Emission spectra and intrinsic optical bistability in a two-level medium

Scattering of resonant radiation in a dense two-level medium is studied theoretically with account for local field effects and renormalization of the resonance frequency. Intrinsic optical bistability is viewed as switching between different spectral patterns of fluorescent light controlled by the incident field strength. Response spectra are calculated analytically for the entire hysteresis loop of atomic excitation. The equations to describe the non-linear interaction of an atomic ensemble with light are derived from the Bogolubov-Born-Green-Kirkwood-Yvon hierarchy for reduced single particle density matrices of atoms and quantized field modes and their correlation operators. The spectral power of scattered light with separated coherent and incoherent constituents is obtained straightforwardly within the hierarchy. The formula obtained for emission spectra can be used to distinguish between possible mechanisms suggested to produce intrinsic bistability.Comment: 18 pages, 5 figure

Emission of photon echoes in a strongly scattering medium

We observe the two- and three-pulse photon echo emission from a scattering powder, obtained by grinding a Pr$^{3+}$:Y$_2$SiO$_5$ rare earth doped single crystal. We show that the collective emission is coherently constructed over several grains. A well defined atomic coherence can therefore be created between randomly placed particles. Observation of photon echo on powders as opposed to bulk materials opens the way to faster material development. More generally, time-domain resonant four-wave mixing offers an attractive approach to investigate coherent propagation in scattering media

Frequency of the C9orf72 hexanucleotide repeat expansion in patients with amyotrophic lateral sclerosis and frontotemporal dementia: a cross-sectional study.

We aimed to accurately estimate the frequency of a hexanucleotide repeat expansion in C9orf72 that has been associated with a large proportion of cases of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD)

Intrinsic optical bistability at atomic and molecular scale

A general model for intrinsic optical bistability is presented for atomic or molecular systems which can be decomposed into two weakly interacting subsystems. It is shown that optical bistability should occur when the interaction between the two subsystems fluctuates faster than the characteristic time of the interaction. The validity of the model is demonstrated in the case of magnetic bistability of conduction electrons. It is extended in the infrared or visible range with pairs of rare earth ions and rare earth-transition metal ions systems

Single-frequency operation of an orange avalanche upconversion laser for high-resolution laser spectroscopy

We report single transverse and longitudinal mode operation of an all solid-state orange laser pumped at 821 nm. Oscillation at 607 nm by avalanche upconversion in Pr, Yb:BaY2F8 pumped by a Ti-Sapphire laser at 821 nm is obtained with a threshold as low as 570 mW. A maximum output power of 12 mW is obtained for a pump power of 2.5 W

Orange avalanche upconversion for high-resolution laser spectroscopy

High resolution spectroscopy of quantum systems is a key point in the quantum information field. Rare earth ions in crystals are interesting candidates for this application because of the long coherence lifetime of some of their transitions. These ions can also be manipulated by optical excitation which has, however, to be produced by ultra-stable laser sources. This proves to be a very difficult task in the case of dye lasers which are necessary to excite Pr3+ doped crystals and especially Pr3+:Y2SiO5. This compound is by far the most used host in rare earth based quantum information studies. In this paper, we discuss the use of Pr3+,Yb3+ codoped materials to build an infrared pumped solid state laser suitable to excite Pr3+:Y2SiO5 around 606 nm. We show by the analysis of a rate equation model that avalanche upconversion is not very efficient to obtain a high power laser. This is more easily obtained if a second laser is set to pump resonantly Yb3+ ions. The spectroscopic properties of a new matrix Pr3+,Yb3+:PbF2 are also investigated. We found that this compound emits at 606.18 nm with a width of 5 nm and would be therefore suitable to excite Pr3+:Y2SiO5. Moreover, it can be excited at 857 nm and 975 nm, i.e. in the range of high power laser diodes

Direct observation of rare-earth-host interactions inEr:Y2SiO5

International audienceWe report the direct observation of Er-Y and Er-Si interactions in Er:Y2SiO5 by spin-echo measurements. Modulations in the spin-echo decay of Er3+ ions are due to magnetic interactions between the rare earth and the host nuclear spins. The closest yttrium ions were found to be out of resonance compared to the yttrium ions farther away from the rare earth. This strong “frozen core” effect around the Er3+ ions suggests that the influence of Y3+ ions on the decoherence processes of erbium is weaker than what can be deduced from the yttrium in the bulk

Hyperfine structure of Tm3+ in YAG for quantum storage applications

International audienceQuantum storage of photons in an atomic ensemble can be obtained by using three-level K systems. In these schemes, two levels are coupled by optical transitions to a third one. Ideally, the two transitions should have similar intensities and long coherence lifetimes. Rare earth ion doped crystals are attractive materials for quantum storage because their hyperfine levels can have coherence lifetimes longer than 100 ls and thus can be used to build K systems. Tm3+ ions are especially interesting since they can be excited by ultra-stable laser diodes. In this paper, the hyperfine structures of the 3H6(0) and 3H4(0) crystal field levels of Tm3+ in Y3Al5O12 are investigated by hole burning spectroscopy under a magnetic field. The results are compared to theoretical calculations and found to be in reasonable agreement. Moreover, it is shown that an appropriate magnetic field is able to relax the selection rule on the nuclear spin projection, an absolutely necessary condition to obtain an efficient three-level K system with Tm3+ in this host. Finally, a magnetic field orientation optimized with respect to the K system transition intensity ratio is predicted for a convenient experimental set-up