Search Results (33)

The high-repetition-rate dual-microcomb interferometry, characterized by its high precision, rapid measurement speed, and ease of integration, shows significant promise in applications such as precision spectroscopy and high-speed precision ranging. As dual-microcomb interferometry usually requires a specific difference in repetition rates, tuning the repetition rate of the microcomb is crucial for integrating dual-microcomb sources and enhancing the measurement performance, including the precision and the update rate. This work demonstrates a coherent dual-microcomb system driven by a single continuous-wave fiber laser at 1560.49 nm. The system employs a hybrid tuning method combing single-sideband (SSB) modulation for precision pump frequency control (enabling continuous repetition rate tuning across a 4.34 MHz range) with thermal control for coarse tuning. The linear dependence between the repetition rate and pump modulation frequency shows a measured coefficient of 143.58 kHz/GHz. This method enables dual microcombs with MHz-level repetition rate tuning, significantly relaxing the fabrication and pairing requirements for microresonators. The advancement is particularly valuable for dual-comb spectroscopy and ranging applications, including gas detection and satellite formation flying. 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

X-ray free electron lasers (XFELs) are the new generation of particle accelerator-based light sources, capable of producing tunable, high-power X-ray pulses that are increasingly vital across various scientific disciplines. Recently, continuous-wave (CW) XFELs driven by superconducting linear accelerators have garnered significant attention due to their ability to enhance availability by supporting multiple undulator lines simultaneously. In this paper, we introduce a novel delay system comprising four triple-bend achromats (TBAs). This delay system was combined with fast kickers and can be employed to generate electron beams on a bunch-to-bunch basis in a CW-XFEL facility. Based on the parameters of the Shanghai High-Repetition-Rate XFEL and Extreme Light Facility, start-to-end simulations demonstrate that the TBA-based delay system achieves excellent electron beam qualities while providing a wide beam-energy-tuning range from 1.39 to 8 GeV. Full article

We present a 520 μJ microsecond burst-mode pulse fiber amplifier with a GHz-tunable intra-burst repetition rate and a nearly flat-top pulse envelope. The amplifier architecture comprises a microsecond pulse seed, a high-bandwidth electro-optic modulator (EOM), two pre-amplifier stages, a waveform-compensated acoustic-optic modulator (AOM), and two main amplifier stages. To address amplified spontaneous emission (ASE) and nonlinear effects, a multistage synchronous pumping scheme that achieved a maximum energy output of 520 μJ and has a peak power of 160 W was used. To produce a flat-topped burst pulse envelope, the AOM generates an editable waveform with a leading edge and a high trailing edge to compensate for waveform distortion, resulting in a 5 μs nearly flat-top pulse envelope at maximum energy. The laser provides an adjustable intra-burst pulse repetition rate range of 1–5 GHz through the high-bandwidth EOM modulation. The intra-burst pulse jitter time of the laser remains below 4.31 ps at different frequencies. Moreover, the beam quality of the amplifier is M²x = 1.04 and M²y = 1.1. This amplifier exhibits promising potential and can be further amplified as an optical drive source for high-power, large-bandwidth microwave photon (MWP) radar applications. Meanwhile, it is also potentially applicable as a pulse source for high-speed optical communications, the high-precision processing of special materials, and LIDAR ranging. Full article

Graphene oxide (GO) and reduced graphene oxide (rGO) have emerged as robust materials in the development of SAs for erbium-doped fiber lasers (EDFLs). Their exceptional optical properties, such as broadband absorption and fast recovery times, make them ideal candidates for achieving ultrashort pulse operation in EDFLs. With its higher oxygen content, GO offers greater nonlinearity and a tunable absorption spectrum, while rGO, yielded through chemical reduction, exhibits enhanced electrical conductivity and higher saturable absorption. These properties facilitate the generation of ultrashort pulses in EDFLs, which are highly desired for various medical imaging, telecommunications, and material processing applications. This review paper comprehensively analyzes the advancements in GO and rGO SAs in the context of EDFLs for mode-locking and Q-switching applications. The performance of EDFLs utilizing GO and rGO SAs is critically evaluated, focusing on key parameters, such as modulation depth, pulse duration, repetition rate, average power, pulse energy, peak power, and signal-to-noise ratio. Additionally, this review delves into the various synthesis methods of GO and rGO thin film, highlighting their impact on the optical properties and performance of SAs. The discussion on techniques to integrate the SAs into laser cavities includes direct deposition of nanoparticles/thin-film-based SAs, tapered-fiber-based SAs, and D-shaped SAs. Furthermore, the paper explores the challenges encountered during the fabrication of ideal GO and rGO SAs, with issues related to uniformity, stability, and tunability, along with proposed solutions to address these challenges. The insights provided offer valuable guidance for future research aimed at enhancing the performance of EDFLs using GO/rGO SAs. Full article

We propose and demonstrate a photonic-assisted approach for generating arbitrary microwave waveforms based on a dual-polarization dual-parallel Mach–Zehnder modulator, offering significant advantages in terms of tunability of repetition rates and anti-dispersion capability. In order to generate diverse microwave waveforms, two sinusoidal radio frequency signals with distinct frequency relationships are applied to the dual-polarization dual-parallel Mach–Zehnder modulator. By adjusting the power of the applied sinusoidal radio frequency signal, the power ratio between these orthogonal polarized optical sidebands can be changed, and thereby desired radio frequency waveforms can be obtained after photoelectric conversion. In our proof-of-concept experiment, we systematically varied the repetition rate of triangular, rectangular and sawtooth waveforms. Meanwhile, we calculated the Root Mean Square Error (RMSE) to assess the approximation error in each waveform. The RMSEs are 0.1089, 0.2182 and 0.1185 for the triangular, rectangular and sawtooth microwave waveforms with repetition rate of 8 GHz, respectively. Furthermore, after passing through 25 km single mode fiber, the optical power decreased by approximately 5.6 dB, which verifies the anti-dispersion transmission capability of our signal generator. Full article

High-average-power narrow-linewidth tunable solid-state lasers in the wavelength region between 2 and 3 μm are attractive light sources for many applications. This paper reports a narrow-linewidth widely tunable laser system based on the polycrystalline Cr²⁺:ZnSe elements pumped by repetitively pulsed 2.1 µm Ho³⁺:YAG laser operating at a pulse rate of tens of kilohertz. An advanced procedure of ZnSe element doping and surface improvement was applied to increase the laser-induced damage threshold, which resulted in an increase in the output power of the Cr²⁺:ZnSe laser system. The high-average-power laser system comprised double master oscillators and power amplifiers: Ho³⁺:YAG and Cr²⁺:ZnSe laser oscillators, and Ho³⁺:YAG and Cr²⁺:ZnSe power amplifiers. The output wavelength was widely tuned within 2.3–2.7 µm by means of an acousto-optical tunable filter inside a Cr²⁺:ZnSe master oscillator cavity. The narrow-linewidth operation at the pulse repetition rate of 20–40 kHz in a high-quality beam with an average output power of up to 9.7 W was demonstrated. Full article

Chirped pulse amplification (CPA) has been a commonly used methodology to obtain powerful ultrashort laser pulses ever since its first demonstration. However, wavelength-tunable CPA systems are much less common. Wavelength-tunable ultrashort and intense laser pulses are desirable in various fields such as nonlinear spectroscopy and optical parametric amplification. In this work, we report a 1720 nm–1800 nm tunable CPA system based on Tm-doped fiber. The tunable CPA system contains a seed laser, a pulse stretcher, two cascaded amplifiers and a pulse compressor. The dispersion-managed seed laser cavity emits wavelength-tunable laser pulses with pulse durations of several ps and spectral widths from 25 nm to 34 nm. After being stretched temporally to tens of ps, the laser pulses are then amplified in two-stage amplifiers and compressed in a Treacy-type compressor. At 1720 nm, the maximum average power of 126 mW is obtained with a pulse duration of 507 fs; at 1800 nm, the maximum average power of 264 mW is obtained with a pulse duration of 294 fs. The pulse repetition rates are around 22.7 MHz. We perform an analysis of the system design based on numerical simulations and go on to suggest further steps for improvement. To the best of our knowledge, this is the first demonstration of a tunable CPA system beyond 1.1 μm. Considering the specific wavelength range, this wavelength-tunable CPA system is highly desirable for biomedical imaging, sensing, and parametric amplifiers. Full article

In this paper, we develop a kW-level high-repetition-rate nanosecond master oscillator power amplifier (MOPA) laser system, employing a structure of fiber, Nd:YVO₄, and Nd:YAG hybrid amplification. A tunable fiber seed source is used for adjustable pulse repetition frequency and pulse width. The Nd:YVO₄ pre-amplifier, which is dual-end-pumped, achieves high gain while maintaining good beam quality, and the high-power side-pumped Nd:YAG slab main-amplifier enables efficient power amplification. The repetition rate of the output laser can be adjusted within the range of 1~20 kHz, and the pulse width can be tuned within the range of 10~300 ns. The seed output is 6 mW at a repetition frequency of 20 kHz; we achieve an average output power of 1240 W with a total power extraction efficiency of 39.1% and single-pulse energy of 62 mJ at a pulse width of 301 ns. This parameter-controllable high-power laser holds promise for applications in the laser cleaning of complex surface contaminants. Full article

We demonstrate the utilization of iron oxide (Fe₂O₃) as light-absorbing material in an erbium-doped fiber laser (EDFL) for the generation of Q-switched pulses. A sandwich-type saturable absorber (SA) with Fe₂O₃ nanoparticles between fiber ferrules is proposed. A fiber ferrule tip is tapped onto a cap of index-matching gel, which is then dipped into Fe₂O₃ nanoparticle powder to allow its deposition through the adhesion effect. By incorporating Fe₂O₃–SA in an EDFL, self-started and stable Q-switched pulses are attained at a threshold power of 50.1 mW. The pulse repetition rate is tunable from 9.92 kHz to 22.47 kHz, whereas the pulse duration reduces from 38.4 µs to 13.8 µs with the pump power increment. The maximum pulse energy achieved is 36.9 nJ. This work offers a simple integration method of Fe₂O₃ nanoparticles as potential SAs for the generation of Q-switched pulses. Full article

As a crucial component of nonlinear polarization rotation (NPR) mode locking, optical fiber gratings offer advantages such as polarization modulation capability, stability, fiber compatibility, and preparation maturity, making them a vital technological foundation for achieving NPR mode locking. Here, a polarization-maintaining fiber helical long-period grating (PMF-HLPG) was designed and fabricated as a polarizer using the ${\mathrm{CO}}_2$-laser direct-write technique to realize the NPR effect. A homemade fiber Bragg grating (FBG) was also introduced into the laser system to enable a narrow-bandwidth lasing output and wavelength tunability. Based on the PMF-HLPG and FBG mentioned above, an all-fiber mode-locked laser with a spectra bandwidth of 0.15 nm was constructed to generate stable short pulses with a fundamental repetition rate of 12.7122 MHz and a pulse duration of 30.08 ps. In particular, its signal-to-noise ratio is up to 84.5 dB, showing the high stability of the laser. Further, the operating wavelength of the laser can be tuned from 1559.65 nm to 1560.29 nm via heating the FBG while maintaining its mode-locked state with stability. The results indicate that the PMF-HLPG could be used as a polarizer to meet the NPR mechanism for ultrashort pulse laser applications in optical communication, optical sensing, and biomedical imaging. Full article

A high-power narrow-linewidth 1.55 μm pulsed laser, based on MgO:PPLN OPO, has been achieved using a F–P etalon. The pump source is a 1064 nm acousto-optical (AO) Q-switched Nd:YAG laser with a repetition rate of 10 kHz. Under the maximum pump power of 18 W, the signal output power of 2.57 W is demonstrated at 1551.1 nm with a linewidth of 0.07 nm, corresponding to a slope efficiency of 16.1%. Different from traditional inversion lasers, the narrow-linewidth wavelength tunability of approximately 1.55 μm can be realized by changing the temperature. Full article

A tunable microwave-pulse-generation scheme is proposed and demonstrated by employing an actively mode-locked optoelectronic oscillator (OEO) based on a microwave photonic filter (MPF). The MPF mainly consists of a phase-shifted fiber Bragg grating (PS-FBG) and a phase modulator. The microwave pulse trains with variable repetition rates are achieved by injecting an external signal, of which the frequencies are equal to an integer multiple of the free spectrum range (FSR) of the OEO. The multi-mode oscillation mechanism is discussed in detail theoretically and experimentally. A microwave pulse train with a central frequency of 9.25 GHz and repetition rate of 1.68 MHz is demonstrated by setting the injecting signal frequency to be the same with the FSR of the OEO. A tunable center frequency of the microwave pulses from 5.47 GHz to 18.91 GHz can be easily generated by tuning the laser frequency benefit from adopting the MPF. Furthermore, the microwave pulses with different pulse periods of 297.62 ns, 198.69 ns, and 148.81 ns are also realized by harmonic mode-locking. The proposed tunable microwave-pulse-generation method has potential applications in the pulse Doppler radar and communications. Full article

We experimentally demonstrate a passively Q-switched wavelength tunable 2.8 μm erbium-doped fiber laser. Fe₃O₄ nanoparticles deposited on a gold mirror are used as a saturable absorber (SA). Stable Q-switched pulses within the tunable range of 2710–2810 nm are obtained. At the wavelength of 2760 nm, a maximum Q-switched output power of 188 mW is achieved with a repetition rate of 115.8 kHz and a pulse width of 1.3 μs. The corresponding pulse energy is 1.68 μJ. This demonstration shows the ability of Fe₃O₄ to function as a broadband mid-infrared SA. Full article

A tunable and compact mid-infrared optical parametric oscillator (OPO) based on BaGa₄Se₇ (BGSe) crystal with a repetition rate up to 250 Hz was demonstrated. A high energy and more approachable side-pumped Q-switched Nd:YAG laser was employed as the pump for the BGSe OPO. Due to the pump double-pass single-resonant oscillator (DP-SRO) configuration, the maximum average power of 250 mW and the maximum pulse energy of 1.28 mJ at 4.06 μm was achieved with the repetition rate of 250 Hz and 100 Hz, respectively. The tunable mid-infrared output from 3.42–4.73 μm was obtained. The influence of repetition rate and cavity length was studied and the thermal effect was analyzed. Full article