96 research outputs found
High power ultra-short pulse lasers based on fiber driven OPCPA
Ultrashort laser pulses enable fundamental studies on small length and time scales. Additionally, high pulse energies allows the access to new regimes of light matter interaction and the investigation of nanometer scale structures on attosecond time scales by XUV pulses produced via high harmonic generation (HHG). Unfortunately, the XUV photon flux is typically very low. Hence, high power and high repetition rate driving laser sources are required in order to improve the performance of current studies and to open the way for new exiting applications, such as seeding of free electron lasers. Regrettably, conventional (Ti:Sa) laser technology is limited in output power due to the thermo optical effects in the amplifier crystals.
The objective of this thesis is the development of a new power scalable laser concept merging OPCPA technology with state-of-the-art high power fiber lasers. Based on modeling of the optical parametric amplifier, important requirements on the OPCPA pump are found which are adopted in choice and development of the pump laser later. Furthermore, the geometry of the optical parametric amplifier is optimized for ultra-broadband amplification. Gain narrowing and saturation effects are investigated in order to achieve high conversion efficiency. In addition, parasitic nonlinear effects, such as second harmonic generation of signal and idler wave, are studied and configurations are found which effectively avoid these unwanted effects.
Experimentally, pulse durations of 8 fs and a pulse peak power as large as 6 GW are achieved with an optimized ultra-broadband OPCPA system. In addition, this few-cycle OPCPA system delivers an average output power as large as 6.7 W, which represents a record value for few-cycle lasers. Finally, high harmonic generation is demonstrated with this laser system and further scaling potential to higher peak and average powers is discussed
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) {\mu}W 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 {\Delta}E/E= 1.8 x
10E-3 has been generated, which is of high interest for high precision
spectroscopy experiments.Comment: 4 Pages, 4 Picture
High-average-power femtosecond laser at 258 nm
We present an ultrafast fiber laser system delivering 4.6 W average power at 258 nm based on two-stage fourth-harmonic generation in beta barium borate (BBO). The beam quality is close to being diffraction limited with an M2 value of 1.3×1.6. The pulse duration is 150 fs, which, potentially, is compressible down to 40 fs. A plain BBO and a sapphire-BBO compound are compared with respect to the achievable beam quality in the conversion process. This laser is applicable in scientific and industrial fields. Further scaling to higher average power is discussed
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 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 W (
photons/s). This concept will greatly advance and facilitate applications in
photoelectron or coincidence spectroscopy, coherent diffractive imaging or
(multidimensional) surface science
Broadband ptychography using curved wavefront illumination
We examine the interplay between spectral bandwidth and illumination
curvature in ptychography. By tailoring the divergence of the illumination,
broader spectral bandwidths can be tolerated without requiring algorithmic
modifications to the forward model. In particular, a strong wavefront curvature
transitions a far-field diffreaction geometry to an effectively near-field one,
which is lees affected by temporal coherence effects. The relaxed temporal
coherence requirements allow for leveraging wider spectral bandwidths and
larger illumination spots. Our findings open up new avenues towards utilizing
pink and broadband beams for increased flux and throughput at both synchrotron
facilities and lab-scale beamlines
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Giant refractometric sensitivity by combining extreme optical Vernier effect and modal interference
The optical Vernier effect consists of overlapping responses of a sensing and a reference interferometer with slightly shifted interferometric frequencies. The beating modulation thus generated presents high magnified sensitivity and resolution compared to the sensing interferometer, if the two interferometers are slightly out of tune with each other. However, the outcome of such a condition is a large beating modulation, immeasurable by conventional detection systems due to practical limitations of the usable spectral range. We propose a method to surpass this limitation by using a few-mode sensing interferometer instead of a single-mode one. The overlap response of the different modes produces a measurable envelope, whilst preserving an extremely high magnification factor, an order of magnification higher than current state-of-the-art performances. Furthermore, we demonstrate the application of that method in the development of a giant sensitivity fibre refractometer with a sensitivity of around 500 µm/RIU (refractive index unit) and with a magnification factor over 850
Visualizing the ultra-structure of microorganisms using table-top extreme ultraviolet imaging
Table-top extreme ultraviolet (EUV) microscopy offers unique opportunities
for label-free investigation of biological samples. Here, we demonstrate
ptychographic EUV imaging of two dried, unstained model specimens: germlings of
a fungus (Aspergillus nidulans), and bacteria (Escherichia coli) cells at 13.5
nm wavelength. We find that the EUV spectral region, which to date has not
received much attention for biological imaging, offers sufficient penetration
depths for the identification of intracellular features. By implementing a
position-correlated ptychography approach, we demonstrate a millimeter-squared
field of view enabled by infrared illumination combined with sub-60 nm spatial
resolution achieved with EUV illumination on selected regions of interest. The
strong element contrast at 13.5 nm wavelength enables the identification of the
nanoscale material composition inside the specimens. Our work will advance and
facilitate EUV imaging applications and enable further possibilities in life
science
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 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
CHI 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
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