nJ Pulse Research Articles

Generation of a 2.2 nJ picosecond optical pulse with blue-violet wavelength using a GaInN master oscillator power amplifier

We report the generation of a picosecond optical pulse with 2.2 nJ pulse energy at blue-violet wavelengths using a GaN-based mode-locked laser diode (MLLD) and a semiconductor optical amplifier (SOA). The picosecond optical pulse generated by MLLD at a frequency of 812 MHz was amplified effectively by SOA. We optimized SOA with a widely flared waveguide structure to generate a high optical pulse energy.

Passively Q-switched fiber lasers using a multi-walled carbon nanotube polymer composite based saturable absorber

We demonstrate a simple, compact and low cost Q-switched fiber lasers based on Erbium-doped fiber (EDF) and Thulium-doped fiber (TDF) to operate at 1534.5nm and 1846.4nm, respectively by exploiting a multi-walled carbon nanotubes (MWCNTs) polymer composite film based saturable absorber (SA). The composite is prepared by mixing the MWCNTs homogeneous solution into a dilute polyvinyl alcohol polymer solution before it is left to dry at room temperature to produce thin film. Then the film is sandwiched between two FC/PC fiber connectors and integrated into the laser cavity for Q-switching pulse generation. The EDF laser generates a stable pulse train with repetition rates ranging from 38.11kHz to 48.22kHz by varying the 980nm pump power from 39.0mW to 65.3mW. At the 65.3mW pump power, the pulse width and pulse energy were 5.3μs and 99.75nJ, respectively. The TDF laser generates a stable pulse train with 10.38kHz repetition rate, 17.52μs pulse width and 11.34nJ pulse energy at 121.1mW 800nm pump power. A higher performance Q switching is expected to be achieved in both fiber lasers with the optimization of the SA and laser cavity.

Pyrene‐Capped Conjugated Amorphous Starbursts: Synthesis, Characterization, and Stable Lasing Properties in Ambient Atmosphere

A family of trigonal starburst conjugated molecules (TrFPy, TrFPy, and TrF2Py) composed of a truxene core and pyrene cappers with various bridge lengths is synthesized and characterized. The incorporation of pyrene cappers successfully depress the crystallization tendency, resulting in enhanced glassy temperature and improved morphological stability of the thin films. The high photoluminescence yield in neat films and excellent thermal stability render these pyrene‐capped starbursts promising lasing optical gain media. Low amplified spontaneous emission (ASE) thresholds (EthASE) of 180 nJ pulse‐1 and 101 nJ pulse–1 were recorded for TrFPy and TrF2Py, respectively. One dimensional distributed feedback (1D DFB) lasers demonstrated lasing threshold of 9.3 kW/cm2 and 7.3 kW/cm2 for TrFPy (at 457 nm) and TrF2Py lasers (at 451 nm), respectively. The ASE performance of TrFPy and TrF2Py in an ambient condition was recorded with various annealing temperature (from 80 to 250 °C, 10 min). Surprisingly, TrFPy exhibited excellent ASE stability in an ambient condition, which is still detectable even after annealing at 250 °C for 10 min. The results suggest the pyrene‐capped molecular design strategy is positive on improving the optical gain stability and meanwhile maintaining excellent lasing properties.

High-power, efficient, semiconductor saturable absorber mode-locked Yb:KGW bulk laser.

A high-power, diode-pumped, semiconductor saturable absorber mode-locked Yb(5%):KGW bulk laser was demonstrated with high optical-to-optical efficiency. Average output power as high as 8.8 W with optical-to-optical efficiency of 37.5% was obtained for Nm-polarized laser output with 162 fs pulse duration and 142 nJ pulse energy at a pulse repetition frequency of 62 MHz. For Np polarization, 143 fs pulses with pulse energy of 139 nJ and average output power of up to 8.6 W with optical-to-optical efficiency of 31% were generated.

Generation of 8 nJ pulses from a normal-dispersion thulium fiber laser.

We report a study of a mode-locked thulium (Tm) fiber laser with varying normal dispersion. It is difficult to reach the high-energy dissipative-soliton regime due to the anomalous dispersion of most fibers at 2 μm. With large normal dispersion, the laser exhibits elements of self-similar pulse evolution, and is the first Tm fiber laser to achieve the performance benefits of normal-dispersion operation. The laser generates 7.6 nJ pulses, which can be dechirped to 130 fs duration. The resulting peak power is 4 times higher than that of previous Tm fiber lasers.

Versatile long cavity widely tunable pulsed Yb-doped fiber laser with up to 27655th harmonic mode locking order.

We report flexible dissipative soliton generation from an all-fiberized all-normal-dispersion (ANDi) long cavity actively mode locked ytterbium doped fiber laser based on improved harmonic mode locking technique. The laser is featured with unusually wide and fine tunabilities in repetition rate and operating wavelength, meanwhile superior stability is maintained. The repetition rate of the laser can be flexibly controlled from 226 kHz to 6.25 GHz (corresponding to the highest 27655th order harmonic mode locking) in the interval of 226 kHz, while supermode suppression is confined above 50 dB and the pulse duration is retained in the range of 38 ps~80 ps. As high as 4.3 nJ pulse energy can be achieved with a low pump power of 160 mW when operating at the fundamental mode locking regime. The operating wavelength of the laser can be tuned in the wide range of 1005 nm~1100 nm. As far as we know, it is the first demonstration of up to ten thousands order stable harmonic mode locking in ANDi fiber laser, which manifests the capability of generating both high energy pulse and ultra-high repetition rate pulse in a single ANDi cavity. The destabilization of dissipative soliton under strong pump is also demonstrated.

Impact of Mode Filtering on the Performance of Femtosecond Pulse Amplification in a Large Mode Area Fiber

We experimentally investigated the impact of the mode filtering technique on the performances of pulse amplification in a fiber with a large core diameter. The technique was applied to a femtosecond pulse amplifier, and was based on a large area double-clad Yb-doped fiber. The mode filtering enabled selective excitation of the lowest transverse mode with minimal contamination of higher order modes. The output pulses with 110 fs duration, > 30 nJ pulse energy (> 3 W average power), and clean spatial/temporal profiles were successfully generated. Benefits of this technique are also discussed.

Sub-100 fs passively mode-locked holmium-doped fiber oscillator operating at 2.06 μm.

We demonstrate a simple and compact Holmium-doped fiber femtosecond oscillator, in-band pumped by a commercial Tm-doped fiber laser. The oscillator operates in the dispersion managed soliton regime at net zero intracavity dispersion and delivers >1 nJ pulse energy at 35MHz repetition rate. The pulse duration directly at the oscillator output is 160fs FWHM, close to the Fourier-limit of 145fs FWHM. Using an additional nonlinear compressor stage, sub-100fs FWHM pulse durations could be achieved. The nonlinear fiber compressor is implemented by a solid core highly nonlinear fiber for spectral broadening and a single mode fiber for pulse compression.

Tunable Q-switched fiber laser based on saturable edge-state absorption in few-layer molybdenum disulfide (MoS₂).

We fabricate a few-layer molybdenum disulfide (MoS₂) polymer composite saturable absorber by liquid-phase exfoliation, and use this to passively Q-switch an ytterbium-doped fiber laser, tunable from 1030 to 1070 nm. Self-starting Q-switching generates 2.88 μs pulses at 74 kHz repetition rate, with over 100 nJ pulse energy. We propose a mechanism, based on edge states within the bandgap, responsible for the wideband nonlinear optical absorption exhibited by our few-layer MoS₂ sample, despite operating at photon energies lower than the material bandgap.

Three-photon excitation source at 1250 nm generated in a dual zero dispersion wavelength nonlinear fiber.

We demonstrate 1250 nm pulses generated in dual-zero dispersion photonic crystal fiber capable of three-photon excitation fluorescence microscopy. The total power conversion efficiency from the 28 fs seed pulse centered at 1075 nm to pulses at 1250 nm, including coupling losses from the nonlinear fiber, is 35%, with up to 67% power conversion efficiency of the fiber coupled light. Frequency-resolved optical gating measurements characterize 1250 nm pulses at 0.6 nJ and 2 nJ, illustrating the change in nonlinear spectral phase accumulation with pulse energy even for nonlinear fiber lengths < 50 mm. The 0.6 nJ pulse has a 26 fs duration and is the shortest nonlinear fiber derived 1250 nm pulse yet reported (to the best of our knowledge). The short pulse durations and energies make these pulses a viable route to producing light at 1250 nm for multiphoton microscopy, which we we demonstrate here, via a three-photon excitation fluorescence microscope.

Energy scaling of a tunable terahertz parametric oscillator with a surface emitted configuration

A high-energy THz-wave output has been experimentally demonstrated with a terahertz-wave parametric oscillator based on a surface-emitted configuration. Through optimizing the cavity length and pump beam size, the maximum THz-wave output energy of 854 nJ pulse−1 was obtained at 1.62 THz. The conversion efficiency was 0.57 × 10–5, corresponding to the photon conversion efficiency of 0.099%. The THz beam profile was measured with a THz imager, which had a Gaussian profile. The measured beam diameter sizes were 423 μm and 258 μm in the horizontal and vertical directions, respectively. A wide tunable range from 0.75 to 2.81 THz was realized.

Hybrid mode-locked erbium-doped all-fiber soliton laser with a distributed polarizer.

A soliton-type erbium-doped all-fiber ring laser hybrid mode-locked with a co-action of arc-discharge single-walled carbon nanotubes (SWCNTs) and nonlinear polarization evolution (NPE) is demonstrated. For the first time, to the best of our knowledge, boron nitride-doped SWCNTs were used as a saturable absorber for passive mode-locking initiation. Moreover, the NPE was introduced through the implementation of the short-segment polarizing fiber. Owing to the NPE action in the laser cavity, significant pulse length shortening as well as pulse stability improvement were observed as compared with a SWCNTs-only mode-locked laser. The shortest achieved pulse width of near transform-limited solitons was 222 fs at the output average power of 9.1 mW and 45.5 MHz repetition frequency, corresponding to the 0.17 nJ pulse energy.

Dissipative Soliton Generation and Amplification in Erbium-Doped Fibers Operating at 1.55 μm

We report on our recent developments on ultrafast pulse generation in erbium-doped fiber laser systems operating in the 1550 nm wavelength range. This work concerns the generation of ultrafast pulses from dissipative soliton fiber lasers featuring resonant saturable absorber mirrors as well as their amplification in highly efficient erbium-doped large-mode-area fibers. Different amplification schemes featuring all-fiber components are studied leading to the achievement of record pulse energy from a high repetition rate laser system. The system delivers 8 W of average power at 35 MHz repetition rate corresponding to 230 nJ pulse energy. After external compression, near transform-limited, 850 fs-long pulses are obtained. The pulse peak power exceeds 180 kW.

SESAM and SWCNT Mode-Locked All-Fiber Thulium-Doped Lasers Based on the Nonlinear Amplifying Loop Mirror

We report on thulium-doped all-fiber lasers based on the nonlinear amplifying loop mirror and mode-locked with a semiconductor saturable absorber (SESAM) or single-walled carbon nanotubes (SWCNTs). An intracavity and external dispersion management was realized with the aid of a passive germanium-silicate fiber. The SESAM mode-locked laser generates as short as 230-fs pulses with a maximum average output power of 106 mW, corresponding to a 3.7 kW peak power and almost 2 nJ pulse energy. In contrast to the SESAM-based laser, the SWCNT mode-locked laser generates 450-fs pulses of mW-level average output power.

Compact femtosecond fiber laser with integrated optical components

A compact femtosecond ytterbium-doped fiber laser has been developed with integrated optical components. The femtosecond fiber laser oscillator was miniaturized by integrating the intracavity wavelength division multiplexer and optical isolator with collimators, and placing a quarter-wave plate before a transmission grating pair to get light retroflection from the intracavity dispersive delay line. Stretched-pulse mode-locking could be self-started at a repetition rate of 65 MHz with pump power as low as 100 mW. The compact femtosecond fiber laser oscillator could be optimized to generate 86 fs pulse duration and 0.5 nJ pulse energy.

High peak-power monolithic femtosecond ytterbium fiber chirped pulse amplifier with a spliced-on hollow core fiber compressor.

We demonstrate a monolithic Yb-fiber chirped pulse amplifier that uses a dispersion matched fiber stretcher and a spliced-on hollow core photonic bandgap fiber compressor. For an output energy of 77 nJ, 220 fs pulses with 92% of the energy contained in the main pulse, can be obtained with minimal nonlinearities in the system. 135 nJ pulses are obtained with 226 fs duration and 82 percent of the energy in the main pulse. Due to the good dispersion match of the stretcher to the hollow core photonic bandgap fiber compressor, the duration of the output pulses is within 10% of the Fourier limited duration.

H‐Shaped Oligofluorenes for Highly Air‐Stable and Low‐Threshold Non‐Doped Deep Blue Lasing

H-shaped oligofluorenes as gain media exhibit excellent photo- (large robustness against oxidation) and thermal stabilities in ambient atmosphere for large σe and low-threshold (0.22 nJ pulse(-1) ) deep blue distributed feedback (DFB) lasers. Their amplified spontaneous emission (ASE) thresholds increase less than 3-fold and the emission spectra exhibit almost no shift with film samples annealed up to 200 °C in open air.

Graphene mode-locked Cr:ZnS laser with 41 fs pulse duration

We report the ultrashort-pulse Cr:ZnS laser mode-locked by graphene-based saturable absorber mirror. Using the combination of bulk material and a chirped mirror, we demonstrate the shortest reported so far mid-IR pulses of only 5.1 optical cycles (41 fs) centered at 2.4 µm with 190 nm spectral bandwidth. The pulse spectrum almost completely fills the water-free atmospheric window. The output parameters reach 2.3 nJ pulse energy and 250 mW average output power at 108 MHz repetition rate.

Self-similar erbium-doped fiber laser with large normal dispersion

We report a large normal dispersion erbium-doped fiber laser with self-similar pulse evolution in the gain fiber. The cavity is stabilized by the local nonlinear attractor in the gain fiber through the use of a narrow filter. Experimental results are accounted for by numerical simulations. This laser produces 3.5 nJ pulses, which can be dechirped to 70 fs with an external grating pair.

Guided continuous-wave and graphene-based Q-switched lasers in carbon ion irradiated Nd:YAG ceramic channel waveguide

We demonstrate the lasing performance in the Nd:YAG ceramic channel waveguide produced by the carbon ion irradiation, including the continuous-wave (cw) and graphene Q-switched configurations. The highest slope efficiency of 56% and the lowest threshold of 40 mW have been obtained for the cw waveguide laser. With graphene as a saturable absorber, the Q-switched laser produces stable pulses with 57 ns pulse duration and 77 nJ pulse energy, respectively. Under the variation of the pumping power, the repetition of the pulse laser could be modified from 1.5 MHz to 4.1 MHz.