Ultrasensitive specific terahertz sensor based on tunable plasmon induced transparency of a graphene micro-ribbon array structure.

We proposed an ultrasensitive specific terahertz sensor consisting of two sets of graphene micro-ribbon with different widths. The interference between the plasmon resonances of the wide and narrow graphene micro-ribbons gives rise to the plasmon induced transparency (PIT) effect and enables ultrasensitive sensing in terahertz region. The performances of the PIT sensor have been analyzed in detail considering the thickness and refractive index sensing applications using full wave electromagnetic simulations. Taking advantage of the electrical tunability of graphene's Fermi level, we demonstrated the specific sensing of benzoic acid with detection limit smaller than 6.35 µg/cm2. The combination of specific identification and enhanced sensitivity of the PIT sensor opens exciting prospects for bio/chemical molecules sensing in the terahertz region.

A multi-spot laser induced breakdown spectroscopy system based on diffraction beam splitter.

A quick simultaneous multispot laser induced breakdown spectroscopy (LIBS) system has been proposed. The basic idea is to combine the Diffraction Beam Splitter (DBS) with the linear-to-linear fiber bundle. The DBS divided the incident laser beam into five sub-beams, and then, a lens focused the incident sub-beam to produce a plasma array, where the distance between the neighbor subplasma was constant and the plasma emission was imaged on the fiber bundle. Each ablated spot on the sample generated the corresponding spectroscopy signals, which were collected by the defined fibers of the fiber bundle, propagated to the spectrograph slit, and then analyzed by the intensified charge-coupled device (ICCD) detector, where the two-dimensional capability of the charge-coupled device detectors was explored for the spectroscopy and position analyses. The five spectroscopy ribbon presented on the ICCD corresponded to the plasma radiation of the five ablated spots. The feasibility of a simultaneous multipoint spectroscopy detection at a single pulse ablation was confirmed by subjecting to the spectroscopy analyses of a copper plane, layered material, and magnesium-molybdenum mixture. The multispot LIBS system can be used in the ejecta research of detonation physics, fluid physics, and so on.

Time-resolved single-shot terahertz time-domain spectroscopy for ultrafast irreversible processes.

Pulsed terahertz spectroscopy is suitable for spectroscopic diagnostics of ultrafast events. However, the study of irreversible or single shot ultrafast events requires ability to record transient properties at multiple time delays, i.e., time resolved at single shot level, which is not available currently. Here by angular multiplexing use of femtosecond laser pulses, we developed and demonstrated a time resolved, transient terahertz time domain spectroscopy technique, where burst mode THz pulses were generated and then detected in a single shot measurement manner. The burst mode THz pulses contain 2 sub-THz pulses, and the time gap between them is adjustable up to 1 ns with picosecond accuracy, thus it can be used to probe the single shot event at two different time delays. The system can detect the sub-THz pulses at 0.1 THz-2.5 THz range with signal to noise ratio (SNR) of ∼400 and spectrum resolution of 0.05 THz. System design was described here, and optimizations of single shot measurement of THz pulses were discussed in detail. Methods to improve SNR were also discussed in detail. A system application was demonstrated where pulsed THz signals at different time delays of the ultrafast process were successfully acquired within single shot measurement. This time resolved transient terahertz time domain spectroscopy technique provides a new diagnostic tool for irreversible or single shot ultrafast events where dynamic information can be extracted at terahertz range within one-shot experiment.