Search

Precision tests of the Standard Model and searches for beyond the Standard Model physics often require nuclear structure input. There has been a tremendous progress in the development of nuclear ab initio techniques capable of providing accurate nuclear wave functions. For the calculation of observables, matrix elements of complicated operators need to be evaluated. Typically, these matrix elements would contain spurious contributions from the center-of-mass (COM) motion. This could be problematic when precision results are sought. Here, we derive a transformation relying on properties of harmonic oscillator wave functions that allows an exact removal of the COM motion contamination applicable to any one-body operator depending on nucleon coordinates and momenta. Resulting many-nucleon matrix elements are translationally invariant provided that the nuclear eigenfunctions factorize as products of the intrinsic and COM components as is the case, e.g., in the no-core shell model approach. An application of the transformation has been recently demonstrated in calculations of the nuclear structure recoil corrections for the beta-decay of 6He., 7 pages, matches version accepted for publication

We investigated the effect of Gd3+ and Ga3+ on Yb:YAG emission at cryogenic temperatures by preparing ceramic pellets by solid state reaction method with different Gd3+ and Ga3+ content. Incorporation of Gd3+ shows only a small effect on spectral broadening whereas incorporation of Ga3+ in Yb:YAG results in significant broadening. Such an inhomogeneous broadening is due to the replacement of larger Ga3+ ion in two different cationic sites of Al3+ which causes a change in local crystal field on the Yb3+ site.

We propose a novel storage scheme for three-nucleon (3N) interaction matrix elements relevant for the normal-ordered two-body approximation used extensively in ab initio calculations of atomic nuclei. This scheme reduces the required memory by approximately two orders of magnitude, which allows the generation of 3N interaction matrix elements with the standard truncation of $E_{\rm 3max}=28$, well beyond the previous limit of 18. We demonstrate that this is sufficient to obtain the ground-state energy of $^{132}$Sn converged to within a few MeV with respect to the $E_{\rm 3max}$ truncation.In addition, we study the asymptotic convergence behavior and perform extrapolations to the un-truncated limit. Finally, we investigate the impact of truncations made when evolving free-space 3N interactions with the similarity renormalization group. We find that the contribution of blocks with angular momentum $J_{\rm rel}>9/2$ to the ground-state energy is dominated by a basis-truncation artifact which vanishes in the large-space limit, so these computationally expensive components can be neglected. For the two sets of nuclear interactions employed in this work, the resulting binding energy of $^{132}$Sn agrees with the experimental value within theoretical uncertainties. This work enables converged ab initio calculations of heavy nuclei., 16 pages, 11 figures. Appendix is added. Published version

We present a diode-pumped, electro-opticallyQ-switched Tm:YAG laser with a cryogenically cooled laser crystal at 120 K. Output pulses of up to 2.55 mJ and 650 ns duration were demonstrated in an activelyQ-switched configuration with a repetition rate of 1 Hz. By using cavity dumping the pulse duration was shortened to 18 ns with only a slightly lower output energy of 2.22 mJ. Furthermore, using a simplified rate equation model, we discuss design constraints on the pump fluence in a pulse pump approach for Tm:YAG to maximize the energy storage capability at a given pump power.

We compare for the first time the influence of different Yb:YAG gain media on the performance of a large-area, high average–power laser system with an output energy of up to 6 J. Monocrystalline slabs grown by a new technique without central growth defect are compared with ceramics. Small signal gain, maximum output energy and thermal lensing are compared for ceramic slabs with co-sintered amplified spontaneous emission (ASE) absorber cladding, monocrystalline slab with and without optically bonded ASE absorber cladding, and surface structured monocrystalline slabs. We show that these large monocrystals with optically bonded absorber cladding have similar performance to cladded ceramics, so far the only material for high-energy Yb:YAG lasers.

Self-swept erbium fiber laser emitting around 1.56 μm is reported in detail. Both sweep directions were registered: pointing toward longer and shorter wavelengths, redshift and blueshift sweeping, respectively. We describe method of determining the direction of the wavelength drift using the monochromator based optical spectrum analyzer. Possible root for this sweeping regime, i.e., the gain modulation along active fiber, is discussed with the help of a simple model calculating the overall cavity gain that can predict the direction of the laser wavelength sweeping.

We report on obtaining output energy of 146 J in 10 ns long pulses at 10 Hz repetition rate from Bivoj, a multi-Joule multi-slab cryogenic gas-cooled diode pumped solid state laser, by overcoming its damage threshold bottleneck. This is a 40% energy and power increase of the laser system in comparison to our previous publication and to the most powerful multi-Joule high power laser system.

Among the excellent active media, thulium-doped yttrium oxide (Tm:Y 2 O 3 ), belonging to the sesquioxide family of laser materials, stands out because it shows very high thermal conductivity, broad gain spectra and a relatively low maximum phonon energy, which makes it very suitable for two micron laser operation in several temporal regimes [1]. However, its main limitation is the crystal growth methodology due to its high melting point making the growth of high quality crystals with large size to be a tedious and expensive task. This is confirmed by the fact that there are only few suppliers in the world. The transparent ceramic fabrication process solves these limitations and paves the way to spread the ceramic-based gain media in the future commercial solid-state laser systems [2]. Besides the substitution of the crystalline gain media by the ceramic ones, cooling them to cryogenic temperatures suppresses thermal issues and enhances the material's properties, such as thermal conductivity and transition cross-sections, being prerequisites for the development of high power lasers. To date, no deep studies on Tm:Y 2 O 3 either in crystalline or ceramic form at cryogenic temperatures are found.

Crytur is a company with long tradition of growing and processing crystals for technical applications, with history reaching back to 1943. Recently we have developed Crystal Improved Growth (CRIG) method for production of large core-free single crystals of YAG. The diameter currently achieved is 140 mm (in case of undoped crystal), and the crystal weight is up to 10 kg. The method was used to grow un-doped YAG crystals, YAG:Ce crystals for large scintillating screens, and Yb:YAG and Nd:YAG for high power solid-state laser systems. Large laser slabs were manufactured from Yb:YAG doped crystals for Diode-Pumped Solid State Laser (DPSSL) system Amos, which operates within Extreme Light Infrastructure in the Czech republic (ELI Beamlines). The dimension of the largest Yb:YAG laser slab produced is 120×120×8 mm, there is no visible stress under crossed polarizers and the wavefront distortion in the clear aperture region is smaller than λ/10 (λ=633 nm) in its Peak-to-Valley value. The edges of the slab are from diffusively bonded Cr:YAG cladding in order to suppress ASE (Amplified Spontaneous Emission). In 2018 the performance of three sets of laser slabs (o55x5 mm) with differently realized ASE suppression was characterized at cryogenic temperatures at HiLASE Centre in terms of small signal gain measurements as well as amplification test under 30 J pumping at 1 Hz and 10 Hz repetition rates. We provide data that show that the crystal slabs have comparable properties to the ceramic slabs (produced by Konoshima company, Japan) currently in use at HiLASE.

We present the laser performance of Yb:YAG at different cryogenic temperatures pumped by a volume Bragg grating (VBG)-stabilized narrowband fiber-coupled diode laser emitting at 968.7 nm for the first time to the best of our knowledge. A maximum output power of 6.54 W with a slope efficiency as high as 64.6% is achieved at 140 K. The optimum temperature for 968.7 nm and 0.35 nm bandwidth VBG-stabilized pump source is found to be 140 K for Yb:YAG.

An overview of the latest developments of kilowatt-level diode pumped solid state lasers for advanced applications at the HiLASE Centre is presented. An overview of subcontracted and in-house-developed laser beamlines is presented. The aim of development is to build kW-class beamlines delivering picosecond pulses between 1- and 100-kHz repetition rates and high-energy nanosecond pulses at 10 Hz. The picosecond beamlines are based on Yb:YAG thin-disk amplifiers and chirped pulse amplification. The current status of the beamlines’ performance is reported. The advantages of zero-phonon line and pulsed pumping are demonstrated with respect to efficiency, thin disk temperature and beam quality. New diagnostics methods supporting the high average power lasers’ development, such as the high-resolution spectroscopy of Yb-doped materials, in situ thin disk deformation measurements, single-shot M2 measurement, realization of wavefront correction by a deformable mirror and the laser performance of a new mixed garnet ceramics, are described. The energetic, thermal and fluid-mechanical numerical modeling for the optimization of the multi-slab amplifiers is also described.

The HiLASE “Bivoj” laser system developed at CLF Rutherford Appleton Laboratory in collaboration with HiLASE team as DiPOLE100 was relocated to Dolni Brezany near Prague, Czechia at the end of 2015 and fully re-commissioned at the end of 2016. In 2016, the system demonstrated average output power of 1kW generating pulses of 105 J at 10 Hz repetition rate for the first time in the world. Since then the system has been subjected to several testing campaigns in order to determine some of its key characteristics. Beam quality, wavefront quality, pointing stability, energy stability and experience with long term operation of 1 kW laser are presented. In addition, depolarization effects have been detected inside the main amplifier. Details on these results along with numerical simulations are presented.

We study cryogenic laser operation of an Yb-doped KLu(WO

Multi-watt continuous-wave (CW) operation of tetragonal rare-earth calcium aluminate Yb:CaLnAlO

In recent years, the development of compact all solid-state lasers has attracted the scientific community because of their vast scientific and technological applications. In particular, ytterbium (Yb3+) laser sources have been developed with a great number of hosts, due to the promise of the Yb3+ ion related to the very simple energy level structure and absence of higher energy levels, as well as a small quantum defect. However, at room temperature (RT) these materials behave as quasi three-level lasers due to a finite population of the ground state leading to reabsorption limited power scaling [1]. To overcome this issue, the material has to be cooled to cryogenic temperatures, where four-level operation is accomplished. The monoclinic potassium lutetium double tungstate crystal, KLu(WO 4 ) 2 , considered here exhibits favourable spectroscopic properties when doped with Yb3+, characterized by large absorption and stimulated-emission cross sections and attractive thermo-optic properties for certain “athermal” crystal cuts (e.g., along the Ng-axis). It is very suitable for moderate power levels as demonstrated with Yb3+ and Tm3+ doping at RT [2]. In this work, we studied the continuous-wave laser characteristics of Yb:KLu(WO 4 ) 2 (Yb:KLuW) at cryogenic temperatures pumped by a VBG-stabilized fiber coupled diode laser at 981 nm.

The concept of system for intracavity interferometry based on the beat note detection in subharmonic synchronously intracavity pumped optical parametrical oscillator (OPO) is presented. The system consisted of SESAM-modelocked, picosecond, diode pumped Nd:YVO 4 laser, operating at wavelength 1.06 μ m and tunable linear intracavity pumped OPO based on MgO:PPLN crystal, widely tunable in 1.5 μ m able to deliver two independent trains of picosecond pulses. The optical length of the OPO cavity was set to be exactly twice the pumping cavity length. In this configuration the OPO produces signal pulses with the same repetition frequency as the pump laser but the signal consists of two completely independent pulse trains. For purpose of pump probe measurements the setup signal with half repetition rate and scalable amplitude was derived from the OPO signal using RF signal divider, electropotical modulator and fiber amplifier. The impact of one pump beam on the sample is detected by one probing OPO train, the other OPO train is used as a reference. The beat note measured using the intracavity interferometer is proportional to phase modulation caused by the pump beam. The bandwidth of observed beat-note was less than 1 Hz (FWHM), it corresponds to a phase shift measurement error of less than 1.5 × 10 -7 rad without any active stabilization. Such compact low-cost system could be used for ultra-sensitive phase-difference measurements (e.g. nonlinear refractive index measurement) for wide range of material especially in spectral range important for telecom applications.

We present an efficient zero-phonon-line pumped cryogenic Yb:YAG laser passively Q-switched by Cr:YAG with different initial transmissions. At 140K, with 85% initial transmission of Cr:YAG, a maximum average output power of 5.19 W with a repetition rate of 24.7 kHz was achieved leading to a slope efficiency of 55.7%. The maximum pulse energy, minimum pulse width and peak output power obtained in this case were 0.21 mJ, 142 ns and 1.48 kW respectively.

In this work, we have shown the possibility of performing pulsed laser operation at cryogenic temperature with innovative modular compact laser cavity. Using Yb:YAG/Cr:YAG configuration, at cryogenic temperature, in the preliminary laser experiments, we obtained a maximum average output power of 2.7 W with a repetition rate of around 50 kHz. The minimum pulse width, maximum pulse energy and peak power obtained were 2.5 ns, 60 μJ. and 25 kW respectively. To the best of our knowledge, an experimental approach on compact pulsed Q-switched lasers based on Yb:YAG/Cr:YAG at cryogenic temperature is tried for the first time.

International audience; Experimental observation of the self-induced laser line sweeping (SLLS) in fiber ring lasers is presented. The SLLS with the same gain fiber is studied in Fabry-Perot cavity for comparison. The SLLS effect manifests itself as a laser wavelength drift with speed of the order of nanometer per second from shorter to longer wavelengths across several nanometers and fast backward jump. Recently, the dynamics of the SLLS in a Fabry-Perot cavity fiber laser was qualitatively described by a dynamic grating induced by spatial-hole-burning in the ytterbium doped fiber where the lifetime of the grating was related to the self-sustained relaxation oscillations. In this paper we address possible discrepancies between the published theoretical model and earlier observations of SLLS, particularly in fiber-ring lasers.We show that the qualitative theoretical model developed for explaining SLLS in the Fabry-Perot cavity can be used also to explain the SLLS effect we observed earlier in fiber-ring lasers.

Multi-watt continuous-wave (CW) operation of tetragonal rare-earth calcium aluminate Yb:CaLnAlO4(Ln=Gd,Y)) crystals in plano–plano microchip lasers was demonstrated with an almost quantum-defect-limited slope efficiency. Pumped at 978 nm by an InGaAs laser diode, a 3.4 mm long 8 at. % Yb:CaGdAlO4 laser generated 7.79 W at 1057–1065 nm with a slope efficiency of η=84% (with respect to the absorbed pump power). An even higher η=91% was achieved with a 2.5 mm long 3 at. % Yb:CaYAlO4 laser, from which 5.06 W were extracted at 1048–1056 nm. Both lasers produced linearly polarized output (σ-polarization) with an almost circular diffraction-limited beam (Mx,y2

The reaction 30Si(d,p)31Si is studied at the incident deuteron energy of 12.3 MeV. Proton groups are analysed using a multi-angle magnetic spectrograph with the resolving power E/ΔE≈1000. Angular distributions of proton groups corresponding to 14 bound states and to 8 unbound states of the 31Si nucleus are analysed using DWBA calculations. Deduced transferred orbital angular momenta and spectroscopic factors differ for some states from those obtained previously. In particular, we attribute l=1 transfer to the state at 5.281 MeV. Shell-model calculations are performed in a complete 0ℏω model space for positive-parity states and in a restricted 1ℏω model space including f7/2, p3/2 and p1/2 neutron orbits for negative-parity states. The excitation energies as well as spectroscopic strengths of most of strongly excited positive- and negative-parity states are reasonably well interpreted within the shell model.

The differential cross section of elastic and inelastic scattering of 3He ions on the 13C nucleus has been measured at an energy of 37.9 MeV. By fitting the shape of the measured angular distribution of the elastic scattering the parameters of the optical model have been found. These parameters have been used for the DWBA calculations of angular distributions corresponding to excitations of the 13C levels 3.09(1/2+) MeV, 3.68(3/2−) MeV, 3.85(5/2+) MeV, 7.55(5/2−) MeV, 8.84(1/2−) MeV and 11.85(7/2+) MeV. Several sets of transition densities calculated with different effective nucleon-nucleon interactions and six different M3Y interactions between a projectile and target nucleon have been tested. Analysis of the inelastic scattering of 135 MeV protons on 13C is also presented, which enabled us to obtain additional information about the tested structure models.

We discuss the appearance of spurious solutions of few-body equations for Faddeev amplitudes. The identification of spurious states, i.e., states that lack the symmetry required for solutions of the Schroedinger equation, as well as the symmetrization of the Faddeev equations is investigated. As an example, systems of three and four electrons, bound in a harmonic-oscillator potential and interacting by the Coulomb potential, are presented., Comment: 11 pages. REVTEX

We use a 4ħΩ shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate the isospin-mixing correction for the10C→10B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence ofT=1 partial waves. Our results suggest the isospin-mixing correctionδ c ≈ 0.1%, which is compatible with previous calculations obtained by other methods. The obtainedδ C correction is about a factor of four too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental data.

We use a 4{h_bar}{Omega} shell-model calculation with a two-body effective interaction derived microscopically from the Reid93 potential to calculate the isospin-mixing correction for the {sup 10}C{r_arrow}{sup 10}B superallowed Fermi transition. The effective interaction takes into account the Coulomb potential as well as the charge dependence of T=1 partial waves. Our results suggest the isospin-mixing correction {delta}{sub C}{approx}0.1{percent}, which is compatible with previous calculations. The correction obtained in those calculations, performed in a 0{h_bar}{Omega} space, was dominated by deviation from unity of the radial overlap between the converted proton and the corresponding neutron. In the present calculation this effect is accommodated by the large model space. The obtained {delta}{sub C} correction is about a factor of 4 too small to obtain unitarity of the Cabibbo-Kobayashi-Maskawa matrix with the present experimental data. {copyright} {ital 1997} {ital The American Physical Society}

We use a large-scale 6 hbar Omega calculation for Li6 with microscopically derived two-body interaction to construct the 0 hbar Omega 0p-shell effective hamiltonian, electric quadrupole, and magnetic dipole operators. While the E2 and M1 6 hbar Omega operators are one-body operators with free nucleon charges, the effective operators are two-body operators with substantially different renormalization for the isoscalar and isovector matrix elements, especially for the E2 operator. We show that these operators can be very well approximated by one-body operators provided that effective proton and neutron charges are used. The obtained effective charges are compatible with those used in phenomenological shell-model studies. The two-body part of the effective operators is estimated., Comment: 10 pages. REVTEX

We have characterized ytterbium–doped fiber laser and described in detail the effect of pump wavelength on self–induced laser line sweeping (SLLS). SLLS is a transient laser regime manifested by a relatively slow laser line shifting and usually observed in the near of pump laser threshold. The fiber laser under consideration is cladding–pumped by a temperature stabilized multimode laser diode (LD) at about 976 nm. The output wavelength of the diode is tunable by changing the diode temperature and current through the diode. The cavity of the laser is formed by perpendicularly cleaved fiber ends. Using this laser layout we made detailed study of sweeping dependences on pump wavelength by adjustment of the LD current and LD case temperature. The laser manifested laser line sweeping within the range of 5–7 nm on a wide span of pump laser diode power and temperature: 15–45°C LD temperature scale and pump range reaching to more than twice the amount of excess over threshold. We performed the measurement of the laser line sweeping span, period and rate as the dependence of pump wavelength.

The M1 properties of even $^{182\mathrm{\ensuremath{-}}186}\mathrm{W}$ isotopes are investigated in the interacting boson model-2 (IBM-2). The E2/M1 mixing ratios, g factors, and summed M1 strength are calculated. A least-squares fit of the excitation energies is used to fix the IBM-1 projected Hamiltonian parameters, while the F-spin-breaking terms are adjusted to reproduce the M1 properties of low-lying states. The influence of F-spin mixing on the summed M1 strength is studied using the coherent state technique in perturbation theory. When the standard boson g factors are used, the M1 properties of the low-lying states are described satisfactorily, but the summed M1 strengths are found to be larger than present experimental values. Possible g factor adjustment, which reconciles the calculated and experimental M1 strength, is discussed. \textcopyright{} 1996 The American Physical Society.

Self-induced laser line sweeping of various regimes of sweep direction is reported for an experimental ytterbium fiber laser. The regimes involve sweeping from shorter to longer wavelengths ( nm)—so-called normal self-sweeping; from longer to shorter wavelengths ( nm)—so-called reverse self-sweeping; and a mixed regime in which a precarious balance of the normal and reverse sweeping exists and the sweep direction can change between consecutive sweeps. The regimes of sweeping were selected by changing the pump wavelength only. A detailed explanation of this sweep direction dynamics is presented based on a semi-empirical model. This model also provides a way to predict the sweep direction of fiber lasers based on other rare-earth-doped laser media.

We present a comparative study on a continuous-wave laser operation of Yb-doped Y3Ga2A13O12 (Yb:YGAG) ceramic at cryogenic temperatures with conventional pumping (940 nm) and zero phonon line pumping (969 nm) under identical experimental conditions. In CW laser operation, at 80 K with ZPL pumping, a maximum output power of 6.53 W with a slope efficiency of 52.0% is achieved with respect to incident power. When compared between two pump sources at cryogenic temperatures, ZPL pumping performs better due to the difference of quantum defect between the two pump sources that results in different heat load in the sample. In passive Q-switching experiment, at 100 K, with 85% initial transmission of Cr:YAG, an average output power of 3.37 W with a repetition rate of 17.6 kHz was achieved. The pulse energy, pulse width and peak power obtained in this case were 0.19 mJ, 164 ns and 1.16 W respectively.

We report laser line self-sweeping phenomenon in rare-earth doped fiber lasers. The effect of self-sweeping is observed in erbium-doped fiber laser and also in the ytterbium-doped one. The former, having linear layout, is core-pumped by laser diode (LD) at 980 nm. Laser cavity is formed with fiber loop mirror and angle cleaved fiber end. Laser operation is delimited by tunable filter; we observed sweeping regime in 0.5 nm wide interval defined by the filter. Yb-doped allfiber laser has linear layout as well. Laser is cladding-pumped by LD at about 976 nm; cavity is constrained by rightangle cleaved fibers. We observed laser line sweeping having a range of 6 – 8 nm. We characterized both lasers with respect to sweeping properties thoroughly. We present output laser line wavelength and instant output intensity versus time; we show dependence of sweeping range, sweeping rate, and sweeping period on output laser power and pump laser temperature (pump laser wavelength).

8 pages; International audience; Rare-earth doped fiber lasers are subject to instabilities and various self-pulsed regimes that can lead to catastrophic damage of their components. An interesting self-pulsing regime accompanied with laser wavelength drift with time is the so called self-induced laser line sweeping (SLLS). Despite the early observations of the SLLS in solid-state ruby lasers, in fiber lasers it was first time mentioned in literature only in 2009 where such a laser wavelength drift with time was observed in a relatively broad range of about 1076 -1084 nm in ring ytterbium-doped fiber laser (YDFL). The main characteristic of the SLLS is the scanning of the laser wavelength from shorter to longer wavelength, spanning over large interval of several nanometers, and instantaneous bounce backward. The period of this sweeping is usually quite long, of the order of seconds. This spectacular effect was attributed to spatial-hole burning caused by standing-wave in the laser cavity. In this paper we present experimental investigation of the SLLS in YDFLs in Fabry-Perot cavity and ring cavities. The SLLS was observed also in erbium-doped fiber laser around 1560 nm. We present for the first time observation of the laser wavelength sweep in reverse direction, i.e., from longer towards shorter wavelengths. It was observed in YDFL around 1080 nm.

We introduce boson mappings of the fermion dynamical symmetry model (FDSM) to investigate and clarify the relation between the FDSM and the proton-neutron interacting boson model (IBM). The Dyson boson mapping is employed in a dual role---it is first used to obtain exact FDSM results and then as the starting point to obtain some hermitized mappings. By hermitizing the Dyson boson image of the FDSM Hamiltonian through a seniority dictated similarity transformation or by using a Belyaev-Zelevinsky mapping and retaining in both instances one- and two-body terms only, one obtains an IBM type Hamiltonian. FDSM and boson mapped results are then compared for a few typical cases. We reexamine, from the boson point of view, recent statements about an effective SO(6) symmetry when [sup 196]Pt is analyzed in the FDSM and about the appearance of normal (maximal [ital F]-spin) and exotic states in an application of the FDSM to [sup 134]Ba. Throughout our analysis possible spurious states, which may appear as a result of an effective overcompleteness in the (linearly independent) boson basis, are properly identified. We discuss when and where these states appear in the spectra, and the possible implications these considerations may have for allowed representations in themore » IBM and FDSM.« less