Microwave emission by nonlinear crystals irradiated with a high-intensity, mode-locked laser

We report on the experimental investigation of the efficiency of some nonlinear crystals to generate microwave (RF) radiation as a result of optical rectification (OR) when irradiated with intense pulse trains delivered by a mode-locked laser at $1064\,$nm. We have investigated lithium triborate (LBO), lithium niobate (LiNbO$_3$), zinc selenide (ZnSe), and also potassium titanyl orthophosphate (KTP) for comparison with previous measurements. The results are in good agreement with the theoretical predictions based on the form of the second-order nonlinear susceptibility tensor. For some crystals we investigated also the second harmonic generation (SHG) to cross check the theoretical model. We confirm the theoretical prediction that OR leads to the production of higher order RF harmonics that are overtones of the laser repetition rate.Comment: accepted for publication in Journal of Optics, in pres

Particle detection in rare gas solid crystals: a feasibility experimental study—exploring new ways for dark matter searches: Exploring new ways for dark matter searches

This article reviews the experimental activity that has been carried out within the INFN DEMIURGOS research and development (R&D) project. This R&D concerns the study of possible innovative experimental approaches for the detection of low-energy-releases of feeble interacting particles within the matter. Possible applications could be the direct investigation of Dark Matter candidates. The idea behind the proposed scheme is to exploit rare gas solid crystals both pure and doped, combined with the in-vacuum single electron detection technology. In pure materials, the signal can be the charge produced directly during the ionization. Laser-assisted processes can instead be used to probe low-energy-releases in doped materials. Both these mechanisms should lead to a detectable electronic signal triggered by the incoming particle. In such a way, energy threshold ranging from meV to tens of eV could in principle be reached, opening-up the possibility to probe theoretically, well-motivated regions of unexplored electroweak parameter-space and thus test the existence of light Dark Matter candidates. The activity presented here has been performed to understand the mechanisms at the basis of the proposed detection scheme and possible showstopper. The experimental investigations refer to the research and development phases about: the crystal growing techniques and the corresponding set-up, the electrons’ extraction from rare gas crystals to the vacuum environment, and finally the spectroscopic studies on atomic species embedded into rare gas matrices

Cathodo- and radioluminescence of Tm3+^{3+}:YAG and Nd3+^{3+}:YAG in an extended wavelength range

We have studied the cathodo- and radioluminescence of Nd:YAG and of Tm:YAG single crystals in an extended wavelength range up to $\approx 5\,\mu$m in view of developing a new kind of detector for low-energy, low-rate energy deposition events. Whereas the light yield in the visible range is as large as $\approx 10^{4}\,$photons/MeV, in good agreement with literature results, in the infrared range we have found a light yield $\approx 5\times 10^{4}\,$photons/MeV, thereby proving that ionizing radiation is particularly efficient in populating the low lying levels of rare earth doped crystals.Comment: submitted for publication in Journal of Luminescenc

A new technique for infrared scintillation measurements

We propose a new technique to measure the infrared scintillation light yield of rare earth (RE) doped crystals by comparing it to near UV-visible scintillation of a calibrated Pr:(Lu$_{0.75}$Y$_{0.25}$)$_{3}$Al$_5$O$_{12}$ sample. As an example, we apply this technique to provide the light yield in visible and infrared range up to \SI{1700}{nm} of this crystal.Comment: submitted to NIM

Laser induced fluorescence for axion dark matter detection: a feasibility study in YLiF4_4:Er3+^{3+}

We present a detection scheme to search for QCD axion dark matter, that is based on a direct interaction between axions and electrons explicitly predicted by DFSZ axion models. The local axion dark matter field shall drive transitions between Zeeman-split atomic levels separated by the axion rest mass energy $m_a c^2$. Axion-related excitations are then detected with an upconversion scheme involving a pump laser that converts the absorbed axion energy ($\sim$ hundreds of $\mu$eV) to visible or infrared photons, where single photon detection is an established technique. The proposed scheme involves rare-earth ions doped into solid-state crystalline materials, and the optical transitions take place between energy levels of $4f^N$ electron configuration. Beyond discussing theoretical aspects and requirements to achieve a cosmologically relevant sensitivity, especially in terms of spectroscopic material properties, we experimentally investigate backgrounds due to the pump laser at temperatures in the range $1.9-4.2$ K. Our results rule out excitation of the upper Zeeman component of the ground state by laser-related heating effects, and are of some help in optimizing activated material parameters to suppress the multiphonon-assisted Stokes fluorescence.Comment: 8 pages, 5 figure

Evidence for core-hole-mediated inelastic x-ray scattering from metallic Fe1.087_{1.087}Te

We present a detailed analysis of resonant inelastic scattering (RIXS) from Fe$_{1.087}$Te with unprecedented energy resolution. In contrast to the sharp peaks typically seen in insulating systems at the transition metal $L_3$ edge, we observe spectra which show different characteristic features. For low energy transfer, we experimentally observe theoretically predicted many-body effects of resonant Raman scattering from a non-interacting gas of fermions. Furthermore, we find that limitations to this many-body electron-only theory are realized at high Raman shift, where an exponential lineshape reveals an energy scale not present in these considerations. This regime, identified as emission, requires considerations of lattice degrees of freedom to understand the lineshape. We argue that both observations are intrinsic general features of many-body physics of metals.Comment: 4 pages, 4 figure

Particle detection through the quantum counter concept in YAG:Er3+^{3+}

We report about a novel scheme for particle detection based on the infrared quantum counter concept. Its operation consists of a two-step excitation process of a four level system, that can be realized in rare earth-doped crystals when a cw pump laser is tuned to the transition from the second to the fourth level. The incident particle raises the atoms of the active material into a low lying, metastable energy state, triggering the absorption of the pump laser to a higher level. Following a rapid non-radiative decay to a fluorescent level, an optical signal is observed with a conventional detectors. In order to demonstrate the feasibility of such a scheme, we have investigated the emission from the fluorescent level $^4$S$_{3/2}$ (540 nm band) in an Er$^{3+}$-doped YAG crystal pumped by a tunable titanium sapphire laser when it is irradiated with 60 keV electrons delivered by an electron gun. We have obtained a clear signature this excitation increases the $^{4}I_{13/2}$ metastable level population that can efficiently be exploited to generate a detectable optical signal

Measurement of magnetic excitations in the two-dimensional antiferromagnetic Sr2CuO2Cl2 insulator using resonant x-ray scattering:Evidence for extended interactions

Using high-resolution resonant inelastic x-ray scattering (RIXS), we performed a momentum-resolved study of magnetic excitations in the model spin-1/2 2D antiferromagnetic insulator Sr_2CuCl_2O_2. We identify both a single-spin-wave feature and a multi-magnon continuum, and show that the X-ray polarization can be used to distinguish these two contributions in the cross-section. The spin-waves display a large (70 meV) dispersion between the zone-boundary points ($\pi$,0) and ($\pi$/2,$\pi$/2). Employing an extended $t$-$t'$-$t"$-$U$ one-band Hubbard model, we find significant electronic hopping beyond nearest-neighbor Cu ions. We conclude that sizeable extended magnetic interactions are present in \scoc{} and probably important in all undoped cuprates.Comment: 4 pages, 4 figure