Generalization of the stabilization method for green functions and quantum resonances

The stabilization method provides an efficient approach to many problems in atomic and molecular dynamics. Real avoided crossings and smoothing techniques provide the relevant information to compute real density of states. The aim of this letter is to present an extension of the stabilization method that allows for a direct determination of full Green functions and resonance energies. The method is based on the use of optical potentials and perturbation theory. Real avoided crossings of the original stabilization method become complex and resonance energies appear to stabilize in the complex-energy plane. A numerical illustration is presented for a simple model of shape resonance. Accurate results are obtained with a small number of real square-integrable functions as in the original stabilization method. The computational efficiency of the approach and its generality are emphasized.     

Homo- and heteronuclear 2D NMR approaches to analyse a mixture of deuterated unlike/like stereoisomers using weakly ordering chiral liquid crystals

We describe several homo- and heteronuclear 2D NMR strategies dedicated to the analysis of anisotropic (2)H spectra of a mixture of dideuterated unlike/like stereoisomers with two remote stereogenic centers, using weakly orienting chiral liquid crystals. To this end, we propose various 2D correlation experiments, denoted "D(H)(n)D" or "D(H)(n)C" (with n=1, 2), that involve two heteronuclear polarization transfers of INEPT-type with one or two proton relays. The analytical expressions of correlation signals for four pulse sequences reported here were calculated using the product-operators formalism for spin I=1 and S=1/2. The features and advantages of each scheme are presented and discussed. The efficiency of these 2D sequences is illustrated using various deuterated model molecules, dissolved in organic solutions of polypeptides made of poly-gamma-benzyl-L-glutamate (PBLG) or poly-epsilon-carbobenzyloxy-L-lysine (PCBLL) and NMR numerical simulations.     

Thermal emission stimulated by excitation of metastable states

Waves interference inside thin films creates fine structures in the thermal emission spectrum of film when the magnitude of film thickness is of the same order than the coherence length of light. Here, we present an alternative to the theory of partially coherent light to explain these ripples pattern and easily predict the radiative properties of films in intermediate regime. The starting point of this theory is based on the observation that unlike vacuum, matter supports the presence of unstable electromagnetic waves with a finite lifetime. For thin absorbing films, we demonstrate that many of these metastable states are quantified and can be excited by an external radiation field. A direct connection is then established between the peaks of emission and these modes. These results open new prospects for the theoretical study and modelling of radiative exchanges inside and between microscale media.     

Équations du type Monge-Ampère sur les variétés Riemanniennes compactes, I

Let (V_n, g) be a C^∞ compact Riemannian manifold. For a suitable function on V_n, let us consider the change of metric: g′ = g + Hess(), and the function, as a ratio of two determinants, M() = ¦g′¦ ¦g¦⁻¹. Using the method of continuity, we first solve in C^∞ the problem: Log M() = λ + ƒ, λ > 0, ƒ ε C^∞. Then, under weak hypothesis on F, we solve the general equation: Log M() = F(P, ), F in C^∞(V_n × ¦α, β¦), using a method of iteration. Our study gives rise to an interesting a priori estimate on ¦¦, which does not occur in the complex case. This estimate should enable us to solve the equation above when λ 0, providing we can overcome difficulties related to the invertibility of the linearised operator. This open question will be treated in our next article.     

Distributed measurement of chromatic dispersion by four-wave mixing and Brillouin optical-time-domain analysis

A new nondestructive method for measuring the spatial distribution of chromatic dispersion along an optical fiber is presented. It is based on using Brillouin optical time-domain analysis to probe the power distribution of the four-wave mixing generated by two continuous-wave lasers. The results obtained prove that this new method is capable of providing better performance than comparable techniques. Furthermore, sensing the variations of Brillouin gain maximum produces additional information about the fiber, such as presence of strain and concentration of GeO2.     

Waveguide electro-optic modulator in fused silica fabricated by femtosecond laser direct writing and thermal poling

An integrated electro-optic waveguide modulator is demonstrated in bulk fused silica. A Mach-Zehnder interferometer waveguide structure is fabricated by direct writing with a femtosecond laser followed by thermal poling. A 20 degrees electro-optic phase shift is achieved at an operating wavelength of 1.55 microm with an applied voltage of 400 V and an interaction length of 25.6 mm, which correspond to an estimated effective electro-optic coefficient of 0.17 pm/V for the TE-polarized mode.     

Calibration and evaluation of optical systems for full-field strain measurement

The design and testing of a reference material for the calibration of optical systems for strain measurement is described, together with the design and testing of a standardized test material that allows the evaluation and assessment of fitness for purpose of the most sophisticated optical system for strain measurement. A classification system for the steps in the measurement process is also proposed and allows the development of a unified approach to diagnostic testing of components or sub-systems in an optical system for strain measurement based on any optical technique. The results described arise from a European study known as SPOTS whose objectives were to begin to fill the gap caused by a lack of standards.     

Experimental investigation of harmonic and subharmonic synchronization of 40 GHz mode-locked quantum-dash laser diodes

Synchronization of a 40 GHz quantum-dash mode-locked (ML) Fabry-Perot laser diode with optically injected pulse streams is experimentally studied. Injected signals consist of nonmodulated and modulated trains of 1.6 ps pulses at various repetition rates, ranging from 10 to 160 GHz and 10 to 160 Gbps, respectively. Subharmonic, fundamental, and harmonic synchronization of the ML laser allows retrieval of stable 40 GHz clock pulses featuring a width of 1.8 ps. Frequency components at 10 and 20 GHz do not create any amplitude modulation on the recovered 40 GHz clock pulses when injecting signals at 10 and 20 GHz/Gbps. In addition, external synchronization of the laser with pulse streams at 80 and 160 GHz/Gbps is sustained despite the absence of significant components at or below 40 GHz.     

Improved measurement of the hydrogen 1S-2S transition frequency

We have measured the 1S-2S transition frequency in atomic hydrogen via two-photon spectroscopy on a 5.8 K atomic beam. We obtain f(1S-2S) = 2,466,061,413,187,035 (10) Hz for the hyperfine centroid, in agreement with, but 3.3 times better than the previous result [M. Fischer et al., Phys. Rev. Lett. 92, 230802 (2004)]. The improvement to a fractional frequency uncertainty of 4.2 × 10(-15) arises mainly from an improved stability of the spectroscopy laser, and a better determination of the main systematic uncertainties, namely, the second order Doppler and ac and dc Stark shifts. The probe laser frequency was phase coherently linked to the mobile cesium fountain clock FOM via a frequency comb.