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Nickel diselenide (NiSe2) microspheres were synthesized using a chemical vapor deposition (CVD) method, and their nonlinear optical properties were investigated. The prepared NiSe2 exhibits good nonlinear characteristics, demonstrating a high modulation depth and a low saturation intensity. Then the NiSe2 was used as a saturable absorber device and integrated into a 1.5 μm erbium-doped fiber laser to generate Q-switched pulse. By optimizing the cavity dispersion and adjusting the polarization state within the cavity, the single pulse tunable Q-switched pulse, Q-switched mode-locking pulse and quasi-mode-locked pulse based on NiSe2 saturable absorber are realized. Among them, the signal-to-noise ratio of the quasi-mode-locked pulse is as high as 68 dB, which proves that the resulting pulse has high stability. The findings of this study suggest that NiSe2 SA devices have the potential to be developed as highly efficient candidates for ultrafast photonics and can find extensive applications in nonlinear optical fields. [ABSTRACT FROM AUTHOR]

The utilization of boron carbide nanoparticles (B4C) as a saturable absorber (SA) for generating pulses by a fiber laser operating in Q-switched mode is the subject of our investigation, the findings of which are presented. This was accomplished by combining boron carbide nanoparticles (B4C-NPs) with polyvinyl alcohol (PVA) to form a thin-film-based SA. This SA was then placed within an erbium-doped fiber laser (EDFL) in a ring cavity configuration to enable passive Q-switching operation. The modulation depth of the B4C-SA was 2.3%. Stable Q-switching laser operation was accomplished with a pump power of 180 mW and central wavelength of 1561 nm by producing laser pulses with a pulse duration of 15.27 µs and pulse repetition rate of 31.6 kHz. A comparable pulse energy, which was attained at the maximum pump power of 275 mW, was approximately 2.61 nJ. The radio-frequency spectrum was examined to verify the pulse stability. The study showed a signal-to-noise ratio of 35 dB. These results expand the potential of B4C-based saturable absorbers, making them strong contenders for innovative photonic devices. [ABSTRACT FROM AUTHOR]

Bound states in the continuum (BIC) are localized states coexisting with extended waves in the continuum spectrum and have infinite lifetimes without emitting radiation. In practice, symmetry‐protected BIC are usually extended to quasi‐BIC by breaking symmetry is commonly employed. A new strategy to realize the dual‐band BIC on an all‐dielectric metasurface is proposed and experimentally proved. This strategy is based on two inverse‐guided modes supported by the double asymmetric periodic gratings (dual‐APGs). In the normal incidence condition, the guided modes are bounded as radiation‐free dark states due to the symmetric incident field and the symmetric structural geometry. By importing symmetry breaking in adjacent gratings or gaps, the guided modes are coupled with radiation mode and converted into resonance states with a high Q‐factor. These two BICs modes supported by air gaps and gratings can be controlled independently. In addition, experimental observation and verification based on the non‐etching fabrication technology in the mid‐infrared band are also implemented. This work provides a new method for the realization and tuning of dual‐frequency BICs, the obtained high Q‐factor independent bi‐quasi BICs have potential applications in nonlinear optics, multi‐mode laser, and optical sensing. [ABSTRACT FROM AUTHOR]

Dielectric metasurfaces are highly sought‐after since they have found a variety of linear and nonlinear applications. Here, a novel transmission modulation is presented for pulsed laser generation by directly exploiting the enhanced Kerr effect from a periodic array of silicon nanodisks. The Mie resonance of the unit cells enhances the Kerr effect of the silicon material and is redshifted by the latter, so that the transmission of the metasurface at the working wavelength is strongly modulated (the observed modulation depth is above 3% under moderate exciting power). By inserting the fabricated metasurface as a self‐modulator into a ring cavity fiber laser, stable Q‐switched pulse laser output is achieved with a duration of 1.4 µs and a repetition rate of 60 kHz. This work opens a door for ultra‐thin low‐loss dielectric metasurfaces to efficiently shape the operation of pulsed lasing based on their enhanced nonlinear effects and flexible propagation manipulation. [ABSTRACT FROM AUTHOR]

High‐entropy alloys (HEAs) possess superior mechanical, thermal, and electronic properties, which attract great interest in the fields of photothermal, electrocatalysis, and magnetic applications. Herein, the nonlinear optical properties of FeCoNiAlTi HEA with a large specific surface area for the first time is investigated. Owing to the strong d–d interaction, the interband transition near the Fermi level could be enhanced in HEAs, leading to broadband optical absorption. Excitation with the picosecond laser source, the FeCoNiAlTi HEA possesses saturable absorption with a large modulation depth of 7.61% and 30.47% at 1 and 1.5 µm, respectively. Furthermore, at the higher excitation level at 1.5 µm, the saturable absorber exhibits a typical reverse saturable absorption property. Subsequently, the FeCoNiAlTi HEA on the tapered fiber first serves as the saturable absorber in the Yb‐doped fiber laser and the Er‐doped fiber laser, leading to the noise‐like pulses at 1 µm, and the stable Q‐switching, conventional soliton, and dissipative soliton resonance mode‐locking operations at 1.5 µm. This work confirms that the enhanced saturable absorption in HEAs can endow the high‐performance ultrashort pulse generation. [ABSTRACT FROM AUTHOR]

[Display omitted] Two-dimensional (2D) transition metal dichalcogenides are highly suitable for constructing junction photodetectors because of their suspended bond-free surface and adjustable bandgap. Additional stable layers are often used to ensure the stability of photodetectors. Unfortunately, they often increase the complexity of preparation and cause performance degradation of devices. Considering the self-passivation behavior of TaSe 2 , we designed and fabricated a novel self-powered TaSe 2 /WS 2 /TaSe 2 asymmetric heterojunction photodetector. The heterojunction photodetector shows excellent photoelectric performance and photovoltaic characteristics, achieving a high responsivity of 292 mA/W, an excellent specific detectivity of 2.43 × 1011 Jones, a considerable external quantum efficiency of 57 %, a large optical switching ratio of 2.6 × 105, a fast rise/decay time of 43/54 μs, a high open-circuit voltage of 0.23 V, and a short-circuit current of 2.28 nA under 633 nm laser irradiation at zero bias. Moreover, the device also shows a favorable optical response to 488 and 532 nm lasers. Notably, it exhibits excellent environmental long-term stability with the performance only decreasing ∼ 5.6 % after exposed to air for 3 months. This study provides a strategy for the development of air-stable self-powered photodetectors based on 2D materials. [ABSTRACT FROM AUTHOR]

In this work, we proposed a mechanical exfoliation technique to compose a saturable absorber (SA) from MAX phase chromium aluminum carbide (Cr2AlC). The performance of a passive Q‐switched erbium‐doped fiber laser (EDFL) based on Cr2AlC‐SA was experimentally demonstrated. The optical properties of SA showed appropriate nonlinear absorption, with a non‐saturable absorption of 92.5%, and saturable absorption of 1.2%. The proposed EDFL was investigated using 50:50 and 80:20 output couplers (OCs). At 167 mW pumping power and 3 dB OC, the EDFL produced pulses with 2 μs width, and 163 kHz repetition rate. Moreover, with 80:20 OC, the EDFL produced shorter laser pulses with 1.46 μs width, and 135.2 kHz pulsing rate. The results reveal that the higher repetition rate with high energy can be obtained with a 3 dB coupler, while narrower pulse width is achieved with an 80:20 OC. [ABSTRACT FROM AUTHOR]

Afterglow luminescence imaging probes, with long‐lived emission after cessation of light excitation, have drawn increasing attention in biomedical imaging field owing to their elimination of autofluorescence. However, current afterglow agents always suffer from an unsatisfactory signal intensity and complex systems consisting of multiple ingredients. To address these issues, this study reports a near‐infrared (NIR) afterglow luminophore (TPP‐DO) by chemical conjugation of an afterglow substrate and a photosensitizer acting as both an afterglow initiator and an energy relay unit into a single molecule, resulting in an intramolecular energy transfer process to improve the afterglow brightness. The constructed TPP‐DO NPs emit a strong NIR afterglow luminescence with a signal intensity of up to 108 p/s/cm2/sr at a low concentration of 10 μM and a low irradiation power density of 0.05 W/cm2, which is almost two orders of magnitude higher than most existing organic afterglow probes. The highly bright NIR afterglow luminescence with minimized background from TPP‐DO NPs allows a deep tissue penetration depth ability. Moreover, we develop a GSH‐activatable afterglow probe (Q‐TPP‐DO NPs) for ultrasensitive detection of subcutaneous tumor with the smallest tumor volume of 0.048 mm3, demonstrating the high potential for early diagnosis and imaging‐guided surgical resection of tumors. [ABSTRACT FROM AUTHOR]

Afterglow luminescence imaging probes, with long‐lived emission after cessation of light excitation, have drawn increasing attention in biomedical imaging field owing to their elimination of autofluorescence. However, current afterglow agents always suffer from an unsatisfactory signal intensity and complex systems consisting of multiple ingredients. To address these issues, this study reports a near‐infrared (NIR) afterglow luminophore (TPP‐DO) by chemical conjugation of an afterglow substrate and a photosensitizer acting as both an afterglow initiator and an energy relay unit into a single molecule, resulting in an intramolecular energy transfer process to improve the afterglow brightness. The constructed TPP‐DO NPs emit a strong NIR afterglow luminescence with a signal intensity of up to 108 p/s/cm2/sr at a low concentration of 10 μM and a low irradiation power density of 0.05 W/cm2, which is almost two orders of magnitude higher than most existing organic afterglow probes. The highly bright NIR afterglow luminescence with minimized background from TPP‐DO NPs allows a deep tissue penetration depth ability. Moreover, we develop a GSH‐activatable afterglow probe (Q‐TPP‐DO NPs) for ultrasensitive detection of subcutaneous tumor with the smallest tumor volume of 0.048 mm3, demonstrating the high potential for early diagnosis and imaging‐guided surgical resection of tumors. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate a Q-switched erbium-doped fiber laser (EDFL), which is passively produced by using a saturable absorber (SA), which is fabricated by mechanical exfoliation of MAX phase molybdenum titanium aluminum carbide (Mo2Ti2AlC3). Physical and optical properties of the SA are experimentally studied. The optical properties showed a good nonlinear absorption where the saturation intensity is 0.65 MW/cm2, with 40% of non-saturable absorption and 17% of modulation depth. The proposed EDFL is investigated using two output couplers (OCs) with split ratios of 50:50 and 80:20, respectively. For pumping power of 142 mW and coupling ratio of 50%, the proposed EDFL produced pulses with a pulse energy of 69.60 nJ, pulse width of 2.97 μs and repetition rate of 90.09 kHz. Besides, with coupling ratio of 20%, the EDFL can generate a pulse train with a pulse width of 1.91 μs, repetition rate of 77.64 kHz, and pulse energy of 89.52 nJ. [ABSTRACT FROM AUTHOR]

Two lasers of the same wavelength (1.06 µm) and various specifications were employed to synthesize silicon nanoparticles. The experimental data reveal the formation of stable silicon nanoparticles with different features such as UV-vis absorption, photoluminescence spectrum, Raman spectrum, Zeta potential, and SEM morphology. Theoretical simulations using COMSOL software were adopted to estimate the surface temperature distribution at the silicon surface and underneath. It is found that maximum temperatures of about (5700 K) and (4600 K) were generated when a Q-switched laser pulse of (10 ns) and fiber laser pulse of (127 ns) were used, respectively. While the recoil pressure at the silicon surface was (6.5*105 N/m2) and (1*103 N/m2) when Nd:YAG and fiber laser were used respectively. It found that increasing the laser energy for Nd:YAG laser and fiber laser power leads to a blue shift of the absorption spectra while the absorption intensity increases with the number of laser pulses and irradiation time. Raman spectroscopy for the prepared silicon nanoparticles was carried out. The Raman peaks for silicon nanoparticles reveal the formation of amorphous silicon. These peaks were observed at (482) and (475 cm-1) when Nd:YAG and fiber lasers were used to produce those nanoparticles. While the photoluminescence of the prepared silicon nanoparticles exhibits peaks at (457 nm) and (495 nm) for Nd:YAG and fiber lasers. The zeta potential reveals that silicon nanoparticle stability is greater for nanoparticles produced by fiber lasers (27 mv) than those produced by Nd:YAG lasers (17 mv) for three months. The corresponding silicon nanoparticle sizes refer to (3.8 nm) and (6 nm). Potential applications of silicon nanoparticles in optoelectronics and biological imaging can be conducted due to the controllable laser micro/nano machining process. [ABSTRACT FROM AUTHOR]

This present study demonstrates the utilization of an electro‐optic modulator (EOM) to actively Q‐switch the pulses produced by an all‐polarization‐maintaining (all‐PM) erbium‐doped fiber (EDF) laser (all‐PM‐EDF laser). Electrical sine waves that produced steady microsecond pulses at 1552 nm were used to power the 10 GHz bandwidth EOM. By altering the frequency of the external modulation signal and the power of the input pump, the width of the pulses produced by the all‐PM‐EDF laser (4 μs) could be further decreased to 2.6 μs. When the modulation frequency of the all‐PM‐EDF laser was 15 kHz, the highest pulse energy that it produced (145 nJ) corresponded to its highest power output (52 mW). Therefore, sources of single‐polarization pulsed lasers that are significantly resistant to mechanical and temperature disturbances can be designed by merging the configuration of an all‐PM with an EOM. [ABSTRACT FROM AUTHOR]

A two‐dimensional titanium disulfide (TiS2) nanosheet film is prepared on a YAG crystal substrate. The saturated absorption behavior of TiS2 on the YAG substrate is investigated. Then, TiS2 is successfully employed as a modulation element to develop a Tm:YAG ceramic eye‐safe pulsed laser. With a 7.04 W absorbed pump light and a 3% transmission of output coupler, the greatest average optical power, and the least pulse width (PD) are 233 mW and 524 ns, separately. The pulse repeated frequency of 69 kHz is generated, while the single pulse energy (SPE) is 3.38 µJ. Based on the experimental results, TiS2 nanosheet films possess the practical value as saturable absorbers for 2.0 μm eye‐safe pulsed lasers. [ABSTRACT FROM AUTHOR]

In this paper, we report the first Q‐switching operation utilizing black phosphorus (BP)/SnSe2 heterojunction as the saturable absorber (SA) in an Er‐doped fiber laser. The BP/SnSe2 heterojunction was prepared by the liquid phase combination method and its properties were observed. Stable Q‐switching operations were achieved based on the BP/SnSe2 SA. The maximum peak power of 71.27 mW and the minimum pulse width of 910 ns were produced, respectively. This paper demonstrates the pulse modulation characteristics of BP/SnSe2 heterojunction SA in the midinfrared region for the first time, laying an important foundation for the application of heterojunction based on BP and two‐dimensional transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

The coupling of TiO2 and phosphorus-doped carbon nanodot and their effective optical limiting applications are explored in the current study. The Z-scan technique is used for probing the characteristic optical limiting properties of the hybrid. It's interesting to point out that the optical limiting value of the P-CND/TiO2 hybrid in its crystalline phase (C-TiO2) displays a lower limiting threshold value (1.98 × 1012 Wm−2) than that of TiO2 alone (2.24 × 1012 Wm−2). The morphology of hybrids, such as the distribution of TiO2 nanoparticles on the exfoliated layers of P-CND (FE-SEM), and the characteristic bonding, Ti–O–C, of the hybrid (FT-IR), point out that there exists a synergistic coupling between the TiO2 nanoparticle and P-CND. The π-conjugated electrons and higher optical density facilitate electron/energy transfer in the hybrid. This apparently enhances the nonlinear optical absorption in C-TiO2. Compared to crystalline phase, TiO2 in the amorphous phase shows substantially lower optical limiting threshold value (1.08 × 1012 Wm−2). This is due to the enhanced oscillation strength induced by the localised excitonic interaction. Conversely, the hybrid in the amorphous phase lowers the nonlinear optical absorption value. The results of hybrids in both crystalline and amorphous phases indicated the optical limiting tunability of the materials. This suggests the use of materials in applications such as fibre optic communication, Q-switching, laser light shielding, etc. [ABSTRACT FROM AUTHOR]

The proposed titanium aluminum carbide (Ti3AlC2) film‐based saturable absorber (SA) for Q‐switching in thulium‐doped fiber laser (TDFL) cavity offers a cost‐effective and practical alternative to conventional SA materials such as graphene or semiconductor. The Ti3AlC2 film was produced using a simple and low‐cost casting approach with polyvinyl alcohol as a binder. The SA was devised from the film using a sandwich‐structured fiber‐ferrule platform and integrated into a TDFL ring cavity. The generated Q‐switched pulses were stable and had a repetition rate of up to 20.82 kHz with a minimum pulse width of 3.167 µs and a maximum pulse energy of 58.12 nJ. The Q‐switched laser produced the bright‐dark pulse pair. These results demonstrate the potential of Ti3AlC2 as a promising SA material for practical applications in the field of fiber lasers. [ABSTRACT FROM AUTHOR]

Using aqueous precursors, we report successfully fabricating thin-solid films of two nucleic acids, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). We investigated the potential of these films deposited on a fiber optic platform as all-fiber integrated saturable absorbers (SAs) for ultrafast nonlinear optics. RNA-SA performances were comparable to those of DNA-SA in terms of its nonlinear transmission, modulation depth, and saturation intensity. Upon insertion of these devices into an Erbium-doped fiber ring-laser cavity, both RNA and DNA SAs enabled efficient passive Q-switching operation. RNA-SA application further facilitated robust mode-locking and generated a transform-limited soliton pulse, exhibiting a pulse duration of 633 femtoseconds. A detailed analysis of these pulsed laser characteristics compared RNA and DNA fiber optic SAs with other nonlinear optic materials. The findings of this research establish the feasibility of utilizing RNA as a saturable absorber in ultrafast laser systems with an equal or higher potential as DNA, which presents novel possibilities for the nonlinear photonic applications of nucleic acid thin solid films. [ABSTRACT FROM AUTHOR]

We use a graphene/WS2 heterojunction as a saturable absorber (SA) in a 2 μm wavelength Thulium-doped Yttrium Aluminum perovskite (Tm:YAP) crystal-based solid-state laser and realize effective modulation performance efficiency in passive Q-switching experiments. At a pump power of 18.80 W, the measured output power is 1.293 W, with a corresponding optical–optical conversion efficiency of 6.9%. Additionally, at a pump power of 11.50 W, we achieve a pulse time of 1.16 μs at a repetition frequency of 90.36 kHz. To the best of our knowledge, this is the first demonstration of the use of graphene/WS2 heterojunctions as SA structures for 2 μm solid-state lasers based on Tm:YAP crystals. [ABSTRACT FROM AUTHOR]

The pulse laser using a saturable absorber as a passive device has the advantages of narrow pulse width, high repetition rate, and high pulse energy. Low‐dimensional materials have attracted research interest in recent years due to their excellent saturable absorption properties, ultra‐fast carrier response speed, high damage threshold, and so on. This paper gives a brief review of the state‐of‐the‐at 2 µm solid‐state lasers using saturable absorbers. The output performance of lasers in repetition rate, pulse energy, pulse width, and wavelength are summarized. The paper is expected to provide a development direction of novel materials as saturable absorbers in 2 µm solid‐state lasers. [ABSTRACT FROM AUTHOR]

Using aqueous precursors, we report successfully fabricating thin-solid films of two nucleic acids, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). We investigated the potential of these films deposited on a fiber optic platform as all-fiber integrated saturable absorbers (SAs) for ultrafast nonlinear optics. RNA-SA performances were comparable to those of DNA-SA in terms of its nonlinear transmission, modulation depth, and saturation intensity. Upon insertion of these devices into an Erbium-doped fiber ring-laser cavity, both RNA and DNA SAs enabled efficient passive Q-switching operation. RNA-SA application further facilitated robust mode-locking and generated a transform-limited soliton pulse, exhibiting a pulse duration of 633 femtoseconds. A detailed analysis of these pulsed laser characteristics compared RNA and DNA fiber optic SAs with other nonlinear optic materials. The findings of this research establish the feasibility of utilizing RNA as a saturable absorber in ultrafast laser systems with an equal or higher potential as DNA, which presents novel possibilities for the nonlinear photonic applications of nucleic acid thin solid films. [ABSTRACT FROM AUTHOR]

The research studies of e-beam sustained discharge gas lasers initiated by Nikolai Basov in early 1970s made it possible to develop lasers based on the fundamental transitions of carbon monoxide molecule with high laser power and efficiency. Soon, under his scientific supervision, lasing on first-overtone transitions of CO molecule was obtained. Following these results, about ten years ago a compact slab CO laser excited by a repetitively pulsed capacitive RF discharge and cryogenic cooling of its electrodes, operating without forced pumping of its active medium was for the first time developed at the N.G. Basov Quantum Radiophysics Division of the P.N. Lebedev Physical Institute. At present, the average power of such lasers with active medium volume of ~ 35 cm3 reaches 40 W on CO molecule fundamental transitions (in the wavelength range of 5.06–5.92 μm) and 6 W on first-overtone transitions (λ = 2.60–3.05 μm). Under Q-switching, those repetitively pulsed lasers allow one to obtain laser emission with a peak power up to 5 kW which made it possible to apply them in experiments on laser radiation frequency conversion in nonlinear crystals into the spectral range of ~ 2–20 μm. [ABSTRACT FROM AUTHOR]

In this letter, we propose a passively Q-switched all-fiber laser and demonstrate how to utilize a multimode double-clad Erbium–Ytterbium co-doped fiber as an active medium. The Q-switching is obtained based on the Kerr effect of multimode interference, which induced intensity modulation inside the linear cavity laser. Stable Q-switched pulses are obtained at 1552.3 nm with the repetition rate varying from 50.3 to 222.2 kHz, when the pump power is changed in the range from 1.00 to 3.09 W. We record the minimum pulse width and the maximum pulse energy at 2.1 μs and 2.7 μJ, respectively, at a pump power of 2.42 W. This proves a new modulation mechanism for obtaining high energy pulses based on all-fiber linear cavity. [ABSTRACT FROM AUTHOR]

In this work, we have demonstrated passive Q-switched and mode-locked erbium-doped fiber lasers (EDFLs) by using metal salt of cadmium chloride hydrate (CdCl2.xH2O) as a saturable absorber (SA). The mechanical exfoliation method was utilized to fabricate the CdCl2.xH2O-SA. The fabricated SA showed a modulation depth of 20% with a saturation intensity of 80 mW/cm2. At a pump power of 167 mW, the proposed Q-switched laser operated at 1542 nm with a maximum repetition rate of 127 kHz and a narrowest pulse width of 1.76 µs. The maximum output power was 23 mW with a signal to noise ratio (SNR) of 76 dB. On the other hand, the mode-locked pulses were generated within a pump power range of 91–167 mW, achieving a repetition rate of 990 kHz. The maximum pulse energy and output power were 7.3 nJ and 7.2 mW, respectively. The SA film demonstrated reliability and simplicity in the fabrication process. [ABSTRACT FROM AUTHOR]

Semiconductors play a critical role in optoelectronic applications, and recent research has identified group-VI 2D semiconductors as promising materials for this purpose. Here, we report the comprehensive excited state carrier dynamics of bilayer, two-dimensional (2D) selenium (Se) in one-photon and multi-photon absorption regimes using transient reflection (TR) spectroscopy. Carrier lifetime obtained from TR measurement is used to theoretically predict the photo-responsivity for 2D Se photo-detectors operating in the one-photon-absorption regime. We also calculate a giant two-photon absorption cross section of 2.9 × 10 5 GM at 750 nm hinting possible application of 2D Se as a sub-bandgap photo-detector. The carrier recombination process is dominated by surface and sub-surface defect states in one- and multi-photon absorption regimes, respectively, resulting nearly one order increased carrier lifetime in a three-photon-absorption regime (1700 ps) compared to a one-photon-absorption regime (103 ps). Femtosecond Z-scan measurement shows saturation behavior for above bandgap excitation, further indicating the possibility of 2D Se as a saturable absorber material for passive Q-switching. Our study provides comprehensive insight into the excited state carrier dynamics of bilayer 2D Se and highlights its potential as a versatile material for various linear and non-linear optoelectronic applications. [ABSTRACT FROM AUTHOR]

MXene materials have shown numerous useful mechanical and electronic properties, and have been found to possess nice potential in the field of optical modulation. Here, we fabricated a MXene Cr2C saturable absorber by the liquid-phase exfoliation method, and systemically analyzed the surface morphology and nonlinear properties of the Cr2C sample. Applying the Cr2C saturable absorber as a Q-switch in a thulium-doped yttrium aluminum perovskite (Tm: YAP) laser, the shortest single pulse was obtained with a width of 602 ns under an absorbed pump power of 3.3 W at a repetition rate of 55 kHz with a T = 1% output coupler. The maximum output power was obtained with a T = 5% output coupler at a repetition rate of 58 kHz. The obtained maximum pulse energy and peak power were 3.96 μJ and 4.36 W, separately, which reveal that the MXene Cr2C can be applied as a promising modulation material in the near-infrared pulsed lasers. [ABSTRACT FROM AUTHOR]

Chalcogenide vitreous semiconductors (ChVSs) find application in rewritable optical memory storage and optically switchable infrared photonic devices due to the possibility of fast and reversible phase transitions, as well as high refractive index and transmission in the near- and mid-infrared spectral range. Formed on such materials, laser-induced periodic surface structures (LIPSSs), open wide prospects for increasing information storage capacity and create polarization-sensitive optical elements of infrared photonics. In the present work, a possibility to produce LIPSSs under femtosecond laser irradiation (pulse duration 300 fs, wavelength 515 nm, repetition rate up to 2 kHz, pulse energy ranged 0.03 to 0.5 μJ) is demonstrated on a large (up to 5 × 5 mm2) area of arsenic sulfide (As2S3) and arsenic selenide (As2Se3) ChVS films. Scanning electron and atomic force microscopy revealed that LIPSSs with various periods (170–490 nm) and orientations can coexist within the same irradiated region as a hierarchical structure, resulting from the interference of various plasmon polariton modes generated under intense photoexcitation of nonequilibrium carriers within the film. The depth of the structures varied from 30 to 100 nm. The periods and orientations of the formed LIPSSs were numerically simulated using the Sipe–Drude approach. A good agreement of the calculations with the experimental data was achieved. [ABSTRACT FROM AUTHOR]

Mamyshev oscillators (MOs), which are based on an effective saturable absorber that arises from offset spectral filtering, are a new type of mode‐locked fiber lasers, but experimentally verifying the theory of the evolution of various dynamic characteristics of optical pulses in MOs has remained a major challenge due to the lack of appropriate filters and the means of real‐time, single‐shot experimental measurement. Here, the starting, extinction, and output dynamics of MOs are studied by designing and using a special temperature‐sensitive band‐pass filter, whose central wavelength can be continuously and accurately adjusted with temperature. The entire automated evolution of light pulses in the MO from start‐up to stable operation and then to extinction can be observed continuously by adjusting only the filter's temperature. What is more interesting is that the start‐up and the extinction processes are mirror symmetric, and both of them experience a double Q‐switching state. Further research has shown that the maximum filter interval corresponding to MO self‐starting is related to the pump power and that the bigger the pump power, the wider the filter interval. By gradually changing the interval between the two filters, the various output characteristics of the MO are also systematically studied. [ABSTRACT FROM AUTHOR]

We present investigations on output power limitations of near-diffraction-limited compact Ho 3 + :YAG laser resonators employing a homogeneous or segmented laser crystal. An approach for designing a segmented crystal is presented. Maximum output powers of 57.6 W and 51.9 W are reached with the homogeneous and segmented crystal, respectively, resulting in pulse energies of 1.14 mJ and 1.04 mJ at a repetition rate of 50 kHz in Q-switched operation. Interferometric experiments are conducted to derive the radial temperature profile for both crystals. Simulations based on a split-step beam propagation method are used to model the longitudinal temperature gradient in both crystals. [ABSTRACT FROM AUTHOR]

In our study, we employed a Mo2TiAlC2 thin film as a passive saturable absorber (SA) to create a stable pulsed fibre laser at 1564.52 nm. We synthesized a Mo2TiAlC2-PVA thin film with a 6% modulation depth and a 10 MW/cm2 saturation intensity. This thin film was integrated into the laser cavity between FC/PC fibre connectors, enabling Q-switching over a pump power range of 30 mW to 120 mW. This resulted in an increased repetition rate from 31.1 kHz to 66.83 kHz and a reduced pulse duration from 13.45 µs to 6.35 µs. The pulse train's stability was confirmed by a high signal-to-noise ratio (SNR) of 58 dB. The laser achieved a maximum output power of 6.56 mW and a pulse energy of 98.16 nJ. These results demonstrate Mo2TiAlC2 as a viable Q-switching modulator in the 1.55-µm wavelength range, with promising applications in compact and efficient pulsed fibre lasers. [ABSTRACT FROM AUTHOR]

We have demonstrated spatiotemporal pulses from a Q-switched ytterbium-doped multimode fiber laser, with a pulse energy of up to 16.5 μJ, a pulse repetition rate of 108.7 kHz, and an average output power of 1.80 W. Benefiting from the weakened spectral filtering effect, there is high pulse energy that can be produced from multimode fiber oscillators. We have observed and analyzed the evolution of multimode Q-switching with spatiotemporal correlation. Furthermore, we find that the polarization control in the saturable absorber has a modulation and selective effect on the transverse modes of the multimode fiber laser. Our results help to understand the spatiotemporal characteristics of pulsed fiber lasers and contribute to developing high-pulse energy lasers. [ABSTRACT FROM AUTHOR]

We report the feasibility of a Ti3SiC2 MAX phase material as absorber for Q-switched pulse generation in the 1550 nm region. The proposed saturable absorber (SA) is fabricated by embedding Ti3SiC2 particles into polyvinyl alcohol (PVA) thin film and incorporated into Erbium-doped fiber laser (EDFL) cavity via a sandwich-structured fiber-ferrule platform. The SA thin film exhibits a linear absorption of 3.8 dB and a modulation depth of 51% in the 1550 nm region. Using the Ti3SiC2/PVA thin filmbased SA within an EDFL ring cavity, a self-started and stable Q-switched pulse train is achieved at a wavelength of 1561.8 nm. It exhibits a maximum pulse energy of 100.7 nJ, a maximum repetition rate of 43.5 kHz, and a minimum pulse width of 5.6 μs at a pump power of 71.5 mW. This result unveils the potential of Ti3SiC2 MAX phase material for use as a low-cost and practical SA for pulse generation in the 1550 nm region. [ABSTRACT FROM AUTHOR]

Compact 589 nm yellow source was reported and generated from intracavity frequency‐doubling of c‐cut YVO4/Nd:YVO4/YVO4 Raman laser. A Cr4+:YAG/YAG composite was adopted for compact passively Q‐switching operation. Double‐end composited Nd:YVO4 crystal was designed to reduce the thermal effect and increase Raman crystal length. Both noncritical phase‐matching (NCPM) LBO crystal and critical phase‐matching (CPM) BBO crystal were used as frequency doubling crystal for comparison. 780 mW output power of 589 nm yellow emission was achieved with an incident pump power of 16 W. The pulse repetition frequency and pulse width were 41 kHz and 3.6 ns at the maximum output power, respectively. The results show passively Q‐switched operation provides a compact method to obtain 589 nm yellow emission. [ABSTRACT FROM AUTHOR]

We report an unexpected pulse repetition rate effect on ultrafast-laser modification of sodium germanate glass with the composition 22Na2O 78GeO2. While at a lower pulse repetition rate (~≤250 kHz), the inscription of nanogratings possessing form birefringence is observed under series of 105–106 pulses, a higher pulse repetition rate launches peripheral microcrystallization with precipitation of the Na2Ge4O9 phase around the laser-exposed area due to the thermal effect of femtosecond pulses via cumulative heating. Depending on the pulse energy, the repetition rate ranges corresponding to nanograting formation and microcrystallization can overlap or be separated from each other. Regardless of crystallization, the unusual growth of optical retardance in the nanogratings with the pulse repetition rate starting from a certain threshold has been revealed instead of a gradual decrease in retardance with the pulse repetition rate earlier reported for some other glasses. The repetition rate threshold of the retardance growth is shown to be inversely related to the pulse energy and to vary from ~70 to 200 kHz in the studied energy range. This effect can be presumably assigned to the chemical composition shift due to the thermal diffusion of sodium cations occurring at higher pulse repetition rates when the thermal effect of the ultrashort laser pulses becomes noticeable. [ABSTRACT FROM AUTHOR]

Thermal emission is an informative tool to study materials' properties at high temperatures under laser irradiation. The kinetics decay of laser-induced thermal emission from carbon microparticles deposited on heat-sink surfaces of transparent dielectrics (glass and sapphire) was studied. A Q-switched YAG:Nd3+ laser (pulse duration τi = 20 ns, energy/power density 0.5 J·cm-2, 25 MW·cm-2) was employed to excite thermal emission. In calculations, the classical heat conduction equation was used. With increasing the thermal conductivity of substrate (from glass to sapphire), reduction in the emission pulse duration has been observed. [ABSTRACT FROM AUTHOR]

In the paper results of single- and double-pulse LIBS (Laser-Induced Breakdown Spectroscopy) measurements in collinear geometry are described. The experiments were performed using a unique self-made Nd:YAG laser operating in the Q-switching regime, where the laser transmission losses are switched. Such a laser allowed for an easy and quick change of the operating mode (one and two pulses), free shaping of the energy ratio of the two pulses (division of the energy of a single pulse into two parts) and a smooth change of the delay time between pulses in the range from 200 ns to 10 µs. To our knowledge, such a laser was used in LIBS measurements for the first time. LIBS experiments revealed strong self-absorption depending on energy ratios carried out in the first and second laser pulse in the double-pulse mode. This was confirmed also by statistical factorial analysis of LIBS spectra. Plasma temperature and LIBS signal enhancement were measured both for energy proportions between the first and the second laser pulse and for the first-to-second-pulse delay. [ABSTRACT FROM AUTHOR]

An accurate knowledge of the optical properties of β-Ga2O3 is key to developing the full potential of this oxide for photonics applications. In particular, the dependence of these properties on temperature is still being studied. Optical micro- and nanocavities are promising for a wide range of applications. They can be created within microwires and nanowires via distributed Bragg reflectors (DBR), i.e., periodic patterns of the refractive index in dielectric materials, acting as tunable mirrors. In this work, the effect of temperature on the anisotropic refractive index of β-Ga2O3 n(λ,T) was analyzed with ellipsometry in a bulk crystal, and temperature-dependent dispersion relations were obtained, with them being fitted to Sellmeier formalism in the visible range. Micro-photoluminescence (μ-PL) spectroscopy of microcavities that developed within Cr-doped β-Ga2O3 nanowires shows the characteristic thermal shift of red–infrared Fabry–Perot optical resonances when excited with different laser powers. The origin of this shift is mainly related to the variation in the temperature of the refractive index. A comparison of these two experimental results was performed by finite-difference time-domain (FDTD) simulations, considering the exact morphology of the wires and the temperature-dependent, anisotropic refractive index. The shifts caused by temperature variations observed by μ-PL are similar, though slightly larger than those obtained with FDTD when implementing the n(λ,T) obtained with ellipsometry. The thermo-optic coefficient was calculated. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a new Q-switched thulium-doped fiber laser (TDFL) by utilizing a passive saturable absorber (SA) based on Molybdenum–Aluminium boride (MoAlB). The MoAlB is a metal–ceramic-based material; it is embedded in polyvinyl-alcohol (PVA) material to operate as the SA. The laser successfully generates stable Q-switched pulses operating at 1974.7 nm with a maximum repetition rate of 57.7 kHz and a minimum pulse width of 1.79 μs. A maximum pulse energy of 90.2 nJ is recorded at 436 mW pump power. Our experiment is the first demonstration on the use of MoAlB for the pulse laser generation in the 2 μm wavelength region. [ABSTRACT FROM AUTHOR]

The regions of stability of homogeneous generation regimes in a wide-aperture laser with a saturable absorber, including a semiconductor laser with a vertical output of radiation, are determined depending on the relative relaxation rate of carriers in active and passive media and on the frequency detunings of working transitions in these media with a resonant frequency of radiation, taking into account its polarization state. The excitation thresholds for relaxation and polarization oscillations are determined within the four-level model. [ABSTRACT FROM AUTHOR]

We demonstrate the Q-switched and mode-locked pulse generation, using Molybdenum Aluminum Boride (MoAlB) material as a saturable absorber (SA). The SA film was obtained by mixing MoAlB with a polyvinyl alcohol (PVA) solution and then evaporating the mixture on a petri-dish. The prepared MoAlB PVA thin film exhibits a saturable absorption characteristic of 10.4%. Being introduced into an Erbium-doped fiber laser (EDFL) cavity, the MoAlB PVA thin film provides a stable Q-switched pulse at 1559 nm, which is achieved by adjusting the pump power above the threshold equal to 30.2 mW. The pulse has a maximum repetition frequency of 82.92 kHz, a minimum pulse width of 2.14 μm, and a maximum energy of 27.49 nJ at the pump power equal to 83.8 mW. Also we obtain the mode-locked pulse at 1560.1 nm, when the cavity length is extended to 205 m. The repetition frequency, pulse width, and time bandwidth product of the mode-locked pulse are 0.989 MHz, 3.82 ps, and 0.329, respectively. To the best of our knowledge, this is the first time that Q-switched and mode-locked pulses are obtained in a fiber laser based on MoAlB material. [ABSTRACT FROM AUTHOR]

We demonstrate the continuous-wave and acousto-optically Q-switching performance of Ho :YVO4 laser with the diode-pumping structure. A fiber-coupled laser diode at 1.91 μm is employed as the pump source. In the continuous-wave operation, a maximum output power of 4.11 W at 2053.2 nm is achieved at an absorbed pump power of 20.4 W, corresponding to a slope efficiency of 37.6% with respect to the absorbed pump power. In the Q-switching regime, a maximum pulse energy of 1.49 mJ at absorbed pump power of 20.4 W is obtained with a pulse repetition frequency of 2 kHz. We achieve simultaneously the minimum pulse width equal to 11.9 ns and the peak power equal to 125.5 kW. [ABSTRACT FROM AUTHOR]

A silver sulfide saturable absorber (SA) was successfully employed in an Erbium‐doped fiber laser (EDFL) cavity for short and ultrashort pulse generations. The Q‐switched laser was obtained with an operation wavelength of 1566 nm, pulse rate of 93.81 kHz, and pulse duration of 1.68 μs at a 187.04 mW pump. As the EDFL cavity was optimized for mode‐locking operation by adding 100 m long single mode fiber, a stable soliton pulse train operating at 1564 nm was realized with a constant repetition rate of 1.88 MHz and pulse duration of 3.01 ps. The good nonlinear characteristics of the SA make synergetic contributions to the generation of high‐performance Q‐switched and mode‐locked lasers. [ABSTRACT FROM AUTHOR]

The goal of this investigation is to prepare zinc oxide (ZnO) nano-thin films by pulsed laser deposition (PLD) technique through Q-switching double frequency Nd:YAG laser (532 nm) wavelength, pulse frequency 6 Hz, and 300 mJ energy under vacuum conditions (10-3 torr) at room temperature. (ZnO) nano-thin films were deposited on glass substrates with different thickness of 300, 600 and 900 nm. ZnO films, were then annealed in air at a temperature of 500 °C for one hour. The results were compared with the researchers' previous theoretical study. The XRD analysis of ZnO nano-thin films indicated a hexagonal multi-crystalline wurtzite structure with preferential growth lines (100), (002), (101) for ZnO nano-thin films with different thicknesses of un-annealed samples and after annealing. While the UV-Visible spectrum manifested that the ZnO has a high absorption at UV range and wide energy gap values of (3.4, 3.42, and 3.46 eV) for the three thicknesses. The surface topography of the films evinced a rough surface which increased with increasing thickness, whereas the grain size decreased, and the average grain size was about 56.68 nm. Furthermore, the nano-thin films showed a granular morphology with a tendency to form smaller particles with increasing thickness. [ABSTRACT FROM AUTHOR]

We report the feasibility of vanadium aluminum carbide (V2AlC) for implementation as a saturable absorber (SA) for Q-switched pulse generation in Erbium-doped fiber laser (EDFL) cavity. The V2AlC, a MAX phase material is successfully combined with polyvinyl alcohol (PVA) to form a SA film for use in generating stable Q-switched pulses operating at 1559 nm with a maximum repetition rate of 53.55 kHz and a minimum pulse width of 2.54 μs. The maximum pulse energy equal to 57.14nJ is recorded at a 71.5 mW pump power. To the best of our knowledge, this is the first report of EDFL passive Q-switching using V2AlC absorber. [ABSTRACT FROM AUTHOR]

Operating regimes of an optical system consisting of a compact pulsed master diode-pumped Q-switched Nd:YAG laser and triple-crystal (KTP) ring cell of an optical parametric oscillator have been investigated. It was experimentally shown that the frequency-selective properties of a passive Q-switched unit in natural mode selection are enhanced by creating a Lyot polarization interference filter with the phase plate in the form of a laser active element with thermally induced birefringence and a polarizer. Such Lyot filter appears in the Nd:YAG laser cavity during operation at relatively high energy and repetition rate of radiation pulses (60–100 mJ, 20 Hz). The combined action of the natural mode selection process and the Lyot filter ensures stable operation of a passive Q-switched Ng:YAG laser in single-frequency lasing mode (the lasing bandwidth is <57 MHz). The master single-frequency pulsed Nd:YAG laser (λ = 1.06 μm) allows the energy of pulses applied to the input of the optical parametric oscillator to be reduced by greater than 1.5 times while maintaining the specified energy level of the output pulses (30 mJ, λ = 1.57 μm). An additional increase in the efficiency of the optical parametric oscillator conversion is achieved by introducing a two-lens 1.3× telescope into the master laser cavity. [ABSTRACT FROM AUTHOR]

The waveguide structure made of lithium niobate crystal (LiNbO3, LN) can further improve the device integration. It has been widely used in electro-optical modulator, frequency conversion, acousto-optic Q-switching and other optoelectronic devices. It has important application prospects in optical fiber communication, photoelectric sensing, lidar, aerospace and other fields. The LN waveguide made by traditional Ti diffusion method has poor resistance to photorefractive damage in short wave applications. The LN waveguide made by annealing proton exchange method only support TM mode (transverse magnetic mode) single polarization transmission, and its application field is limited. In this paper, a new Zn diffusion method is proposed to fabricate magnesium doped LN ridge waveguide. By establishing the diffusion model and simulation of the waveguide, the technological conditions were explored and tested. The lowest transmission loss of LN waveguide is 0.86 dB/cm, and the photorefractive damage threshold can reach 184 kW/cm². It will provide a better preparation way for the research and development of high power lithium niobate waveguide integrated optoelectronic devices. [ABSTRACT FROM AUTHOR]

The amplification and generation properties of erbium-doped laser crystals (Er:YAG, Er:YSGG, Cr:Er:YSGG) with a high (up to 50%) concentration of an activator ion for obtaining high-power 3-μm nanosecond laser pulses on a self-terminating transition have been studied. The measured gain in them under high-power nonselective lamp (up to 260 J) and selective diode (up to 3 J) pumping ranges from 1.2 to 2.1 and ensures the possibility of development of efficient amplifiers. It has been shown that the excitation of high-lying energy levels ( and ) is decisive for the population inversion in Er:YAG, whereas this is less important for other erbium-doped media. Pulses with an energy of 62 mJ at 10 Hz have been obtained in the ТЕМ00 mode in the developed electro-optically Q-switched Er:YAG oscillator and two single-pass amplifiers. The optomechanical Q-switching based on a rotating mirror opens access to a higher output energy due to the absence of losses in optical elements and depolarization. Single pulses with an energy of 75 mJ and a duration of 123 ns at a repletion rate of 10 Hz have been obtained in the Er:YAG laser, whereas a high gain of Cr:ErYSGG limits obtaining single nanosecond pulses with this Q-switching method. The development of such sources with high peak and average powers is of interest for terawatt chirped-pulse amplification laser systems based on iron-ion-doped chalcogenides in the mid-infrared range (3–5 μm). [ABSTRACT FROM AUTHOR]