Conventional Excitation Sources Research Articles

Fluoride nanocrystals and quantum dots nanocomposite for efficient luminescence nanothermometer in NIR-II biological window

Biosensors working in the second near-infrared (NIR-II) spectral region have recently gained great attention owning to their deep tissue bioimaging and high spatiotemporal resolution. However, there is still a challenge to develop efficient nanothermometers based on NIR-II luminescence. Herein, we present a pioneering advancement in the field of nanothermometry by synthesizing a novel nanothermometer, a composite of fluoride nanocrystals and quantum dots. This NaYF4:1Nd-Ag2S QDs@SiO2 nanocomposite demonstrates exceptional functionality, being excited by a single light irradiation at 808 nm for NIR-II luminescence imaging. Notably, the composite emits at two distinct wavelengths-1064 nm and 1125 nm, attributable to Nd3+ and Ag2S QDs, respectively. This unique emission profile enables deeper tissue penetration, mitigating overheating risks compared to conventional excitation sources at 980 nm. Furthermore, the nanomaterials exhibit remarkable temperature-sensing capabilities, with maximum sensitivities of 0.81%K−1 (SR) at 333 K. These superior sensitivities outperform many existing temperature sensors relying on thermally coupled Stark sublevels. The SiO2 matrix not only encapsulates and protects the fluoride nanocrystals and quantum dots but also shields them from aqueous environments, ensuring outstanding luminescence stability. Our findings highlight the potential of this nanothermometer as a highly efficient temperature sensor with promising applications in cutting-edge bioapplications. This development introduces a new frontier in temperature sensing and bioimaging, showcasing its potential for transformative contributions to the field.

Plasmon-enhanced optoacoustic transducer with Ecoflex thin film for broadband ultrasound generation using overdriven pulsed laser diode.

Ultrasonic transducers facilitate noninvasive biomedical imaging and therapeutic applications. Optoacoustic generation using nanoplasmonic structures provides a technical solution for highly efficient broadband ultrasonic transducer. However, bulky and high-cost nanosecond lasers as conventional excitation sources hinder a compact configuration of transducer. Here, we report a plasmon-enhanced optoacoustic transducer (PEAT) for broadband ultrasound generation, featuring an overdriven pulsed laser diode (LD) and an Ecoflex thin film. The PEAT module consists of an LD, a collimating lens, a focusing lens, and an Ecoflex-coated 3D nanoplasmonic substrate (NPS). The LD is overdriven above its nominal current and precisely modulated to achieve nanosecond pulsed beam with high optical peak power. The focused laser beam is injected on the NPS with high-density electromagnetic hotspots, which allows for the efficient plasmonic photothermal effect. The thermal expansion of Ecoflex finally generates broadband ultrasound. The overdriven pulsed LD achieves a maximum optical peak power of 40W, exceeding the average optical power of 3W. The thick Ecoflex-coated NPS exhibits an eightfold optoacoustic enhancement with a fractional bandwidth higher than 160% and a peak frequency of 2.5MHz. In addition, the optoacoustic amplitude is precisely controlled by the optical peak power or the laser pulse width. The PEAT-integrated microfluidic chip clearly demonstrates acoustic atomization by generating aerosol droplets at the air-liquid interface. Plasmon-enhanced optoacoustic generation using PEAT can provide an approach for compact and on-demand biomedical applications, such as ultrasound imaging and lab-on-a-chip technologies.

Visual observations of an atmospheric-pressure solution-cathode glow discharge

The solution-cathode glow discharge (SCGD) is an optical emission source for atomic spectrometry comprised of a moderate-power atmospheric-pressure DC glow discharge sustained directly upon the surface of an electrically conductive solution. The SCGD boasts a simple, inexpensive design and has demonstrated detection limits similar to those of more conventional excitation sources used in atomic spectrometry. Although the analytical performance of the SCGD as an optical emission source is well characterized, the mechanism through which the discharge atomizes and excites analyte from the sample solution remains a point of debate. The current paper presents visual observations of the SCGD from a variety of imaging techniques. The implications of the images regarding the mechanism of analyte solution-to-plasma transport and excitation in the SCGD are discussed.

Behaviour of scintillators under XUV free electron laser radiation

Free electron lasers (FEL) are new generation accelerator-based short wavelength light sources providing high pulse intensity and femtosecond pulse duration, which enable investigation of interaction of elementary excitations in solids under extreme conditions. Using the FLASH facility of HASYLAB at DESY (Hamburg, Germany), we investigated the response of different materials with scintillating properties based on intrinsic emissions to the 25.6 and 13.8 nm FEL radiation by means of time-resolved luminescence spectroscopy. FLASH delivered single pulses of 25 fs duration having energy per pulse up to 30 μJ resulting in power densities of ∼10 12 W/cm 2 on crystals. As a function of excitation density we observed the shortening of lifetime and non-exponential behaviour of emission decays in CaWO 4, while the emission spectra recorded are comparable to those obtained at conventional excitation sources.

Flip-flop jet nozzle extended to supersonic flows

An experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic to supersonic. Unsteady velocity and pressure measurements were made using hot wires, piezoresistive pressure transducers, and pitot probes. In addition, smoke flow visualization using high-speed photography was used to document the oscillation of the jet. For the subsonic flip-flop jet, it was found that the apparent time-mean widening of the jet was not accompanied by an increase in the mass flux. Fluidically oscillated jets up to a Mach number of about 0.5 have been reported before, but to our knowledge there is no information on fluidically oscillated supersonic jets. It was found that it is possible to extend the operation of these devices to supersonic flows. The streamwise velocity perturbation levels produced by this device were much higher than the perturbation levels that could be produced using conventional excitation sources such as acoustic drivers. In view of this ability to produce high amplitudes, the potential for using a small-scale fluidically oscillated jet as an unsteady excitation source for the control of shear flows in full-scale practical applications seems promising.

Effect of axial injection of argon on conventional spectrochemical excitation sources at atmospheric pressure—I: Behaviour of line intensities and their profiles under various experimental conditions

The axial injection of argon into the conventional excitation sources through a hole drilled in the upper electrode is discussed. In spite of a simple electrode arrangement the argon produces unexpected and significant changes in emission phenomena. Self-reversal is practically eliminated. Intensity enhancements were studied as a function of line character, excitation potential, electrode type, concentration of analytes and concomitants, the presence of organic materials (solvents and solutes) and the purity of the argon. It was observed, that the intensity enhancement deteriorated if the concentration of excitable particles (atoms, molecules, free-radicals, etc.) in the plasma increased. Using krypton instead of argon similar results were obtained.