Picosecond Fiber Research Articles

Over 3.8 W, 3.4 µm picosecond mid-infrared parametric conversion based on a simplified one-to-many scheme

In this paper, we demonstrate a simplified one-to-many scheme for efficient mid-infrared (MIR) parametric conversion. Such a scheme is based on a continuous wave (CW) single longitudinal mode master oscillator power-amplifier (MOPA) fiber system as the signal source and a picosecond pulsed MOPA fiber system, exhibiting multiple longitudinal modes, as the pump source. The signal and pump beams are combined and co-coupled into a piece of 50-mm long 5% MgO-doped PPLN crystal for the parametric conversion. As high as ∼3.82 W average power at a central idler wavelength of ∼3.4 µm is achieved when the launched pump and signal powers are ∼41.73 and ∼11.45 W, respectively. Above some threshold value, the delivered idler power shows a roll-over effect against the signal power and saturation-like effect against the pump power. Consequently, the highest conversion efficiency is observed at such a threshold pump power. To the best of our knowledge, our result represents the highest average power produced from any single-pass parametric conversion source with >3 µm idler wavelength feeding with a CW signal. Moreover, our proposed scheme can simplify the design of parametric conversion system significantly and meanwhile make the system more robust in applications. This is attributed to two main aspects. Firstly, the scheme’s one-to-many feature can reduce wavelength sensitivity remarkably in the realization of quasi-phase-matching. Secondly, for moderate power requirement it does not always require a high peak power synchronized pulsed signal source; a CW one can be an alternative, thereby making the system free from complex time synchronization and the related time jitter.

Picosecond gain-switched polymer fiber random lasers

Picosecond gain-switched polymer fiber random lasers

Picosecond Pulse Tapered Fiber Amplifier Operated near 1030 nm with Peak Power up to 1 MW

We demonstrated an optimization of a picosecond fiber amplifier based on Yb-doped tapered fiber in a spectral range of 1030 nm. Nonlinear effects limiting peak power scaling (stimulated Raman scattering and four-wave mixing) were studied and factors affecting their threshold were established, such as gain, diameter profile along the length of taper, output mode field diameter, and numerical aperture of a pump. By determining the optimal amplification regime and manufacturing advanced tapered fibers, we amplified 13 ps pulses to a record-high peak power of 1 MW at a wavelength of 1029 nm directly at the output of the fiber at an average power of 13.8 W. Four-wave mixing was the limiting factor, and the total fraction of deleterious components in the output spectrum was ~2%. The quality of the output beam was close to being diffraction limited (M2 < 1.2).

978 Nm All-Polarization-Maintaining Mode-Locked Fiber Laser Based on Phase-Biased Nonlinear Amplifying Loop Mirror

Terahertz (THz) wave generation based on ultrafast laser are one of the most predominant and popular technologies. In particular, for THz generation by photoconductor antenna and optical rectification, higher optical to THz conversion efficiency usually requires ultrafast laser excitation into semiconductor or nonlinear crystal, therefore it is of great desire to develop ultrafast laser with high performance. CW Yb-doped lasers at 980 nm have been applied to generate THz wave range from 0.5 to 6 THz by DFG technique. To meet the demand of some THz wave generation (e.g. BNA crystal, gold nanoplasma), 980 nm ultrafast fiber laser are ideal pump sources and in desire to be developed. Here we demonstrate a 978 nm robust all-polarization-maintaining (PM) picosecond fiber laser mode- locked by phase-biased nonlinear amplifying loop mirror (PB- NALM). By introducing a nonreciprocal - <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pi$</tex-math></inline-formula> /2 phase shifter into the fiber loop, a self-starting stable mode-locking is obtained with the center wavelength of 978.14 nm and a 3-dB bandwidth of 0.43 nm. The pulse duration is 8.1 ps corresponding to the time bandwidth product (TBP) of 1.09. The maximum average output power is 14.5 mW with a repetition rate of 45.438 MHz. After a master oscillator power amplification system, the 978 nm average output power reaches 2.12 W, which is then injected into a PPLN crystal for second harmonic generation and 52 mW 489 nm ultrashort lasers is obtained. This is, to the best of our knowledge, the first report of PB-NALM-based mode-locked fiber laser at 978 nm. The 978 nm ultrafast fiber laser and SHG to 489 nm have great potential in terahertz emission by shorter NIR and blue light.

Effect of physical parameters of laser radiation on the process of weld formation in transparent dielectrics

The article determines the influence of pulse duration, energy density and focusing parameters on the process of formation of a weld of transparent dielectrics. A comparative analysis of laser welding of borosilicate and quartz glass with different pulse durations and energies of picosecond and femtosecond fiber lasers was carried out. Basic regularities of weld shape change depending on pulse duration and energy are obtained. The combination of physical parameters of laser radiation and focusing allows welding along gaps up to 6 μm.

Compact Long-Range Single-Photon Underwater Lidar With High Spatial–Temporal Resolution

Oceanic lidar has emerged as a strong technology for oceanic three-dimensional remote sensing. However, most existing oceanic lidars are bulky and high-power consumption, thus difficult to enable underwater operation. Here we present a compact single-photon lidar system for long-range underwater measurement. A single-photon detector was adopted to achieve a high signal-to-noise ratio. Benefiting from the single-photon sensitivity in detection, long-range active detection was realized with a low pulse energy laser at 1 μJ and a small-aperture coupler at 12 mm. Moreover, a narrow linewidth picosecond fiber laser with high repetition rate was employed to guarantee a high spatial resolution and high update rate. A fiber-connected configuration was specially designed for the miniaturized and robust structure in an optical receiver. In an experimental demonstration, the profile of backscattered signal from clean water was obtained over 70 m with high spatial-temporal resolution to demonstrate the capability of this lidar system. The maximum detection distance of the single-photon lidar reaches ~3.6/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K_d</i> ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K_d</i> , diffuse attenuation coefficient) for waterbody and up to 5.5/ <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K_d</i> for a hard target. Furthermore, it exhibits a high update rate capability and realizes the localization and quantification of underwater bubbles up to 26 m away at a high update rate of 100 Hz. These results indicate its potential in a variety of applications including remote sensing of marine biogeochemical parameters, the quantification of seabed gas emissions, and long-range underwater imaging.

Visible‐Wavelength Spatiotemporal Mode‐Locked Fiber Laser Delivering 9 ps, 4 nJ Pulses at 635 nm

AbstractSpatiotemporal mode‐locking (STML) in fiber lasers are of interest in applications such as optical communications, nonlinear imaging, and precision machining. To date, STML fiber lasers in the near‐infrared region have been well demonstrated, yet operation at visible wavelengths is still challenging. Here, a STML picosecond fiber laser at 635 nm with the implementation of Pr/Yb co‐doped few‐mode fiber and nonlinear polarization rotation technology is reported. By solving the modified generalized multimode nonlinear Schrödinger equation, the 635 nm STML formation is theoretically predicted and analyzed. The stable 635 nm STML with a 9 ps pulse duration, which is two orders of magnitude narrower than previously reported, is realized experimentally. Moreover, spatiotemporal profiles are illustrated by investigating the locking of transverse and longitudinal modes simultaneously. By further establishing visible ultrafast fiber amplifier, the 635 nm average power is boosted up to 440 mW, corresponding to a maximum pulse energy and peak power of 4 nJ and 280 W, respectively. The experimental results are in good agreement with the numerical simulations. This work helps to understand nonlinear dynamics in STML fiber laser and directly generate large‐energy ultrashort pulses in visible region.

Tapered active fiber simultaneously enabled 141 W high average and 1.3 MW high peak power via all-fiber and polarization-maintained picosecond amplifier

An all-fiber and polarization-maintained (PM) picosecond pulses laser system is demonstrated based on tapered active fiber, which simultaneously enables high average and peak power. By carefully adjusting the input signal power and combining the advantages of tapered active fiber for high power scaling, the amplified spontaneous emission (ASE) and the stimulate Raman scattering (SRS) are effectively balanced and suppressed. An average output power of 141 W and peak power of ∼1.3 MW pulse laser is achieved with 3.4 ps pulse width at the repetition rate of 30 MHz. The polarization extinction ratio (PER) and beam quality (M2 factor) are measured to be ∼16 dB and 1.19, respectively. As far as we know, this is the first demonstration of all-fiberized picosecond fiber source beyond megawatt (MW) peak power and hectowatt-level average power along with linear polarization and near-diffraction-limited beam quality.

Watt-level all-fiber 1.7-μm picosecond synchronously pumped Raman laser

A synchronously pumped fiber Raman laser (SPFRL) operating at 1.7 µm is proposed and experimentally demonstrated for the first time to the best of our knowledge. Through the third harmonic pumping by a 1563 nm picosecond pulsed fiber laser, the Stokes pulses are generated with an average power of 1.9 W, a pulse duration of 21 ps, and a repetition frequency of 52.9 MHz. The center wavelength and the 3-dB bandwidth are 1694.3 nm and 0.96 nm respectively. This work provides a pathway to a power scalable ultrafast laser at 1.7 µm via a compact and elegant all-fiber solution.

Modified Frantz–Nodvik equation for CW end-pumped high-repetition-rate picosecond laser amplifier

The modified Frantz–Nodvik equation considering the pulse repetition rate (PRR) for continuous-wave end-pumped picosecond laser amplifier is theoretically developed for the first time by analogizing Q-switch theory and solving rate equations. Based on the modified Frantz–Nodvik equation, a simple finite-element slice model is established to simulate the output characteristics of the end-pumped high-repetition-rate picosecond amplifier. Moreover, the validity of the theory and model is well verified by the experimental results of a two-staged diode-end-pumped Nd : YVO4 amplifiers using a picosecond fiber laser with adjustable PRRs as the seed source. The agreement between the experimental and theoretical results illustrates that the as-developed pulse amplification theory and model are a powerful tool for designing and optimizing adjustable-high-repetition-rate solid-state picosecond laser amplifiers.

A shower of mid-infrared Raman solitons at designed wavelength of ∼3 μm from a tapered fluorotellurite fiber

Optical temporal soliton generation in optical fibers and resonators has achieved great breakthroughs and found significant applications in many fields. Despite recent advances on optical soliton generation in optical fibers, it remains challenging to realize a shower of Raman solitons at a certain wavelength in optical fibers, i.e. put all the generated Raman solitons at a same wavelength on demand. Here we propose and experimentally demonstrate a shower of mid-infrared Raman solitons at designed wavelength of 3 μm from a tapered fluorotellurite fiber pumped by a 1960 nm picosecond fiber laser. Tapered fluorotellurite fibers have an untapered region length of ∼49 cm and a tapered transition region length of ∼1 cm. The fiber segment at the end of the tapered region has a 2nd zero-dispersion wavelength of ∼3 μm. Firstly, multiple Raman solitons with different wavelengths are generated in the untapered region pumped by the 1960 nm picosecond laser. Then, as Raman solitons propagate into the tapered region, the redshift of all the generated Raman solitons with different wavelengths are accelerated due to the dramatic increase of the nonlinear coefficient. Finally, as Raman solitons move out from the tapered region, all the accelerated Raman solitons are stopped around 3 μm owing to the occurrence of soliton self-frequency shift cancellation, causing the generation of a shower of mid-infrared Raman solitons around 3 μm. This phenomenon may find applications in super-efficient nonlinear light generation and signal processing.

Hybrid high spectral resolution broadband mid-infrared SFG spectrometer development and demonstration.

In this work, we present the development of a femtosecond tunable middle infrared (mid-IR) radiation source for the realization of a hybrid concept compact broadband high-resolution sum-frequency generation (SFG) spectroscopy system. For the realization of the new concept, we used a two-channel picosecond fiber laser as a seed for narrowband (∼1.5 cm-1) and broadband ultrafast radiation sources operating at 1 kHz repetition rate. In order to achieve >500 cm-1 bandwidth widely tunable microjoule level pulses in the mid-IR spectral region (2-10 µm), broadband femtosecond source optimization was performed. Numerical simulations with different nonlinear crystals and optical parametric amplification layouts at given fixed initial conditions paved a way to experimentally realize an optimal scheme for a femtosecond mid-IR channel. Fully operating SFG spectrometer setup was assembled and tested. The developed SFG spectrometer demonstrates a unique combination of parameters: excellent spectral resolution (<3 cm-1) similar to a narrowband scanning picosecond spectrometers and fast simultaneous acquisition of broadband spectra up to more than 850 cm-1.

Design guidelines for ultrashort pulse generation by a Mamyshev regenerator.

We study numerically the possibility of using various gain-switched seed laser pulse parameters and fibers for a low-cost, all-fiber Mamyshev regenerator scheme. We find that for increasing pulse durations, sufficient spectral broadening will be difficult to achieve in practice and careful design of the system parameters is required for the regenerator to function. Furthermore, an optimal input peak power level can be defined for a given fiber and pulse duration that results from a balance of competing Kerr effect and stimulated Raman scattering. We also demonstrate experimental results of 3 ps pulse generation seeded by an 80 ps gain-switched diode. Our results pave the way for designing pulse-on-demand picosecond scale fiber sources for applications.

Intracavity second harmonic generation from a WSe2 monolayer in a passively mode-locked picosecond fiber laser

A single layer WSe2 crystal is transferred on the tip of a single mode fiber that is placed in the cavity of a Yb3+ doped picosecond fiber oscillator. This intracavity monolayer generates second harmonics without affecting the stable mode-locking and laser output of the fiber oscillator. This method utilizes the higher intracavity optical intensities to increase the SHG conversion efficiency, thus combining the high nonlinear susceptibility and the phase-matching independence of a monolayer with the versatility of a fiber laser in an all-fiber integrated system. We also demonstrated a procedure to verify the monolayer placement on the fiber core by hyperspectral mapping. This intracavity SHG has possible applications for self-referencing f-2f interferometry in fiber-laser frequency combs.

Fiber-solid hybrid end-pumped Nd:YVO4 picosecond amplifier with high beam quality

In recent years, high-brightness picosecond lasers have been widely used in high-end precision processing, spectroscopy and high harmonic generation. To obtain higher power and excellent beam quality, it is an ideal solution to add a high-gain amplifier to the back end of the high-stability picosecond fiber or solid seed. In this article, a fiber-solid hybrid end-pumped Nd:YVO4 picosecond laser system with high beam quality is demonstrated. The influence of the self-developed picosecond fiber seed output characteristics on solid amplifiers has been studied in detail, including the energy, repetition rate and spectrum. After two-stage traveling wave amplifiers, the maximum 155 μJ single pulse energy is obtained with 20 kHz repetition rate, and the corresponding peak power reaches 14.9 MW with 10.4 ps pulse duration. Meanwhile, the beam quality factors under the maximum 18.4 W average power are measured to be M x 2 = 1.27 and M y 2 = 1.25, respectively.

The effect of laser in-situ induced graphene-like micro-texture on the friction and wear properties of ductile cast iron

Picosecond fiber laser was subjected on surface of ductile cast iron to induce graphene-like micro-texture array and enhance the tribological properties. The size of the dimples was regulated in the range of 5 μm–110 μm. The in-situ fabrication process was carried out on the workpiece surface in parallel manner and the scanning speed can be up to 3 m/s. The formation mechanism of graphene-like structure was analyzed. The tribological properties of the textured samples were investigated using a ball-on-disk tribometer. The results showed that the laser textured samples exhibit low coefficient of friction and the anti-wear properties were improved significantly. The textured sample showed no distinct wear pit, while the non-textured sample showed typical wear pit with depth up to 15 μm. Volume wear rate was reduced by 69.6 ± 6.9%. The graphene-like micro-texture array conducted by picosecond fiber laser scanning will not change the material isotropic, and the improved tribological properties are attributed to the combined effects of the increased surface hardness, improved heat dispersion property and entrapment of wear debris.

Efficient third-harmonic generation of broadband picosecond radiation by employing spectrally noncritical phase-matching KDP crystal and cascaded LBO crystals

To improve the nonlinear frequency conversion efficiency of a broadband picosecond fiber laser, the spectrally noncritical phase matching for frequency doubling, dual-crystal cascaded design for frequency tripling is employed. By this method, we obtain 2.39 W of output power at the third-harmonic wavelength, when the spectral full width at half maximum of the fundamental light is 5.5 nm and the input fundamental light power is 8.6 W. The frequency conversion efficiency of IR-UV is 27.8%. To the best of our knowledge, this is the first time of the broadband third harmonic picosecond ultraviolet laser generation by the combination of the spectrally noncritical phase matching for frequency doubling and dual-crystal cascaded design for frequency tripling.

Scaling of average power in sub-MW peak power Yb-doped tapered fiber picosecond pulse amplifiers.

Prospects for average power scaling of sub-MW output peak power picosecond fiber lasers by utilization of a Yb-doped tapered fiber at the final amplification stage were studied. In this paper, it was shown experimentally that a tapered fiber allows the achievement of an average power level of 150 W (limited by the available pump power) with a peak power of 0.74 MW for 22 ps pulses with no signs of transverse mode instability. Measurements of the mode content using the S2 technique showed a negligible level of high order modes (less than 0.3%) in the output radiation even for the maximum output power level. Our reliability tests predict no thermal issues during long-term operation (105 hours) of the developed tapered fiber laser up to kilowatt output average power levels.

Simulation and experimental results of a high-gain two-stage and double-pass off-axis Nd:YVO4 picosecond laser amplifier.

A high-gain two-stage double-pass off-axis Nd:YVO4 picosecond laser amplifier has been developed. The comprehensive influence of crystal doping concentration and pump beam quality on the small-signal gain of the Nd:YVO4 amplifier is theoretically analyzed with a model developed by considering energy transfer upconversion and pump light absorption saturation effect. The thermal effect of Nd:YVO4 crystal with different doping concentrations, undoped end cap lengths, and pump beam quality is investigated as well. Based on the theoretical analysis, a high-gain two-stage and double-pass off-axis Nd:YVO4 amplifier based on picosecond fiber seed source is realized by choosing long-composite low-doping Nd:YVO4 crystal and with high brightness laser diode pumping, delivering a gain of 28 dB and an output pulse energy of 67.5 µJ at a repetition rate of 200 kHz.

Two key frontier issues on picosecond pulses generated by mode-locked fiber lasers

Narrowband dissipative soliton mode-locked fiber lasers can produce transform-limited picosecond pulses. Unfortunately, due to the limitation of allowable nonlinear phase shift for the intracavity pulse, the repetition rate of the pulses generated by such lasers cannot be reduced by increasing the cavity length; the pulse energy is only below 0.1 nJ. These seriously restrict the practical application of such picosecond pulsed fiber lasers. In this paper, we propose a method that allows the cavity length to be increased to reduce the repetition rate of the narrowband dissipative soliton picosecond fiber laser pulses by extracting the pulse energy out of the cavity with a coupler to suppress the accumulation of nonlinear phase shift of the intracavity pulses. Using this method, the laser repetition rate was successfully reduced from 35.2 MHz to 1.77 MHz, and the pulse time-frequency characteristics remained unchanged. We also propose a method to suppress spectral broadening in picosecond pulse fiber amplification based on inter-stage FBG notch filtering. By simply using the inter-stage notch filter, the output pulse spectrum width after the first-stage fiber amplifier can be narrowed, allowing the second-stage fiber amplifier to further increase the pulse energy, and also, the pulse can be reshaped to be nearly Gaussian-shaped, allowing the second-stage fiber amplifier to increase the pulse energy higher by using the Gaussian pulse characteristics of the smaller spectral broadening slope. Using this method, on the premise of keeping the RMS spectral width within 0.4 nm, after a 10 ps pulse passes through a standard single-mode fiber amplifier, the pulse energy can be increased from 0.2 nJ to more than 10 nJ.