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We report an optical parametric amplifier (OPA), providing a maximum pulse energy of ∼200 µJ at 700-950 nm and a pulse duration of ∼1 ps. The OPA is driven by a ∼1 ps pulse with ∼2.5 mJ energy at 1 kHz, provided by a commercial thin-disk based laser. Using the output pulse of the OPA as pump, the thin-disk laser pulses at 1030 nm as Stokes, and the second harmonic (515 nm) as probe, we investigate the coherent anti-Stokes Raman scattering (CARS) of N

We investigate the spectral properties of ps laser-induced filamentation in air using an ultrafast thin-disk based amplifier at a central wavelength of 1030 nm with a maximum pulse energy of 60 mJ at a repetition rate of 1 kHz. We show that the spectrum induced by filamentation in air is sufficiently broad to excite ro-vibrational Raman transitions in N2, O2 and CH4. The excitation is probed with the second harmonic (515 nm) to generate CARS signals in air. Furthermore, we investigate the influence of optical windows on the CARS signal for applications in combustion and gasification diagnostics.

We investigate the coherent anti-Stokes Raman scattering (CARS) in air generated by the spectral broadening of laser induced filamentation at a pulse duration of ~1 ps and a central wavelength of ~1 μm.

Coherent anti-Stokes Raman spectroscopy (CARS) is a powerful tool in combustion diagnostics [1] . It requires three beams, the pump, Stokes and probe beam with at least two different wavelengths. For high pressure applications, the use of fs-pulses is of additional benefit, as the CARS signal is free from distortions from molecular collisions, if the excited Raman level is probed within a few ps [2] . On the other hand, too short pulses (~100-500 fs) result in poor spectral resolution [3] . In this study, we present an optical parametric amplifier (OPA), providing a maximum pulse energy of ~200 µJ, at 700-900 nm and a pulse duration of ~1 ps. Using a pump source at 1030 nm, this setup may serve as a customized fs-CARS system for high pressure gas analysis.

We investigated ultrashort pulse filamentation and lasing action of

Due to ageing populations the number of tumors is increasing worldwide. Successful surgical treatment requires complete resection of tumors to reduce recurrence rates. To reach this goal, novel methods combining in vivo tumor and tumor margin detection with low invasive precision surgical tools are needed. Coherent anti-Stokes Raman scattering (CARS) imaging is a highly promising optical tool for visualizing tumors based on characteristic changes in tissue morphology and molecular composition, while fs-laser ablation is to date the most precise surgical tool established in ophthalmology. In this contribution, CARS imaging has been combined with fs-laser ablation as a new approach for image-guided precision surgery for the first time. CARS guided fs-ablation has been applied to ablate brain, liver, skin, muscular and vascular tissues with μm-precision using sub-100 fs pulses of μJ level. We demonstrate superior imaging performance and contrast as well as detection of tissue margins by coherent Raman microscopy in comparison to laser reflectance imaging. The combination of CARS-image-guided tissue ablation is a promising tool for minimally invasive surgeries particularly in the vicinity of functional structures in the future.

The newly developed HITECOM reactor provides the possibility of in-situ analysis of single particle reactions. It combines the capabilities of a magnetic suspension thermobalance with state of the art optical analysis. The surface temperature and carbon conversion of single particles are measured under well-defined flow conditions. The generated data enables the detailed validation of CFD single particle models. For this reactor, a special temperature resistant particle holder had to be constructed, which is able to fix various particles in direct flow during gasification. An in-situ Raman spectroscopy setup was established for quantitative gas analysis at pressures between 1 and 20 bar and temperatures up to 965 °C. Here, a pulsed Nd:YAG laser at 355 nm was used as excitation source. The Rayleigh/Raman scattering was measured perpendicular to the flow direction with a spectrograph and ICCD camera. From the recorded spectra the gas concentrations were calculated. Generally, the calculated concentrations of CO, CO2 and N2 match the reference values from the gas chromatograph. In the present study, single coal particles of one Central German lignite and one hard coal were analyzed and monitored during gasification. The particle diameter ranged from 1 to 3 mm. Gasification experiments with CO2 were carried out under isothermal conditions at 1 bar total pressure and temperatures of 800–1200 °C. The experimental data were adjusted with models by data fitting. It was found that the Random Pore Model (RPM) matches the carbon conversion of the hard coal sample and the Shrinking Core Model (SCM) matches the carbon conversion of the lignite sample. Further analysis revealed that inhomogeneous particles affect gasification kinetics. The differences in reactivity between several particles from the hard coal are significantly larger than for the lignite particles, which is in accordance to the results of the respective ultimate and proximate analyses. Additionally, it was discovered that the difference between gas and particle temperature is negligible for low reactive feedstocks within the investigated temperature range (ΔT ⩽ 5 K at 1070 °C, hard coal), whereas there was a significant difference for reactive particles (ΔT ⩽ 40 K at 1070 °C, lignite).

We propose a method using the non-resonant signal measured in pure argon for gas concentration measurements based on ultrabroadband fs/ps coherent anti-Stokes Raman scattering. Measurement accuracies are greatly improved to 5% for CO2/N2/CH4 gas mixtures.

Due to their large spectral bandwidth sub ∼20 fs pulses are a versatile tool in spectroscopy, but for applications in gases comparably high pulse energies are required. These pulses are easily subject to distortions of the spectral shape, phase and shot-to-shot stability. We investigate the excitation efficiency for two-beam ultrabroadband fs/ps coherent anti-Stokes Raman scattering (CARS) using a shot-to-shot stable BBO-based optical parametric chirped pulse amplifier (OPCPA). Up to 10 bar, quantitative concentration measurements with and without consideration of the excitation efficiency measured in argon are investigated for ternary gas mixtures with Raman shifts up to ∼3000 cm−1.

The test reactor HITECOM was designed to study in situ the conversion of an isolated particle in a well-defined gas flow at a gas temperature up to 1400 ° C and a pressure up to 40 bar. As is typical of high-temperature, high-pressure systems, the temperature field inside the reactor is not perfectly constant and causes natural convection, which interferes with the gas flow in the test rig. To gain a deeper insight into the complex flow field and temperature and species distribution, a detailed CFD study was carried out and the results validated against experimental data. The numerical model comprised reactive gas flow, heat and mass exchange with a reactive char particle, convective and radiative heat transfer in the reactor and heat conduction in the solid parts of the reactor. The present study revealed that, depending on the operating conditions, the flow field shifts from an idealized parabolic profile to a complex, buoyancy-driven flow. It could be shown that comprehensive CFD modeling is necessary to identify critical operating conditions and estimate the real species and temperature distribution around the reacting particle, facilitating an improved evaluation of the experimental data.

Femtosecond (fs)-CARS is a promising approach for gas spectroscopy under high pressure and temperature conditions, as it allows probing molecular states on a time scale which is significantly shorter than the typical decay time induced by interfering collisions. Usually, fs-CARS is performed in a three beam setup, which requires maintaining spatial and temporal overlap of the pulses at the focal point. This is a challenging task, especially in harsh environments such as in a combustion chamber. In this study, we present an alternative approach, which uses two beams in a collinear configuration. An ultra-broadband, sub 7 fs laser pulse acts as pump and Stokes pulse, and a ∼500 fs pulse is used for probing. We show that this configuration is suitable for measuring the gas temperature and concentration. Furthermore, possible single shot measurements of the gas temperature are evaluated.

We investigated ultrashort pulse filamentation and lasing action of N 2 + for pump-probe experiments in gases. Using femtosecond coherent anti-Stokes Raman scattering, the white-light supercontinuum generated in the filament was used to excite ro-vibrational Raman transitions in air, C O 2 and C H 4 . We show that the lasing pulse acts as a probe for the excited levels by detecting the corresponding anti-Stokes Raman spectroscopy signals. This feature may be applied to remote sensing applications, as the temporal and spatial alignment of the probe beam and the filament is intrinsically provided.

Using two beam femtosecond coherent anti-Stokes Raman scattering (fs-CARS), temperature and concentration measurements are performed on relevant combustion species such as H2, N2, CO, and CO2.

International audience; Ultrashort pulse lasers enable reliable and versatile high precision ablation and surface processing of various materials such as metals, polymers and semiconductors. However, when modifications deep inside the bulk of transparent media are required, nonlinear pulse material interactions can decrease the precision, since weak focusing and the long propagation of the intense pulses within the nonlinear media may induce Kerr self-focusing, filamentation and white light generation. In order to improve the precision of those modifications, simultaneous spatial and temporal focusing (SSTF) allows to reduce detrimental nonlinear interactions, because the ultrashort pulse duration is only obtained at the focus, while outside of the focal region the continuously increasing pulse duration strongly reduces the pulse intensity. In this paper, we review the fundamental concepts of this technology and provide an overview of its applications for purposes of multiphoton microscopy and laser materials processing. Moreover, numerical simulations on the nonlinear pulse propagation within transparent media illustrate the linear and nonlinear pulse propagation, highlighting the differences between conventional focusing and SSTF. Finally, fs-laser induced modifications in gelatine are presented to compare nonlinear side-effects caused by conventional focusing and SSTF. With conventional focusing the complex interplay of self-focusing and filamentation induces strongly inhomogeneous, elongated disruptions. In contrast, disruptions induced by SSTF are homogeneously located at the focal plane and reduced in length by a factor >2, which is in excellent agreement with the numerical simulations of the nonlinear pulse propagation and might favor SSTF for demanding applications such as intraocular fs-laser surgery.

We analyze the temperature in air and neat N2 under high pressure using ultrabroadband, two-beam femtosecond coherent Anti-Stokes Raman scattering. The derived temperatures are compared to numerical simulations.

In der Literatur gibt es eine Reihe von Hinweisen, die auf ein unzureichendes strategisches Management in kleinen und mittelstandischen Unternehmen (KMU) im deutschen Sprachraum hindeuten. Im vorliegenden Beitrag erfolgt eine gestaltungsorientierte aktuelle Bestandsaufnahme konzeptioneller und empirischer Gegebenheiten mit Fokus auf Schweizer KMU der ICT-Branche. Ausgehend von einer Kennzeichnung von Grundorientierung, Prozess und Denkperspektiven des strategischen Managements und einem situations- und evolutionstheoretischen Zugang zur strategischen Fuhrung werden die wichtigsten Aspekte einer Umsetzung des strategischen Managements in KMU thematisiert: dessen Verbreitung und Eignung, die Rolle der Fuhrungskrafte, die Relevanz des strategischen Denkens sowie Planungsformen und Instrumente. Die empirische Bestandsaufnahme erfolgt im Kern uber eine qualitative Erhebung bei zehn Fuhrungskraften Deutschschweizer ICT-KMUs, die durch eine quantitative internetbasierte Befragung von Fuhrungskraften der Schweizer ICT-Branche rudimentar erganzt wird. Die Ergebnisse deuten auf eine derzeit noch unzureichende Umsetzung des strategischen Managements und auf situative, flexiblere Implementierungsansatze bei den untersuchten Deuschschweizer ICT-KMU hin. Vor dem Hintergrund eines erkannten Differenzierungsbedarfs werden spezifische Handlungsempfehlungen zum strategischen Management fur KMU der ICT-Branche abgeleitet.

We show that two-beam femtosecond coherent anti-Stokes Raman scattering can be effectively used for thermometry on CO2 for temperatures between ∼100 °C and ∼600 °C at a maximum pressure of 8.5 bar. The temperature measurement is based on probing the vibrationally excited states of CO2, using a ∼7 fs pump/Stokes pulse and a narrowband (∼0.3 nm) probe pulse. The temperatures can be derived from a single spectrum, obviating the need for a delay scan or a chirped probe pulse.