PHASE-CONTROLLED DUAL-COMB COHERENT ANTI-STOKES RAMAN SPECTROSCOPIC IMAGING

Coherent Raman microscopy can intrinsically enable label-free imaging by measuring vibrational spectra of biomolecules. Nevertheless, trade-off between high chemical-specificity and high imaging-speed currently exists in transition from spectroscopy to spectroscopic imaging when capturing dynamics in complex living systems. Here, we present a dual-comb scheme to substantially beat this trade-off and facilitate high-resolution broadband coherent anti-Stokes Raman spectroscopic imaging by combining dual-comb asynchronous optical scanning and phase-controlled spectral focusing excitation. A rapid measurement of vibrational micro-spectroscopy on sub-microsecond scale over a spectral span ~700 \wn with solid signal-to-noise ratio provides access to well-resolved molecular signatures within the fingerprint region. We demonstrate this high-performance spectroscopic imaging for spatially inhomogeneous distributions of chemical substances. This technique offers an unprecedented route for broadband CARS imaging with hundreds of kHz spectroscopic refresh rate using available 1-GHz oscillators

A point mutation in recC associated with subclonal replacement of carbapenem-resistant Klebsiella pneumoniae ST11 in China.

Adaptation to selective pressures is crucial for clinically important pathogens to establish epidemics, but the underlying evolutionary drivers remain poorly understood. The current epidemic of carbapenem-resistant Klebsiella pneumoniae (CRKP) poses a significant threat to public health. In this study we analyzed the genome sequences of 794 CRKP bloodstream isolates collected in 40 hospitals in China between 2014 and 2019. We uncovered a subclonal replacement in the predominant clone ST11, where the previously prevalent subclone OL101:KL47 was replaced by O2v1:KL64 over time in a stepwise manner. O2v1:KL64 carried a higher load of mobile genetic elements, and a point mutation exclusively detected in the recC of O2v1:KL64 significantly promotes recombination proficiency. The epidemic success of O2v1:KL64 was further associated with a hypervirulent sublineage with enhanced resistance to phagocytosis, sulfamethoxazole-trimethoprim, and tetracycline. The phenotypic alterations were linked to the overrepresentation of hypervirulence determinants and antibiotic genes conferred by the acquisition of an rmpA-positive pLVPK-like virulence plasmid and an IncFII-type multidrug-resistant plasmid, respectively. The dissemination of the sublineage was further promoted by more frequent inter-hospital transmission. The results collectively demonstrate that the expansion of O2v1:KL64 is correlated to a repertoire of genomic alterations convergent in a subpopulation with evolutionary advantages

High-precision gas refractometer by comb-mode-resolved spectral interferometry

Abstract High-accuracy knowledge of gas refractivity is typically crucial for optical interferometry, precise optical systems, and calculable pressure standard development. Here, we demonstrate an absolute gas refractometer by spectral interferometry and a high-resolution spectrometer. The spectral interferometry relies on a comb with fiber Fabry–Pérot filtering cavity, and a double-spaced vacuum cell. The spectrometer employs a virtually imaged phased array, diffraction grating and near-infrared camera to fully resolve the comb modes. Finally, by means of fast-Fourier-transform, the group refractivity can be derived from the spectrally resolved interferograms of the two beams propagating in the inside and outside of the vacuum cell. To confirm the feasibility and performance of the gas refractometer, the measurement of ambient air was conducted. The proposed scheme has a combined uncertainty of 1.3 × 10−9 for air and a single measurement only takes 10 ms, which is applicable for gas refractivity monitoring and compensating in real time

Reliability Assessment and Residual Life Estimation of Concrete Girder Bridges Strengthened by Carbon Fiber during the Service Stage

In recent decades, carbon fiber reinforced plastics (CFRP) have been widely used to repair and maintain concrete structures around the world. Since the parameter uncertainties of load and resistance are very important for the reliability assessment of RC bridge strengthened by CFRP, this paper presents a method to estimate the reliability and residual life of RC bridges strengthened by CFRP. In the proposed method, uncertainties of material properties, geometry parameters, load model, and time-dependent resistance model are taken into account. The proposed method combines the inverse reliability method and the calculation method of load and resistance of RC bridge strengthened by CFRP and is illustrated by an example RC bridge strengthened by CFRP during the service stage. The results indicate that the proposed approach can provide valid information regarding parameter uncertainties for the reliability of RC bridge strengthened by CFRP during the service stage. Additionally, the effects of parameter uncertainty of the reliability and residual life of RC bridge strengthened by CFRP during the service stage are analyzed and discussed. The proposed method is more robust and reliable than the traditional method

Performance Estimation Of Dual-Comb Spectroscopy In Different Frequency-Control Schemes

Dual-comb spectroscopy (DCS) has shown unparalleled advantages but at the cost of highly mutual coherence between comb lasers. Here, we investigate spectral degradation induced by laser frequency instabilities and improvement benefited from active laser stabilization. Mathematical models of DCS in the cases of direct radio-frequency (RF) locking and optical phase stabilization were separately established first. Numerical simulations are utilized to study the impact of laser intrinsic stability and the improvement by different locking strategies on spectral performance in the following. Finally, both simulations are proven by corresponding experiments. It shows that an optically phase-stabilized system owns a better immunity of laser frequency fluctuations than a direct RF-stabilized one. Furthermore, the performance improvement by the feedback servos is also more effective in the optically phase-stabilized system. In addition, the simulations could instruct optimal design and system improvement

A Fano-resonance plasmonic assembly for broadband-enhanced coherent anti-Stokes Raman scattering

Abstract Surface-enhanced coherent anti-Stokes Raman scattering (SECARS) technique has triggered huge interests due to the significant signal enhancement for high-sensitivity detection. Previous SECARS work has tended to focus only on the enhancement effect at a certain combination of frequencies, more suitable for single-frequency CARS. In this work, based on the enhancement factor for broadband SECARS excitation process, a novel Fano resonance plasmonic nanostructure for SECARS is studied. In addition to the 12 orders of magnitude enhancement effect that can be realized under single-frequency CARS, this structure also shows huge enhancement under broadband CARS in a wide wavenumber region, covering most of the fingerprint region. This geometrically-tunable Fano plasmonic nanostructure provides a way to realize broadband-enhanced CARS, with potentials in single-molecular monitoring and high-selectivity biochemical detection

Visualization 2: Dual-soliton Stokes-based background-free coherent anti-Stokes Raman scattering spectroscopy and microscopy

The evolution of the generated pulse as the input polarization is rotated. Originally published in Optics Letters on 01 June 2016 (ol-41-11-2628