280 research outputs found
Compression of extreme-ultraviolet ultrashort pulses by grating configurations
The design and realization of grating instruments to condition the spectral phase of ultrashort extreme-ultraviolet pulses are discussed. The main application of such configurations is the temporal compression of pulses by compensating the phase chirp and getting close to the Fourier limit. We discuss the two configurations useful for the realization of ultrafast grating compressors, namely, the classical diffraction mount and the off-plane one. The configuration may be applied to free-electron lasers and high-order laser harmonics
Design study of time-preserving grating monochromators for ultrashort pulses in the extreme-ultraviolet and soft X-rays
The design of grating-based instruments to handle and condition coherent ultrafast
pulses in the extreme-ultraviolet is discussed. The main application of such instruments is the
monochromatization of high-order laser harmonics and free-electron-laser pulses in the femtosecond
time scale. Broad-band monochromators require the use of diffraction gratings at grazing incidence.
A grating can be used for the spectral selection of ultrashort pulses without altering the pulse duration
in a significant way, provided that the number of illuminated grooves is equal to the resolution.
We discuss here the design conditions to be fulfilled by a grating monochromator that does not
increase the pulse duration significantly longer than the Fourier limit
Analytical computation of the epidemic threshold on temporal networks
The time variation of contacts in a networked system may fundamentally alter
the properties of spreading processes and affect the condition for large-scale
propagation, as encoded in the epidemic threshold. Despite the great interest
in the problem for the physics, applied mathematics, computer science and
epidemiology communities, a full theoretical understanding is still missing and
currently limited to the cases where the time-scale separation holds between
spreading and network dynamics or to specific temporal network models. We
consider a Markov chain description of the Susceptible-Infectious-Susceptible
process on an arbitrary temporal network. By adopting a multilayer perspective,
we develop a general analytical derivation of the epidemic threshold in terms
of the spectral radius of a matrix that encodes both network structure and
disease dynamics. The accuracy of the approach is confirmed on a set of
temporal models and empirical networks and against numerical results. In
addition, we explore how the threshold changes when varying the overall time of
observation of the temporal network, so as to provide insights on the optimal
time window for data collection of empirical temporal networked systems. Our
framework is both of fundamental and practical interest, as it offers novel
understanding of the interplay between temporal networks and spreading
dynamics.Comment: 22 pages, 6 figure
Design of a time-compensated EUV and soft X-ray monochromator with multilayer mirrors for high-order harmonics
A time-compensated monochromator for ultrashort high-order
harmonics in the EUV and soft X-ray regions is presented.
The system consists of two grazing-incidence toroidal mirrors
used, respectively, as collimating and refocusing elements
and of two multilayer normal-incidence plane mirrors illuminated
in parallel light that rotate along a vertical axis to
select the operative wavelength, but remain parallel to
guarantee the constant direction of the exit beam. This
is performed by simultaneously rotating and translating
one of the two mirrors along an axis parallel to the exit
direction. The pulse time duration is not altered up to
few femtoseconds
Optical concept of a compressor for XUV pulses in the attosecond domain.
We discuss the phase properties of a double-grating compressor with grazing-incidence gratings in the off-plane mount, designed for the temporal compression of XUV attosecond pulses produced with the technique of high-order harmonic generation. Its purpose is to introduce a negative chirp that compensates for the intrinsic chirp of the pulse. The study is based on the path lengths of the rays at different wavelengths, and their control in order to achieve either positive or negative group-delay dispersion. We demonstrate that the sign and the amount of the dispersion introduced is controlled by a linear translation of a grating. Beside the instrument is expected to present a high throughput, constant along the spectrum of interest. The compressor can be designed for any spectral region in the XUV and soft X-ray domain. As a test case, the applications to the compression of attosecond pulses centered at 70 eV and at 160 eV are discussed. (C) 2008 Optical Society of America
A non-dispersive approach for a Raman gas sensor
Although Raman spectroscopy is widely used on solids and liquids, its application on gaseous samples is far less commonplace due to technical issues related to dealing with very weak signals over a strong background. A demonstration of a possible approach for a simple, noninvasive Raman-based gas detector is presented and evaluated. This setup is meant to perform nitrogen and oxygen gas concentration measurements through Raman scattering working with optical filters instead of the traditional spectrograph and a lighting-grade 532 nm diode-pumped solid state laser as the pumping source. An industrial-grade CMOS camera is used as the detector, taking full advantage of the low noise and spatial resolution of this device. The system has been tested for both oxygen and nitrogen in a gas flow cell. Nitrogen measurement in a glass vial is reported in order to demonstrate and show some of the advantages that could be obtained with the use of an imaging detector instead of a single pixel one. The reported measurements show that even without using a dispersion spectrometer, this approach enables an indicative, noninvasive gas detection through glass vials with significant rejection of the elastic scattering contribution
Advanced instrumentation for spectral and spatial investigations of high-order laser harmonics
We report on the design and characterization of a
grazing-incidence flat-field spectrograph that allows
simultaneously the measurement of spectrum, beam divergence,
and absolute flux of EUV and soft X-ray radiation for a beam
of high-order laser harmonics generated by the interaction between
an ultrashort femtosecond laser pulse and a gas jet. The instrument
seems a very powerful tool for the understanding of the generation
process
Phase Manipulation of Ultrashort Soft X-Ray Pulses by Reflective Gratings
In this chapter, we discuss the use of reflective diffraction gratings to manipulate the phase of ultrashort pulses in the extreme ultraviolet (XUV) and soft X-ray spectral regions. Gratings may be used to condition the spectral phase of ultrashort pulses, e.g., to compensate for the pulse chirp and compress the pulse, similarly to what is routinely realized for visible and infrared pulses. The chirped pulse amplification technique has been already proposed for soft X-ray free-electron laser radiation; however, it requires the use of a compressor to compensate for the pulse chirp and get closer to the Fourier limit. There are fundamental differences when operating the gratings at wavelengths shorter than ≈40 nm on a broad band: (a) the gratings are operated at grazing incidence; therefore, the optical design has to be consequently tailored to this peculiar geometry; (b) the grating efficiency is definitely lower; therefore, the number of diffractions has to be limited to two. We discuss the different configurations that can be applied to the realization of a grating stretcher/compressor
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