Effect of X-ray free-electron laser-induced shockwaves on haemoglobin microcrystals delivered in a liquid jet

X-ray free-electron lasers (XFELs) enable obtaining novel insights in structural biology. The recently available MHz repetition rate XFELs allow full data sets to be collected in shorter time and can also decrease sample consumption. However, the microsecond spacing of MHz XFEL pulses raises new challenges, including possible sample damage induced by shock waves that are launched by preceding pulses in the sample-carrying jet. We explored this matter with an X-ray-pump/X-ray-probe experiment employing haemoglobin microcrystals transported via a liquid jet into the XFEL beam. Diffraction data were collected using a shock-wave-free single-pulse scheme as well as the dual-pulse pump-probe scheme. The latter, relative to the former, reveals significant degradation of crystal hit rate, diffraction resolution and data quality. Crystal structures extracted from the two data sets also differ. Since our pump-probe attributes were chosen to emulate EuXFEL operation at its 4.5 MHz maximum pulse rate, this prompts concern about such data collection.

Gain-switched semiconductor laser driven soliton microcombs

Dissipative Kerr soliton generation using self-injection-locked III-V lasers has enabled fully integrated hybrid microcombs that operate in turnkey mode and can access microwave repetition rates. Yet, continuous-wave-driven soliton microcombs exhibit low energy conversion efficiency and high optical power threshold, especially when the repetition frequencies are within the microwave range that is convenient for direct detection with off-the-shelf electronics. Here, by actively switching the bias current of injection-locked III-V semiconductor lasers with switching frequencies in the X-band and K-band microwave ranges, we pulse-pump both crystalline and integrated microresonators with picosecond laser pulses, generating soliton microcombs with stable repetition rates and lowering the required average pumping power by one order of magnitude to a record-setting level of a few milliwatts. In addition, we unveil the critical role of the phase profile of the pumping pulses, and implement phase engineering on the pulsed pumping scheme, which allows for the robust generation and the stable trapping of solitons on intracavity pulse pedestals. Our work leverages the advantages of the gain switching and the pulse pumping techniques, and establishes the merits of combining distinct compact comb platforms that enhance the potential of energy-efficient chipscale microcombs.

Rationale for vacuum-pulse pump devices applied on cattle farms

One of the main elements to foster technological processes in animal husbandry are vacuumpulse pump devices designed to support dosing, mixing, transporting, lines for forage preparation and feeding, milking cows, milk processing, as well as a large number of technological processes in agriculture. The paper discusses a vacuum-pulse pumping device widely used in all industries and agriculture, a feature of which is to improve technical characteristics of the pump avoiding direct mechanical energy consumption and boasting a fairly simple design. In vacuum-pulse pumping devices, transient events are caused deliberately to increase ejection coefficient, productivity, etc. Oscillating flows of materials being transported are very diverse, due to an increased number of similarity criteria that determine flow patterns. Whereas superficial velocity and the Reynolds number are commonly used for a steady flow, for an oscillating flow, the relative frequency and the relative amplitude of oscillations are added. The objects of experimental research were ejectors with oscillating flows. The wider objective of the experiments was to determine the most effective performance indicators of the ejectors, including the degree of pressure increase, the ejection coefficient and the geometric parameter. Resulting from the experiments, a direct relationship was established between changes in the performance of a pulse-vacuum pumping device and valve material and magnitude of its oscillations. A pulse ejector is recommended to have metal-seated ball valves with a pulsation frequency of 90–100 min−1. Once applied, the proposed pulse ejector will eventually increase the transportation productivity by 14.5 %.

Diode-pumped, electro-optically Q-switched, cryogenic Tm:YAG laser operating at 1.88 μm

We present a diode-pumped, electro-optically Q-switched Tm:YAG laser with a cryogenically cooled laser crystal at 120 K. Output pulses of up to 2.55 mJ and 650 ns duration were demonstrated in an actively Q-switched configuration with a repetition rate of 1 Hz. By using cavity dumping the pulse duration was shortened to 18 ns with only a slightly lower output energy of 2.22 mJ. Furthermore, using a simplified rate equation model, we discuss design constraints on the pump fluence in a pulse pump approach for Tm:YAG to maximize the energy storage capability at a given pump power.

Towards a spectroscopic protocol for unambiguous detection of quantum coherence in excitonic energy transport

We propose a witness for quantum coherence in EET that can be extracted directly from two-pulse pump–probe spectroscopy experimental data.