Ultrashort Pulse Operation Research Articles

Ultrashort Pulse Generation in Modeless Laser Cavity

We demonstrate experimentally that random phase modulation of an erbium-doped fiber ring-laser by an intra-cavity electro-optic phase modulator did not inhibit ultrashort-pulse operation. Stable and self-starting ultrashort-pulse operation with a single pulse circulating in the cavity was achieved even when the phase modulator was driven with random sequences sufficiently fast and strong to render the laser cavity modeless, in the sense that heterodyning of the laser output did not show any spectral lines corresponding to a mode spectrum. No significant change in measured pulse characteristics was observed, compared to conventional mode-locking in the unmodulated cavity. The insensitivity to the random phase modulation is expected, given the lack of phase-sensitive elements in the cavity.

2D GeP-based photonic device for near-infrared and mid-infrared ultrafast photonics

Abstract Germanium phosphide (GeP), a rising star of novel two-dimensional (2D) material composed of Group IV–V elements, has been extensively studied and applied in photonics thanks to its broadband optical absorption, strong light–matter interaction and flexible bandgap structure. Here, we show the strong nonlinear optical (NLO) properties of 2D GeP nanoflakes in the broadband range with open-aperture Z-scan technique to explore the performance of 2D GeP microfiber photonic devices (GMPDs) in near-infrared (near-IR) and mid-infrared (mid-IR) ultrafast photonics. Our results suggest that employing the GMPD as an optical device in an erbium-doped fiber laser (EDFL) system results in ultrashort pulses and rogue waves (RWs) at 1.55 μm. Likewise, by the incorporation of GMPD into a thulium-doped fiber laser (TDFL) system, stable ultrashort pulse operation is also achieved at 2.0 μm. We expect these findings to be an excellent GMPD that can be applied in mode-locked fiber lasers to open up new avenues for its development and application in ultrafast photonics.

Mode-locking Instabilities for High-Gain Semiconductor Disk Lasers Based on Active Submonolayer Quantum Dots

Optically pumped continuous-wave (cw) semiconductor disk lasers (SDLs) have an established commercial impact, and recent progress in ultrashort-pulse operation makes them attractive for applications in frequency metrology. There is, however, a tradeoff between femtosecond pulse lengths and average output power. Quantum-dot (QD) materials could potentially solve this problem---but not just any dots. The authors show that SDLs based on active submonolayer QDs produce record-high cw output power, but without stable mode locking, which is due to fundamental physical reasons.

High power linearly polarized fiber laser: Generation, manipulation and application

Linearly-polarized (LP) fiber lasers, which could find wide potential applications such as coherent detection, coherent/spectral beam combining, nonlinear frequency conversion, have been a research focus in recent years. In this paper, we will present a general review on the achievements of various kinds of high power LP fiber laser and its applications for the first time. The recent progress in high power LP fiber oscillator, including fiber oscillator based on active fiber, Raman fiber laser and Random distributed feedback fiber laser are summarized. Power scaling of LP fiber laser by using active-fiber based power amplifier, passive-fiber based Raman amplifier, and active/passive fiber based hybrid fiber amplifier has been achieved. Polarization-maintained active fiber based power amplifier and non-polarization-maintained active fiber based power amplifier incorporating active polarization control are specially introduced in detail. High power LP fiber laser with diversified property, such as narrow-linewidth, wavelength-tunable and ultrashort pulse operation, are summarized. Various kinds application of high power LP fiber laser, including beam combining, supercontinumm generation, mid-infrared lasing, structured light field and ultrasonic generation, are presented at the end of this paper.

Intracavity terahertz generation inside a high-energy ultrafast soliton fiber laser

Intracavity terahertz emission inside a high-energy ultrafast Yb-doped fiber laser is presented. The terahertz radiation is generated by a transient photocurrent induced at the surface of a saturable InGaAs multiquantum well grown by molecular beam epitaxy on top of a semiconductor Bragg reflector. This device simultaneously works as the saturable absorber mirror for initiating and managing the passive mode locking required for the ultrashort pulse operation of the laser system. The maximum terahertz average power achieved is 4.2μW, which reveals a net conversion efficiency of 3.1×10−5.

Proposed few-optical cycle laser-driven particle accelerator structure

We describe a transparent dielectric grating accelerator structure that is designed for ultrashort laser pulse operation. The structure is based on the principle of periodic field reversal to achieve phase synchronicity for relativistic particles; however, to preserve ultrashort pulse operation it does not resonate the laser field in the vacuum channel. The geometry of the structure appears well suited for application with high average power lasers and high thermal loading. Finally, it shows potential for an unloaded gradient of $10\text{ }\text{ }\mathrm{GeV}/\mathrm{m}$ with 10 fs laser pulses and the possibility to accelerate ${10}^{6}$ electrons per bunch at an efficiency of 8%. The fabrication procedure and a proposed near term experiment with this accelerator structure are presented.

Fiber laser mode-locked with a semiconductor saturable absorber etalon operating in transmission

We demonstrate a ring cavity ytterbium fiber laser mode-locked with a semiconductor saturable absorber used in transmission. The resonant cavity-enhanced nonlinear response corresponding to the low-loss transmission state enables a robust self-starting mode-locking. Such a transfer function is opposite to that of the resonant absorber operating in the reflection mode, where the highest modulation depth matches the high-loss state. The device ensures ultrashort pulse operation with the wavelength self-adjusted to the optimal value corresponding to the low-loss state of the laser cavity. When using a saturable absorber etalon in transmission mode, the mode-locking mechanism is also highly tolerant to the total cavity dispersion

Ultra-short pulse operation of all-optical fiber passively mode-locked ytterbium laser

The generation regimes of an all-fiber passively mode-locked ytterbium laser with intra-cavity photonic crystal fiber have been studied with the aim to provide recipes for obtaining chirp-free sub-picosecond pulses directly from the cavity. Small-beam area photonic-crystal fiber is used for dispersion compensation of the intra-cavity normal dispersion of b-doped and single-mode fibers as well as for spectrum expanding due to enhanced nonlinearity. Regions of the gain and fiber parameters near the generation threshold were found in both cases of normal and anomalous net intra-cavity dispersion, which provide a stable generation of ultra-short sub-picosecond pulses directly from the cavity. Laser parameters of a transition to the multi-pulsed generation regimes were also found.

Carrier Dynamics in Semiconductors under MIR FEL Excitation

Free electron lasers have unique advantages; wide-range wavelength tunability, ultrashort pulse operation and intense peak power. The high-power coherent laser beam in the mid-infrared (MIR) region provides unique opportunities to investigate carrier dynamics in semiconductors. Band-gap luminescence from a variety of compound semiconductors has been observed with an intense MIR radiation beam being directed to the samples. The band-gap luminescence is attributed to impact-ionization following scattering-induced free-electron heating.

Calcium niobium gallium and calcium lithium niobium gallium garnets doped with rare earth ions––effective laser media

The results of spectroscopy and laser action of disordered calcium niobium gallium (CNGG) and calcium lithium niobium gallium (CLNGG) garnets doped with Nd3+, Eu3+, Er3+, Ho3+ and Tm3+ were displayed. The structure and some optical and physical properties of CNGG and CLNGG-crystals were studied. Activator centers construction and the mechanism of inhomogeneous broadening and splitting of spectral lines of rare earth ions (TR3+) in CNGG and CLNGG-crystals were analyzed. Possibilities of laser media based on CNGG and CLNGG with TR3+-ions for pulse free running, Q-switch, CW and ultrashort pulse operation regimes were considered.

Free electron laser annealing of N-ion-implanted 3C-SiC films

Infrared laser annealing at a variety of wavelengths (10.0–13.0 μm) was performed under room temperature for cubic silicon carbide (3C-SiC) films after N-ion implantation by using a free electron laser with features of wide-range tunability, ultrashort pulse operation (∼10 ps), and intense peak power (∼MW). Infrared absorption spectroscopy indicated that the annealing at 12.6 μm, which corresponds to the absorption peak of Si–C stretch mode, was effective for removing the crystalline damage induced by the ion implantation. On the other hand, Hall effect measurements showed an increase of carrier density for samples annealed at around 10.4 μm, whereas the absorption was weak at this wavelength. This important result is most likely attributed to the activation of N donors caused by the direct excitation of a local vibration mode associated with N atoms in the SiC matrix.

Free electron laser annealing of silocon carbibe

We have applied a free electron laser (FEL) to crystallize amorphous silicon carbide (a-SiC) and to remove the damage and activate the dopant of a damaged layer of nitrogen implanted cubic silicon carbide (3C-SiC) films at room temperature. The FEL has two main characteristics, wavelength tunability and ultrashort-pulse operation (~10 ps) with intense peak power (~MW). The wave-length was selected at the energy of the Si-C stretch mode in order to excite the lattice vibration directly. We observed the crystallization of a-SiC occurs at room temperature when irradiation with a 12.6 µm FEL. The present results indicate that FEL annealing (12.6 µm: transverse optical mode, 10.3 µm: longitudinal optical mode) is effective for recrystallization and activation of an ion-implanted SiC films.

Interferometric 2D imaging amplitude correlator for ultrashort pulses

A new and convenient method is demonstrated to measure the amplitude correlation and crosscorrelation for either single or multiple ultrashort pulse operation using diffraction grating and a two-dimensional CCD array. A single-shot crosscorrelation detection of a femtosecond pulse train is experimentally demonstrated.