Optical sensors, with great potential to convert invisible bioanalytical response into readable information, have been envisioned as a powerful platform for biological analysis and early diagnosis of diseases. However, the current extraction of sensing data is basically processed via a series of complicated and time-consuming calibrations between samples and reference, which inevitably introduce extra measurement errors and potentially annihilate small intrinsic responses. Here, we have proposed and experimentally demonstrated a calibration-free sensor for achieving high-precision biosensing detection, based on an optically controlled terahertz (THz) ultrafast metasurface. Photoexcitation of the silicon bridge enables the resonant frequency shifting from 1.385 to 0.825 THz and reaches the maximal phase variation up to 50° at 1.11 THz. The typical environmental measurement errors are completely eliminated in theory by normalizing the Fourier-transformed transmission spectra between ultrashort time delays of 37 ps, resulting in an extremely robust sensing device for monitoring the cancerous process of gastric cells. We believe that our calibration-free sensors with high precision and robust advantages can extend their implementation to study ultrafast biological dynamics and may inspire considerable innovations in the field of medical devices with nondestructive detection.

Terahertz radiation from tunneling ionization of gaseous atoms and molecules in the two-color laser fields with various polarizations has been investigated. We experimentally demonstrate that the efficiency of terahertz emission in the circularly polarized laser fields with the same helicity is 5 times higher than that with linearly polarized two-color femtosecond pulses in high laser intensity. By solving time-dependent Schrödinger equation, this enhancement is well explained based on the analysis of electron tunneling ionization and subsequent dynamics.

Air-plasma is a convenient and table-top source for the broadband and coherent terahertz (THz) wave generation. However, the lack of enhancement and frequency-selecting methods for this source impedes its wide applications. Dealing with this issue, here we demonstrate a unique methodology using two spatially crossed air-plasmas. THz yields can be significantly enhanced by a factor of 7 when the two temporally overlapped THz waves are in-phase or nearly eliminated when in antiphase. This enhancement could be interpreted by using the four-wave mixing model. Meanwhile, the spectral interference of the THz amplitudes is observed and reconstructed. It enables the frequency-selectable narrow-band THz output under the suitable time delays between the two air-plasmas. These results overcome the saturation and suppression of the plasma-based THz technology and emphasize that the coherence between the THz emissions from the two filaments is a prerequisite of our methodology. Our research provides an unusual approach in enhancing and engineering the THz wave and can help to gain more insight into the mechanism of plasma-based THz generation.

Understanding the evolution of molecular electronic structures is the key to explore and control photochemical reactions and photobiological processes. Subjected to strong laser fields, electronic holes are formed upon ionization and evolve in the attosecond timescale. It is crucial to probe the electronic dynamics in real time with attosecond-temporal and atomic-spatial precision. Here, we present molecular attosecond interferometry that enables the in situ manipulation of holes in carbon dioxide molecules via the interferometry of the phase-locked electrons (propagating in opposite directions) of a laser-triggered rotational wave packet. The joint measurement on high-harmonic and terahertz spectroscopy (HATS) provides a unique tool for understanding electron dynamics from picoseconds to attoseconds. The optimum phases of two-color pulses for controlling the electron wave packet are precisely determined owing to the robust reference provided with the terahertz pulse generation. It is noteworthy that the contribution of HOMO-1 and HOMO-2 increases reflecting the deformation of the hole as the harmonic order increases. Our method can be applied to study hole dynamics of complex molecules and electron correlations during the strong-field process. The threefold control through molecular alignment, laser polarization, and the two-color pulse phase delay allows the precise manipulation of the transient hole paving the way for new advances in attochemistry.

Plasma is the optimal choice for acquiring and modulating the extremely high visible and near-infrared light. However, few attempts have been made to apply this strategy for the terahertz (THz) wave modulation in an ex situ manner. Here, we show a laser-driven plasma-based THz modulator (PTM) to ex situ control the incident THz waves. The presented PTM allows for the amplification or extinction of the incident THz waves covering 0.1–2.0 THz within a few picoseconds, simply by adjusting its dipole phase. This modulation is a result of the interaction between the PTM’s dipole and THz wave, which can be accurately reproduced by the spectral analysis method. Our technique offers promising opportunities to explore the plasma-based THz optics and potential applications across different disciplines, such as THz-sensing and near-field THz technology.

We study the generation of terahertz radiation from atoms and molecules driven by an ultrashort fundamental laser and its second-harmonic field by solving the time-dependent Schrödinger equation (TDSE). The comparisons between one-, two-, and three-dimensional TDSE numerical simulations show that the initial ionized wave packet and its subsequent acceleration in the laser field and rescattering with long-range Coulomb potential play key roles. We also present the dependence of the optimum phase delay and yield of terahertz radiation on the laser intensity, wavelength, duration, and ratio of two-color laser components. Terahertz wave generation from model hydrogen molecules is further investigated by comparing with high harmonic emission. It is found that the terahertz yield follows the alignment dependence of the ionization rate, while the optimal two-color phase delays vary by a small amount when the alignment angle changes from 0 to 90 degrees, which reflects the alignment dependence of attosecond electron dynamics. Finally, we show that terahertz emission might be used to clarify the origin of interference in high harmonic generation from aligned molecules by coincidentally measuring the alignment-dependent THz yields.