Showing papers on "Doppler broadening published in 2017"
TL;DR: Supercontinuum generation in a solid-state medium was investigated experimentally and a continuum covering 460 to 950 nm was obtained when 0.8 mJ/30 fs Ti:sapphire laser pulses were applied to seven thin fused silica plates at a 1 kHz repetition rate.
Abstract: Supercontinuum generation in a solid-state medium was investigated experimentally. A continuum covering 460 to 950 nm was obtained when 0.8 mJ/30 fs Ti:sapphire laser pulses were applied to seven thin fused silica plates at a 1 kHz repetition rate. The primary processes responsible for spectral broadening were self-phase modulation (SPM) and self-steepening, while SPM and self-focusing were balanced to optimize the spectral broadening and suppress the multiphoton process. The output was compressed to a 5.4 fs and a 0.68 mJ pulse, corresponding to two optical cycles and 0.13 TW of peak power.
101 citations
TL;DR: A review of the state-of-the-art of defect characterization in bulk metallic materials by positron annihilation spectroscopy is provided in this article, where the authors discuss the recent developments in the field and discuss examples of defect studies of metallic materials.
94 citations
TL;DR: The results show that this recently introduced compression scheme for peak powers above the threshold for catastrophic self-focusing can be scaled to smaller pulse energies and can achieve a larger compression factor than previously reported.
Abstract: We demonstrate nonlinear pulse compression by multi-pass cell spectral broadening (MPCSB) from 860 fs to 115 fs with compressed pulse energy of 7.5 µJ, average power of 300 W and close to diffraction-limited beam quality. The transmission of the compression unit is >90%. The results show that this recently introduced compression scheme for peak powers above the threshold for catastrophic self-focusing can be scaled to smaller pulse energies and can achieve a larger compression factor than previously reported. Good homogeneity of the spectral broadening across the beam profile is verified, which distinguishes MPCSB among other bulk compression schemes.
93 citations
TL;DR: Efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip that can enable mode-locked lasers to attain unprecedented tunable spectral reach for spectroscopy, bioimaging, tomography and metrology.
Abstract: Short duration, intense pulses of light can experience dramatic spectral broadening when propagating through lengths of optical fibre. This continuum generation process is caused by a combination of nonlinear optical effects including the formation of dispersive waves. Optical analogues of Cherenkov radiation, these waves allow a pulse to radiate power into a distant spectral region. In this work, efficient and coherent dispersive wave generation of visible to ultraviolet light is demonstrated in silica waveguides on a silicon chip. Unlike fibre broadeners, the arrays provide a wide range of emission wavelength choices on a single, compact chip. This new capability is used to simplify offset frequency measurements of a mode-locked frequency comb. The arrays can also enable mode-locked lasers to attain unprecedented tunable spectral reach for spectroscopy, bioimaging, tomography and metrology.
91 citations
TL;DR: A tunable library of N,N,N'-trisubstituted selenourea precursors and their reaction with lead oleate at 60-150 °C to form carboxylate-terminated PbSe nanocrystals in quantitative yields is reported.
Abstract: We report a tunable library of N,N,N′-trisubstituted selenourea precursors and their reaction with lead oleate at 60–150 °C to form carboxylate-terminated PbSe nanocrystals in quantitative yields. Single exponential conversion kinetics can be tailored over 4 orders of magnitude by adjusting the selenourea structure. The wide range of conversion reactivity allows the extent of nucleation ([nanocrystal] = 4.6–56.7 μM) and the size following complete precursor conversion (d = 1.7–6.6 nm) to be controlled. Narrow size distributions (σ = 0.5–2%) are obtained whose spectral line widths are dominated (73–83%) by the intrinsic single particle spectral broadening, as observed using spectral hole burning measurements. The intrinsic broadening decreases with increasing size (fwhm = 320–65 meV, d = 1.6–4.4 nm) that derives from exciton fine structure and exciton–phonon coupling rather than broadening caused by the size distribution.
87 citations
TL;DR: In this paper, a spiral phaseplate is used to generate a light beam carrying orbital angular momentum and the frequency shift is measured arising from its rotational and/or linear motion.
Abstract: The well-known linear Doppler effect arises from the linear motion between source and observer, while the less well-known rotational Doppler effect arises from the rotational motion. Here, we present both theories and experiments illustrating the relationship between the rotational and linear Doppler effects. A spiral phaseplate is used to generate a light beam carrying orbital angular momentum and the frequency shift is measured arising from its rotational and/or linear motion. By considering either the motion-induced time-evolving phase or the momentum and energy conservation in light-matter interactions, we derive the rotational Doppler shift, linear Doppler shift, and overall Doppler shift associated with rotational and linear motions. We demonstrate the relationship between rotational and linear Doppler shifts, either of which can be derived from the other effect, thereby illustrating their shared origin. Moreover, the close relationship between rotational and linear Doppler effects is also deduced for a more general moving rough surface.
77 citations
TL;DR: In this paper, the authors investigated spectral broadening of droplet size distributions through a mechanism referred to as eddy hopping, where droplets arriving at a given location within a turbulent cloud follow different trajectories and thus experience different growth histories.
Abstract: This paper investigates spectral broadening of droplet size distributions through a mechanism referred to as the eddy hopping. The key idea, suggested a quarter century ago, is that droplets arriving at a given location within a turbulent cloud follow different trajectories and thus experience different growth histories and that this leads to a significant spectral broadening. In this study, the adiabatic parcel model with superdroplets is used to contrast droplet growth with and without turbulence. Turbulence inside the parcel is described by two parameters: (i) the dissipation rate of the turbulent kinetic energy e and (ii) the linear extent of the parcel L. As expected, an adiabatic parcel without turbulence produces extremely narrow droplet spectra. In the turbulent parcel, a stochastic scheme is used to account for vertical velocity fluctuations that lead to local supersaturation fluctuations for each superdroplet. These fluctuations mimic the impact of droplets hopping turbulent eddies in a ...
73 citations
TL;DR: This study shows that structural resonances in a gas-filled antiresonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, which enables the generation of more than three octaves of broadband light that ranges from deep UV wavelengths to near infrared.
Abstract: Ultrafast supercontinuum generation in gas-filled waveguides is an enabling technology for many intriguing applications ranging from attosecond metrology towards biophotonics, with the amount of spectral broadening crucially depending on the pulse dispersion of the propagating mode. In this study, we show that structural resonances in a gas-filled antiresonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, which enables the generation of more than three octaves of broadband light that ranges from deep UV wavelengths to near infrared. Our observation relies on the introduction of a geometric-induced resonance in the spectral vicinity of the ultrafast pump laser, outperforming gas dispersion and yielding a unique dispersion profile independent of core size, which is highly relevant for scaling input powers. Using a krypton-filled fiber, we observe spectral broadening from 200 nm to 1.7 μm at an output energy of ∼ 23 μJ within a single optical mode across the entire spectral bandwidth. Simulations show that the frequency generation results from an accelerated fission process of soliton-like waveforms in a non-adiabatic dispersion regime associated with the emission of multiple phase-matched Cherenkov radiations on both sides of the resonance. This effect, along with the dispersion tuning and scaling capabilities of the fiber geometry, enables coherent ultra-broadband and high-energy sources, which range from the UV to the mid-infrared spectral range.
69 citations
TL;DR: It is demonstrated that energetic femtosecond pulses tunable from 1.3 to 1.7 µm can be achieved using self-phase modulation enabled spectral broadening followed by spectral lobe filtering using a home-built 5-W Er-fiber laser system.
Abstract: We demonstrate that energetic femtosecond pulses tunable from 1.3 to 1.7 µm can be achieved using self-phase modulation enabled spectral broadening followed by spectral lobe filtering. Based on a home-built 5-W Er-fiber laser system operating at 31-MHz repetition rate, we obtain femtosecond pulses that can be continuously tuned from 1.3 to 1.7 µm with >4.5 nJ pulse energy. We further optimize the spectral broadening process using a fiber with larger mode area and scale up the pulse energy to >10 nJ; the resulting pulse duration is as short as ~50 fs. Such a widely tunable, energetic femtosecond source is well suited for driving a laser scanning microscope to perform deep tissue multiphoton microscopy.
59 citations
TL;DR: In this article, the authors used optical spectroscopy to observe spectral broadening of exciton reflectance peaks in heterostructures of monolayer graphene capped with mono-to few-layer graphene.
Abstract: We have used optical spectroscopy to observe spectral broadening of ${\mathrm{WS}}_{2}$ exciton reflectance peaks in heterostructures of monolayer ${\mathrm{WS}}_{2}$ capped with mono- to few-layer graphene. The broadening is found to be similar for the A and B excitons and on the order of 5--10 meV. No strong dependence on the number of graphene layers was observed within experimental uncertainty. The broadening can be attributed to charge- and energy-transfer processes between the two materials, providing an observed lower bound for the corresponding time scales of 65 fs.
52 citations
TL;DR: The presented scheme displays a pathway to coherently control the optical properties of semiconductors on an ultrafast time scale by a strong THz field.
Abstract: We report on the experimental observation of extreme laser spectral broadening and a change in optical transmission in gallium phosphite induced by $\text{25 }\mathrm{MV}/\mathrm{cm}$ terahertz (THz) single-cycle internal field. Such intense THz radiation leads to twofold transient modifications of the optical properties in the electro-optical crystal. First, the electric field provokes extensive cross-phase modulation via the ${\ensuremath{\chi}}^{(2)}$ and ${\ensuremath{\chi}}^{(3)}$ nonlinearities on a copropagating 50 fs near infrared laser pulse which turns into 500% spectral broadening. Second, we observe an instantaneous change of the optical transmission occurring at the THz field which is alleged to interband Zener tunneling and charge carrier density modification by impact ionization turning the semiconductor in a metal-like transient state. The presented scheme displays a pathway to coherently control the optical properties of semiconductors on an ultrafast time scale by a strong THz field.
TL;DR: In this paper, structural resonances in gas-filled anti-resonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, allowing for the generation of more than three octaves of broadband light ranging deep UV wavelength towards the near infrared.
Abstract: Ultrafast supercontinuum generation in gas-filled waveguides is one enabling technology for many intriguing application ranging from attosecond metrology towards biophotonics, with the amount of spectral broadening crucially depending on the pulse dispersion of the propagating mode. Here we show that the structural resonances in gas-filled anti-resonant hollow core optical fiber provide an additional degree of freedom in dispersion engineering, allowing for the generation of more than three octaves of broadband light ranging deep UV wavelength towards the near infrared.Our observation relies on the introduction of a geometric-induced resonance in the spectral vicinity of the pump laser outperforming the gas dispersion, thus yielding a dispersion being independent of core size, which is highly relevant for scaling input powers.Using a Krypton filled fiber we observe spectral broadening from 200 nm towards 1.7 \mu m at an output energy of about 23 \mu J within a single mode across the entire spectral bandwidth. Simulations show that the efficient frequency generation results from a new physical effect the soliton explosion originating from the strongly non-adiabatic mode dispersion profile.This effect alongside with the dispersion tuning capability of the fiber will enable compact ultrabroadband high energy sources spanning from the UV to the mid-infrared spectral range.
TL;DR: In this article, the multi-particle structure of type-II quantum dots with spatially separated electrons and holes was studied theoretically and experimentally, and it was shown that exciton complexes containing holes interacting with two or more electrons exhibit fairly large antibinding energies.
Abstract: In this work we study theoretically and experimentally the multi-particle structure of the so-called type-II quantum dots with spatially separated electrons and holes. Our calculations based on customarily developed full configuration interaction ap- proach reveal that exciton complexes containing holes interacting with two or more electrons exhibit fairly large antibinding energies. This effect is found to be the hallmark of the type-II confinement. In addition, an approximate self-consistent solution of the multi-exciton problem allows us to explain two pronounced phenomena: the blue-shift of the emission with pumping and the large inhomogeneous spectral broadening, both of those eluding explanation so far. The results are confirmed by detailed intensity and polarization resolved photoluminescence measurements on a number of type-II samples.
TL;DR: Pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal is reported.
Abstract: We report on the pulse compression of an 18.5 MHz repetition rate pulse train from 230 fs to sub-40 fs by nonlinear spectral broadening in a multi-pass cell and subsequent chirp removal. The compressed pulse energy is $4.5~\mu \text{J}$ , which corresponds to 84 W of average power, with a compression efficiency of 88%. This recently introduced compression scheme is suitable for a large pulse energy range and for high average power. In this paper, we show that it can achieve three times shorter pulses than previously demonstrated.
TL;DR: In this paper, the authors present spectral measurements that uncover the detailed dynamics of the supercontinuum generation in fused silica, YAG, and LiF crystals when pumped with 100fs pulses with a central wavelength of 2.3μm, which falls into the range of anomalous group velocity dispersion of the media.
Abstract: We present spectral measurements that uncover the detailed dynamics of the supercontinuum generation in fused silica, YAG, and LiF crystals when pumped with 100 fs pulses with a central wavelength of 2.3 μm, which falls into the range of anomalous group velocity dispersion of the media. The multi-octave supercontinuum spectra, which span from the ultraviolet to the mid-infrared, are recorded by means of high-dynamic range measurements over the entire wavelength range covered by the supercontinuum radiation. The spectral dynamics versus the input pulse energy uncovers different mechanisms of spectral broadening, which are characterized by the occurrence of specific but well-distinguished spectral signatures and which are interpreted in terms of plasma-induced and anomalous group velocity dispersion-induced compression of the driving pulse.
TL;DR: An analytical estimate of the maximal spectral extension is given and it is shown that super-Gaussian waveforms favor the generation of flat-topped spectra and that the weak residual background of the modulator produces undesired spectral ripples.
Abstract: We investigate analytically, numerically, and experimentally the spectral broadening of pulses that undergo the formation of dispersive shocks, addressing in particular pulses in the range of tens of ps generated via electro-optic modulation of a continuous-wave laser. We give an analytical estimate of the maximal spectral extension and show that super-Gaussian waveforms favor the generation of flat-topped spectra. We also show that the weak residual background of the modulator produces undesired spectral ripples. Spectral measurements confirm our estimates and agree well with numerical integration of the nonlinear Schrodinger equation.
23 Apr 2017
TL;DR: In this article, a simple analytical expression to describe the Brillouin gain spectral broadening as a function of the spatial resolution in time-domain distributed fiber sensors is deduced.
Abstract: A novel and simple analytical expression to describe the Brillouin gain spectral broadening as a function of the spatial resolution in time-domain Brillouin distributed fiber sensors is deduced. The proposed model is experimentally validated using a pump-probe Brillouin sensing setup and also compared with numerical and approximate results. In addition, a compact mathematical form is presented for the peak gain reduction resulting from incomplete acoustic-wave activation in Brillouin sensors with short spatial resolution. Both mathematical expressions can be used together to quantitatively predict the impact of the spatial resolution on the signal-to-noise ratio and frequency uncertainty of the sensor.
TL;DR: In this paper, the theory of fusion neutron line shape is reviewed, and examples of non-Gaussian line shapes and directional variations in NIF data are described in radiation-hydrodynamics simulations of implosions.
Abstract: Doppler broadening of the 14 MeV DT and 2.45 MeV DD fusion neutron lines has long been our best measure of temperature in a burning plasma. At the National Ignition Facility (NIF), yields are high enough and our neutron spectrometers accurate enough that we see finer details of the peak shape. For example, we can measure the shift of the peak due to the bulk motion of the plasma, and we see indications of non-thermal broadening, skew, and kurtosis of the peak caused by the variations of temperature and fluid velocity during burn. We can also distinguish spectral differences among several lines of sight. This paper will review the theory of fusion neutron line shape, show examples of non-Gaussian line shapes and directional variations in NIF data, and describe detailed spectral shapes we see in radiation-hydrodynamics simulations of implosions.
TL;DR: It is found that accounting for the spectral broadening effect is crucial for achieving the best performance of DBP in both single-channel and multi-channel communication systems, independent of modulation formats used.
Abstract: Nyquist-spaced transmission and digital signal processing have proved effective in maximising the spectral efficiency and reach of optical communication systems. In these systems, Kerr nonlinearity determines the performance limits, and leads to spectral broadening of the signals propagating in the fibre. Although digital nonlinearity compensation was validated to be promising for mitigating Kerr nonlinearities, the impact of spectral broadening on nonlinearity compensation has never been quantified. In this paper, the performance of multi-channel digital back-propagation (MC-DBP) for compensating fibre nonlinearities in Nyquist-spaced optical communication systems is investigated, when the effect of signal spectral broadening is considered. It is found that accounting for the spectral broadening effect is crucial for achieving the best performance of DBP in both single-channel and multi-channel communication systems, independent of modulation formats used. For multi-channel systems, the degradation of DBP performance due to neglecting the spectral broadening effect in the compensation is more significant for outer channels. Our work also quantified the minimum bandwidths of optical receivers and signal processing devices to ensure the optimal compensation of deterministic nonlinear distortions.
TL;DR: In this article, the authors proposed a high fidelity resonance (HFR) method for radiative neutron capture, which was shown to provide similar results as the traditional Hauser Feshbach (HF) approach for nuclei with a high level density but to deviate and be more realistic than HF predictions for light and neutron-rich nuclei or at relatively low sub-keV energies.
TL;DR: In this article, various implementations of the SDV function based on Humlicek's rational approximations are examined for typical speed dependences of pressure broadening and the range of wavenumber distances and Lorentz to Doppler width ratios encountered in infrared applications.
Abstract: The increasing quality of atmospheric spectroscopy observations has indicated the limitations of the Voigt profile routinely used for line-by-line modeling, and physical processes beyond pressure and Doppler broadening have to be considered. The speed-dependent Voigt (SDV) profile can be readily computed as the difference of the real part of two complex error functions (i.e. Voigt functions). Using a highly accurate code as a reference, various implementations of the SDV function based on Humlicek׳s rational approximations are examined for typical speed dependences of pressure broadening and the range of wavenumber distances and Lorentz to Doppler width ratios encountered in infrared applications. Neither of these implementations appears to be optimal, and a new algorithm based on a combination of the Humlicek (1982) and Weideman (1994) rational approximations is suggested.
TL;DR: In this paper, an element analysis method, coincidence Doppler broadening spectroscopy of slow positron annihilation, was employed to detect helium in ion-irradiated Fe9Cr alloys.
Abstract: An element analysis method, coincidence Doppler broadening spectroscopy of slow positron annihilation, was employed to detect helium in ion-irradiated Fe9Cr alloys. Spectra with higher peak to background ratio were recorded using a two-HPGe detector coincidence measuring system. It means that information in the high-momentum area of the spectra can be used to identify helium in metals. This identification is not entirely dependent on the helium concentration in the specimens, but is related to the structure and microscopic arrangement of atoms surrounding the positron annihilation site. The results of Doppler broadening spectroscopy and transmission electron microscopy show that vacancies and dislocations were formed in ion-irradiated specimens. Thermal helium desorption spectrometry was performed to obtain the types of He traps.
TL;DR: In this article, the authors demonstrate the generation of squeezed, bright twin beams that arise due to competing gain and absorption, in a medium that is overall transparent, using a nondegenerate four-wave mixing process in warm potassium vapor such that one of the twin beams experiences strong absorption.
Abstract: We experimentally demonstrate the generation of squeezed, bright twin beams that arise due to competing gain and absorption, in a medium that is overall transparent. To accomplish this, we make use of a nondegenerate four-wave-mixing process in warm potassium vapor such that one of the twin beams experiences strong absorption. At room temperature and above, due to Doppler broadening and smaller frequency detunings compared to other schemes, the ground-state hyperfine splittings used in the present double-$\mathrm{\ensuremath{\Lambda}}$ setup are completely overlapped. We show that despite the resulting significant asymmetric absorption of the twin beams, quantum correlations may still be generated. Our results in this regime demonstrate that the simplified model of gain, followed by loss, is insufficient to describe the amount of quantum correlation resulting from the process.
TL;DR: In this article, a pair of probe and coupling laser pulses propagating in a Doppler broadened three-level cascade atomic medium were studied in a wide region of pulse duration, from micro to pico second.
TL;DR: In this paper, the authors investigate nonlinear picosecond pulse propagation at 532 nm in an optical fiber capillary filled with toluene liquid and demonstrate supercontinuum generation from 550 nm up to 870 nm.
Abstract: We investigate nonlinear picosecond pulse propagation at 532 nm in an optical fiber capillary filled with toluene liquid and demonstrate supercontinuum generation from 550 nm up to 870 nm. Although it operates in the strong normal dispersion regime, we show that supercontinuum light is generated through the combined effects of multiple cascaded Raman scattering and stimulated Raman–Kerr scattering, which enables a large spectral broadening of the Raman lines owing to the strongly anisotropic orientational relaxation of liquid molecules. We further present numerical simulations of the nonlinear Schrodinger equation, including the Raman scattering, to show the spectro-temporal dynamics.
TL;DR: In this paper, the evolution of the multi-Peregrine soliton is investigated in a multicomponent plasma and found to be critically dependent on the initial bound state.
TL;DR: In this article, a quasi-simultaneous XMM-Newton and INTEGRAL observations of the X-ray transient EXO 1745−248 located in the globular cluster Terzan 5, performed ten days after the beginning of the outburst (on 2015 March 16) of the source between March and June 2015.
Abstract: Context. Transient low-mass X-ray binaries (LMXBs) often show outbursts that typically last a few weeks and are characterized by a high X-ray luminosity (L x ≈ 1036 −1038 erg s-1 ), while most of the time they are found in X-ray quiescence (L X ≈ 1031 −1033 erg s-1 ). The source EXO 1745−248 is one of them. Aims. The broad-band coverage and sensitivity of the instrument on board XMM-Newton and INTEGRAL offers the opportunity of characterizing the hard X-ray spectrum during the outburst of EXO 1745−248.Methods. We report on quasi-simultaneous XMM-Newton and INTEGRAL observations of the X-ray transient EXO 1745−248 located in the globular cluster Terzan 5, performed ten days after the beginning of the outburst (on 2015 March 16) of the source between March and June 2015. The source was caught in a hard state, emitting a 0.8−100 keV luminosity of ≃ 1037 erg s-1 .Results. The spectral continuum was dominated by thermal Comptonization of seed photons with temperature k T in ≃ 1.3 keV, by a cloud with a moderate optical depth τ ≃ 2, and with an electron temperature of k T e ≃ 40 keV. A weaker soft thermal component at temperature k T th ≃ 0.6−0.7 keV and compatible with a fraction of the neutron star radius was also detected. A rich emission line spectrum was observed by the EPIC-pn on board XMM-Newton ; features at energies compatible with K-α transitions of ionized sulfur, argon, calcium, and iron were detected, with a broadness compatible with either thermal Compton broadening or Doppler broadening in the inner parts of an accretion disk truncated at 20 ± 6 gravitational radii from the neutron star. Strikingly, at least one narrow emission line ascribed to neutral or mildly ionized iron is needed to model the prominent emission complex detected between 5.5 and 7.5 keV. The different ionization state and broadness suggest an origin in a region located farther from the neutron star than where the other emission lines are produced. Seven consecutive type I bursts were detected during the XMM-Newton observation, none of which showed hints of photospheric radius expansion. A thorough search for coherent pulsations from the EPIC-pn light curve did not result in any significant detection. Upper limits ranging from a few to 15% on the signal amplitude were set, depending on the unknown spin and orbital parameters of the system.
TL;DR: In this article, the spectrum broadening in continuous-wave, sub-nanometer linewidth high power fiber amplifiers caused by the multiple four-wave mixing (FWM) process was investigated.
TL;DR: In this paper, the Goos-Hanchen shifts of a probe light field in a four-level tripod-type cold and hot atomic medium were studied in reflection and transmission beams in the presence of the coherent Kerr effect and the Doppler broadening effect.
Abstract: We study and examine the Goos–Hanchen shifts of a propagating probe light field in a four-level tripodtype cold and hot atomic medium. The behavior of Goos–Hanchen shifts is studied in reflection and transmission beams in the presence of the coherent Kerr effect and the Doppler broadening effect. We observe that these shifts can be controlled by the relative propagation direction of the control field to that of the probe field.
TL;DR: In this article, an integral form for a generalized Doppler Broadening Function is obtained in the scope of the single-level formalism given by the Beth-Plackzec approximations.