Daryoush Abdollahpour

Terahertz (THz) radiation generation through two-color femtosecond pulse filamentation has become a standard method in ultrafast optics due to its broadband nature and high intensity. However, achieving precise control over the temporal characteristics of this radiation at the sub-picosecond scale—which is vital for applications such as time-domain spectroscopy and coherent control of light-matter interactions—remains a fundamental challenge. In this article, a novel approach is presented for engineering the waveform of emitted terahertz radiation by redesigning the temporal profiles of the input optical pulses and employing a dual pulse excitation scheme. Using the “photocurrent” model, the effect of temporal interference between plasma currents generated by the combination of Gaussian pulses with different time delays was investigated. Numerical results show that, by carefully adjusting the pulse intensities to avoid premature saturation of ionization, a stepwise evolution of the plasma density can be induced, which in turn leads to shaping of the net photocurrent. The findings indicate that for time delays shorter than the current relaxation time, constructive or destructive interference between currents enables selective control of certain field half-cycles and the generation of novel temporal profiles. In contrast, for delays longer than the current decay time, the terahertz pulses form separately as multi-component waveforms. These results outline a new pathway for developing tunable terahertz sources and their applications in ultrafast dynamical studies.

The ability to manipulate the multiple properties of light diversifies light-matter interaction and light-driven applications. Here, using quantum control, we introduce an approach that enables the amplitude, sign, and even configuration of the generated light fields to be manipulated in an all-optical manner. Following this approach, we demonstrate the generation of “flying doughnut” terahertz (THz) pulses. We show that the single-cycle THz pulse radiated from the dynamic ring current has an electric field structure that is azimuthally polarized and that the space- and time-resolved magnetic field has a strong, isolated longitudinal component. We apply the flying doughnut pulse for a spectroscopic measurement of the water vapor in ambient air. Pulses such as these will serve as unique probes for spectroscopy, imaging, telecommunications, and magnetic materials.

Vimentin is a main type 3 intermediate filament protein. It seems that abnormal expression of vimentin is contributed to the appearance of the aggressive feature of cancer cells. So that it has been reported that malignancy and epithelial–mesenchymal transition in solid tumors, and poor clinical outcomes in patients with lymphocytic leukemia and acute myelocytic leukemia have been associated with the high expression of vimentin. Vimentin is a non-caspase substrate of caspase-9 although its cleavage by caspase-9 in biological processes has not been reported. In the present study, we sought to understand whether vimentin cleavage mediated by caspase-9 could reverse the malignancy in leukemic cells. Herein, to address the issue, we investigated vimentin changes in differentiation and took advantage of the inducible caspase-9 (iC9)/AP1903 system in human leukemic NB4 cells. Following the transfection and treatment of the cells using the iC9/AP1903 system, vimentin expression, cleavage, and subsequently, the cell invasion and the relevant markers such as CD44 and MMP-9 were evaluated. Our results revealed the downregulation and cleavage of vimentin which attenuates the malignant phenotype of the NB4 cells. Considering the favorable effect of this strategy in keeping down the malignant features of the leukemic cells, the effect of the iC9/AP1903 system in combination with all-trans-retinoic acid (ATRA) treatment was evaluated. The obtained data prove that iC9/AP1903 significantly makes the leukemic cells more sensitive to ATRA.

In this Letter, we report on the experimental investigation of three-dimensional (3D) optical trapping by a tightly focused circular Airy beam (CAB). We compare the trapping strength of the beam for 800 nm polystyrene particles, with two equivalent Gaussian beams of the same envelope (SEGB) and the same spot-size (SSGB). Through video microscopy, we found that SEGB is incapable of forming a 3D trap, and particles are pushed along the beam propagation direction, while SSGB and CAB could form stable 3D traps. Measurements of trap stiffness revealed that although both beams have similar lateral trap stiffnesses, interestingly CAB has a 6.6-fold stronger axial trap, owning to its autofocusing nature. Furthermore, we found that trap stiffness at various trapping depths is nearly constant for CAB, in contrast with the Gaussian beam, implying that CAB is robust against spherical aberration.

Superposition of two circular Airy vortex beams (CAVB), with opposite sign topological charges (l), produces a new type of petal beams called petal-like circular Airy beam (PCAB) with a transverse field distribution in the form of azimuthally modulated concentric rings that follow Airy function over the radial distance on a transverse plane. In this paper, tight focusing of truncated PCAB and its application in optical trapping is numerically investigated. It is shown that by adjusting the beam parameters four different trapping configurations can be achieved: a single transverse trap at a single axial position, a multi-trap geometry at a single axial position, two single transverse traps at two positions along the axial direction, and two multi-trap geometries at two different axial positions. It is also shown that the number of trapped particles in the multi-trap configurations is 2l per focal plane, while the number of axial trap positions is determined by the truncation aperture size. Finally, trap stiffnesses and corresponding potential energies for the trapping configurations are presented and discussed.