Drohnenbilder zur Untersuchung von Pflanzenwachstum und Nährstoffdynamik

Ein besseres Verständnis der Dynamik hinter der Freisetzung von pflanzenverfügbaren Nährstoffen aus Boden oder organischen Dünger und eine Verbesserung der Nährstoffverwertung von Ackerfrüchten sind zwei wichtige Herausforderungen, um die Produktivität im ökologischem Ackerbau zu erhöhen. Doch diese Prozesse sind stark sowohl von biotischen (z.B. Bodenmikroben) als auch abiotischen (z.B. Temperatur, Niederschlag, Bodenfeuchtigkeit, Bodenstruktur) Faktoren beeinflusst und erschweren effiziente Untersuchungen. Fernbilderkundung-Technologien (remote sensing) haben sich in den letzten Jahren stark weiterentwickelt und bieten heute neue Ansätze und Methoden, um der Ernährungsstatus von Pflanzen sowie die Dynamik des Pflanzenwachstums nicht destruktiv zu untersuchen. In diesem Beitrag wird, anhand ersten Untersuchungen, die Möglichkeit aus Drohnenbilder Pflanzenwachstum-Parameter zu erfassen und das Potential dieser Technik für wissenschaftliche Untersuchungen und agronomische Beratung diskutiert

Mid-infrared entangled photon generation in optimised asymmetric semiconductor quantum wells

The optimal design of asymmetric quantum well structures for generation of entangled photons in the mid-infrared range by spontaneous parametric down- conversion is considered, and the efficiency of this process is estimated. Calcu- lations show that a reasonably good degree of entanglement can be obtained, and that the optical interaction length required for optimal conversion is very short, in the few μm range

Linewidth of a quantum-cascade laser assessed from its frequency noise spectrum and impact of the current driver

We report on the measurement of the frequency noise properties of a 4.6-μm distributed-feedback quantum-cascade laser (QCL) operating in continuous wave near room temperature using a spectroscopic set-up. The flank of the R(14) ro-vibrational absorption line of carbon monoxide at 2196.6cm−1 is used to convert the frequency fluctuations of the laser into intensity fluctuations that are spectrally analyzed. We evaluate the influence of the laser driver on the observed QCL frequency noise and show how only a low-noise driver with a current noise density below {\approx} 1~\mbox{nA/}\sqrt{}\mbox{Hz} allows observing the frequency noise of the laser itself, without any degradation induced by the current source. We also show how the laser FWHM linewidth, extracted from the frequency noise spectrum using a simple formula, can be drastically broadened at a rate of {\approx} 1.6~\mbox{MHz/}(\mbox{nA/}\sqrt{}\mbox{Hz}) for higher current noise densities of the driver. The current noise of commercial QCL drivers can reach several \mbox{nA/}\sqrt{}\mbox{Hz} , leading to a broadening of the linewidth of our QCL of up to several megahertz. To remedy this limitation, we present a low-noise QCL driver with only 350~\mbox{pA/}\sqrt{}\mbox{Hz} current noise, which is suitable to observe the ≈550kHz linewidth of our QC

Quantum cascade laser frequency stabilisation at the sub-Hz level

Quantum Cascade Lasers (QCL) are increasingly being used to probe the mid-infrared "molecular fingerprint" region. This prompted efforts towards improving their spectral performance, in order to reach ever-higher resolution and precision. Here, we report the stabilisation of a QCL onto an optical frequency comb. We demonstrate a relative stability and accuracy of 2x10-15 and 10-14, respectively. The comb is stabilised to a remote near-infrared ultra-stable laser referenced to frequency primary standards, whose signal is transferred via an optical fibre link. The stability and frequency traceability of our QCL exceed those demonstrated so far by two orders of magnitude. As a demonstration of its capability, we then use it to perform high-resolution molecular spectroscopy. We measure absorption frequencies with an 8x10-13 relative uncertainty. This confirms the potential of this setup for ultra-high precision measurements with molecules, such as our ongoing effort towards testing the parity symmetry by probing chiral species