arXiv subjects

Jens Limpert

Publications and source records attributed to Jens Limpert.

41 records · Page 3Linked to original sources

arXiv2017

Confining Brownian motion of single nanoparticles in an ABELtrap

Trapping nanoscopic objects to observe their dynamic behaviour for extended periods of time is an ongoing quest. Particularly, sub-100nm transparent objects are hard to catch and most techniques rely on immobilisation or transient diffusion through a confocal laser focus. We present an Anti-Brownian ELectrokinetic trap (pioneered by A. E. Cohen and W. E. Moerner) to hold nanoparticles and individual FoF1-ATP synthase proteins in solution. We are interested in the conformational dynamics of this membrane-bound rotary motor protein that we monitor using single-molecule FRET. The ABELtrap is an active feedback system cancelling the nano-object's Brownian motion by applying an electric field. We show how the induced electrokinetic forces confine the motion of nanoparticles and proteoliposomes to the centre of the trap.

q-bio.QM↗

arXiv2016

Table-Top Milliwatt-Class Extreme Ultraviolet High Harmonic Light Source

Extreme ultraviolet (XUV) lasers are essential for the investigation of fundamental physics. Especially high repetition rate, high photon flux sources are of major interest for reducing acquisition times and improving signal to noise ratios in a plethora of applications. Here, an XUV source based on cascaded frequency conversion is presented, which delivers due to the drastic better single atom response for short wavelength drivers, an average output power of (832 +- 204) μW at 21.7 eV. This is the highest average power produced by any HHG source in this spectral range surpassing precious demonstrations by more than a factor of four. Furthermore, a narrow-band harmonic at 26.6 eV with a relative energy bandwidth of only ΔE/E= 1.8 x 10E-3 has been generated, which is of high interest for high precision spectroscopy experiments.

physics.optics↗

arXiv2016

High-repetition-rate and high-photon-flux 70 eV high-harmonic source for coincidence ion imaging of gas-phase molecules

Unraveling and controlling chemical dynamics requires techniques to image structural changes of molecules with femtosecond temporal and picometer spatial resolution. Ultrashort-pulse x-ray free-electron lasers have significantly advanced the field by enabling advanced pump-probe schemes. There is an increasing interest in using table-top photon sources enabled by high-harmonic generation of ultrashort-pulse lasers for such studies. We present a novel high-harmonic source driven by a 100 kHz fiber laser system, which delivers 10$^{11}$ photons/s in a single 1.3 eV bandwidth harmonic at 68.6 eV. The combination of record-high photon flux and high repetition rate paves the way for time-resolved studies of the dissociation dynamics of inner-shell ionized molecules in a coincidence detection scheme. First coincidence measurements on CH$_3$I are shown and it is outlined how the anticipated advancement of fiber laser technology and improved sample delivery will, in the next step, allow pump-probe studies of ultrafast molecular dynamics with table-top XUV-photon sources. These table-top sources can provide significantly higher repetition rates than the currently operating free-electron lasers and they offer very high temporal resolution due to the intrinsically small timing jitter between pump and probe pulses.

physics.atom-ph↗

arXiv2014

High photon flux table-top coherent extreme ultraviolet source

High harmonic generation (HHG) enables extreme ultraviolet radiation with table-top setups. Its exceptional properties, such as coherence and (sub)-femtosecond pulse durations, have led to a diversity of applications. Some of these require a high photon flux and megahertz repetition rates, e.g. to avoid space charge effects in photoelectron spectroscopy. To date this has only been achieved with enhancement cavities. Here, we establish a novel route towards powerful HHG sources. By achieving phase-matched HHG of a megahertz fibre laser we generate a broad plateau (25 eV - 40 eV) of strong harmonics, each containing more than $10^{12}$ photons/s, which constitutes an increase by more than one order of magnitude in that wavelength range. The strongest harmonic (H25, 30 eV) has an average power of 143 $μ$W ($3\cdot10^{13}$ photons/s). This concept will greatly advance and facilitate applications in photoelectron or coincidence spectroscopy, coherent diffractive imaging or (multidimensional) surface science.

physics.optics↗

arXiv2014

Enhancing narrowband high order harmonic generation by Fano resonances

Resonances in the photo-absorption spectrum of the generating medium can modify the spectrum of high order harmonics. In particular, window-type Fano resonances can reduce photo-absorption within a narrow spectral region and, consequently, lead to an enhanced emission of high-order harmonics in absorption-limited generation conditions. For high harmonic generation in argon it is shown that the 3s3p6 np 1P1 window resonances (n=4,5,6) give rise to enhanced photon yield. In particular, the 3s3p6 4p 1P1 resonance at 26.6 eV allows a relative enhancement up to a factor of 30 compared to the characteristic photon emission of the neighboring harmonic order. This enhanced, spectrally isolated and coherent photon emission line has a relative energy bandwidth of only ΔE/E=3*10-3. Therefore, it might be directly applied for precision spectroscopy or coherent diffractive imaging without the need of additional spectral filtering. The presented mechanism can be employed for tailoring and controlling the high harmonic emission of manifold target materials.

physics.optics↗