We present an integrated repetition rate tunable Yb-fiber laser system delivering microjoule pulses with compressed pulse duration below 350 fs. The system uses a chirped fiber Bragg grating as fiber stretcher, which is specially designed to match the second and third order dispersion of transmission grating pair compressor with a groove density of 1740 l/mm. 1 μJ pulse in 266 fs and 10 μJ pulse in 325 fs pulse duration are obtained at rep-rate of 2 MHz and 200 kHz, respectively. The pulse rep-rate can be tuned from 200 kHz to 2 MHz while maintaining ⪅350 fs microjoule pulses output. This rep-rate tunable, μJ-level fiber laser source is built for applications in ophthalmology, such as cornea flap cutting and tissue vaporization.

In this work, we investigated an active ytterbium double-clad tapered spun fiber with low intrinsic birefringence (1.45×10⁻⁸ rad/m) and a mode field diameter of 35 μm. These fiber properties significantly increase the nonlinear threshold in amplifiers, enabling high average and peak output powers. The low birefringence also ensures stable output polarization despite variations in pump power. We demonstrated a MOPA system based on this fiber, operating at 1040 nm, achieving a peak power of 160 kW (50 ps pulses at 20 MHz, 160 W average power, 63% slope efficiency) with high beam quality (M² = 1.15 at 115 W). We explored polarization changes under pump power up to 270 W at 976 nm, finding that polarization drift due to heating (quantum defect) caused minimal azimuth and ellipticity changes. The degradation in DOP was attributed to unpolarized ASE rather than fiber polarization properties. Over two hours, polarization drift was minimal, with azimuth and ellipticity deviations of 0.4° and 0.5°, and a DOP variation of 1.5%.

This paper presents all-fiber master oscillator-power amplifier systems that deliver high average power picosecond pulses with durations of 6 to 50ps, a tunable repetition rate within 360 kHz to 1 GHz range, and peak powers of up to 2 MW. The experimental investigations incorporate two Yb-doped spun tapered double-clad fibers gain modules with 60 μm and 92 μm core diameters. Utilizing the 92 μm core module picosecond pulses with high average power of 625 W average power at 20 MHz, and 645 W at 1 GHz were achieved. The gain module with 60 μm core diameter enabled to deliver a high peak power pulsed- signal with 2 MW peak power at 360 kHz and 50 ps pulse duration, while 26 MHz and 6 ps pulses reached 1 MW peak power. In all configurations, near-diffraction-limited beam quality, M² ⪅ 1.4, was maintained without any traces of Transverse Mode Instability (TMI). These compact, TMI-free, high-power amplifiers offer a promising platform for high-power ultrafast fiber lasers for the vast majority of industrial applications.

The Yb-doped thin-disk laser is an ultrashort pulsed laser source with the highest average output power and pulse energy at present, due to its small thermo-optical distortion and nonlinear optical effects suppression. Although Yb:YAG has been widely used as a gain medium in thin-disk lasers, its narrow fluorescence bandwidth has limited availability of shorter pulses. Therefore, we are developing a thin-disk laser using a potassium double tungstate gain medium, Yb:KREW (Yb:KRE(WO4)2, RE = Y, Gd, Lu) for future applications to broadband ultrashort pulse laser oscillators and amplifiers. Yb:KREW is a promising group of gain media that combines a wide gain bandwidth and high gain coefficient, while they have drawbacks such as strong anisotropy in thermal and mechanical properties. In this study, we demonstrated the first Kerr lens mode-locked thin-disk laser operation with one of the tungstates gain media, Yb:KLuW by reducing anisotropic thermal distortion through low thermal resistance bonding techniques. Under OC transmittance of 0.6% and GDD-1400 fs2 conditions, the pulse duration of 48.9 fs and spectral bandwidth of 32.0 nm were demonstrated. This is the first KLM thin-disk laser demonstration of this material and its family (Yb-doped tungstate-based gain medium), and the pulse duration obtained was the smallest value using the same material reported so far. The average power, however, was limited to 425 mW by the low OC transmittance. In the future, through optimization of the cavity, further increases in power output are expected while maintaining the short pulse duration.

We present the design and construction of a mode-locked Master Oscillator Power Amplifier (MOPA) laser system, featuring a passive mode-locked oscillator operating at 1064 nm and a novel single-stage power amplifier with up to 40 dB gain. The amplifier delivers over 500 W peak power through a single-mode, 6 μm core Polarization-Maintaining (PM) fiber, producing 10 ps pulses with an ideal Gaussian beam profile. Amplified Spontaneous Emission (ASE) is effectively suppressed to -50 dB relative to the laser signal in the output spectrum. The system has demonstrated stable operation for over 10,000 hours, including continuous operation and intermittent on-off cycling. Throughout this period, no variations in self-starting behavior, output power, wavelength, or spectral bandwidth were observed.

We experimentally investigated the build-up dynamics of single-cavity dual-wavelength-comb pulses emitted from a ring fiber cavity with Lyot filter configuration. Dual-wavelength lasers are firstly observed by adjusting the polarization controller to control Lyot filter effect. When the pump powers of the bidirectional pumps are set as 57 mW and 49 mW respectively, dual-wavelength pulses with the center wavelengths of 1546.2 nm and 1563.6 nm and spectral bandwidths of 2 nm and 1.6 nm are obtained. Subsequently, time-stretched dispersive Fourier transform spectroscopy is adopted to monitor the build-up process of dual-wavelength pulses. When switching on the pump diode, the three-stage build-up process from background noise to stable dual-wavelength pulses is experimentally observed. The build-up time is at the level of hundreds of milliseconds. These results provide a deep understanding of single-cavity dual-wavelength-comb pulse generation and contribute to the design and control of the single-cavity dual-comb pulses.

We proposed the triple-wavelength pulses across the 1530- and 1550-nm gain regions are emitted from a carbon nanotube mode-locked ring fiber laser by simultaneously exploiting intracavity loss-based gain profile tuning, Lyot filter effect, and nonlinear polarization evolution. A polarization beam splitter with 2×1-m intracavity polarization-maintaining fiber pigtails is additionally introduced in a typical ring fiber cavity. Polarization-dependent loss is firstly adjusted to equalize the 1530- and 1550-nm gain regions. Except for the triple-wavelength pulses based on Lyot filter and loss-based gain profile tuning, another type of triple-wavelength pulses, i.e. single-wavelength pulse centered at 1530-nm gain region and spectral-overlapping dual-wavelength pulses centered at 1550-nm gain region, are observed by additionally introducing nonlinear polarization evolution. These intriguing results show the feasibility of multi-wavelength pulse generation based on multiple soliton formation mechanisms and the high potential to construct a single-cavity multiple-comb source with versatile pulse characteristics.

We devise and implement two variants of mid-infrared Optical Parametric Oscillators (OPOs) based on a polarization-maintaining fiber-feedback cavity, which allow to robustly deliver sub-picosecond MIR pulses without the need of active stabilization. The first one integrates an erbium-doped fiber into the OPO cavity as the additional gain medium. The synergistic dual-gain operation significantly reduces the pump threshold to launch a stable MIR pulse formation. The other OPO configuration adopts a chirped-poling nonlinear crystal in a passive-fiber cavity to achieve a broader operational spectral range. The wide phase-matching bandwidth facilitates easy wavelength tuning by simply adjusting the cavity length through the dispersion filtering effect. Therefore, the presented mid-infrared OPO source is featured with high compactness, robust operation, and wide tunability, which would be attractive for subsequent applications, such as infrared photonics, biomedical examination, and molecular spectroscopy.

We demonstrate a low threshold 0.5 at.%-doped Er: YAG micro-NPRO with a short round-trip path length designed to reduce the effects of Energy-Transfer Upconversion (ETU) and reabsorption. A single-frequency laser output of up to 354 mW at 1645 nm was achieved using a 1470 nm LD with a pump power of 3.5 W through resonant pumping, corresponding to a slope efficiency of 44.6% and threshold pump power of 2.7W.

A high-energy 588 nm yellow laser based on external-cavity frequency doubling of Raman amplifier was demonstrated. First, a 40 mJ pure high-performance 1177 nm first-order Stokes seed light was achieved with a KGd(WO₄)₂ (KGW) Raman oscillator pumped by 1064 nm pulse laser. Then, a single-pass KGW Raman amplifier scheme was employed to obtain 152 mJ 1177nm Raman output. Finally, by external-cavity frequency doubling with an LBO crystal, a 74.1 mJ Raman yellow laser at 588nm with a pulse duration of 10.4 ns was obtained under the total 1064 nm pumping energy of 650 mJ. The corresponding optical to optical conversion efficiency was 11.4%.

We experimentally demonstrated a fast and effective intelligent optimization algorithm to obtain the self-correcting ultrashort pulse emission from a nonlinear polarization rotation mode-lock fiber laser. The temporal trace corresponding to the optical spectrum is measured by the time-stretched dispersive Fourier transform technique, which functions as the monitoring signal. Subsequently, the genetic algorithm is proposed to finely control the electronic polarization controller for self-correcting pulse generation. The target state could be realized after five generations of iterations. By combining dispersive Fourier transform technique and genetic algorithms, the total adjustment time can be minimized to six seconds. These findings indicate an effective route to obtain robust and self-correcting ultrashort fiber lasers.

Notch filter serves as a vital optical filter, selectively blocking specific wavelength bands while transmitting both shorter and longer wavelengths. Traditional notch filter, designed by alternating layers of high and low refractive index materials, often suffer from undesired higher-order reflection bands. To address this problem, rugate filters with a sinusoidal variation in refractive index eliminate this issue. The refractive index distribution will affect the performance of the notch film. Therefore, the impact of refractive index distribution on the sidelobes of rugate filters was investigated using a developed software. The factors influencing the bandwidth and reflectance of rugate filters were also investigated. It was found that the sinusoidal index distribution modulation function could be more effective in sidelobe suppression. Furthermore, we found that index distribution modulation function decreases the reflectance of the reflection band, and the bandwidth was determined by maximum refractive index contrast. Additionally, we proposed a method for designing arbitrary multi-band rugate filters.

The Dispersive Mirrors (DMs) offer high reflectivity and precise control of dispersion compensation, making them essential elements in ultrashort pulse systems. With the development of ultrashort pulse technology, the dispersion oscillations of the DMs become more stronger with the increase of the dispersion compensation bandwidth and target group delay dispersion (GDD) value. To reduce the GDD oscillation of DMs, two pairs of chirped mirrors with a central wavelength of 800 nm and a bandwidth of about 200 nm were designed and fabricated, which provide about -100fs² and -200fs² GDD respectively in the wavelength range of 700-900 nm. The GDD oscillation is reduced from ±100 fs² for a single chirped mirror to nearly 0 fs² using chirped mirror pairs. The chirped mirror pairs were fabricated by dual-ion beam sputtering deposition, and their GDD was tested with a white light interferometer. To verify the compression performance, we simulated the propagation of a Gaussian pulse through our chirped mirrors. We added +1200 fs² of positive dispersion to a Gaussian pulse at the Fourier transform limit and reflected it 12 times on a pair of fabricated chirped mirrors with a GDD of -100 fs². The simulated results showed that the fabricated chirped mirror pairs closely match the design specifications and effectively reduce the oscillation of GDD.

Vortex beams have been applied in multiple engineering and scientific applications due to their distinctive orbit angular momentum and vortex phase characteristics. Traditional methods suffer from complicated setup for the generation of vortex beams not only costly but also non-scalable. In this study, we propose a novel approach for the direct generation of vortex beams and coaxial muti-vortex beams through the use of laser resonator mirror. We have designed a diffractive output mirror of the laser resonator using Gerchberg-Saxton (GS) algorithm inspired by the mode matching theory and optical diffraction principles. Through the analysis of the pumping power in a four-level laser configuration, we have established correlations between ring-shaped pumping light and target vortex beam characteristics, thereby providing essential design guidelines for vortex beam generation within resonators.

The periodical pulse bundles were presented in a Yb-doped double-clad distributed Bragg reflector all-fiber configuration. With a pumped power of 529.2 mW, the periodical pulse bundles is obtained. Furthermore, a single pulse bundle composes of one main pulse and two sub-pulses. The pulse width of the main pulse and the sub-pulse are 2.2 μs and 7.7 μs, respectively. The separations of between main pulse, right sub-pulse and left are 22.70 μs and 22.15 μs, respectively. The average period of the pulse bundle is approximately 75 μs with repetition rate of 13.3 kHz. The number of sub-pulses between adjacent main pulses decreases to one when the pumped power does to 450.2mW. When the pumped power increases to 594.4 mW, the number goes to three.

Frequency stability of laser sources is critical in ensuring laser-based measurement accuracy and reliability. In this paper, we report a method to assure high frequency stability of multi-wavelength lasers through the Pound-Drever-Hall technique. Three lasers with wavelength spacing of about 5G and 15nm around 1.55μm were simultaneously locked to the same Fabry-Pérot cavity with free spectral range of 5G. When locked, the laser frequencies were observed to drift all within 200 kHz, validating the feasibility of the system design. Frequency-locking of more lasers with different wavelengths can be realized to satisfy the requirement of different applications in this way.

Broadband lasers have extensive applications in many fields such as spectroscopy, photochemistry, medicine, and biology, so they have obtained significant attention, particularly for their enormous potential in broadband imaging, pollution monitoring, and semiconductor material processing. This paper presents a 1-micron femtosecond laser with a broadened spectrum, achieved by integrating both intracavity and extracavity spectral broadening methods. Initially, a 1-micron single-mode fiber is introduced into the laser cavity to reduce the total dispersion. Subsequently, the collimated output laser is directed onto a negative dispersion grating. After being reflected by the dual grating system, the laser is measured, all while maintaining a stable mode-locked state. To address spectral distortion caused by the loss in non-target gain intervals, dual filtering is employed to retain only the 1064 nm gain interval. Through the balance between these two negative dispersions, the laser’s spectral width is expanded by approximately six times from its original 5 nm to 30 nm. During the experiments, the laser demonstrated remarkable stability and compared to using only intracavity single-mode fiber expansion or extracavity grating expansion, this approach offers superior results and greater potential. It aids in the precise measurement of pollutants and plays a crucial role in enhancing the resolution of broadband imaging.

Precise dispersion measurement is important for various applications, including optical communications, laser cavity design, and nonlinear optics. In this work, we present a dispersion measurement method for the fiber under test inside the Fourier Domain Mode-Locked (FDML) laser by locating the sweet spot regime under the different driving frequencies of the Fabry-Perot tunable filter. The group delay resolution achieved is 2.88 ps, an order of magnitude higher than other dispersion measurement methods based on phase shift or pulse delay. The proposed dispersion measurement method has high resolution and simple configuration, making it promising for measuring the dispersion of special fibers or conventional fibers near their zero-dispersion wavelengths.

In this work, thermal injection was used to create CsPbBr1.8I1.2 perovskite Quantum Dots (QDs). The nonlinear optical characteristics and morphology of the quantum dots were characterized. A passively mode-locked Nd:YVO₄ laser operating at 1064 nm was able to run consistently with the use of CsPbBr_1.8I_1.2 QDs SA. The passively mode-locked pulse output with a maximum output power of 287 mW and a repetition frequency of 80.645 MHZ was attained at a pump power of 3.3 W.

In this paper we report on a simple method for characterizing ultrashort vortex laser pulses generated from Erbium-doped fiber laser. The single-mode fiber oscillator can produce mode-locked pluses with duration of 316 fs around 1550 nm. By passing linearly polarized TEM00 Gaussian mode-locked pulses through vortex retarders, ultrashort vortex laser pulses are created, and the topological charge numbers of the vortex beams are characterized through far field multi-pinhole interferometer. The experiment results agree well with simulation. This diagnostic method will benefit vortex beam generation and advance its application for ultrafast science.

In high-power laser systems, ultra-short laser pulses commonly possess broad spectral bandwidths, leading to space-time coupling effects when interacting with optical elements, which can alter the quality of pulses. Traditional measurement techniques for characterizing these pulses often rely on time-consuming scanning methods or are restricted by limited spectral channels, making them unsuitable for broad-spectral, space-time measurements. To address these limitations, this paper introduces a model combining snapshot compressive imaging and quadri-wave lateral shearing for broad-spectral space-time measurements. Our analysis focuses on the effects of the number of channels, the number of code patterns, and the ratio of the interference points to coded pixel size on measurement accuracy. Utilizing the TWIST-TV algorithm and Fourier phase retrieval, we can reconstruct wavefront over a wide spectral range of 100 nm across 100 channels with RMSE of up to 0.012λ. The research establishes guidelines to maximize recovery accuracy, marking a substantial advancement in broad-spectral space-time field measurement technology.

Based on PbS quantum dots and single-walled carbon nanotube, we have successfully demonstrated a Er-doped fiber laser capable of switching between two different types of output pulses. By finely adjusting both the pump power and the states of polarization controller, flexible switchable Q-switched and mode-locked pulses can be achieved. At pump power of 29 mW, Q-switched pulses are obtained at a central wavelength of 1560.2 nm. When the pump power increases from 29 mW to 92 mW, the Q-switched rate varies from 25 kHz to 75.22 kHz. Accordingly, the output pulse energy rises from 3 nJ to 5.46 nJ, and the output power changes from 0.08 mW to 0.41 mW. When the pump power is set in the ranges of 92 mW to 107 mW, the fiber laser enters the transition region of Q-switching operation. In this region, evident Q-switched instability with large fluctuations is observed, which is independent of the polarization states. When the laser pump power exceeds 107 mW, the Q-switched pulse disappears, and mode-locked pulses are obtained by altering the state of the polarization controller. The central wavelength of the mode-locked pulses output spectrum is 1561.1 nm, and the corresponding 3 dB spectral bandwidth is 4.22 nm. Coupled Ginzburg-Landau equation are provided to reveal the underlying principles of the transition of these pulse trains. Our work provides a new prospect for achieving fiber lasers capable of flexibly switching output pulse types, further expanding their applications in fields such as laser microprocessing, optical communication and medical lasers.

Recently, the nonlinear multimodal interference-based all fiber saturable absorber has been the focus of attention on ultrafast fiber lasers, owing to its intriguing properties of versatility, high damage threshold and instantaneous response time. Although, challenges present in the technology, such as complex perturbation induced by quasi-degenerate modes in multimode fiber, it is presented as an effective solution to control the output characterization and study the nonlinear dynamics in fiber lasers. In this work, we experimentally and numerically demonstrate the spectral sidebands in a passively Er-doped fiber laser based on multimodal interference technique. Kelly-type and triangular-type sidebands are achieved, and can be switchable by changing the polarization states of cavity, which are asymmetric distribution on both sides of the output spectrum. When the polarization states are varied, a wide sideband is obtained, which the width of sideband can be tuned from 0.13 nm to 2.3 nm. Coupled complex Ginzburg-Landau equation are provided to reveal the underlying principles of the tunable features in sidebands. The results of numerical simulation show the relevance between filtering induced by modal interference, high-order dispersion, polarization modal dispersion and experimental results. Our work lays a foundation for understanding of nonlinear dynamics in mode locking fiber lasers based on multimodal interference effect and provides a new way to generating versatile ultrafast source in engineering and scientific research.

High-quality, ultrafast fiber lasers have long been favored by both research and industry for many desirable properties. Here, we present an Yb-doped fiber laser system by utilizing a directly spliced photonic crystal fiber to amplify a seed source, and sub-100 fs ultrashort pulses are obtained with an average power of 6.55 W and at a repetition rate of 100.15 MHz. The M2 factors are measured to be about M_x^2=1.13 an M_y^2=1.12, respectively. The standard deviation of output power over a 2.5-hour period is determined to be 0.72 % and no significant wavelength drifts or intensity fluctuations are observed. These results demonstrate the promising potential of this compact fiber laser system for both research and industrial applications.

In response to the significant demand for high-damage threshold, broadband high-reflection films for high-power laser systems, composite high-reflection films have been developed. The composite high-reflection films combine the advantages of high-damage threshold materials with the advantages of high-refractive index materials by adding several cycles of high-damage threshold material Al₂O₃/SiO₂ on the surface of traditional Ta₂O₅/SiO₂ high-reflection films. The impact of the number of the Al₂O₃/SiO₂ protective layer cycles on the damage resistance of the composite high-reflection films in the 532nm band is examined. The 1-on-1 laser damage test demonstrated that there was no significant distinction in the laser damage threshold of the composite films with three or six cycles of protective layer. This was primarily due to the presence of various impurities and defects in the films. Six cycles of protective layer protection were found to be more effective. All laser damage of the composite films with six cycles protective layer was observed to occur within the protective layer. Moreover, the interface of Al₂O₃/SiO₂ and Ta₂O₅/SiO₂ was identified as a potential weak region in the composite films. This study provides a valuable reference for the subsequent application of composite dielectric films in high-power laser systems.

Molecular alignment and orientation are two special rotation states of gaseous molecules. Nowdays, molecular alignment and orientation has been a hot topic of atoms, molecules and optical physics since they not only can reveal the deep quantum mechanisms of the molecules in the external field but also pave a way for the quantum information science, intense field physics. Here, we investigate the molecular alignment of gaseous carbon monoxide (CO) induced by the near-infrared few-cycle laser pulses through nonresonant process by numerical methods. The Hamiltonian of the molecules in the ultrashort laser pulses is obtained based on the rigid rotor approximation theory, then the time-dependent Schrodinger equation of the system is solved by split-step Fourier transform. It is found that the momentum of the molecules increases rapidly in a very short time, and then keeps stably for a long time; the alignment degree of molecules is an oscillation signal in the time domain even the laser pulses have propagated away. The alignment degree is transformed into the frequency domain to explore the deep mechanisms. The relationship between the laser wavelength and the alignment degree is also discussed based on the simulation results. This work might help to understand the interactions between the gaseous diatomic molecules and few-cycle laser pulse.

We demonstrate 1.54 W of laser emission at 905 nm from a fully fiber-based polarization-maintained master oscillator power amplifier (MOPA). The laser system comprises a directly modulated Fabry-Perot laser diode emitting at 905 nm, which is subsequently amplified by a three-stage pre-amplifier and a main amplifier. The system achieved an output energy of 0.15 mJ at a repetition frequency of 10 kHz with a pulse width of 20 ns.