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The angular distribution of the ions coming from Coulomb explosion following femtosecond ionisation of methyl iodide is studied in the spectral range of 600 to 1450 nm. Under these conditions, iodi...

We present a compact polarimeter, which can perform sensitive measurements of optical rotation in vapor. The operation of the polarimeter is based on a Cavity Ring-Down scheme which employs two signal reversals, which increase sensitivity and reduce noise, allowing the realization of sensitive measurements in the presence of spurious birefringence. We describe the operation of the polarimeter, give the basic equations for the signal analysis and retrieval of optical rotation angle, and present measurements that demonstrate a sensitivity of ~80μdeg/pass.

An improved optical cavity-based polarimetry method is employed to measure the optical activity of lysozyme in water solution, in the concentration range of 0–2mg/ml. We employ a signal reversing technique, which gives the absolute optical rotation, without needing to remove the sample for a null measurement. We report an absolute sensitivity limit on the order of 0.1 mdeg, corresponding to a detection limit of

In a recent letter [Phys. Rev. Lett. 118, 253001 (2017)PRLTAO0031-900710.1103/PhysRevLett.118.253001] we have described how studies of the recoil velocity distribution in the photodissociation of OCS in the energy interval 42 600-42 900 cm-1 revealed an unexpected behavior: the recoil velocity distribution of only the lowest-kinetic-energy photofragments exhibited rapid, resonantlike variations with energy and caused complete inversion of the recoil direction. Periodic orbit analysis and quantum nonadiabatic calculations unveiled the existence of a resonance state localized at large bending angles towards the exit of the dissociation channel. In this article, we present an extensive theoretical study and we show how the fingerprints of these resonances are identified by the analysis of the nonadiabatic transitions and the stereodynamics of photofragments trajectories. Additionally, the experimental study is extended to a second photolysis energy region, 43 300-43 650 cm-1, where a similar rapid variation of the recoil direction is detected. The energy separation between this second resonance region and the one previously reported is ∼800cm-1, which is twice the calculated period of the localized resonant state, offering a second point of convergence between the experiment and the theory.

We report the electron-spin polarization of D atoms from the photodissociation of DI, at 213 nm and 266 nm, by measuring the magnetization quantum beats of the D atoms with a pick-up coil. We determine that the polarization P is large at both wavelengths (|P| ∼ 1), however it is positive at 213 nm, and negative at 266 nm. These results, in both cases, are of opposite sign to calculations, which assume adiabatic dissociation along the A1Π1 or a3Π1 states. We interpret these results as evidence that nonadiabatic coupling between these states needs to be included for the theoretical treatment of DI photodissociation.

We measure nuclear and electron spin-polarized H and D densities of at least ${10}^{19}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ with $\ensuremath{\sim}10\text{ }\text{ }\mathrm{ns}$ lifetimes, from the photodissociation of HBr and DI with circularly polarized UV light pulses. This density is $\ensuremath{\sim}6$ orders of magnitude higher than that produced by conventional continuous-production methods and, surprisingly, at least 100 times higher than expected densities for this photodissociation method. We observe the hyperfine quantum beating of the H and D magnetization with a pickup coil, i.e., the respective 0.7 and 3 ns periodic transfer of polarization from the electrons to the nuclei and back. The ${10}^{19}\text{ }\text{ }{\mathrm{cm}}^{\ensuremath{-}3}$ spin-polarized H and D density is sufficient for laser-driven ion acceleration of spin-polarized electrons, protons, or deuterons, the preparation of nuclear-spin-polarized molecules, and the demonstration of spin-polarized D-T or $\mathrm{D}\text{\ensuremath{-}}^{3}\mathrm{He}$ laser fusion, for which a reactivity enhancement of $\ensuremath{\sim}50%$ is expected.

The use of nuclear polarized fuel, {\it{i.e.}}~polarized D, T or $^3$He, for coming fusion reactors promises to increase their energy output and to optimize the complete fusion process in various ways. But before these advantages can be utilized, several questions have to be answered and technical issues must be overcome. Among others, the members of the PREFER collaboration started to investigate the different challenges of ``polarized fusion''.

We review the development of cavity ring-down polarimetry, which is a cavity-based method using pulsed lasers, for enhancing chiral-optical-rotation signals by the number of the cavity passes (typically 102–104), while suppressing non-chiral backgrounds, and isolating the chiral signals from the backgrounds through signal reversals. The advantages of this method is demonstrated in measurements of optical rotation of chiral samples in an evanescent wave near the surface of a prism. We also discuss the future prospects for perming cavity-based polarimetry with continuous lasers, for which the opticalrotation sensitivity should surpass current commercial instruments by several orders of magnitude.

We report on the concept of an innovative laser-driven plasma accelerator for polarized proton (or deuteron) beams with a kinetic energy up to several GeV. In order to model the motion of the particle spins in the plasmas, these have been implemented as an additional degree of freedom into the Particle-in-Cell simulation code VLPL. For the experimental realization, a polarized HCl gas-jet target is under construction, where the degree of proton polarization is determined with a Lamb-shift polarimeter. The final experiments, aiming at the first observation of a polarized particle beam from laser-generated plasmas, will be carried out at the 10 PW laser system SULF at SIOM/Shanghai.

We report the observation of recoil inversion of the CO ($v=0$, ${J}_{\mathrm{CO}}=66$) state in the UV dissociation of lab-frame oriented carbonyl sulfide (OCS). This state is ejected in the opposite direction with respect to all other ($g30$) states and in absence of any OCS rotation, thus resulting in spatial filtering of this particular high-$J$ rovibrational state. This inversion is caused by resonances occurring in shallow local minima of the molecular potential, which bring the sulfur closer to the oxygen than the carbon atom, and is a striking example where such subtleties severely modify the photofragment trajectories. The resonant behavior is observed only in the photofragment trajectories and not in their population, showing that stereodynamic measurements from oriented molecules offer an indispensable probe for exploring energy landscapes.

Loading a dipole trap from an atomic reservoir is considered to be an efficient method for the preparation of trapped atoms at high density, which has led to notable results for the case of Rb and Cr atoms. It was also theoretically predicted to provide efficient loading also in the cesium case. In this article, we report on the experimental study of the loading of a single-arm and of a crossed dipole trap for cesium atoms. This study is performed by comparing several types of reservoirs from which the atoms are loaded: a magnetic trap, a Dark-SPOT and a compressed MOT. In all cases the number of atoms is found to decrease shortly after the beginning of the loading process. A few possible phenomena leading to such a behavior, namely the limited reservoir lifetime and/or a possible heating in the reservoir, are discussed. The loading dynamics is fitted by a phenomenological rate equation. From an experimental point of view, the reservoir loading method can be considered efficient in terms of number of transferred atoms for the single arm dipole trap. On the contrary, it does not seem to provide, for the case of cesium atoms in a crossed dipole trap, an attractive alternative in comparison with existing loading methods such as Raman sideband cooling.

International audience; A review of our recent experiments on broadband vibrational cooling of cold cesium molecules and of the related theory is presented. Our method is based on repetitive optical pumping cycles driven by laser light which is broad enough to excite all populated vibrational levels. Originally, the accumulation of molecular population in a particular, pre-selected vibrational level was achieved by removing from the broadband light all frequencies that could excite that vibrational level and thus making it a 'dark state' of the system. Here, we focus onto an additional, more sophisticated shaping method, which consists of selecting only specific frequency components that excite molecules into vibrational levels that favourably decay into the pre-selected level. The population transfer to any desired state can thus be optimised, i.e. the total population transfer to the desired vibrational level is maximised while the number of absorption-emission cycles required for the vibrational cooling is minimised. Finally, we apply this optimised technique to some more complex and still experimentally open cases: the pumping into the ground state for the case of Cs2 homonuclear molecules, the rotational pumping into a pre-selected ro-vibrational level and the NaCs as an example for heteronuclear molecules.

International audience; Recent experiments on formation of translationally cold ground state molecules, their subsequent broadband vibrational cooling and study of rotations are presented together with the related modeling. We produce cold molecules by photoassociating pairs of cold cesium atoms that can decay into ground state molecules in different vibrational levels. Then we laser cool the vibrational degree of freedom by selecting a single target vibrational level. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. Results for vibrational cooling into the v = 0, v = 1, v = 2 and v = 7 level of the singlet X 1Σ g ground electronic state are presented. Depletion spectroscopy is performed to study the rotational distribution of the created molecules. In the theoretical modeling of the process we are able to reproduce our results and investigate the prospects for a 'complete' cooling of molecules, including also their rotational degree of freedom

We present the theory and experimental details for chiral-cavity-ring-down polarimetry and magnetometry, based on ring cavities supporting counterpropagating laser beams. The optical-rotation symmetry is broken by the presence of both chiral and Faraday birefringence, giving rise to signal reversals which allow rapid background subtractions. We present the measurement of the specific rotation at 800 nm of vapors of α-pinene, 2-butanol, and α-phellandrene, the measurement of optical rotation of sucrose solutions in a flow cell, the measurement of the Verdet constant of fused silica, and measurements and theoretical treatment of evanescent-wave optical rotation at a prism surface. Therefore, these signal-enhancing and signal-reversing methods open the way for ultrasensitive polarimetry measurements in gases, liquids and solids, and at surfaces.

We present an experimental apparatus that allows microsecond-resolved ellipsometric and absorption measurements. The apparatus is based on an optical cavity containing a Dove prism, in which light undergoes total internal reflection (TIR), while the data acquisition is based on software defined radio technology and custom-built drivers. We demonstrate the ability to sense rapid variations in the refractive index above the TIR interface for arbitrarily long times with a temporal resolution of at least 2 μs.

We discuss how nuclear spin can be highly polarized from the transfer of molecular rotational polarization via the hyperfine interaction, and how large atomic electronic polarization can be produced via molecular photodissociation with polarized light. In combination, these two pulsed-laser techniques can be used to produce highly polarized atoms at densities close to the density of the parent molecules. We compare these methods to existing methods for producing polarized atoms and present specific examples.

We identify a pair of near-degenerate states of opposite parity in atomic Xe, the $5p^5 10s \,\, ^2[3/2]_2^o$ at $\rm{E}=94759.927$ cm$^{-1}$ and $5p^5 6f \,\, ^2[5/2]_2$ at $\rm{E}= 94759.935$ cm$^{-1}$, for which parity- and time-odd effects are expected to be enhanced by the small energy separation. We present theoretical calculations which indicate narrow widths for both states and we report a calculated value for the weak matrix element, arising from configuration mixing, of $|W|=2.1$ Hz for $^{132}$Xe. In addition, we measured the Stark effect of the $5p^5\,6f$ $^2[5/2]_{2}$ and $5p^5 \,6f \ ^2[3/2]_2$ ($\rm{E} =94737.121\,\rm{cm}^{-1}$) states. The Stark-shift of the $6f$ states is observed to be negative, revealing the presence of nearby $6g$ states at higher energies, which have not been observed before. The Stark-shift measurements imply an upper limit on the weak matrix element of $|W|\!, Comment: 11 pages, 6 figures

We report the measurement of the spin polarization of hydrogen (SPH) atoms by (2+1) laser-induced fluorescence, produced via the photodissociation of thermal HBr molecules with circularly polarized 193 nm light. This scheme, which involves two-photon laser excitation at 205 nm and fluorescence at 656 nm, offers an experimentally simpler polarization-detection method than the previously reported vacuum ultraviolet detection scheme, allowing the detection of SPH atoms to be performed more straightforwardly, from the photodissociation of a wide range of molecules and from a variety of collision experiments.

We demonstrate selective vibrational population transfer in cold cesium dimers using a simple approach based on the use of a shaped incoherent broadband diode laser near threshold. Optical pumping into a single vibrational level is accomplished with an incoherent light source by eliminating transitions from the targeted vibrational level. The broadband spectrum of the laser is wide enough to electronically excite several vibrational states of the molecule simultaneously. This method is relatively inexpensive, simple, and flexible to allow for development of new applications, in particular, the preparation of optically closed molecular system, opening the way to direct laser cooling of molecules.

Some of us have recently reported in Science 321 232 (2008) vibrational cooling of translationally cold Cs_2 molecules into the lowest vibrational level v=0 of the singlet X 1Sigma_g ground electronic state. Starting from a sample of cold molecules produced in a collection of vibrational levels of the ground state, our method was based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but frequency-limited in such a way to eliminate transitions from v=0 level, in which molecules accumulate. In this paper this method is generalized to accumulate molecules into an arbitrary selected "target" vibrational level. It is implemented by using ultrashort pulse shaping techniques based on Liquid Crystal spatial light modulator. In particular a large fraction of the initially present molecule is transferred into a selected vibrational level such as v=1, 2 and 7. Limitations of the method as well as the possible extension to rotational cooling are also discussed., Comment: TO be published in New Journal of Physics

International audience; The use of a broadband, frequency shaped femtosecond laser on translationally cold cesium molecules has recently demonstrated to be a very efficient method of cooling also the vibrational degree of freedom. A sample of cold molecules, initially distributed over several vibrational levels, has thus been transfered into a single selected vibrational level of the singlet X1Σg ground electronic state. Our method is based on repeated optical pumping by laser light with a spectrum broad enough to excite all populated vibrational levels but limited in its frequency bandwidth with a spatial light modulator. In such a way we are able to eliminate transitions from the selected level, in which molecules accumulate. In this paper we briefly report the main experimental results and then address, in a detailed way by computer simulations, the perspectives for a "complete" cooling of the molecules, including also the rotational degree of freedom. Since the pumping process strongly depends on the relative shape of the ground and excited potential curves, ro-vibrational cooling through different excited states is theoretically compared.

An aligned sample of HD(v = 1, J = 2, M(J) = 0) molecules is prepared under collision-free conditions using the S(0) stimulated Raman pumping transition. Subsequent coupling to the spins of the deuteron I(D) and the proton I(H) causes the initial degree of alignment to oscillate and decrease as monitored over the time range from 0-13 mus via the O2 line of the [2 + 1] REMPI E,F(1)Sigma-X(1)Sigma (0,1) band. The time dependence of the rotational alignment is also calculated using both a hierarchical coupling scheme in which the rotational angular momentum J is regarded first to couple to I(D), and then the resultant F(i) to couple to I(H), to form the total angular momentum F and a non-hierarchical coupling scheme in which the HD energy level structure is not assumed to be diagonal in the |I(H)(JI(D))F(i)FM(F)basis set. The experimental data is in good agreement with the non-hierarchical calculation but not with the hierarchical calculation, as expected for this system. Additionally, we calculate the time dependence of the H and D nuclear spin polarizations.

We demonstrate directly the nanosecond-timescale production of spin-polarized hydrogen (SPH) atoms from photodissociation of thermal HBr molecules, and the spin-state and Doppler-resolved detection using polarized fluorescence at 121.6 nm, without requiring hyperfine resolution. These techniques allow a variety of spin-dependent, nanosecond pump-probe experiments with SPH, which were not previously realizable. The potential of surpassing the SPH densities and production rates of current techniques is discussed.

H(35)Cl(v=0,J=0) molecules in a supersonic expansion were excited to the H(35)Cl(v=2,J=1,M=0) state with linearly polarized laser pulses at about 1.7 microm. These rotationally aligned J=1 molecules were then selectively photodissociated with a linearly polarized laser pulse at 220 nm after a time delay, and the velocity-dependent alignment of the (35)Cl((2)P(32)) photofragments was measured using 2+1 REMPI and time-of-flight mass spectrometry. The (35)Cl((2)P(32)) atoms are aligned by two mechanisms: (1) the time-dependent transfer of rotational polarization of the H(35)Cl(v=2,J=1,M=0) molecule to the (35)Cl((2)P(32)) nuclear spin [which is conserved during the photodissociation and thus contributes to the total (35)Cl((2)P(32)) photofragment atomic polarization] and (2) the alignment of the (35)Cl((2)P(32)) electronic polarization resulting from the photoexcitation and dissociation process. The total alignment of the (35)Cl((2)P(32)) photofragments from these two mechanisms was found to vary as a function of time delay between the excitation and the photolysis laser pulses, in agreement with theoretical predictions. We show that the alignment of the ground-state (35)Cl((2)P(32)) atoms, with respect to the photodissociation recoil direction, can be controlled optically. Potential applications include the study of alignment-dependent collision effects.

We demonstrate time-dependent polarization transfer from molecular rotation to nuclear spin. The ${\mathrm{H}}^{35}\mathrm{Cl}$ $(v=2,J=1,M=1)$ state is excited with a $1.7\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ laser pulse, and then dissociated with a delayed $235\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ laser pulse to produce $^{35}\mathrm{Cl}$ atoms. Time-dependent polarizations of both $\mathrm{H}^{35}\mathrm{Cl}$ $(v=2,J=1)$ molecules and $^{35}\mathrm{Cl}(^{2}\mathrm{P}_{3∕2})$ atoms, which vary due to hyperfine quantum beating, are measured. The $^{35}\mathrm{Cl}$ nuclear spin is highly polarized $(⟨{M}_{\mathrm{Cl}}⟩\ensuremath{\approx}1.1)$ at a pump-probe delay of $145\phantom{\rule{0.3em}{0ex}}\mathrm{ns}$. Densities surpassing ${10}^{14}\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}3}$ are achieved. The technique is applicable to many atoms not amenable to optical pumping.

It has been proposed recently that hyperfine depolarization of selected molecular rotational states can be used to produce molecules with highly polarized nuclear spins, and formulas for two distinct nuclei have been given in the limit of hierarchical approximation. Here we present the general, nonhierarchical coupling formalism for the derivation of the ${H}_{[i]}^{(k)}(I,t)$ factors that govern the time dependence of the nuclear polarizations. The described technique, especially when combined with methods that polarize the electronic angular momentum, can lead to the production of highly polarized atoms from molecular photodissociation, at densities close to that of the parent molecule. In addition, we calculate the time dependence of the H and F nuclear spin polarizations, following the pulsed-laser preparation of the HF $(v=1,J=1,m=1)$ state. It is shown that the polarization of the F and H nuclear spins attain values of about 85% and 70% at time delays of about $1\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{s}$ and $4\phantom{\rule{0.3em}{0ex}}\mathrm{\ensuremath{\mu}}\mathrm{s}$, respectively. Similar results are shown for the pulsed preparation of the DF $(v=0,J=1,m=1)$ state, demonstrating the D atoms can also be significantly polarized.

We demonstrate a method to increase the sensitivity of the s-p phase shift under total internal reflection (TIR) for optical sensing. This is achieved by the introduction of two simple dielectric layers to the TIR surface of a fused silica prism. The enhanced sensitivity is demonstrated using evanescent-wave cavity-ring-down-ellipsometry by measuring the refractive index of liquid mixtures and by studying the adsorption of polymers to the TIR surface of the fused silica prism.

By using broadband lasers, we demonstrate the possibilities for control of cold molecules formed via photoassociation. Firstly, we present a detection REMPI scheme (M. Viteau et al., Phys. Rev. A, 2009, 79, 021402) to systematically investigate the mechanisms of formation of ultracold Cs2 molecules in deeply bound levels of their electronic ground state X1sigma(g)+. This broadband detection scheme could be generalized to other molecular species. Then we report a vibrational cooling technique (M. Viteau et al., Science, 2008, 321, 232) through optical pumping obtained by using a shaped mode locked femtosecond laser. The broadband femtosecond laser excites the molecules electronically, leading to a redistribution of the vibrational population in the ground state via a few absorption-spontaneous emission cycles. By removing the laser frequencies corresponding to the excitation of the v = 0 level, we realize a dark state for the so-shaped femtosecond laser, leading, with the successive laser pulses, to an accumulation of the molecules in the v = 0 level, ie. a laser cooling of the vibration. The simulation of the vibrational laser cooling allows us to characterize the criteria to extend the mechanism to other molecular species (R. V. Krems, Int. Rev. Phys. Chem., 2005, 24, 99). We finally discuss the generalization of the technique to laser cooling of the rotation of the molecule.

Thermal HCl and HBr molecules were photodissociated using circularly polarized 193 nm light, and the speed-dependent spin polarization of the H-atom photofragments was measured using polarized fluorescence at 121.6 nm. Both polarization components, described by the a(0)(1)(perpendicular) and Re[a(1)(1)(parallel, perpendicular)] parameters which arise from incoherent and coherent dissociation mechanisms, are measured. The values of the a(0)(1)(perpendicular) parameter, for both HCl and HBr photodissociation, are within experimental error of the predictions of both ab initio calculations and of previous measurements of the polarization of the halide cofragments. The experimental and ab initio theoretical values of the Re[a(1)(1)(parallel, perpendicular)] parameter show some disagreement, suggesting that further theoretical investigations are required. Overall, good agreement occurs despite the fact that the current experiments photodissociate molecules at 295 K, whereas previous measurements were conducted at rotational temperatures of about 15 K.

H(35)Cl(v=0,J=0) molecules in a supersonic expansion were excited to the H(35)Cl(v=2,J=1,M=0) state with linearly polarized laser pulses at about 1.7 microm. These rotationally aligned J=1 molecules were then selectively photodissociated with a linearly polarized laser pulse at 220 nm after a time delay, and the velocity-dependent alignment of the (35)Cl((2)P(32)) photofragments was measured using 2+1 REMPI and time-of-flight mass spectrometry. The (35)Cl((2)P(32)) atoms are aligned by two mechanisms: (1) the time-dependent transfer of rotational polarization of the H(35)Cl(v=2,J=1,M=0) molecule to the (35)Cl((2)P(32)) nuclear spin [which is conserved during the photodissociation and thus contributes to the total (35)Cl((2)P(32)) photofragment atomic polarization] and (2) the alignment of the (35)Cl((2)P(32)) electronic polarization resulting from the photoexcitation and dissociation process. The total alignment of the (35)Cl((2)P(32)) photofragments from these two mechanisms was found to vary as a function of time delay between the excitation and the photolysis laser pulses, in agreement with theoretical predictions. We show that the alignment of the ground-state (35)Cl((2)P(32)) atoms, with respect to the photodissociation recoil direction, can be controlled optically. Potential applications include the study of alignment-dependent collision effects.

The photolysis of pyrrole has been studied in a molecular beam at wavelengths of 250, 240, and 193.3 nm, using two different carrier gases, He and Xe. A broad bimodal distribution of H-atom fragment velocities has been observed at all wavelengths. Near threshold at both 240 and 250 nm, sharp features have been observed in the fast part of the H-atom distribution. Under appropriate molecular beam conditions, the entire H-atom loss signal from the photolysis of pyrrole at both 240 and 250 nm (including the sharp features) disappear when using Xe as opposed to He as the carrier gas. We attribute this phenomenon to cluster formation between Xe and pyrrole, and this assumption is supported by the observation of resonance enhanced multiphoton ionization spectra for the (Xe...pyrrole) cluster followed by photofragmentation of the nascent cation cluster. Ab initio calculations are presented for the ground states of the neutral and cationic (Xe...pyrrole) clusters as a means of understanding their structural and energetic properties.

An improved optical cavity-based polarimetry method is employed to measure the optical activity of lysozyme in water solution, in the concentration range of 0–2 mg/ml. We employ a signal reversing technique, which gives the absolute optical rotation, without needing to remove the sample for a null measurement. We report an absolute sensitivity limit on the order of 0.1 mdeg, corresponding to a detection limit of