The extensive application of optical frequency comb technology has profoundly transformed the developments of time-frequency transfer, optical frequency measurement, and absolute distance measurement. Optical frequency combs can serve as conversion tools for high-precision frequency transfer and comparison among different optical frequency standards in different locations. This work has developed a highly robust all-fiber polarization-maintaining optical frequency comb, with a spectral bandwidth of 11 nm, a repetition rate of 117 MHz, an output power of 2.8 mW, and a pulse width of 218 fs, laying a foundation for conducting free-space precise time-frequency transfer and further fulfilling the requirements of applications in complex environments.

Supercontinuum (SC) generation in fibers offers an effective solution for nonlinear wavelength conversion, significantly broadening the laser spectrum with high spatial coherence [1]. In many applications, for example, in spectrum calibrations, a flat SC is required. Traditional methods for generating femtosecond SC rely on soliton dynamics within nonlinear fibers. These solitons undergo fission and emit dispersive waves, which contribute to spectral broadening. However, this approach often results in SC spectra that lack smoothness, with spectral gaps between the dispersive waves and the pump wavelength. Alternatives, such as noise-like pulse pumping and the use of nonlinear fibers doped with special materials, have been explored to improve spectral flatness [2]. In this work, we experimentally and theoretically demonstrate a flat SC spectrum using higher-order soliton pre-compression. Our results show a spectrum flatness of 9 dB within the wavelength range of 960 nm to 1550 nm without the residual wavelength component of the pump laser. Using a custom-built $f-to-2 f$ interferometer, this flat SC spectrum enable the detection of the carrier-envelope offset frequency $\left(f_{\text{CEO}}\right)$ signal with a signal-to-noise ratio (SNR) exceeding 35 dB, confirming the high coherence of the SC generation.

SummaryUltrashort pulse lasers are widely utilized in medical, material processing, and other fields because of their high resolution and pulse power. Realized on this basis, optical frequency combs enable precision measurement, low-phase-noise microwave generation, and high-precision time synchronization. This paper presents the construction of an Erbium-doped mode-locked fiber laser incorporating a Nonlinear Amplifying Loop Mirror (NALM). This laser can achieve self-starting and employs a polarization-maintaining fiber design to suppress noise, excluding the free space optics. Additionally, a non-reciprocal optical element is added in the laser cavity to shorten its length, rendering the entire cavity highly compact and stable. Consequently, the 155 MHz mode-locked laser produces a stable femtosecond-scale pulse output, which is 135 fs, and when the frequencies are stabilized by EOM and PZT, it can be utilized as a seed source for the subsequent construction of an optical frequency comb.

SummaryThe economical, reciprocal, low-loss, and compact optical terminals are essential for establishing high-precision optical time and frequency transfer networks in a turbulent free-space atmosphere. In this paper, we propose an optical terminal designed for long-distance time and frequency transfer, which includes a coarse tracking module and an angle-of-arrival compensation control module. The coarse tracking module consists of a telescope with repeatability and theoretical step resolution each less than 10 arcseconds, a visible guidance laser, and a visible camera. The angle-of-arrival compensation control module is composed of beam splitter, a position-sensitive quadrant photodetector (QPD), a fast steering mirror (FSM), a beam expander, and a PID control circuit. Additionally, the system minimizes insertion loss to maximize the power margin of the signal light. The terminal is capable of optimizing the aperture to reduce the fluctuation of the angle-of-arrival in different turbulence conditions. The proposed optical terminal design will show a potential in optical clock network spanning ground-to-satellite and inter-satellite distances.

SummaryThe accurate distribution of frequency standards over long-haul link is essential for collaborative detection and high-precision global satellite navigation. In this paper, we present a method for parallel frequency transfer using bidirectional heterodyne phase-locked loops, enabling the simultaneous regeneration of optical and microwave frequency standards at the remote site over a single fiber channel. Fiber noise is cancelled by active compensation loops at the master site, meanwhile, the incoming frequency standard signals are regenerated at the remote site. Furthermore, the fractional instability of frequency transfer was evaluated through a loopback configuration. This approach optimizes the utilization of fiber link channels and provides a feasible solution for spatial dissemination of optical and microwave frequency standards in large-scale networks.

SummaryThe stable transfer and precise regeneration of multiple time and frequency signals is crucial for establishing time and frequency references in large-scale spatial networks, including satellite navigation systems, optical clock comparisons, and high-speed inter-satellite laser communication. Here, we demonstrate a parallel transfer method for a one pulse per second (1PPS) signal, radio frequency, and ultra-stable optical frequency over a single free-space laser link. Crosstalk between the signals can be effectively suppressed through frequency band isolation and code-division multiplexing. This approach minimizes the number of required laser links, thus maintaining the bidirectional reciprocity. We also present the measured fractional instability over a 500-m free-space link using the common reference arrangement. The time deviation of 1 PPS signal transfer reaches 47.5 fs and 63.3 fs at 1-s and 103-s averaging times, respectively. The fractional frequency instability of radio frequency transfer reached 8.23×10-14 and 1.10×10-16 at 1-s and 103-s averaging times, respectively. The fractional frequency instability of optical reference frequency transfer reached 8.80×10-16 and 7.94×10-18 at 1-s and 103-s averaging times, respectively. This method holds significant potential for the next-generation optical time and frequency standard distribution.

Ultra-stable lasers with high-precision middle- and long-term stability are important in scientific researches. Generally, the middle- and long-term stabilities of ultra-stable laser are mainly determined by temperature control of the optical reference cavity. In this work, we focus on high-precision temperature control for the 30-cm-long high-finesse optical cavity. Overall, a combination of active and passive thermal control methods is applied. Thermoelectric coolers are used to create a temperature-constant housing inside the vacuum chamber, while heating foils are used for precision temperature control inside the thermal shields. Preliminary test shows that the thermoelectric coolers assisted by a water-cooled plate can lower the temperature of the vacuum chamber by 8 degrees Celsius than ambient environment. Theoretically, the calculated time constant of thermal isolation of the home-built 30-cm-long high-finesse optical cavity system is about 11.5 days.

With the continued improvements in quantum frequency standards, there has been a brisk demand for free-space optical links for time and frequency transfer. The effects of turbulence on the femtosecond pulses need to be further clarified. In this work, we explore the effects of turbulence on the comb pulses and dual-comb interference signals with theoretical analysis. A comb-based free-space optical transfer link is used for verification with the use of a reciprocal optical terminal. The results indicate that atmospheric turbulence does aggravate the relative linewidth and phase noise of the dual-comb interference signals.

The remote regeneration of coherent optical frequency technique finds increasing applications in the fields of large-scale optical clock networks, precision spectroscopy, very-long baseline interferometry, and high-sensitivity tests of fundamental physics. Meanwhile, with the improvements of coherent optical frequency generation, the requirement of stable transfer is more and more demanding. Here, we demonstrate a regeneration system of coherent optical frequency based on bidirectional phase locking, in which the locking loop at the local site is for eliminating optical phase noise over the link, and the locking loop at the remote site is for locking to the incoming coherent optical frequency. Preliminary experiment over a 1.5 km fiber link indicates that the additional frequency stability can reach 5.9x10(-17) and 7.0 x10(-19) at an averaging time of 1 s and 10(3) s, respectively. This method can be further extended to remote optical frequency comparisons for multiple users.

We established a frequency comb-based two-way time and frequency transfer system, which is adequate for the comparison of state-of-the-art optical clocks. However, the surrounding environment (such as temperature and vibration) and data processing methods will affect the measurement precision of the system for clock offset. In the setup, we used homemade fiber box housing most of optical fibers in our system to suppress the impact of temperature fluctuations. For data processing, we filtered the interference signals generated by linear optical sampling by digital bandpass filter. Hilbert transform was applied to extract the envelopes, then used parabolic fitting to figure out the peak of the envelopes (one-way time delays). The optical two-way time transfer test through a short fiber link shows that the noise floor-equivalent fractional timing stability is 0.07 fs at a gate time of 0.4 s.

This paper presents a home-made rack-mounted ultra-stable laser. To analyze and optimize its performance, a noise model for the locking system was established. Various noise sources were tested and analyzed to determine their contributions to the overall system performance. The system achieved a frequency stability below 3.0x10(-15) at the average time between 1 s and 10 s, approaching the thermal noise limit. This work provides a clear direction for further system optimization.

We present parallel transfer of optical frequency, radio frequency, and time reference over single optical carrier. This method makes full use of both coherent optical detection and pseudo-coded spread spectrum modulation, which benefits with simultaneous detection of the multiple time and frequency signals, effectively reducing the dispersion and non-reciprocal effect of WDM-based fiber link. UTC (BIRM) is precisely regenerated through parallel transfer and feedback control at the remote site. Preliminary experiments over a 120 km single fiber channel indicate that the fractional optical frequency instability reaches 7.27 x10(-16) and 3.25x10(-18) at 1 s and 10(4) s averaging time, respectively. Meanwhile, the fractional time instability and radio frequency instability reach 0.02 ps and 7.81x10(-17) at 10(5) s averaging time, respectively. This approach has a potential in extending to free-space simultaneous transfer of time and frequency to support satellite-to-ground/inter-satellite precise time-frequency comparisons and high-speed laser communications.

The attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR) detection was used to investigate the mechanisms of cold atmospheric plasma (CAP) treatment in wound healing. The peaks of ester carbonyl and α-helix in proteins, serving as the spectral fingerprints in the original infrared spectra and their second derivative spectra, of the wound samples were analyzed. The experimental results showed that the CAP treatment resulted in the reduction of the ester carbonyl contents, and the increase of the contents of α-helix in the proteins. This indicates that the CAP treatment accelerated the lipid metabolism to provide required energy for the protein production, which was also supported by the fact that the fibrin deposition in the wounds was more obvious in the plasma group than that in the control group.

Ultra-stable laser has important applications in many scientific research fields. The limited frequency stability of the ultra-stable laser is restricted by the thermal noise of the optical reference cavity. Increasing the length of the optical reference cavity is one of the effective methods to reduce thermal noise, but at the cost of higher sensitivity to vibration. In this work, we focused on the vibration sensitivity optimization of our home-built 30-cm-long high-finesse optical reference cavity. By establishing a finite element multi-body model, including the vacuum chamber, three layers of the thermal shields, and U-shaped Zerodur mount. We calculated the vibration sensitivity of the 30-cm-long high-finesse optical reference cavity under various parameters. Finally, the optimal parameters of zero vibration sensitivity of the 30-cm-long high-finesse optical reference cavity are obtained.

Open-path dual-comb spectroscopy has emerged as a promising technique for regional multigas mon-itoring with its conspicuous advantages of broadband spectral coverage, high spectral resolution, and rapid update rate. However, it is challenging to realize its full potential due to the undesirable mutual coherence of the dual-comb source and turbulence in the air path, which hinder it from field-deployed open-path applications. Here, phase-sensitive open-path dual-comb spectroscopy based on free-running combs is reported, in which dual-purpose compensation is proposed to provide immunity against both the time jitter of comb sources and turbulent noise. Broadband and high-fidelity atmospheric amplitude and phase spectra containing gas absorption and dispersion information over a 900-m turbulent air path are acquired. For the rovibrational resonances of CO2 and H2O in 6250-6660 cm-1, the achieved residual of the amplitude spectrum is no more than 0.01, and the average residual of the phase spectrum is 0.2 mrad, corresponding to about 0.2 as of relative timing noise or a refraction-index change of about 6 x 10-14 over the target path. The precision of concentration retrieval is about 3 ppm for CO2 in 30 s. A simulated gas -leakage measurement validates the dynamic monitoring capability of this system. This highly effective noise-compensation method provides the possibility of deploying the portable configuration and holds the potential to propel environmental protection and atmospheric science.

For gas-solid two-phase flow, the moisture of solid particles affects the change of flow movement and flow field greatly, thereby impacting industrial output. Different measurement methods have been employed to study the effects of moisture under different conditions, and these methods often yield complementary results. Therefore, a classification method for two-phase flow, based on a pseudo-Siamese neural network (pSNN), is proposed. Using a 12-electrode electrical capacitance tomography (ECT) sensor and a charge-coupled device (CCD) camera, we conduct dynamic experiments under five different moisture conditions to collect ECT data and image data. The observation directions of these data are perpendicular to each other. Afterward, we develop a two-layer long short-term memory (LSTM) network and a residual neural network (ResNet) to train on ECT and image data, respectively. Additionally, we add a granularity selection experiment to the ECT data subnetwork training. By feature concatenation, the overall model can forecast moisture more accurately than a single measurement method, with an accuracy of 99.3%, and it also acquires 3-D dynamic information on gas-solid two-phase flow through data fusion.

Sepsis is an acute systemic infectious disease with high mortality, which urgently needs more effective treatment. Scutellariae radix (SR), a commonly used traditional Chinese medicine (TCM) for clearing heat and detoxification, contains rich natural products possessing anti-inflammatory activity. In previous studies, it was found that the anti-inflammatory activities of SR extracts from different ecological conditions varied wildly. Based on this, in the present study, a screening strategy of antisepsis active components from SR based on correlation analysis between plant metabolomics and pharmacodynamics was established, and the mechanism was explored. First of all, a mass spectrum database of SR (above 240 components) was established to lay the foundation for the identification of plant metabolomics by liquid chromatography tandem mass spectrometry (LC–MS/MS). Through the correlation analysis between plant metabolomics and anti-inflammatory activity of SR from different ecology regions, 10 potential components with high correlation coefficients were preliminarily screened out. After the evaluation of anti-inflammatory activity and toxicity at the cellular level, the pharmacodynamic evaluation in vivo found that oroxylin A had the potentiality of antisepsis both in LPS- and CLP-induced endotoxemia mice. Network pharmacology and Western blot (WB) results indicated that oroxylin A significantly inhibited the toll-like receptor 4/nuclear factor-kappa B (TLR4/NF-κB) signaling pathway, which was further confirmed by secreted embryonic alkaline phosphatase (SEAP) assay. Moreover, the molecular docking analysis indicated that oroxylin A might competitively inhibit LPS binding to myeloid differentiation 2 (MD-2) to block the activation of TLR4. The study provided a feasible research strategy for the screening and discovery of antisepsis candidate drugs from TCM.

The elasto-optic coefficient, which describes the interaction of acoustic waves and light in a medium, allows a contrast mechanism in optomechanics. However, the non-contact measurement is a challenge, limiting the study of some materials such as liquids. We present a high-speed non-contact method based on laser-induced phonons. The elasto-optic coefficients of common liquids are measured with only 10 ms and an averaged relative standard deviation of 1.52%, complementing the rare liquid data. By deciphering Brillouin spectra, the elasto-optic coefficient and viscoelastic parameters can be obtained simultaneously, and the introduction of the elasto-optic coefficient makes the characterization more sensitive. Benefiting from spatially resolved measurement, the elasto-optic coefficient is mapped to provide another contrast mechanism for mechanical imaging and may prove useful to characterize biological cells and tissues.

ETHNOPHARMACOLOGICAL RELEVANCE:Senkyunolide H (SNH) is a bioactive phthalide isolated from Ligusticum chuanxiong Hort rhizome and was reported to have multiple pharmacological effects. AIM OF THE STUDY:The study was performed to verify the potency of SNH protecting PC12 cells from oxygen glucose deprivation/reperfusion (OGD/R)-induced injury and to elucidate the underlying mechanisms. MATERIALS AND METHODS:OGD/R model was established in PC12 cells and the cell viability was measured by MTT assay. The cell morphology was observed using scanning electron microscope (SEM). The potential targets of SNH and related targets of OGD/R were screened, and a merged protein-protein interaction (PPI) network of SNH and OGD/R was constructed based on the network pharmacology analysis. Kyoto Encyclopedia of Genes and Genomes (KEGG) database was used for pathway analysis. Intracellular cAMP level and the protein expression levels were measured to elucidate the underlying mechanisms. RESULTS:SNH pretreatment protected PC12 cells against OGD/R-induced cell death. SNH also significantly protected the cell protrusion. A merged PPI network was constructed and the shared candidate targets significantly enriched in cAMP signaling pathway. The level of intracellular cAMP and the protein level of p-CREB, p-AKT, p-PDK1 and PKA protein were up-regulated after the treatment of SNH compared with OGD/R modeling. CONCLUSIONS:The present study indicated that SNH protected PC12 cells from OGD/R-induced injury via cAMP-PI3K/AKT signaling pathway.

Cold atmospheric plasmas (CAPs) used in plasma medicine have shown great potential in various aspects including wound healing, dermatology, cancer therapy, etc. It is one of the important issues to determine the plasma dosage in plasma medicine because it dominates the specific plasma treatment results. However, the multi-process interactions between CAPs and biological materials make it rather challenging to give an accurate and versatile definition for plasma dosage. In this study, the ratio of the discharge energy to the number of the treated in vitro kidney cells (mJ/cell) was employed as the unit of the plasma dosage. Additionally, inspired by basic knowledge of pharmacy, the median lethal dose (LD50) was employed to help estimate the plasma dosage. The experimental results show that the value of LD50 using the newly designed CAP Bio-Med Platform for the kidney cells is 34.67 mJ/cell. This biology-based method has the advantages of easy operation, independence of specific CAP sources, and also independence of complex interactions between CAPs and the treated biological targets, and consequently, may provide a new direction to quantitatively define the plasma dosage in various plasma medical applications.