Brillouin laser-driven terahertz oscillator up to 3 THz with femtosecond-level timing jitter

The terahertz (THz) frequency range, spanning 0.1 to 10 THz, is a field ripe for innovation with vast, developing potential in areas like wireless communication and molecular spectroscopy. Our work introduces a dual-wavelength laser design that utilizes stimulated Brillouin scattering in an optical fiber cavity to effectively generate two highly coherent optical Stokes waves with differential phase noise inherently mitigated. To guarantee robust operation, the Stokes waves are optically injected into their respective pump lasers, which also serves to greatly improve the resulting coherence. The frequency difference between the two wavelengths is converted into THz waves through a uni-traveling-carrier photodiode. This innovative design facilitates the generation of THz waves with phase noise levels of less than -100 dBc/Hz, translating to timing noise below 10~$\mathrm{as} / \sqrt{\mathrm{Hz}}$ at 10 kHz Fourier frequency, over a carrier frequency range from 300 GHz to 3 THz. This development in phase noise reduction establishes a new benchmark in the spectral purity of tunable THz sources. Such advances are pivotal for applications to move beyond oscillator constraints

60 Gbps real-time wireless communications at 300 GHz carrier using a Kerr microcomb

Future wireless communication infrastructure will rely on terahertz systems that can support an increasing demand for large-bandwidth, ultra-fast wireless data transfer. In order to satisfy this demand, compact, low-power, and low noise sources of terahertz radiation are being developed. A promising route to achieving this goal is combining photonic-integrated optical frequency combs with fast photodiodes for difference frequency generation in the THz. Here, we demonstrate wireless communications using a 300 GHz carrier wave generated via photomixing of two optical tones originating from diode lasers that are injection locked to a dissipative Kerr soliton frequency microcomb. We achieve transfer rates of 80 Gbps using homodyne detection and 60 Gbps transmitting simultaneously both data and clock signals in a dual-path wireless link. This experimental demonstration paves a path towards low-noise and integrated photonic millimeter-wave transceivers for future wireless communication systems

Selective excitation of plasmon resonances with single V-point cylindrical vector beams

We use a rigorous group theoretical method to identify a class of cylindrical vector beams that can selectively excite the plasmon modes of axially symmetric plasmonic structures. Our choice of the single V-point cylindrical vector beams as the basis to decompose cylindrical beams dramatically simplifies the symmetry analysis in the group theory framework. With numerical simulations, we demonstrate that any plasmon eigenmodes, bright or dark, can be selectively excited individually or jointly. A straightforward protocol to get access to the desired plasmon mode using symmetry coupling is presented. &nbsp;</p

Observation of the rotational Doppler shift with spatially incoherent light

The rotational Doppler shift (RDS) is typically measured by illuminating a rotating target with a laser prepared in a simple, known orbital angular momentum (OAM) superposition. We establish theoretically and experimentally that detecting the rotational Doppler shift does not require the incident light to have a well-defined OAM spectrum but instead requires well-defined correlations within the OAM spectrum. We demonstrate measurement of the rotational Doppler shift using spatially incoherent light. &nbsp;</p

Femtosecond diode-based time lens laser for multiphoton microscopy

We demonstrate a near-infrared, femtosecond, diode laser-based source with kW peak power for two-photon microscopy. At a wavelength of 976 nm, the system produces sub-ps pulses operating at a repetition rate of 10 MHz with kilowatt class peak powers suitable for deep tissue two-photon microscopy. The system, integrated with a laser-scanning microscope, images to a depth of 900 &micro;m in a fixed sample of PLP-eGFP labeled mouse brain tissue. This represents a significant development that will lead to more efficient, compact, and accessible laser sources for biomedical imaging. &nbsp;</p

Two-photon, fiber-coupled, super-resolution microscope for biological imaging

Imaging sub-diffraction dynamics of neural nanostructures involved in behaviors such as learning and memory in a freely moving animal is not possible with existing techniques. Here, we present a solution in the form of a two-photon (2P), fiber-coupled, stimulated emission depletion microscope and demonstrate its capabilities by acquiring super-resolution imaging of mammalian cells. A polarization-maintaining fiber is used to transport both the 2P excitation light (915 nm) and the donut-shaped depletion beam (592 nm), which is constructed by adding two temporally incoherent and orthogonally polarized Hermite&ndash;Gaussian fiber modes. The fiber output is insensitive to bending or temperature changes and is the first demonstration toward deep tissue super-resolution imaging in awake behaving animals. &nbsp;</p

The Sudden Dominance of blaCTX–M Harbouring Plasmids in Shigella spp. Circulating in Southern Vietnam

Shigellosis is a disease caused by bacteria belonging to Shigella spp. and is a leading cause of bacterial gastrointestinal infections in infants in unindustrialized countries. The Shigellae are dynamic and capable of rapid change when placed under selective pressure in a human population. Extended spectrum beta lactamases (ESBLs) are enzymes capable of degrading cephalosporins (a group of antimicrobial agents) and the genes that encode them are common in pathogenic E. coli and other related organisms in industrialized countries. In southern Vietnam, we have isolated multiple cephalosporin-resistant Shigella that express ESBLs. Furthermore, over two years these strains have replaced strains isolated from patients with shigellosis that cannot express ESBLs. Our work describes the genes responsible for this characteristic and we investigate one of the elements carrying one of these genes. These finding have implications for treatment of shigellosis and support the growing necessity for vaccine development. Our findings also may be pertinent for other countries undergoing a similar economic transition to Vietnam's and the corresponding effect on bacterial populations

Decadal increases in carbon uptake offset by respiratory losses across northern permafrost ecosystems

Tundra and boreal ecosystems encompass the northern circumpolar permafrost region and are experiencing rapid environmental change with important implications for the global carbon (C) budget. We analysed multi-decadal time series containing 302 annual estimates of carbon dioxide (CO2) flux across 70 permafrost and non-permafrost ecosystems, and 672 estimates of summer CO2 flux across 181 ecosystems. We find an increase in the annual CO2 sink across non-permafrost ecosystems but not permafrost ecosystems, despite similar increases in summer uptake. Thus, recent non-growing-season CO2 losses have substantially impacted the CO2 balance of permafrost ecosystems. Furthermore, analysis of interannual variability reveals warmer summers amplify the C cycle (increase productivity and respiration) at putatively nitrogen-limited sites and at sites less reliant on summer precipitation for water use. Our findings suggest that water and nutrient availability will be important predictors of the C-cycle response of these ecosystems to future warming

Terahertz microcomb oscillator stabilized by molecular rotation

Controlling the coherence between light and matter has enabled the radiation of electromagnetic waves with a spectral purity and stability that defines the Système International (SI) second. Transitions between hyperfine levels in atoms are accessible in the microwave and optical domains, but faithfully transferring such stability to other frequency ranges of interest requires additional components such as optical frequency combs. Such spectral purity and stability are specifically sought out for the terahertz domain for both scientific and commercial applications, including precision studies of molecular physics, next-generation wireless communications, quantum sensors, and terahertz frequency standards. Currently, there is a lack of native frequency references in this spectral range, which is essential for the consistency of measurements and traceability. Small-scale terahertz oscillators, which leverage dissipative Kerr soliton microcombs, present a promising avenue for the generation of terahertz waves that rival the spectral purity of electronic alternatives. Here, we experimentally demonstrate the rotational spectroscopy of nitrous oxide (N2O) with a microcomb-based oscillator. To mitigate the frequency drift encompassed in such waves, we lock the frequency of the microcomb terahertz oscillator to that of a rotational transition of N2O, reducing the fractional frequency stability to a level of 5 × 10−12 at 10 s of averaging time. These results constitute a high performance terahertz oscillator that can be scaled down to a compact size while circumventing the need for frequency multiplication or division of frequency standards. This demonstrates a foundational component needed for future terahertz applications

Photonic Generation of Millimeter-Waves Disciplined by Molecular Rotational Spectroscopy

Optical generation of millimeter-waves (mm-wave) is made possible by an optical heterodyne of two diode lasers on a uni-traveling-carrier photodiode (UTC-PD). We utilized this technique to produce a mm-wave oscillator with desirable phase-noise characteristics, which were inherited from a pair of narrow-linewidth diode lasers. We present the long-term stabilization of our oscillator, achieved by referencing it to a rotational transition of gaseous nitrous oxide (N2O). Direct frequency modulation spectroscopy at 301.442 GHz (J=11) generated an error signal that disciplined the frequency difference between the diode lasers and thus, locked the millimeter-wave radiation to the molecular rotational line. The mm-wave frequency was down-converted using an electro-optic (EO) comb, and recorded by a frequency counter referenced to a Rubidium (Rb) clock. This resulted in short-term fractional frequency stability of $1.5 \times 10^{-11}/\sqrt{\tau}$ and a long term-stability of $4\times 10^{-12}$ at 10,000 s averaging time