Photomechanical meta-molecule array for real-time terahertz imaging

Real-time terahertz(THz)imaging offers remarkable application possibilities,especially in the security and medical fields.However,most THz detectors work with scanners,and a long image acquisition time is required.Some thermal detectors can achieve realtime imaging by using a focal plane array but have the drawbacks of low sensitivity due to a lack of suitable absorbing materials.In this study,we propose a novel photomechanical meta-molecule array by conveniently assembling THz meta-atom absorbers and bi-material cantilevers together,which can couple THz radiation to a mechanical deflection of the meta-molecules with high efficiency.By optically reading out the mechanical deflections of all of the meta-molecules simultaneously,real-time THz imaging can be achieved.A polyimide sacrificial layer technique was developed to fabricate the device on a glass wafer,which facilitates the transmission of a readout light while the THz wave radiates onto the meta-molecule array directly from the front side.THz images and video of various objects as well as infrared images of the human body were captured successfully with the fabricated metamolecule array.The proposed photomechanical device holds promise in applications in single and broadband THz as well as infrared imaging.

PHOTOCARRIER:THE PRINCIPLE OF PHASE MODULATION OF OPTIC AL WAVE

This paper presents the principle of phase modulation of the optical wave,that is using a dense fringe family to modulate another fringe pattern,and its applicationin fringe multiplication.It is of universal significance in optically experimental mechanics.

Tailorable Multi-Photoresponsive Behavior Triggered by Different Sulfur Oxidation States

Photoresponsive materials are considered as promising systems for intelligent technology applications owing to the contactless spatial and temporal control.Herein,controllable multi-photoresponsive behaviors are realized in benzo[b]thiophene derivatives(o-DMP-S,o-DMP-SO,and o-DMP-SO_(2))by modulating the sulfur oxidation state.Among them,o-DMP-S is photo-unreactive but possesses denser molecular packing upon ultraviolet(UV)light irradiation,exhibiting photoenhanced room-temperature phosphorescence properties.Through stoichiometric oxidation of the sulfur atom in o-DMP-S,the resulting sulfoxide compound o-DMP-SO undergoes a radical photolysis reaction involving photodeoxygenation and photochemical rearrangement,thereby leading to the photomechanical effect.The sulfone compound o-DMP-SO_(2)displays prominent reversible photochromism,resulting from the radical photocyclization under 365 nm UV light irradiation.Based on comprehensive experimental and computational investigations,the diverse photoresponsive behaviors of these benzo[b]thiophene derivatives are demonstrated to depend on the intersystem crossing efficiency and radical-mediated photochemical reaction activity in excited states due to the different sulfur oxidation states.This work provides an insightful understanding of the relationship between molecular structure and photoresponsive behavior and opens up the opportunity for the development of photoresponsive materials with potential applications.

Photo-responsive Behaviors of Hydrogen-Bonded Polymer Complex Fibers Containing Azobenzene Functional Groups

Two azobenzene compounds,Disperse Red 1(DR1)and 4-aminoazobenzene(Aazo),were separately linked to poly(acrylic acid)(PAA)side chains to form PAA-DR1 and PAA-Aazo,which were then associated with poly(ethylene oxide)(PEO)to produce hydrogen-bonded polymer complex fibers.After UV irradiation,the initial modulus and yielding strength of PAA-Aazo/PEO fiber were both increased tremendously,while the mechanical properties of PAA-DR1/PEO fiber only slightly changed.After drawn and dried in vacuum,PAA-DR1/PEO and PAA-Aazo/PEO fibers with an extended length exhibited a contraction of 20%and 25%under UV irradiation,showing potential for photo-actuation.

Positive/Negative Phototropism:Controllable Molecular Actuators with Different Bending Behavior

Herein,a series of molecular actuators based on the crystals of(E)-2-(4-fluorostyryl)benzo[d]oxazole(BOAF4),(E)-2-(2,4-difluorostyryl)benzo[d]oxazole(BOAF24),(E)-2-(4-fluorostyryl)benzo[d]thiazole(BTAF4),and(E)-2-(2,4-difluorostyryl)benzo[d]thiazole(BTAF24)showed unique bending behavior under UV irradiation.The one-dimensional(1D)crystals of BOAF4 and BTAF4 bent toward light,whereas those of BOAF24 and BTAF24 bent away from light.Although the chemical structures of these compounds are similar,the authors found that F···H–C interaction played a key role in the different molecular packing in structures crystals,which led to the positive/negative phototropism of the actuators.Moreover,theoretical calculations were carried out to reveal the mechanical properties of the crystals.Taking advantage of these photomechanical properties,the authors achieved the potential application in pushing objects,as well as enriching and removing pollutants.Hence,the molecular actuators with different bending behavior could be fabricated by introducing different number of F atom,which may open a novel gate for crystal engineering.

A BRIEF REVIEW AND PROSPECT OF EXPERIMENTAL SOLID MECHANICS IN CHINA

In this review, acritical look at the research progress ofexperimentalsolid mechanics in China for the past years is presented. Issues are discussed of the discovery and development of new fundamental methods and techniques versus performance benchmarking for many of their applications. Included herein are photoelasticity and various forms of modern photomechanics, acoustical techniques, image processing and videometrics, radial and spectrum techniques, and experimental mechanics on micro/nano scale. It is also noticed that both the ever developed instrumentation and specialized synthetical techniques have played important roles in advancing experimental mechanics in scientific researches and industrial applications. Finally, an attempt is made to look into the future of experimental solid mechanics with personal opinions offered on what the future trends will be for the researches in the field.