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Mode-locked lasers with low noise performance, such as low timing jitter and relative intensity noise are essential for high-precision applications. In this letter, we demonstrated a 122-MHz all-polarization-maintaining mode-locked Er-doped fiber laser based on a nonlinear amplifying loop mirror. A hybrid component integrating a wavelength division multiplexer and a phase shifter is applied to increase the repetition rate. The relative intensity noise is 0.004% and 0.76% rms (integrated from 1 MHz to 100 Hz) from two output ports. The timing jitter characteristic is measured by the delayed optical heterodyne method. The timing jitter is ~1.9 fs rms (integrated from 1 MHz to 10 Hz) of both two output ports. The origin of the timing jitter of this laser is analyzed numerically based on the well-established theoretical model using the laser’s repetition rate, cavity dispersion, etc.

When a laser cavity supports the propagation of several ultrashort pulses, these pulses interact and can form compact bound states called soliton molecules. Soliton molecules are fascinating objects of nonlinear science, which present striking analogies with their matter molecules counterparts. The soliton pair, composed of two identical pulses, constitutes the chief soliton molecule of fundamental interest. The relative timing and phase between the two propagating pulses are the most salient internal degrees of freedom of the soliton molecule. These two internal degrees of freedom allow self-oscillating soliton molecules, which have indeed been repeatedly observed, whereas the lowdimensional chaotic dynamics of a soliton-pair molecule remains elusive, noting that it would require at least three degrees of freedom. We here report the observation of chaotic soliton-pair molecules within an ultrafast fiber laser, by means of a direct measurement of the relative optical pulse separation with sub-femtosecond precision in real time. Moreover, we demonstrate an all-optical control of the chaotic dynamics followed by the soliton molecule, by injecting a modulated optical signal that resynchronizes the internal periodic vibration of soliton molecule., 11 pages, 5 figures

We demonstrate that our theoretical scheme developed in the previous study on the caustics of the abruptly autofocusing vortex beams [Xiao et al., Opt. Express 29, 19975 (2021)10.1364/OE.430497] is universal for all the axially symmetric vortex beams. Further analyses based on this method show the complex compositions of the vortex caustics in real space. Fine features of the global caustics are well reproduced, including their deviations from the trajectories of the host beams. Besides, we also show the possibility of tailoring the vortex caustics in paraxial optics based on our theory. The excellent agreements of our theoretical results with both numerical and experimental results confirm the validity of this scheme.

Transparent luminescent solar concentrators (TLSCs) have been attracting wide attentions for their applications in transparent photovoltaic (PV) windows, smart greenhouses, and mobile electronics on account of the simple architecture and low-cost preparation. We report a novel strategy to fabricate TLSCs using the heterophase lead-free perovskites. The heterophase nanolayered films which combined CsCu2I3 and Cs3Cu2I5 were prepared in one step using a dual-source coevaporation technique. The CsCu2I3/Cs3Cu2I5 films exhibited UV light absorption, a high average visible transmission (AVT) of 86.70%, and dual-color white emission between 350 and 760 nm. Importantly, the TLSCs incorporated with the CsCu2I3/Cs3Cu2I5 films exhibited an impressive optical conversion efficiency of 1.15% under keeping a high AVT of 86.70%. Meanwhile, the TLSCs incorporated with the heterophase films showed considerable stability under ambient conditions. The CIE 1960 color coordinates (0.2082, 0.4680) of the TLSCs incorporated with the CsCu2I3/Cs3Cu2I5 films showed excellent aesthetic quality as compared with those of the TLSCs incorporated with lead-based perovskites. Our finding offers a strategy to prepare lead-free metal halides toward high-performance TLSCs and future transparent PV windows.

Optical soliton molecules in ultrafast lasers present striking analogies with their matter molecule counterparts, such as internal vibrations. However, the vibrations of soliton molecules are nonlinear, with frequencies that are sensitive to the system parameters, thus presenting an opportunity of control. Here, we experimentally demonstrate the synchronization of the internal vibrations of self-excited vibrating soliton molecules through a modulated optical injection. We show efficient sub-harmonic, fundamental and super-harmonic synchronization, forming a pattern of Arnold tongues with respect to the injection strength. Our observations are supported by numerical simulations., This work is supported by the National Natural Science Foundation of China (Grant 61975144, 61827821); Ph.G. acknowledges support from the EIPHI Graduate School (ANR-17-EURE-0002) and from PIA3 ISITE-BFC (ANR-15-IDEX-0003); O. Gat acknowledges support from the Israel Science Foundation (ISF) (Grant No. 2403/20)

As an imperative method of investigating the internal mechanism of femtosecond lasers, traditional femtosecond laser modeling relies on the split-step Fourier method (SSFM) to iteratively resolve the nonlinear Schrodinger equation suffering from the large computation complexity. To realize inverse design and optimization of femtosecond lasers, numerous simulations of mode-locked fiber lasers with different cavity settings are required further highlighting the time-consuming problem induced by the large computation complexity. Here, a recurrent neural network is proposed to realize fast and accurate femtosecond mode-locked fiber laser modeling for the first time. The generalization over different cavity settings is achieved via our proposed prior information feeding method. With the acceleration of GPU, the mean time of the artificial intelligence (AI) model inferring 500 roundtrips is less than 0.1 s. Even on an identical CPU-based hardware platform, the AI model is still 6 times faster than the SSFM method. The proposed AI-enabled method is promising to become a standard approach to femtosecond laser modeling.

Based on femtosecond laser ablated processing, one-dimensional arrays with different line spacings were fabricated on titanium disulfide (TiS2) nanosheet. Optical modulated measurements with these devices were demonstrated. Photo-induced complex conductivity changes of the TiS2 nanosheet devices were studied by an optical-pump THz-probe (OPTP) measurement system. For the 700 μm line spacing device, the optically introduced modulation depth (MD) reached up to 70%. Our experimental results have demonstrated the ultrafast dynamics and photoconductivity for the TiS2 nanosheet devices in the THz frequency range. TiS2 nanosheet based devices would be suitable as the photoelectric modulators of THz wave.

We utilize singular spectrum analysis (SSA) for post-processing distance measurement data obtained by a dual-comb femtosecond laser rangefinder. Signal denoising technique based on SSA allows detection of low amplitude vibrations from time series of distance data with limited signal-to-noise ratio (SNR). Various one-dimensional vibrations, including harmonic, amplitude modulated harmonic, and sinc-function vibrations, with micrometer amplitude comparable with measurement uncertainty of laser rangefinder, have been imposed on the target mirror by a piezo positioner. These vibrations have been extracted by SSA and the obtained vibration amplitudes agree with that imposed on the target very well. A commercial interferometer is used to evaluate the accuracy of SSA. Standard deviations of residuals between the SSA extractions and interferometer measurements are smaller than 0.6 $\mu$ m. This technique is promising for complex moving pattern detection in object tracking and remote sensing.

Traditional Light Detection and Rangings (LiDARs) can quickly collect high-accuracy of three-dimensional (3D) point cloud data at a designated wavelength (i.e., cannot obtain hyperspectral data), w...

Silicon-vacancy (VSi) centers in silicon carbide (SiC) are expected to serve as solid qubits, which can be used in quantum computing and sensing. As a new controllable color center fabrication method, femtosecond (fs) laser writing has been gradually applied in the preparation of VSi in SiC. In this study, 4H-SiC was directly written by an fs laser and characterized at 293 K by atomic force microscopy, confocal photoluminescence (PL), and Raman spectroscopy. PL signals of VSi were found and analyzed using 785 nm laser excitation by means of depth profiling and two-dimensional mapping. The influence of machining parameters on the VSi formation was analyzed, and the three-dimensional distribution of VSi defects in the fs laser writing of 4H-SiC was established.

Although higher order Poincare (HOP) beams are attractive due to their unique advantages and various efforts have been made for the generation of HOP sphere beams, the current generation technologies suffer from both limited output power and narrow bandwidth, preventing further practical applications. In this paper, we report on a femtosecond optical parametric oscillator (OPO) which can deliver high average power, on-demand arbitrary HOP sphere beams tunable across a wide spectral range in the near-infrared. The desired beam mode can be achieved by manipulating the geometric phase inside the OPO cavity to map the polarization to orbital angular momentum (OAM). Pumped by a Gaussian beam from an Yb-fiber laser, the generalized vector vortex femtosecond signal beams with spectral coverage from 1367 to 1650 nm are obtained. The device can produce over 200 mW structured beam signal power cross the complete tuning range with as much as 377 mW at 1480 nm for 2 W of input pump power. The proposed configuration, which shows superiorities of high average output power, flexible wavelength tunability and complete mode controlling property, may have direct implications in applications such as quantum optics and material processing.

We investigate on bound-state mode-locking in the close-to-zero dispersion regime of an Er-fiber laser. A two-soliton bound state with 82 fs pulse duration and 0.58 ps pulse separation is achieved. Compound 2+1 type bound state solitons with ~100 fs pulse duration has also been observed. Both the double-pulse and the 2+1 type bound states could experience period-doubling bifurcations and exhibit the pumping hysteresis characteristics as the single pulse. To the best of our knowledge, this work provides the first observation of sub-100 fs bound solitons in a fiber laser. Such ultra-short bound state solitons show potential applications of multilevel coding unit for high-capacity telecommunication systems.

We demonstrate a dual-wavelength, compact femtosecond optical parametric oscillator (OPO) with high-repetition-rate, which is harmonically pumped by a ~101 MHz Yb-doped fiber laser system. The dual-wavelength output is realized by exploiting the bidirectional off-axis pumping technique, and the multiplication of repetition rate is derived by placing a nonlinear crystal in a miniaturized V-type cavity with only 16.5 cm length. By adjusting the detuning degree of the pump at one end, the maximum dual-wavelength gap is 66 nm from 1497 to 1563 nm. The time interval between the dual wavelengths can be adjusted freely. This is the first report on a dual-wavelength with the high-repetition-rate of GHz-level, femtosecond OPO system.

We propose an effective scheme to interpret and engineer the caustics of the synthesized vortex beams which would be beneficial to a broad range of applications such as particle trapping and micromachining.

Collision refers to a striking nonlinear interaction in dissipative systems, revealing the particle-like properties of solitons. In dual-wavelength mode-locked fiber lasers, collisions are inherent and periodic. However, how collisions influence the dynamical transitions in the dual-wavelength mode-locked state has still not been explored. In our research, dispersion management triggers the complex interactions between solitons in the cavity. We reveal the smooth or reversible Hopf-type bifurcation transitions of dual-color soliton molecules (SMs) during collision by real-time spectral measurement technique of TS-DFT. The reversible transitions from stationary SM to vibrating SM, revealing that cavity parameters pass through a bifurcation point in the collision process without active external intervention. The numerical results confirm the universality of collision-induced bifurcation behavior. These findings provide new insights into collision dynamics in dual-wavelength ultrafast fiber lasers. Furthermore, the study of intermolecular collisions is of great significance for other branches of nonlinear science., Comment: 11 pages, 4 figures

Soliton molecules, exhibiting similarities to molecular-like behavior, have attracted tremendous attention. With the dramatic recent advances in real time spectroscopic techniques as well as time-domain probes, the detailed nature of various soliton molecular has been revealed. Particularly, time-stretch dispersive Fourier transform (DFT) technique has been applied to unveil the complex internal dynamics of bound states. Nevertheless, the observation time frame of such technique is limited to hundreds of micro seconds mainly confined by the storage capability of the real time oscilloscopes, as well as by the number and the distribution of soliton pulses. Here, we experimentally demonstrate a new probing concept, orbital angular momentum (OAM)-resolved method, for visual extraction of long-term internal phase motions within soliton molecules produced by a mode locked laser.

An all-fiber linear sampling device for dual-comb time-of-flight (TOF) distance measurement is demonstrated. We studied the impact of optical filter and adjustable attenuator on the symmetry of the interferometric beat-note, the optimization of which is crucial for TOF extraction. In an absolute ranging experiment, a ranging precision of 49 um is obtained at an update rate of 2 kHz and the precision can be improved to 7 um with 100 ms averaging time. This technique shows the potential of high precision absolute ranging in many practical industrial scenarios.

After five decades of development, mode-locked lasers have become significant building blocks for many optical systems in scientific research, industry, and biomedicine. Advances in noise measurement and reduction are motivated for both shedding new light on the fundamentals of realizing ultra-low-noise optical frequency combs and their extension to potential applications for standards, metrology, clock comparison, and so on. In this review, the theoretical models of noise in mode-locked lasers are first described. Then, the recent techniques for timing jitter, carrier-envelope phase noise, and comb-line noise measurement and their stabilization are summarized. Finally, the potential of the discussed technology to be fulfilled in novel optical frequency combs, such as electro-optic (EO) modulated combs, microcombs, and quantum cascade laser (QCL) combs, is envisioned.

We develop a single cavity, single crystal, bidirectional-pumped femtosecond optical parametric oscillator. Unlike the conventional single-pumped OPO, the pump pulses are injected into the OPO cavity from the front and reverse directions, respectively, which can double the tolerable maximum pump power onto the nonlinear crystal. By means of synchronizing the two signals generated from the bidirectional pump pulses, distinct improvements for optical-to-optical conversion efficiency, maximum signal power, and operational stability in the bidirectional pumped OPO have been demonstrated.

We report a single method for measuring the effective electro-optics (EO) coefficient only by spectral intensity modulation with a terahertz time-domain spectroscopy (THz-TDS) device. Compared with conventional methods, the measuring device based on THz-TDS by probing the spectral intensity modulation is simple, rapid, and highly sensitive. It does not require special preparation process, electrode contact or applying high voltage on the sensor samples. The EO coefficients of four kinds of materials, namely, ZnTe and GaP crystals, DAST wafer and GaSe film, are measured at 1040 nm. The results showed good agreement with literature data by the conventional methods.

Structured light beams that possess unique polarization distribution could offer a new degree of freedom for a variety of applications, and hence its flexible polarization manipulation is necessary. Here we experimentally report a heterodyne interference-based method for generating femtosecond cylindrical vector beam (CVB) with high-speed controllable rotated polarization states. The femtosecond CVBs are created through the superposition of two optical vortices with opposite handedness. The use of two acoustic-optical modulators (AOMs) with frequency differences allows to achieve polarization rotation in a hopping-free scheme at on demand speed. Up to 1 MHz of the rotation frequency is demonstrated by visualizing the fast rotation events through a fast-frame-rate CCD camera. Moreover, we show our method can be readily extended to produce higher order CVBs with more complex rotated polarization distributions. Such a simple yet versatile femtosecond polarization-controlled laser system has the capability to act as a nonlinear trapping platform, thus opening tremendous potential opportunities in the fields of micromachining, nanofabrication, and so force.

Nondestructive testing of packaged chips is essential for ensuring product performance, yet existing methods have serious drawbacks. Here, we apply photoacoustic remote sensing microscopy using a high-frequency pulse laser with a pulse width of 1.2 ps and a wavelength of 1030 nm to inspect silicon-based semiconductor chips for internal defects. Joint optical-mechanical scanning allowed high-resolution imaging of a large field of view. The basis for photoacoustic imaging was explained using a solid-state physics model, which was confirmed experimentally by measuring photoacoustic amplitudes at different doping concentrations. Our method appears capable of rapidly imaging chips over a large field of view with depth-to-resolution ratios of around 200 without the need for a couplant, which could support nondestructive inspection in industrial applications.

In this letter, we propose and demonstrate a practically compact 1-GHz repetition-rate femtosecond optical parametric oscillator (OPO) based on MgO:PPLN crystal, which is harmonically pumped by a 53 MHz Yb-doped fiber laser. The multiplication of the repetition rate is derived by placing the nonlinear crystal in a miniaturized V-type cavity with 13.9 cm length. The near-infrared signal output pulses are tunable from 1350 nm to 1650 nm. The signal pulse duration across the complete tuning range is measured to be around 125 fs. Thanks to the high repetition rate, broadband tenability, and simplicity of the optical setup, this type of OPO holds promise for many applications.