Jiaming Jiang

Dual nonlinear dielectric resonance and strong natural resonance in Ni/ZnO nanocapsules

The electromagnetic characteristics of Ni/ZnO nanocapsules were studied at 2–18 GHz. The dual nonlinear dielectric resonance and strong natural resonance at 16.6 GHz contribute to excellent electromagnetic absorption. A reflection loss (RL) exceeding −20 dB was calculated in 14–18 GHz for an absorber thickness of 2.05 mm, and RL exceeds −10 dB in the whole X-band (10–12.4 GHz) and the whole Ku-band (12.4–18 GHz) for a thickness of 2.50 mm. The equivalent circuit model was used to explain the dual nonlinear dielectric resonance, which is ascribed to a cooperative consequence of the core/shell interfaces and the dielectric ZnO shells.

Microstructure and magnetic properties of graphite-coated Gd nanocapsules

Gd nanocapsules, which are stable in air with the protection of graphite shells, are prepared by a modified arc-discharge technique. A size-induced structural transformation from the hexagonal-close-packed (hcp) to the higher-symmetry face-centered-cubic structure is observed. The graphite-coated hcp-Gd nanocapsules display a blocked state below 35 K, superparamagnetism between 35 and 290 K, and typical paramagnetism above 290 K. The hcp-Gd nanocapsules have a magnetic-entropy change −ΔSm of 48.8 J kg−1 K−1 at 6 K for an applied-field change from 1 to 7 T.

Selective generation of an intense single harmonic from a long gas cell with loosely focusing optics based on a three-color laser field

The selective generation of an intense single harmonic has been experimentally achieved in argon from a long gas cell with loosely focusing optics using a three-color laser field. When compared with the single harmonic emission from a continuous gas jet, both the intensity and the purity of the selected single harmonic emission from the long gas cell show dramatic improvements; the peak intensity is more intense by as much as 1–2 orders of magnitude, while the contrast ratio (i.e., the spectral purity) is simultaneously increased by several times. The underlying physics of this enhancement can be explained using the strong field approximation model with the propagation effect.

Enhanced high-order harmonic generation from spatially prepared filamentation in argon

We experimentally demonstrate enhanced high-order harmonic generation (HHG) from spatially prepared filamentation in Argon. Upon shifting the focus position of an elliptically polarized laser pulse over the filament induced by a linearly polarized laser pulse, an obvious enhancement of harmonic yield by nearly one order of magnitude is observed. The result could be interpreted in terms of the double contributions from both the excited states of target atom and the phase-matching effect of harmonic beam. In contrast to the enhancement phenomena, an obvious suppression of harmonic yield is also presented, which could be attributed to both the ground-state depletion and the plasma effect.

Observation of CEP effect via filamentation in transparent solids

We report on the first direct observation of carrier-envelope-phase (CEP) effect during the interaction between few-cycle laser pulses and bulk solid materials. Using 2-cycle mid-infrared laser pulses with stabilized CEP, the CEP effect of tunneling ionization during the laser filamentation in a fused silica is revealed. The phase variation of the accompanying supercontinuum (SC) emission with filamentation at different CEPs of laser pulses can be measured by means of spectral interference technique, as a direct manifestation of the strong field tunneling ionization dynamics in transparent solids.

Enhanced high-order harmonic generation from excited argon

We experimentally demonstrate an effective scheme to generate the enhanced high-order harmonics from a coherent superposition state of ground state and excited states in Argon. By controlling the time delay between the pump and probe laser pulses, a surprising enhancement plateau of high-order harmonic generation is observed, with a half lifetime of dozens of picoseconds. In the plateau, the harmonic intensity is enhanced by nearly one order of magnitude compared to the case without pre-excitation. Moreover, the gradual enhancement process is also presented when the pump intensity is increasing for improving the population of excited states, which can be attributed to the Rydberg states created by frustrated tunneling ionization.

Efficient selection of a single harmonic emission using a multi-color laser field with an aperture-iris diaphragm

The efficient selection of an almost pure single harmonic emission (the 14th harmonic at 57 nm) from the harmonic comb has been experimentally achieved in an argon gas cell using a multi-color laser field with an aperture-iris diaphragm. When compared with the non-diaphragm case, the purity of the selected single harmonic emission (i.e. the contrast ratio) in the case of using the aperture-iris diaphragm is dramatically increased by approximately order of magnitude. Therefore, the modification of the multi-color laser field by using such an aperture-iris diaphragm before focusing is demonstrated to be an effective way of improving the phase-matching conditions for selective enhancement of the single harmonic emission.

Spatially and spectrally resolved quantum-path tracing in high-order harmonic generation

We experimentally demonstrate the macroscopic evolution of quantum-path distributions in harmonic emission with spatial and spectral resolution from an argon gas jet, and obviously observe that the spatial profiles of harmonics are gradually split into two components (the red and blue shifts) when the driving laser intensity is increased. Moreover, the red and blue shifts in quantum-path distributions are experimentally traced and clarified in the spatial and spectral domain by choosing the focal position. These results give a more comprehensive understanding and therefore a better control of harmonic emission.