Xinbing Wang

Perfect narrow band absorber for sensing applications

We design and numerically investigate a perfect narrow band absorber based on a metal-metal-dielectric-metal structure which consists of periodic metallic nanoribbon arrays. The absorber presents an ultra narrow absorption band of 1.11 nm with a nearly perfect absorption of over 99.9% in the infrared region. For oblique incidence, the absorber shows an absorption more than 95% for a wide range of incident angles from 0 to 50°. Structure parameters to the influence of the performance are investigated. The structure shows high sensing performance with a high sensitivity of 1170 nm/RIU and a large figure of merit of 1054. The proposed structure has great potential as a biosensor.

Few-cycle attosecond pulses with stabilized-carrier-envelope phase in the presence of a strong terahertz field

High-order harmonic generation in the presence of a strong terahertz field is investigated, and phase stabilization of the few-cycle laser pulses is extended to the extremely ultraviolet region. It is found that the strong terahertz field significantly breaks the symmetry between the consecutive half-cycle and greatly extends the harmonic cutoff, producing both odd and even harmonics which are covered with an extremely broad bandwidth and well locked in phase. These results can support the generation of few-cycle attosecond pulse trains with stabilized carrier-envelope phase from pulse to pulse, and also enables the generation of phase-stabilized pulse train with tunable wavelength.

Control of quantum paths in the multicycle regime and efficient broadband attosecond pulse generation

We theoretically investigate the broadband isolated attosecond generation in a two-color multicycle laser pulse. It is shown that quantum path selection can be realized and then a sub-100-as isolated attosecond pulse is straightforwardly obtained. By adding an UV attosecond pulse to the synthesized two-color field, the continuous harmonic yield is significantly enhanced by 2 orders and the bandwidth is further broadened, which is beneficial to the efficient generation of a sub-100-as isolated attosecond pulse.

Double ionization of HeH+ molecules in intense laser fields.

We present quantum mechanical calculations of double ionization of HeH(+) molecules by intense laser pulses at various intensities. The resulting two-electron momentum distributions exhibit a clear asymmetry, which depends on the laser intensity. The asymmetric charge configuration of HeH(+) is responsible for the asymmetric two-electron momentum distributions. An approach to control the dynamics of double ionization of heteronuclear molecules is proposed.

Time and space resolved visible spectroscopic imaging CO2 laser produced extreme ultraviolet emitting tin plasmas

Experiments involving laser produced tin plasma have been carried out using a CO2 laser with an energy of 800 mJ/pulse and a full width at half maximum (FWHM) of 80 ns in vacuum. Time-integrated extreme ultraviolet spectral measurement showed that the peak of the extreme ultraviolet lithography spectrum was located at 13.5 nm and the spectrum profile’s FWHM of the unresolved transition arrays was 1.1 nm. Plasma parameters of the electron temperature and density measurements in both axial and radial directions at later times had been obtained from a two-dimensional time and space resolved image spectra analysis. The axial spatial distribution of the electron density showed a 1/d2.6 decrease profile, and the radial spatial distribution of the electron density showed a 1/r1.1 profile, in which d is the axial distance from the target surface and r is the radial distance. The electron density was found to maintain symmetry across the radial distance at all delay times. Near the plasma plume center, the electro...

Tunable middle infrared radiation generation in a GaSe crystal

Tunable second harmonic generation of pulsed CO2 laser radiation in a GaSe crystal was demonstrated. The nonlinear optical properties of GaSe and phase-matching conditions were investigated, and the best fitted dispersion relationships for this crystal were also determined. External conversion efficiency of 0.1% with unfocused pumped radiation had been achieved and maximum single pulse energy of 0.19 mJ was generated at 5.3 μm.

Simulations for transversely diode-pumped metastable rare gas lasers

The transverse pumping geometry simplifies the laser system design by separating pump and laser beams and providing space for multiple diode laser pump sources with poor beam quality. A transverse pumping double-pass model for metastable rare gas lasers is presented in this paper, in which some intra-cavity information can be obtained. The comparison with Yang’s longitudinally pumped calculation results demonstrated the validity of our model. Several important factors having influence on optical conversion efficiency are simulated and discussed. Simulation of the effects of the required plasma size in transverse pumping model shows that a small size of 0.3  cm×10  cm×10  cm is capable of emitting 9 kW with an optical conversion efficiency over 55% and a megawatt-class output would only need an active medium of several liters if the metastable atoms concentration reaches 3×1013  cm−3.

Tunable plasmon-induced transparency and slow-light based on graphene metamaterials

Graphene has attracted much attention due to its unique optical properties as a new kind of plasmonic metamaterial in the terahertz regime. Here, we theoretically investigated a wavelength tunable plasmon induced transparency (PIT) device based on graphene metamaterials which is composed of periodically patterned graphene nanostructures. The interactions and coupling between plasmonic modes are investigated in detail by analyzing the field distributions and spectral responses. The coupled Lorentz oscillator models are used to explain the physical mechanism of the PIT. The finite-difference-time-domain (FDTD) method is used to investigate the tunable properties of the structure. It is shown that the coupling strength between the bright mode and dark mode is tuned by the coupling distance between the elements of the proposed structure. By varying the Fermi level of graphene, the PIT resonant frequency can be dynamically tuned. Furthermore, we demonstrate numerically that tunable slow light can be realized in our patterned graphene metamaterials.

Narrow spectral width laser diode for metastable argon atoms pumping

Diode laser pump source with narrow emitting spectrum for optically pumped metastable rare gas laser (OPRGL) of argon was achieved by employing a complex external cavity coupled with volume Bragg grating (VBG). A commercially available c-mount laser diode with rated power of 6 W was used and studied in both the free running mode and VBG external cavity. The maximum output power of 3.9 W with FWHM less than 25 pm and peak wavelength locked around 811.53 nm was obtained from the VBG external cavity laser diode. Precise control of VBG temperature enabled fine tuning of the emission wavelength over a range of 450 pm. Future researches on OPRGL of argon will benefit from it.