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In this article, we demonstrate a high-energy, wide-spectrum, spatiotemporal mode-locked (STML) fiber laser. Unlike traditional single-mode fiber lasers, STML fiber lasers theoretically enable mode-locking with various combinations of transverse modes. The laser can deliver two different STML pulse sequences with different pulse widths, spectra and beam profiles, due to the different compositions of transverse modes in the output pulses. Moreover, we achieve a wide-spectrum pulsed output with a single-pulse energy of up to 116 nJ, by weakening the spectral filtering and utilizing self-cleaning. Strong spatial and spectral filtering are usually thought to be necessary for achieving STML. Our experiment verifies the necessity of spatial filtering for achieving STML, and we show that weakening unnecessary spectral filtering provides an effective way to increase the pulse energy and spectrum width of mode-locked fiber lasers. [ABSTRACT FROM AUTHOR]

This paper presents the investigations toward the direct use of bentonite clay (Al2H2O6Si) nanoparticles to act like a saturable absorber (SA) for the Q-switched pulse operation of an erbium-doped fiber laser (EDFL). The measured results reveal that with the incorporation of bentonite clay nanopowder as a SA, an EDFL is realized with a Q-switching mechanism starting at a pump power of 30.8 mW, and a Q-switched emission wavelength was noticed at 1562.94 nm at 142 mW pump power. With an increased pump from 30.8 mW to 278.96 mW, the temporal pulse parameters including minimum pulse duration and maximum pulse repetition rates were reported as 2.6 µs and 103.6 kHz, respectively. The highest peak power, signal-to-noise ratio, output power and pulse energy were noticed to be 16.56 mW, 51 dB, 4.6 mW, and 47 nJ, respectively, at a highest pump power of 278.96 mW. This study highlights the significance of bentonite clay (Al2H2O6Si) nanoparticles as a potential candidate for a saturable absorber for achieving nonlinear photonics applications. [ABSTRACT FROM AUTHOR]

In this article, we demonstrate a high-energy, wide-spectrum, spatiotemporal mode-locked (STML) fiber laser. Unlike traditional single-mode fiber lasers, STML fiber lasers theoretically enable mode-locking with various combinations of transverse modes. The laser can deliver two different STML pulse sequences with different pulse widths, spectra and beam profiles, due to the different compositions of transverse modes in the output pulses. Moreover, we achieve a wide-spectrum pulsed output with a single-pulse energy of up to 116 nJ, by weakening the spectral filtering and utilizing self-cleaning. Strong spatial and spectral filtering are usually thought to be necessary for achieving STML. Our experiment verifies the necessity of spatial filtering for achieving STML, and we show that weakening unnecessary spectral filtering provides an effective way to increase the pulse energy and spectrum width of mode-locked fiber lasers.

This paper presents the investigations toward the direct use of bentonite clay (Al2H2O6Si) nanoparticles to act like a saturable absorber (SA) for the Q-switched pulse operation of an erbium-doped fiber laser (EDFL). The measured results reveal that with the incorporation of bentonite clay nanopowder as a SA, an EDFL is realized with a Q-switching mechanism starting at a pump power of 30.8 mW, and a Q-switched emission wavelength was noticed at 1562.94 nm at 142 mW pump power. With an increased pump from 30.8 mW to 278.96 mW, the temporal pulse parameters including minimum pulse duration and maximum pulse repetition rates were reported as 2.6 µs and 103.6 kHz, respectively. The highest peak power, signal-to-noise ratio, output power and pulse energy were noticed to be 16.56 mW, 51 dB, 4.6 mW, and 47 nJ, respectively, at a highest pump power of 278.96 mW. This study highlights the significance of bentonite clay (Al2H2O6Si) nanoparticles as a potential candidate for a saturable absorber for achieving nonlinear photonics applications.

Passively Q-switching and mode-locking technologies can generate short pulses with durations that differ by several orders of magnitude widely used in different applications. Recently, Q-switching and mode-locking realized in an identical laser cavity with saturable absorbers was reported. The analysis of pulse conversion is helpful for us to further understand the pulse dynamics of a laser. In this paper, the pulse evolution from Q-switching, Q-switched mode-locking to mode-locking, is demonstrated by using a tungsten trioxide saturable absorber in a ring-cavity erbium-doped fiber laser. Firstly, self-started Q-switching at 1563 nm is observed, the repetition rate continuously increases, and the duration decreases when the pump power increased. Then, with an adjusting intra-cavity state of polarization under a high pump power level, stable Q-switched mode-locking pulses evolved from Q-switching, are observed. The amplitude of the emerged pulse sequence with a period of 36.8 ns, determined by cavity length, is modulated by the Q-switched envelope with the period of 10.3 μs. By optimizing the intracavity polarization carefully, stable continuous wave mode-locking operation is achieved eventually. To the best of our knowledge, this is the first experimental demonstration of Q-switching and mode-locking, respectively, in an identical transition-metal-oxides-based pulsed fiber laser without modification of cavity structure. [ABSTRACT FROM AUTHOR]

We investigated 2 and 2.9 μm mid-infrared fiber lasers passively Q-switched by MIL-68(Al) and MIL-68(Fe), which were fabricated via the hydrothermal method. The modulation depth of MIL-68(Al) was found to be 9.12% at 1.99 μm. And the modulation depths of MIL-68(Fe) were found to be 18.89% and 15.79% at 1.99 μm and 2.87 μm, respectively. We report Q-switching pulse generation in both Tm3+-doped and Ho3+/Pr3+ co-doped fiber lasers by using the as-prepared MIL-68 (M, M = Al3+, Fe3+) as SAs. The center wavelengths were at 1.99 μm and 2.87 μm, respectively. These results indicate that MIL-68(M) has wideband nonlinear optical properties and promising application prospects in the field of optical modulators at 2- and 2.9-μm mid-infrared waveband. Work clearly accessible to a broad readership.

The metal‐to‐insulator transition behavior and the fast and reversible phase transition behavior in vanadium dioxide (VO2) have attracted widespread attention to study various potential applications. However, few studies have been focused on its nonlinear properties and applications in the pulsed laser field. Here, the authors report the design and synthesis of monoclinic nano‐VO2(M) saturable absorber with broadband absorption which spans the entire near‐infrared region, and high optical nonlinearity which is much higher than those of carbon nanomaterials, gold nanocrystals, and Cu1.8S nanocrystals, as measured in the same condition. The nano‐VO2(M) optical modulators are integrated into the fiber laser cavities, and demonstrate wideband Q‐switching operations at 1, 1.56, and 2 µm and mode‐locking operation at 2 µm, with a pulse duration of 765 fs. This work first reveals the outstanding nonlinear optical properties of nano‐VO2(M) and lays a foundation for its development in advanced nonlinear optical and photonic devices. [ABSTRACT FROM AUTHOR]

Passively Q-switching and mode-locking technologies can generate short pulses with durations that differ by several orders of magnitude widely used in different applications. Recently, Q-switching and mode-locking realized in an identical laser cavity with saturable absorbers was reported. The analysis of pulse conversion is helpful for us to further understand the pulse dynamics of a laser. In this paper, the pulse evolution from Q-switching, Q-switched mode-locking to mode-locking, is demonstrated by using a tungsten trioxide saturable absorber in a ring-cavity erbium-doped fiber laser. Firstly, self-started Q-switching at 1563 nm is observed, the repetition rate continuously increases, and the duration decreases when the pump power increased. Then, with an adjusting intra-cavity state of polarization under a high pump power level, stable Q-switched mode-locking pulses evolved from Q-switching, are observed. The amplitude of the emerged pulse sequence with a period of 36.8 ns, determined by cavity length, is modulated by the Q-switched envelope with the period of 10.3 μs. By optimizing the intracavity polarization carefully, stable continuous wave mode-locking operation is achieved eventually. To the best of our knowledge, this is the first experimental demonstration of Q-switching and mode-locking, respectively, in an identical transition-metal-oxides-based pulsed fiber laser without modification of cavity structure.

High average power (>50 W) nanosecond pulsed fiber lasers are now routinely available owing to the demand for high throughput laser applications. However, in some applications, scale-up in average power has a detrimental effect on process quality due to laser-induced thermal accumulation in the workpiece. To understand the laser–material interactions in this power regime, and how best to optimize process performance and quality, we investigated the influence of laser parameters such as pulse duration, energy dose (i.e., total energy deposited per unit area), and pulse repetition frequency (PRF) on engraving 316L stainless steel. Two different laser beam scanning strategies, namely, sequential method (SM) and interlacing method (IM), were examined. For each set of parameters, the material removal rate (MRR) and average surface roughness (Sa) were measured using an Alicona 3D surface profilometer. A phenomenological model has been used to help identify the best combination of laser parameters for engraving. Specifically, this study has found that (i) the model serves as a quick way to streamline parameters for area engraving (ii) increasing the pulse duration and energy dose at certain PRF results in a high MRR, albeit with an associated increase in Sa, and (iii) the IM offers 84% reduction in surface roughness at a higher MRR compared to SM. Ultimately, high quality at high throughput engraving is demonstrated using optimized process parameters. [ABSTRACT FROM AUTHOR]

• The extracavity propagation of amplified bound-state soliton pulses. • The controllable pulse separation of bound soliton pulses affected by the SMF after the extracavity EDFA. • The evolution of pulse separation of amplified bound soliton pulses when adjusting the extracavity PC. We have experimentally investigated the extracavity propagation of amplified bound-state soliton pulses from a passively single-wall carbon nanotube mode-locked fiber laser. Under proper configuration of pump power and state of polarization, bound-state pulses exhibit a modulated optical spectrum. Except for the two main center wavelengths of 1557.3 and 1560.5 nm, additional five sidelobes centered at 1548.9, 1552.8, 1565.5, 1569.0 and 1573.1 nm are observed. Besides, the propagation after the extracavity erbium-doped fiber amplification is also investigated. It is demonstrated the significant change of the pulse separation is experimentally obtained when adjusting the extracavity PC before the autocorrelator, which is attributed to the coherent nonlinear soliton-soliton interaction. In addition, when different lengths of single-mode fiber after extracavity amplifier is removed or added, the significant change of the pulse separation is also observed, which matches well with the simulated evolution of pulse separation with respect to the SMF length. The pulse separation change of amplified bound soliton pulses is experimentally and theoretically investigated. These results provide further physical understanding of the generation and extracavity propagation of bound-state soliton pulses. [ABSTRACT FROM AUTHOR]

High average power (>50 W) nanosecond pulsed fiber lasers are now routinely available owing to the demand for high throughput laser applications. However, in some applications, scale-up in average power has a detrimental effect on process quality due to laser-induced thermal accumulation in the workpiece. To understand the laser–material interactions in this power regime, and how best to optimize process performance and quality, we investigated the influence of laser parameters such as pulse duration, energy dose (i.e., total energy deposited per unit area), and pulse repetition frequency (PRF) on engraving 316L stainless steel. Two different laser beam scanning strategies, namely, sequential method (SM) and interlacing method (IM), were examined. For each set of parameters, the material removal rate (MRR) and average surface roughness (Sa) were measured using an Alicona 3D surface profilometer. A phenomenological model has been used to help identify the best combination of laser parameters for engraving. Specifically, this study has found that (i) the model serves as a quick way to streamline parameters for area engraving (ii) increasing the pulse duration and energy dose at certain PRF results in a high MRR, albeit with an associated increase in Sa, and (iii) the IM offers 84% reduction in surface roughness at a higher MRR compared to SM. Ultimately, high quality at high throughput engraving is demonstrated using optimized process parameters.

Abstract: The coherent beam addition of pulsed fiber lasers is an effective way to improve the average power and the peak pulse power. We demonstrate a new architecture based on mutual injection and phase modulation to generate synchronous pulsed fiber lasers. Firstly, we realize the synchronization of the pulses of three fiber lasers using this technique. Secondly, coherent addition of three synchronous pulsed fiber lasers is obtained. Experimental results show that the three fiber lasers are phase locked and have good temporal and spatial coherence under mutual injection locking. This method can be extended to combine more beams. [Copyright &y& Elsevier]

Innovative new method for the pulsed laser assisted radio-frequency sputtering at low temperature process was successfully applied for the β phase Ga 2 O 3 thin film as wide band gap materials. Thin film of wide bandgap material, β-Ga 2 O 3 , was successfully deposited on SiO 2 /Si and quartz substrates by employing radio-frequency sputtering system with assisting process of ytterbium-laser irradiation. Both sputtering system and infrared pulsed laser irradiation process were employed at the same time to increase the acquired energy densities for the adatoms on the thin film growth process. X-ray diffraction patterns (XRD) showed the prominent peaks of unique crystalline properties of Ga 2 O 3 thin films in β phase. The optical energy bandgap of Ga 2 O 3 thin films derived from spectral transmittance was measured in the range of 4.90–5.06 eV for a variation of laser power. High resolution X-ray photon spectroscopy (XPS) analysis showed that O 1s and Ga 3d position in core level. We confirm that infrared optical energy was effectively added to fabricate β-Ga 2 O 3 thin film by employing the Yb-laser-assisted RF sputtering process. • Innovative new method based on laser assisted RF sputter system was designed and demonstrated. • For the first time, β-Ga 2 O 3 film was deposited by laser assisted rf-sputtering process at low temp. • RTA annealing and laser irradiation effects for the thin film process were measured and analysed. • Successful synthesis of β phase Ga 2 O 3 thin film was proved by XRD and XPS analysis. [ABSTRACT FROM AUTHOR]

For the first time, we demonstrate a novel passively mode-locked fiber laser operating at 1300 nm using purified single-walled carbon nanotubes (CNTs) as a saturable absorber. The saturable absorber incorporates diameter-controlled CNTs with peak absorption ∼1300 nm, guaranteeing mode-locking over the same wavelength region. The ring laser uses praseodymium-doped fiber as a gain medium. The pulse repetition rate is 3.18 MHz, and the spectral half-width is 0.15 nm. Dual-wavelength mode-locking is also demonstrated with a channel spacing of 1.1 nm. [ABSTRACT FROM PUBLISHER]