Polyimide/crown ether composite film with low dielectric constant and low dielectric loss for high signal transmission.

Dielectric properties of polyimide (PI) are constrained by its inherent molecular structure and inter-chain packing capacities. The compromised dielectric properties of PI, however, could be rescued by introducing trifluoromethyl and forming a host-guest inclusion complex with the introduction of crown ethers (CEs). Herein, we report PI/crown ether composite films as a communication substrate that could be applied under high frequency circumstances. In this work, three kinds of bisphenol A-containing diamine (2,2'-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(2-methyl-4-aminophenoxy)phenyl]propane, and 2,2-bis[4-(2-trifluoro methyl-4-aminophenoxy)phenyl]propane) are synthesized and polymerized with 4,4'-(hexafluoroisopropylidene)diphthalic anhydride to prepare low-dielectric PI films by means of thermal imidization. Crown ethers are introduced into the PI with different mass fractions to obtain three series of PI films. Following the combination of trifluoromethyl into the molecular chain of PI, high frequency dielectric loss of modified PI films can be effectively reduced. The properties of these materials (especially the dielectric properties) are thoroughly explored by crown ether addition. The results show that the crown ether addition process can offer crown ethers with increased free volume of PI matrix, thus allowing them to generate a special necklace-like supramolecular structure, which makes the crown ether disperse more uniformly in the PI matrix, resulting in improved dielectric properties. Importantly, the dielectric constant and dielectric loss of the composite films at high frequencies are remarkably reduced to 2.33 and 0.00337, respectively. Therefore, these composite films are expected to find extensive use as a 5G communication substrate at high frequencies in the future.

Label-Free Spectral Imaging Unveils Biochemical Mechanisms of Low-Level Laser Therapy on Spinal Cord Injury.

BACKGROUND/AIMS: Low-level laser therapy (LLLT) leads to complex photochemical responses during the healing process of spinal cord injury (SCI). Confocal Raman Microspectral Imaging (in combination with multivariate analysis) was adopted to illustrate the underlying biochemical mechanisms of LLLT treatment on a SCI rat model. METHODS: Using transversal tissue sections, the Raman spectra can identify areas neighboring the injury site, glial scar, cavity, and unharmed white matter, as well as their correlated cellular alterations, such as demyelination and up-regulation of chondroitin sulfate proteoglycans (CSPGs). Multivariate data analysis methods are used to depict the underlying therapeutic effects by highlighting the detailed content and distribution variations of the biochemical constituents. RESULTS: It is confirmed that photon-tissue interactions might lead to a decay of the inhibitory response to remyelination by suppressing CSPG expression, as also morphologically demonstrated by reduced glial scar and cavity areas. An inter-group comparison semi-quantitatively confirms changes in lipids, phosphatidic acid, CSPGs, and cholesterol during SCI and its LLLT treatment, paving the way for in vitro and in vivo understanding of the biochemical changes accompanying pathobiological SCI events. CONCLUSION: The achieved results in this work not only have once again proved the well-known cellular mechanisms of SCI, but further illustrate the underlying biochemical variability during LLLT treatment, which provide a sound basis for developing real-time Raman methodologies to monitor the efficacy of the SCI LLLT treatment.

946 nm Nd: YAG double Q-switched laser based on monolayer WSe2 saturable absorber.

In this paper, we report a 946nm double Q-switched laser side pumped by an 808-nm pulse laser diode (LD). A layered tungsten diselenide (WSe2) saturable absorber (SA) together with an MgO doped LiNbO3 electro-optic (EO) modulator is applied to double Q-switch the Nd: YAG laser, producing trains of nanosecond-duration pulses with 500 Hz repetition rate. Such WSe2 saturable absorbers are fabricated by chemical vapor deposition (CVD) in a hot wall chamber and then embedded into a resonant mirror. The achieved pulse energy of double Q-switched laser at 946 nm is approximately 2.63 mJ with 10.8 ns pulse width and the peak power is round 244 kW, corresponding to the beam quality factors of M2x = 3.846,M2y = 3.861. Monolayer WSe2 nanosheets applied in the experiment would be a promising SA for passive Q-switching operation.