TTFDNet: Precise Depth Estimation from Single-Frame Fringe Patterns.

This work presents TTFDNet, a transformer-based and transfer learning network for end-to-end depth estimation from single-frame fringe patterns in fringe projection profilometry. TTFDNet features a precise contour and coarse depth (PCCD) pre-processor, a global multi-dimensional fusion (GMDF) module and a progressive depth extractor (PDE). It utilizes transfer learning through fringe structure consistency evaluation (FSCE) to leverage the transformer's benefits even on a small dataset.

Direct space-time manipulation mechanism for spatio-temporal coupling of ultrafast light field.

Traditionally, manipulation of spatiotemporal coupling (STC) of the ultrafast light fields can be actualized in the space-spectrum domain with some 4-f pulse shapers, which suffers usually from some limitations, such as spectral/pixel resolution and information crosstalk associated with the 4-f pulse shapers. This work introduces a novel mechanism for direct space-time manipulation of ultrafast light fields to overcome the limitations. This mechanism combines a space-dependent time delay with some spatial geometrical transformations, which has been experimentally proved by generating a high-quality STC light field, called light spring (LS).

FISI: frequency domain integration sequential imaging at 1.26×10 frames per second and 108 lines per millimeter.

High spatial resolution on the image plane (intrinsic spatial resolution) has always been a problem for ultrafast imaging. Single-shot ultrafast imaging methods can achieve high spatial resolution on the object plane through amplification systems but with low intrinsic spatial resolutions. We present frequency domain integration sequential imaging (FISI), which encodes a transient dynamic by an inversed 4f (IFF) system and decodes it using optical spatial frequencies recognition (OFR), which overcomes the limitation of the spatial frequencies recognition algorithm.

Local OAM manipulation of a terahertz wave from the air filament by chirping the few-cycle vortex pump laser.

We propose a scheme to manipulate the local orbital angular momentum (OAM) of the ultra-broadband (0.1-30 THz) terahertz (THz) waves from the laser-induced short air filament via chirping the few-cycle vortex laser pump. The simulation results show that either the THz vortex pulses with linear azimuth-dependent phases or the THz angular accelerating vortex beams (AAVBs) with nonlinear azimuth-dependent phases can be produced by tuning the chirp parameter of the pump.

All-optical high spatial-temporal resolution photography with raster principle at 2 trillion frames per second.

A novel single-shot ultrafast all-optical photography with raster principle (OPR) that can capture real-time imaging of ultrafast phenomena is proposed and demonstrated. It consists of a sequentially timed module (STM), spectral-shaping module (SSM), and raster framing camera (RFC). STM and SSM are used for linearly encoding frequency-time mapping and system calibration, respectively.

Enhance terahertz radiation and its polarization- control with two paralleled filaments pumped by two-color femtosecond laser fields.

We present experimentally an obvious enhancement of the terahertz (THz) radiation with two paralleled filaments pumped by two-color laser fields for a full use of a high laser power, compared with single filament. By mapping the 3-dimensional electric trajectories of generated THz fields with a (111) ZnTe crystal, we observe that the total THz polarization from two filaments can be manipulated by varying the time delay between the two orthogonally polarized pumps, which agrees well with the simulations under the photocurrent model. Notably, the power and spectrum of the THz field almost keep unchanged while manipulating the ellipticity of the THz polarization, which is important for a polarization-controllable THz source.

Liquid crystal-based order electrically controlled q-plate system.

This paper proposes a liquid crystal-based order adjustable q-plate system. The system, which is solid-state and electrically controlled without any mechanical components, consists of several bit cells and one symbol cell. The bit cells can be electrically selected whether to modulate the beam.

Generation of terahertz vortex pulses without any need of manipulation in the terahertz region.

Converting a Gaussian mode to a vortex beam is much more inconvenient in the terahertz (THz) region than in the near-infrared (NIR) region due to underdevelopment of THz components and strong THz diffraction. This Letter reports the direct generation of THz vortex pulses by optical difference-frequency between two NIR chirped pulses with different topological charges (TCs). By designing a passive and transmissive device for a collinear NIR pulse pair with conjugated TCs, we have experimentally obtained stable THz vortex pulses with a TC value of 2 or -2.

Improve polarization topological order sorting with the diffractive splitting method.

Vector beams with different polarization topological orders (PTOs) are the eigenmodes of traditional optical fibers and are orthogonal to each other, so the PTO multiplexing channel is a promising candidate for the oncoming generation of optical communication. Here we demonstrate experimentally a PTO sorting system with high separation resolution based on the diffractive splitting (DS) method. Our experiments show that our design with the DS method helps to enhance the separation resolution to 77.

Two-step phase-shifting SPIDER.

Comprehensive characterization of ultrafast optical field is critical for ultrashort pulse generation and its application. This paper combines two-step phase-shifting (TSPS) into the spectral phase interferometry for direct electric-field reconstruction (SPIDER) to improve the reconstruction of ultrafast optical-fields. This novel SPIDER can remove experimentally the dc portion occurring in traditional SPIDER method by recording two spectral interferograms with π phase-shifting.

Modified THz electro-optic sampling for high optical modulation depth, large dynamical range, and low background noises.

We present a modified THz electro-optic sampling method to combine the advantages of its two traditional counterparts at near 0° and 45° optical biases: excellent ability to cancel the background noises, high optical modulation, and large dynamical range. The first advantage results from the method's symmetrical layout to get dynamical noise cancellation. By setting the static birefringent phases of the two balanced beams with a pair of opposite numbers, our setup can record THz waveforms without distortion with its maximal modulation depth, thus optimal signal-to-noise ratio (SNR).

Design for the optical retardation in broadband zero-order half-wave plates.

This paper presents a novel design for broadband zero-order half-wave plates to eliminate the first-order or up to second-order wavelength-dependent birefringent phase retardation (BPR) with 2 or 3 different birefringent materials. The residual BPRs of the plates increase monotonously with the wavelength deviation from a selected wavelength, so the plates are applicable to the broadband light pulses which gather most of the light energy around their central wavelengths. The model chooses the materials by the birefringent dispersion coefficient and evaluates the performances of the plates by the weighted average of the absolute value of residual BPR in order to emphasize the contributions of the incident spectral components whose possess higher energies.