Raman parametric four-wave mixing mechanism of the first-order Stokes generated in CO2 and H2.

Without the axial component, an annular spatial profile of the first-order Stokes (S1) was observed during the SRS process in low-energy pumped CO2 gas, which is supposed to be generated by a parametric four-wave mixing process (PFWM), i.e., 2ωP = ωAS1 + ωS1. In order to verify such a mechanism, similar experiments were conducted in H2, and the annular S1 intensity distribution was also noticed. Furthermore, simulations of S1 radial intensity distributions were carried out based on the proposed PFWM phase matching geometry. The PFWM has been verified to be a process that directly annihilates two pump photons and simultaneously produces one AS1 photon and one S1 photon.

Time sequence variation of incoherent and coherent random laser based on positive replica of abalone shell.

Besides the scattering structures, the energy transfer (ET) process in the gain medium plays a significant role in the competition between coherent (comprising strongly coherent components) and incoherent (consisting of weakly coherent or "hidden" coherent components) modes of random lasers. In this study, bichromatic emission random lasers were successfully created using polydimethylsiloxane (PDMS) replicas with grooved structures that imitate the inner surface of abalone shells as scattering substrates. The influence mechanism of the ET process from the monomer to dimer in the Rhodamine 640 dye on the competition of random laser modes was thoroughly investigated from both spectral and temporal dimensions. It was confirmed that the ET process can reduce the gain of monomers while amplifying the gain of dimers. By considering the dominant high-efficiency ET processes, an energy transfer factor associated with the pump energy density was determined. Notably, for the first time, it was validated that the statistical distribution characteristics of the time sequence variations in the coherent random laser generated by dimers closely resemble a normal distribution. This finding demonstrates the feasibility of producing high-quality random number sequences.

High efficiency stimulated rotational Raman scattering of hydrogen pumped by 1064 nm.

Laser-induced breakdown (LIB) and the competition of other Raman processes are major reasons restricting photon conversion efficiency (PCE) of Raman lasers. In this work, 1064 nm was used as the pump source, and stimulated rotational Raman scattering of hydrogen was investigated. The configuration of zooming out and focusing pump beam was applied, and the dimension of the pump beam at the focus spot increased significantly; consequently, LIB was suppressed, and Raman PCE was improved dramatically. With the help of the Raman gas pressure optimization, vibrational Raman could be fully suppressed, and other competition Raman processes could be well controlled. The optimal PCEs of different rotational Raman lasers could be achieved under different conditions. The maximum PCE of the first rotational Stokes (RS1) was improved to 60.7%, and the maximum energy of RS1 reached 204.5 mJ. With the increment of hydrogen pressure, the maximum PCE of the second rotational Stokes (RS2) was improved to 28.2%, and the maximum energy of RS2 reached 123.9 mJ. Furthermore, a 2.1 µm Raman laser was also generated, the maximum PCE of 2.1 µm reached 44.8%, and its pulse energy reached 106.1 mJ.

Diagnostic value of plasma and blood cells metagenomic next-generation sequencing in patients with sepsis.

BACKGROUND: Several studies have investigated the detection of plasma cell-free DNA (cfDNA) using metagenomic next-generation sequencing (mNGS). However, to our knowledge, no study has evaluated the diagnostic value of mNGS detection using blood cells. In this study, we aimed to evaluate the performance of a whole blood mNGS assay which includes the results of plasma and blood cells mNGS detection. METHODS: We selected a panel of seven microorganisms to validate both the plasma and blood cells assay for their limits of detection (LoD), linearity, precision, and robustness to interference. In a multicentered prospective study conducted from January 2021 to April 2022, we tested 253 septic patients with plasma and blood cells mNGS and compared it with blood cultures (BCs). The performance of pathogen detection was compared between mNGS and BCs. RESULTS: The LoD for plasma and blood cells mNGS was 8.3-140 genome equivalents (GE)/mL and 26 to 534 colony-forming units (CFU) or copies/mL, respectively. The inter- and intra-assay reproducibility of both plasma and blood cells mNGS was 100%. Compared to plasma mNGS alone, the sensitivity of whole blood mNGS was increased by 18.04% when using BCs as the standard (67.21% vs 85.25%). Furthermore, the sensitivity of whole blood mNGS in diagnosing bloodstream infections (BSIs) was 85.21%, which was significantly higher than that of BCs (36.09%, P＜0.0001) and plasma mNGS (69.82%; P = 0.0007). Additional analysis showed that blood cells mNGS was able to detect bacteria missed by plasma mNGS, while plasma mNGS was effective at detecting viruses. CONCLUSIONS: Our findings indicate that whole blood mNGS shows great potential as a promising diagnostic technique for BSIs owing to its ability to identify pathogens with higher sensitivity.

Stimulated vibrational-rotational Raman scattering of hydrogen pumped at a 1064-nm laser.

A ∼2.1-µm laser is within an atmospheric transmission window and can be used in remote sensing. In this work, a 1064-nm laser was used as the pump source, pressurized hydrogen was used as the Raman active medium, and a dual-wavelength ∼2.1-µm Raman laser was generated. The 2147-nm laser was generated by a combination processes of stimulated vibrational Raman scattering and stimulated rotational Raman scattering, while a 2132-nm laser was generated by stimulated S-branch vibrational Raman scattering. Optimizing experimental conditions yielded a maximum pulse energy of 76.1 mJ, a peak power of ∼9.2M W, and a photon conversion efficiency of 29.8%.

Virome analysis of ticks and tick-borne viruses in Heilongjiang and Jilin Provinces, China.

Ticks transmit diverse human and animal pathogens, leading to an increasing number of public health concerns. In the forest area of northeast China, the spread of tick-borne diseases (TBDs) is severe; however, little is known about the tick virome composition and evolution. Herein, we investigate the geographical distribution of tick species and related viruses in Heilongjiang and Jilin Provinces in Northeast China. To reveal the diversity of tick-borne viruses in parts of Heilongjiang and Jilin, ticks were collected at 9 collection points in these provinces in 2018. Morphology and molecular biology were used to identify tick species, and 1411 ticks from nine sampling sites were collected and analysed by next-generation sequencing (NGS). Four Ixodidae were identified, including Ixodes persulcatus, Haemaphysalis japonica, Dermacentor silvarum, and Haemaphysalis concinna. After removal of host genome sequences, 13,003 high-quality NGS reads were obtained and annotated as viruses. Further phylogenetic analysis based on amplicons revealed that these viral sequences belong to Beiji nairovirus, Alongshan virus, bovine parvovirus-2, and tick-associated circovirus; some distinct sequences are closely related to Songling virus, Changping tick virus, Norway luteo-like virus 2, and Norway partiti-like virus 1. In summary, this study describes the prevalence of local ticks and variety of tick-borne viruses in northeastern China, providing a basis for further research on tick-borne viruses in the future.

Wavelength-tunable narrow-linewidth gaseous Raman laser.

Gaseous Raman lasers cover a range of wavelengths but lack wavelength tunability. Here, a 1cm-1 linewidth 532 nm laser was used as a pump laser, and with a narrow-linewidth seed laser injection, a narrow-linewidth first Stokes (S1) Raman laser was achieved. By tuning the wavelength of the seed laser, a tuning range of S1 up to 1cm-1 was obtained. The wavelengths of the first anti-Stokes and second Stokes lasers could also be tuned. A theoretical model was developed, and spectral profiles of Raman lasers from experiments and simulations agreed well; further simulation predicted that the linewidth of S1 could be compressed to as narrow as 0.01cm-1 under optimal conditions. A universal method of fine-tunable Raman lasers is presented that can be utilized in several important applications.

Method to improve the resolution of a non-parallel Fabry-Perot etalon.

A new method to improve the resolution of a slightly non-parallel solid etalon is proposed. The method is aimed to reduce the spectrum broadening caused by non-parallel surfaces; it contains a theoretical formula for adjusting image distances, and an algorithm for processing the corresponding fringe patterns. Theoretical consideration, computer simulation, experimental results, and application demonstration are given. The fringe patterns captured by a CCD showed good agreement with the computer simulation, and the resolution of a λ/10-wavefront-error etalon was improved from 3.1 GHz to 0.51 GHz. In comparison with other methods, this new method is convenient and economical.

Direct bleaching of a Cr4+:YAG saturable absorber in a passively Q-switched Nd:YAG laser.

In this work, the anisotropy of nonlinear absorption in a crystal Q-switch was considered when we established coupled rate equations of a passively Q-switched laser. A [100]-cut Cr4+:YAG crystal, with initial transmission T0=40%, was used as the Q-switch to evaluate the theoretical model, and the results of the simulation were in good accordance with the experiment. In order to control timing jitter of the passively Q-switched laser, an actively Q-switched Nd:YAG laser was applied to directly bleach the [100]-cut Cr4+:YAG crystal. The timing jitter was more than 1 µs without bleaching light. While there was a bleaching light, the time lag between the laser pulse and the bleaching light was less than 100 ns, which meant the timing jitter decreased. The pulse width of the passively Q-switched laser was found to decrease from 45 to 35 ns due to the existing of bleaching light. As the peak power of bleaching light was increased, the laser pulse energy increased from 18.2 to 24.6 mJ, which meant a 35% increment in the pulse energy. The increase in pulse energy can be explained by the increase of α coefficient, and the results of simulation agreed well with the experiment.

Powder sum-frequency generation as a versatile method for infrared optical alignment.

The sum-frequency generation (SFG) in potassium dihydrogen phosphate (KDP) powder with µm-grade particle size is successfully demonstrated under various experimental conditions. Two focused beams of 870 nm and 1369 nm are used for SFG excitation. SFG is observed under different excitation energies. The SFG intensity shows isotropy with different observation azimuths. The intersection angle between two excitation beams is not limited by conventional phase-matching conditions, and it owns the flexibility of a very large allowed range, e.g., it can be 0°âˆ¼100° in this work. The polarization combination of excitation beams is not limited either. Thanks to the non-toxicity, low price, and low SFG threshold properties of KDP material and the optical flexibility, this powder SFG technology is a versatile method and is expected to be applied to various situations of optical alignment, e.g., surface SFG, four-wave mixing, coherent anti-Stokes Raman spectroscopy, multi-color laser excitation, etc. The effect of potential powder SFG-assisted optical alignments is also discussed. Extension of this method to multi-beams, tight focusing beams, and plasmonic polariton devices is proposed.