er-Yb pulsed master oscillator and an EDFA emitting ∼400 μs pulses with an energy of 9.3 mJ. Using this setup, we made a Tm-doped fiber laser that provided 2 mJ pulses in the 2 μm spectral region with a slope efficiency of 28% from pulses at 1.57 μm. Full article

A wavelength-switchable ring-cavity ytterbium-doped fiber laser utilizing an all-fiber Lyot interferometer filter was proposed and experimentally demonstrated. Firstly, the Lyot filter was constructed using a polarization-maintaining fiber (PMF) to obtain a comb interferometer effect, and the free spectrum ranges corresponding to 2.5 and 1 m PMF were 2.2 and 6.4 nm, respectively. Then, wavelength-switchable ytterbium-doped fiber emission was realized in the experiment, and the tunable range for the single-wavelength laser was from 1073.76 to 1086.78 nm, with a power variation of less than 1.959 dB. During the experiment, four different sets of double-wavelength lasers were achieved by adjusting the polarization controller (PC) from 1071.64 to 1081.65 nm; in addition, three different sets of triple-wavelength lasers were realized, and the signal-to-noise ratio (SNR) was more than 33.031 dB. For stable single-, double-, and triple-wavelength lasers, the power shifts were less than 0.574, 0.631, and 1.195 dB, respectively. Through adjusting the PC, quadruple-wavelength-switchable lasers could be realized with an SNR exceeding 26.233 dB. Full article

Active waveguide Bragg gratings (AWBGs) are promising photonic structures that combine the very efficient reflective properties of a Bragg grating with the power amplification character of rare earths. This combination may lead to a potential monolithic laser under the proper conditions. However, the photonic response of these structures highly depends on the grating design and operating parameters, so modeling its response for their laser performance is a must. In this work, a numerical method is employed to calculate the optical power propagation along an Er/Yb-codoped integrated AWBG. A complete database of the AWBG response as a function of the most relevant operational parameters is obtained. As a result, the critical values of each design and operating parameter to achieve its laser performance have been determined, which represents very useful information for further experimental design, optimization, and fabrication of these photonic structures. Full article

The generation of unwanted higher-order Raman effects is the main factor restricting the power scaling of Raman fiber amplifiers (RFAs). This phenomenon arises from an interplay of physical processes, including stimulated Raman scattering (SRS), four-wave mixing (FWM), and the intricate temporal and spectral dynamics. Tapered fibers have demonstrated excellent nonlinear effects suppression characteristics due to the varying core diameter along the fiber, which is widely used in ytterbium-doped fiber lasers. In this paper, a comprehensive numerical investigation is conducted on the core-pumping tapered fiber RFAs considering Raman-assisted FWM. The higher-order Raman power in the tapered fiber is always kept at a low level, showing a weak Raman-assisted FWM effect. A numerical investigation is conducted to study the impact of the tapering ratio, the lengths of the thin part, tapered region, and thick part on the higher-order Raman threshold of RFAs. Furthermore, the impact of phase mismatch variations caused by changes in the seed wavelength, on the output signal power and nonlinear effects is analyzed. This paper presents, for the first time, a study on core-pumped RFAs using tapered fibers, providing a novel perspective on enhancing the power of RFAs. Full article