Harmonic splitting phenomenon of bright-dark pulse pairs in a passive mode-locked Thulium-Holmium co-doped fiber laser

This study reports a passive mode-locked Thulium-Holmium co-doped fiber laser featuring a figure-9 shaped resonator structure.The laser utilizes a nonlinear amplifying loop mirror(NALM)as the mode-locking device.By increasing pump power,the laser’s output evolution was experimentally observed,showing that bright-dark pulse pairs first split into double pulses and then into a second harmonic state.Additionally,the time intervals between bright and dark pulses and between double pulses increased with higher pump power.The RF spectrum of the bright-dark pulse pairs exhibited envelope modulation,with a modulation frequency approximately equal to the reciprocal of the time interval between bright and dark pulses.When the pump power increased from 0.46 W to 0.72 W,the reciprocal of the modulation frequency showed a linear growth trend.These findings contribute to understanding the evolution patterns of bright-dark pulse pairs in passive mode-locked fiber lasers.

Generation of cavity-birefringence-dependent multi-wavelength bright-dark pulse pair in a figure-eight thulium-doped fiber laser

We experimentally demonstrated a stable multi-wavelength bright-dark pulse pair in a mode-locked thulium-doped fiber laser(TDFL).The nonlinear polarization rotation(NPR)and nonlinear optical loop mirror(NOLM)were employed in a figure-eight cavity to allow for multi-wavelength mode-locking operation.By incorporating different lengths of high birefringence polarization-maintaining fiber(PMF),the fiber laser could operate stably in a multi-wavelength emission state.Compared with the absence of the PMF,the birefringence effect caused by PMF resulted in rich multi-wavelength optical spectra and better intensity symmetry and stability of the bright-dark pulse pair.

Interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser

We numerically investigate the formation and interaction of a parabolic-shaped pulse pair in a passively mode-locked Yb-doped fiber laser. Based on a lumped model, the parabolic-shaped pulse pair is obtained by controlling the intercavity average dispersion and gain saturation energy, Moreover, pulse repulsive and attractive motion are also achieved with different pulse separations. Simulation results show that the phase shift plays an important role in pulse interaction, and the interaction is determined by the inter-cavity average dispersion and gain saturation energy, i.e., the strength of the interaction is proportional to the gain saturation energy, a stronger gain saturation energy will result in a higher interaction intensity. On the contrary, the increase of the inter-cavity dispersion will counterbalance some interaction force. The results also show that the interaction of a parabolic-shaped pulse pair has a larger interaction distance compared to conventional solitons.

Calcium-mediated paired pulse depression in juvenile rat dorsal striatum

As the major division of the basal ganglia, neostriatum forms mutual connections with multiple brain areas and is critically involved in motor control and learning/memory. Long-term synaptic plasticity has been widely studied in different species recently. However, there are rare reports about the short-term synaptic plasticity in neostratium. In the present study, using field excitatory postsynaptic potentials recording, we reported one form of short-term synaptic plasticity that is paired pulse depression in juvenile rat dorsal striatum slices induced by stimuli of the white matter. The field excitatory postsynaptic potentials could be abolished by α-amino-3-hydroxy-5-methylizoxazole-4-propionic acid receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione, but not by gamma-aminobutyric acid type A receptor antagonist bicuculline or dopamine D1 receptor antagonist SKF-81297. The paired pulse depression in the corticostratial pathway was different from paired pulse facilitation in the hippocampal CA1 synapse. In addition, the paired pulse depression was not affected by bath application of gamma-aminobutyric acid type A receptor antagonist or dopamine D1 receptor antagonist. However, low calcium and high magnesium could attenuate the paired pulse depression. These findings suggest a more complicated plasticity form in the dorsal striatum of juvenile rats that is different from that in the hippocampus, which is related with extracellular calcium.

Electron vortices in photoionization by a pair of elliptically polarized attosecond pulses

The photoionization by two elliptically polarized, time delayed attosecond pulses is investigated to display a momentum distribution having the helical vortex or ring structuresi The results are obtained by the strong field approximation method and analyzed by the pulse decomposition. The ellipticities and time delay of the two attosecond pulses are found to determine the rotational symmetry and the number of vortex arms. For observing these vortex patterns, the energy bandwidth and temnoral duration of the attosecond pulses are ideal.

Modification of laser-induced state in atomic attosecond transient absorption by the XUV pulse pair

Attosecond transient absorption(ATA)has been developed as an all-optical technique for probing electron dynamics in matter.Here we present a scheme that can modify the laserinduced state and the corresponding ATA spectrum via excitation by a pair of XUV attosecond pulses and by a time-delayed mid-infrared(MIR)laser probe.Different from the scheme of the electronic excitation by a single XUV attosecond pulse,the application of a pair of XUV pulses provides extra degrees of freedom,such as the time delay and the intensity ratio between two XUV pulses,which make it possible to adjust the pump process,resulting in the modification of the ATA spectrum.We show that by varying the time delay between the two XUV pulses,the population of the dark state and the ATA spectrum of the laser-induced state have periodic modulations.We also demonstrate that the peak of the ATA spectrum of the laser-induced state appears at a fixed time delay between the XUV pair and the MIR laser when the intensity ratio is large,and it changes with the time delay when the intensity ratio is small,which can be related to either one of two peaks in the population of the dark state.