Study on pump pulse characteristics of QCW diode-side-pumped Nd:YAG laser

The influence of pumping laser pulse on the property of quasi-continuous-wave diode-side-pumped Nd:YAG laser is investigated theoretically and experimentally here. Under remaining a fixed duty cycle, the average output power increases, and the corresponding thermal focal length shorten with the increase of the pump pulse duration, which attributes to the decrease of the ratio of pulse buildup time to the pulse duration. At a pump power of 146 W, the laser output power changes from 65.1 W to 81.2 W when the pulse duration is adjusted from 150 μs to 1000 μs, confirming a significant enhancement of 24.7%. A laser rate equation model incorporating the amplified spontaneous emission is also utilized and numerically solved, and the simulated results agree well with the experimental data.

The effects of pump pulse fluence on the output energy and amplified spontaneous emission of a femtosecond regenerative amplifier

In this paper, the effects of pump pulse fluence on the output energy and amplified spontaneous emission (ASE) of a femtosecond regenerative amplifier are investigated. One can easily enhance the output energy of laser amplifiers by increasing their pump fluence. This in turn can increase the ASE and reduce the performance of amplifiers in terms of output beam quality, beam stability, etc. This effect would eventually lead to what is called ‘temporal intensity contrast deterioration’. In this work, it is shown that an optimum state of the pump pulse fluence can indeed optimize the amount of the output energy from a regenerative amplifier without much reducing the performance of the amplifier due to the higher ASE. Temporal gain characteristics were employed to achieve this optimum value for a better design, performance, and maintenance of femtosecond laser amplifiers. The results of the current study can be effectively used in designing a wide range of regenerative amplifiers for femtosecond pulses.

Duration-controllable mid-infrared pulse from bias-pumped Er:ZBLAN fiber laser

We experimentally demonstrate the generation of duration-controllable pulses at 2.8 µm based on bias-pump technique for the first time. Bias-pumped by a 976 nm continuous-wave (CW)-pulsed combined laser, duration-controllable pulses are produced from an Er:ZBLAN fiber laser and the duration is entirely determined by the duration of pump pulse. Numerical simulations agree with experimental results well, and further predict that the temporal profile of output pulse from bias-pumped Er:ZBLAN fiber laser can also be identical with that of pump pulse under certain conditions. The pump-controlled mid-infrared pulse may have more applications in various areas due to its manageable temporal characteristics.

Anomalous ultrafast all-optical Hall effect in gapped graphene

We propose an ultrafast all-optical anomalous Hall effect in two-dimensional (2D) semiconductors of hexagonal symmetry such as gapped graphene (GG), transition metal dichalcogenides (TMDCs), and hexagonal boron nitride (h-BN). To induce such an effect, the material is subjected to a sequence of two strong-field single-optical-cycle pulses: A chiral pump pulse followed within a few femtoseconds by a probe pulse linearly polarized in the armchair direction of the 2D lattice. Due to the effect of topological resonance, the first (pump) pulse induces a large chirality (valley polarization) in the system, while the second pulse generates a femtosecond pulse of the anomalous Hall current. The proposed effect is fundamentally the fastest all-optical anomalous Hall effect possible in nature. It can be applied to ultrafast all-optical storage and processing of information, both classical and quantum.

Supercontinuum generation in photonic crystal fibers infiltrated with tetrachloroethylene

This study proposes a photonic crystal fiber made of fused silica glass, with the core infiltrated with tetrachloroethylene (C2Cl4) as a new source of supercontinuum (SC) spectrum. We studied numerically the guiding properties of the several different fiber structures in terms of characteristic dispersion, mode area, and attenuation of the fundamental mode. Based on the results, the structural geometries of three C2Cl4-core photonic crystal fibers were optimized in order to support the broadband SC generations. The first fiber structure with lattice constant 1.5 μm and filling factor 0.4 operates in all-normal dispersion. The SC with a broadened spectral bandwidth of 0.8–2 μm is generated by a pump pulse with a central wavelength of 1.56 μm, 90 fs duration and energy of 1.5 nJ. The second proposed structure, with lattice constant 4.0 μm and filling factor 0.45, performs an anomalous dispersion for wavelengths longer than 1.55 μm. With the same pump pulse as the first fiber, we obtained the coherence SC spectrum in an anomalous dispersion range with wavelength range from 1 to 2 μm. Meanwhile, the third selected fiber (lattice constant 1.5 μm, filling factor 0.55) has two zero dispersion wavelengths at 1.04 μm and 1.82 μm. The octave-spanning of the SC spectrum formed in this fiber was achieved in the wavelength range of 0.7–2.4 μm with an input pulse whose optical properties are 1.03 μm wavelength, 120 fs duration and energy of 2 nJ. Those fibers would be good candidates for all-fiber SC sources as cost-effective alternatives to glass core fibers.