P1 Transition Research Articles

Bi-color atomic beam slower and magnetic field compensation for ultracold gases

Transversely loaded bidimensional-magneto-optical-traps (2D-MOTs) have been recently developed as high flux sources for cold strontium atoms to realize a new generation of compact experimental setups. Here, we discuss on the implementation of a cross-polarized bi-color slower for a strontium atomic beam, improving the 2D-MOT loading and increasing the number of atoms up to ∼109 atoms in the 461 nm MOT. Our slowing scheme addresses simultaneously two excited Zeeman substates of the 88Sr 1S0→ 1P1 transition at 461 nm. We also realized a three-axis active feedback control of the magnetic field down to the microgauss regime. Such a compensation is performed thanks to a network of eight magnetic field probes arranged in a cuboid configuration around the atomic cold sample and a pair of coils in a quasi-Helmholtz configuration along each of three Cartesian directions. Our active feedback is capable of efficiently suppressing most of the magnetically induced position fluctuations of the 689 nm intercombination-line MOT.

Efficient Near‐Infrared Luminescence in Lanthanide‐Doped Vacancy‐Ordered Double Perovskite Cs2ZrCl6 Phosphors via Te4+ Sensitization

All-inorganic lead-free perovskite-derivative metal halides have shown great promise in optoelectronics, however, it remains challenging to realize efficient near-infrared (NIR) luminescence in these materials. Herein, we report a novel strategy based on Te4+ /Ln3+ (Ln=Er, Nd, and Yb) co-doping to achieve efficient NIR luminescence in vacancy-ordered double perovskite Cs2 ZrCl6 phosphors, which are excitable by a low-cost near-ultraviolet light-emitting diode (LED) chip. Through sensitization by the spin-orbital allowed 1 S0 →3 P1 transition of Te4+ , intense and multi-wavelength NIR luminescence originating from the 4f→4f transitions of Er3+ , Nd3+ , and Yb3+ was acquired, with a quantum yield of 6.1 % for the Er3+ emission. These findings provide a general approach to achieve efficient NIR emission in lead-free metal halides through ns2 -metal and lanthanide ion co-doping, thereby opening up a new avenue for exploring NIR-emitting perovskite derivatives towards versatile applications such as NIR-LEDs and bioimaging.

Crosstalk-Free Excitation Scheme for Quantitative OH Laser-Induced Fluorescence in Environments Containing Excited CO

Spectral overlap in the single-photon laser-induced fluorescence between the 3064 Å system of OH and the third positive system of CO is detected in a highly-excited environment, namely, a CO2-H2O plasma. The overlap is distorting excitation and fluorescence spectra as well as fluorescence time decays of commonly used excitation transitions of OH. As a consequence, systematic errors are introduced into the determination of temperatures, gas compositions, and absolute number densities. The P1(2) transition is proposed to circumvent the distortion while still allowing for quantitative measurements due to the availability of non-radiative rate coefficients.

Solution of semi-flexible self-avoiding trails on a Husimi lattice built with squares

We study a model of semi-flexible self-avoiding trails, where the lattice paths are constrained to visit each lattice edge at most once, with configurations weighted by the number of collisions, crossings and bends, on a Husimi lattice built with squares. We find a rich phase diagram with five phases: a non-polymerised phase (NP), low density (P1) and high density (P2) polymerised phases, and, for sufficiently large stiffness, two additional anisotropic (nematic) (AN1 and AN2) polymerised phases within the P1 phase. Moreover, the AN1 phase which shows a broken symmetry with a preferential direction, is separated from the P1 phase by the other nematic AN2 phase. Although this scenario is similar to what was found in our previous calculation on the Bethe lattice, where the AN–P1 transition was discontinuous and critical, the presence of the additional nematic phase between them introduces a qualitative difference. Other details of the phase diagram are that a line of tri-critical points may separate the P1–P2 transition surface into a continuous and a discontinuous portion, and that the same may happen at the NP–P1 transition surface, details of which depend on whether crossings are allowed or forbidden. A critical end-point line is also found in the phase diagram.

Complex Structural Behavior of BiMn7O12 Quadruple Perovskite.

Structural properties of a quadruple perovskite BiMn7O12 were investigated by laboratory and synchrotron X-ray powder diffraction between 10 and 650 K, single-crystal X-ray diffraction at room temperature, differential scanning calorimetry (DSC), second-harmonic generation, and first-principles calculations. Three structural transitions were found. Above T1 = 608 K, BiMn7O12 crystallizes in a parent cubic structure with space group Im3̅. Between 460 and 608 K, BiMn7O12 adopts a monoclinic symmetry with pseudo-orthorhombic metrics (denoted as I2/m(o)), and orbital order appears below T1. Below T2 = 460 K, BiMn7O12 is likely to exhibit a transition to space group Im. Finally, below about T3 = 290 K, a triclinic distortion takes place to space group P1. Structural analyses of BiMn7O12 are very challenging because of severe twinning in single crystals and anisotropic broadening and diffuse scattering in powder. First-principles calculations confirm that noncentrosymmetric structures are more stable than centrosymmetric ones. The energy difference between the Im and P1 models is very small, and this fact can explain why the Im to P1 transition is very gradual, and there are no DSC anomalies associated with this transition. The structural behavior of BiMn7O12 is in striking contrast with that of LaMn7O12 and could be caused by effects of the Bi3+ lone electron pair.

The force-generation process in active muscle is strain sensitive and endothermic: a temperature-perturbation study.

In experiments on active muscle, we examined the tension decline and its temperature sensitivity at the onset of ramp shortening and at a range of velocities. A segment (∼1.5 mm long) of a skinned muscle fibre isolated from rabbit psoas muscle was held isometrically (sarcomere length ∼2.5 µm) at 8-9°C, maximally Ca2+-activated and a ramp shortening applied. The tension decline with a ramp shortening showed an early decrease of slope (the P1 transition) followed by a slower decrease in slope (the P2 transition) to the steady (isotonic) force. The tension level at the initial P1 transition and the time to that transition decreased as the velocity was increased; the length change to this transition increased with shortening velocity to a steady value of ∼8 nm half-sarcomere-1 A small, rapid, temperature jump (T-jump) (3-4°C, <0.2 ms) applied coincident with the onset of ramp shortening showed force enhancement by T-jump and changed the tension decline markedly. Analyses showed that the rate of T-jump-induced force rise increased linearly with increase of shortening velocity. These results provide crucial evidence that the strain-sensitive cross-bridge force generation, or a step closely coupled to it, is endothermic.

A versatile dual-species Zeeman slower for caesium and ytterbium.

We describe the design, construction, and operation of a versatile dual-species Zeeman slower for both Cs and Yb, which is easily adaptable for use with other alkali metals and alkaline earths. With the aid of analytic models and numerical simulation of decelerator action, we highlight several real-world problems affecting the performance of a slower and discuss effective solutions. To capture Yb into a magneto-optical trap (MOT), we use the broad (1)S0 to (1)P1 transition at 399 nm for the slower and the narrow (1)S0 to (3)P1 intercombination line at 556 nm for the MOT. The Cs MOT and slower both use the D2 line (6(2)S1/2 to 6(2)P3/2) at 852 nm. The slower can be switched between loading Yb or Cs in under 0.1 s. We demonstrate that within a few seconds the Zeeman slower loads more than 10(9) Yb atoms and 10(8) Cs atoms into their respective MOTs. These are ideal starting numbers for further experiments on ultracold mixtures and molecules.

Proton Transfers in a Channelrhodopsin-1 Studied by Fourier Transform Infrared (FTIR) Difference Spectroscopy and Site-directed Mutagenesis

Channelrhodopsin-1 from the alga Chlamydomonas augustae (CaChR1) is a low-efficiency light-activated cation channel that exhibits properties useful for optogenetic applications such as a slow light inactivation and a red-shifted visible absorption maximum as compared with the more extensively studied channelrhodopsin-2 from Chlamydomonas reinhardtii (CrChR2). Previously, both resonance Raman and low-temperature FTIR difference spectroscopy revealed that unlike CrChR2, CaChR1 under our conditions exhibits an almost pure all-trans retinal composition in the unphotolyzed ground state and undergoes an all-trans to 13-cis isomerization during the primary phototransition typical of other microbial rhodopsins such as bacteriorhodopsin (BR). Here, we apply static and rapid-scan FTIR difference spectroscopy along with site-directed mutagenesis to characterize the proton transfer events occurring upon the formation of the long-lived conducting P2 (380) state of CaChR1. Assignment of carboxylic C=O stretch bands indicates that Asp-299 (homolog to Asp-212 in BR) becomes protonated and Asp-169 (homolog to Asp-85 in BR) undergoes a net change in hydrogen bonding relative to the unphotolyzed ground state of CaChR1. These data along with earlier FTIR measurements on the CaChR1 → P1 transition are consistent with a two-step proton relay mechanism that transfers a proton from Glu-169 to Asp-299 during the primary phototransition and from the Schiff base to Glu-169 during P2 (380) formation. The unusual charge neutrality of both Schiff base counterions in the P2 (380) conducting state suggests that these residues may function as part of a cation selective filter in the open channel state of CaChR1 as well as other low-efficiency ChRs.

Lamb-Dicke spectroscopy of atoms in a hollow-core photonic crystal fibre.

Unlike photons, which are conveniently handled by mirrors and optical fibres without loss of coherence, atoms lose their coherence via atom–atom and atom–wall interactions. This decoherence of atoms deteriorates the performance of atomic clocks and magnetometers, and also hinders their miniaturization. Here we report a novel platform for precision spectroscopy. Ultracold strontium atoms inside a kagome-lattice hollow-core photonic crystal fibre are transversely confined by an optical lattice to prevent atoms from interacting with the fibre wall. By confining at most one atom in each lattice site, to avoid atom–atom interactions and Doppler effect, a 7.8-kHz-wide spectrum is observed for the 1S0−3P1(m=0) transition. Atoms singly trapped in a magic lattice in hollow-core photonic crystal fibres improve the optical depth while preserving atomic coherence time.

Polarons, Compressed Polarons, and Bipolarons in Conjugated Polymers

Extensive reductive chemical doping in four conjugated polymers showed evolution of optical spectra for negative polarons and more reduced species. Delocalization lengths of the polarons, which ranged from 2 to 6 nm, were determined from measurements of bleaching of the neutrals, with the extinction coefficients measured by pulse radiolysis. A particular advantage of reductive doping is the ability to encapsulate the Na+ counterions in the C222 cryptand to control the interaction of charges with counterions. For lightly doped chains C222 had little effect on the delocalization lengths or spectra of the two polaron transitions P1 and P2, perhaps because most were completely dissociated to free ions. C222 did strongly alter the spectra when many electrons were added to a chain. For the shortest polarons, 2 nm in poly(phenylene-vinylene) (PPV), energies of the P1 and P2 transitions increased with the extent of reduction. The effect on the P1 transition was greater in the absence of C222 indicating ion-pairing equilibria for the short PPV polarons. Highly reduced ions formed upon injection of multiple electrons included polarons compressed by factors of four or more from their normal lengths to ∼1 charge/nm: a highly reduced 60 nm long chain contained ∼60 electrons. For compressed polarons the transitions shifted with increasing reduction indicating sensitivity to counterions: ion pairing is an important determinant of the behavior upon multiple reductions.

Force Transients during Shortening of Activated Skeletal Muscle Fibers

During a ramp shortening, the force response of an active muscle shows an early change in slope (P1 transition) followed by a gradual change in slope (P2 transition), that happen at given sarcomere length (SL) extension (SL1 and SL2, respectively). In this study, we investigated the mechanisms of forces produced during an imposed shortening to active muscles, by altering either the number of crossbridges attached to actin or the crossbridge state prior to shortening. Three sets of experiments were performed with permeabilized psoas muscle fibers: (i) fibers were activated and shortened by 10% Lo, at 1.0 Lo•s−1 in different pCa2+ (4.5, 5.0, 5.5, 6.0), (ii) fibers were activated and shortened by 10% Lo at 1.0 Lo•s−1 in pCa2+ 4.5 containing either 5µM of blebbistatin (+/-) or its inactive isomer (+/+), or (iii) fibers were activated then shotened by 10% at speeds ranging from 0.125 to 2.0 Lo•s−1 in pCa2+ 4.5 or pCa2+ 6.0 and 5µM blebbistatin (+/-). All shortenings started at a SL 2.5µm. P1, P2 SL1 and SL2 were not affected by different Ca2+ concentrations; the pooled experiments provided P1 and P2 of 0.79 + 0.003 and 0.27 + 0.01 times Po, respectively, and SL1 and SL2 of 4.62 + 0.16 and 24.17+ 0.20 nm•HS−1 respectively. P1 and P2 diminished, and SL1 and SL2 augmented with increasing shortening velocity. Blebbistatin (+/-) decreased P1 (0.74 ± 0.04 times Po) when compared to control fibers (0.81 ± 0.02 times Po), but it did not change the P2. Blebbistatin did not change SL1 and SL2. The results suggest that pre-powerstroke crossbridges contributes to changes in P1, as they may be pushed into the powerstroke during shortening. Such crossbridges detach from actin at the same SL extension.

Dimension-based attention modulates early visual processing

Target selection can be based on spatial or dimensional/featural mechanisms operating in a location-independent manner. We investigated whether dimension-based attention affects processing in early visual stages. Subjects searched for a singleton target among an 8-item array, with the search display preceded by an identical cue array with a dimensionally non-predictive, but spatially predictive singleton. Reaction times (RTs) were increased for changes in the target-defining dimension but not for featural changes within a dimension. This RT effect was mirrored by modulations of the P1 and anterior transition N2 (tN2). Current density reconstructions revealed increased activity in dorsal occipital cortex and decreased activity in left frontopolar cortex owing to repeated dimensional pop-out identities. These findings strengthen dimension-based theories of visual attention by indicating dimension-, rather than feature-, specific influences within the first 110 ms of visual processing.

Frequency shifts of the 88Sr 1S0 – 3 P1 transition induced by buffer gas collisions

Buffer gas induced collision shift for 88Sr1S0−3 P1 transition is investigated by precision saturation spectroscopy of thermal gas in a heat cell. The cell was filled with rare gas of helium, neon, argon, and xenon as buffer gasees. Helium showed the largest fractional shift coefficient of 1.6 × 10−9 Torr−1. The result could be useful to evaluate the background gas collision shift of Sr lattice clocks.

Absolute frequency and isotope shift measurements of the cooling transition in singly ionized indium

We report greater than two orders of magnitude improvements in the absolute frequency and isotope shift measurements of the In + 5s 21 S0 (F =9 /2)-5s5p 3 P1 (F =1 1/2) transition near 230.6 nm. The laser-induced fluorescence from a single In + in a radio-frequency trap is detected. The fourth-harmonic of a semiconductor laser is used as the light source. The absolute frequency is measured with the help of a frequency comb referenced to a Cs atomic clock. The resulting transition frequencies for isotopes 115 In + and 113 In + are measured to be 1 299 648 954.54(10) MHz and 1 299 649 585.36(16) MHz, respectively. The deduced cooling transition frequency difference is 630.82(19) MHz. By taking into account of the hyperfine interaction, the isotope shift is calculated to be 695.76(1.68) MHz.

Determination of thes-Wave Scattering Length and theC6van der Waals Coefficient ofYb174via Photoassociation Spectroscopy

We report photoassociation spectroscopy of 174Yb for the 1S(0)-1P1 transition at 1 microK, where only the s-wave scattering state contributes to the spectra. The wave function of the s-wave scattering state is obtained from the photoassociation efficiency, and we determine that the C6 potential coefficient is 2300+/-250 a.u. and the s-wave scattering length is 5.53+/-0.11 nm. Based on these parameters, we discuss the scattering properties of s- and d-wave states.

Characterization and Photochemistry of 13-Desmethyl Bacteriorhodopsin

The photochemistry of the 13-desmethyl (DM) analogue of bacteriorhodopsin (BR) is examined by using spectroscopy, molecular orbital theory, and chromophore extraction followed by conformational analysis. The removal of the 13-methyl group permits the direct photochemical formation of a thermally stable, photochemically reversible state, P1(DM) (lambda(max) = 525 nm), which can be generated efficiently by exciting the resting state, bR(DM) with yellow or red light (lambda > 590 nm). Chromophore extraction analysis reveals that the retinal configuration in P1(DM) is 9-cis, identical to that of the retinal configuration in the native BR P1 state. Fourier transform infrared and Raman experiments on P1(DM) indicate an anti configuration around the C15=N bond, as would be expected of an O-state photoproduct. However, low-temperature spectroscopy and ambient, time-resolved studies indicate that the P1(DM) state forms primarily via thermal relaxation from the L(D)(DM) state. Theoretical studies on the BR binding site show that 13-dm retinal is capable of isomerizing into a 9-cis configuration with minimal steric hindrance from surrounding residues, in contrast to the native chromophore in which surrounding residues significantly obstruct the corresponding motion. Analysis of the photokinetic experiments indicates that the Arrhenius activation energy of the bR(DM) --> P1(DM) transition in 13-dm-BR is less than 0.6 kcal/mol (vs 22 +/-5 kcal/mol measured for the bR --> P (P1 and P2) reaction in 85:15 glycerol:water suspensions of wild type). Consequently, the P1(DM) state in 13-dm-BR can form directly from all-trans, 15-anti intermediates (bR(DM) and O(DM)) or all-trans, 15-syn (K(D)(DM)/L(D)(DM)) intermediates. This study demonstrates that the 13-methyl group, and its interactions with nearby binding site residues, is primarily responsible for channeling one-photon photochemical and thermal reactions and is limited to the all-trans and 13-cis species interconversions in the native protein.

Demonstration of a Ni-like Kr optical-field-ionization collisional soft x-ray laser at 32.8 nm.

We report the first experimental demonstration of a Ni-like optical-field ionization collisional soft x-ray laser. The amplifying medium is generated by focusing a circularly polarized 760 mJ, 30 fs, 10-Hz Ti:sapphire laser beam in a few mm cell filled with krypton. We have measured a gain coefficient of 78 cm(-1) on the 3d(9)4d 1S0-3d(9)4p(1)P1 transition at 32.8 nm, which is here amplified for the first time. This radiation source represents the shortest wavelength optical-field ionization collisional soft x-ray laser ever produced. The influence of the gas pressure and the pumping energy on the lasing output are also presented.

Simultaneous multi-isotope trapping of ytterbium

Working with ytterbium ~Yb!, we demonstrate dual-isotope magneto-optic traps of extreme experimental simplicity yet containing either fermion-boson or boson-boson isotope pairs. Pairs studied include Yb1Yb ~a fermion-boson mixture! and Yb1Yb and Yb1Yb ~boson-boson mixtures!. Trapping is performed using the Yb (6s)S0-(6s6p) P1 transition, an uncooled thermal source, and bichromatic trapping beams. Static and dynamic properties of the composite cloud are conveniently probed on the spinforbidden (6s)S0-(6s6p) P1 transition. A unique strategy for continuously loading these samples into magnetic traps is described.

Linkage of human spermatid-specific basic nuclear protein genes. Definition and evolution of the P1–>P2–>TP2 locus.

Protamines and transition proteins are highly basic sperm-specific nuclear proteins that serve to compact the DNA within the condensing spermatid nucleus. It has been proposed that the genes for protamine P1 and P2 and transition protein 2 may be clustered at a single loci. This may have marked implications for their evolution and coordinate developmental regulation. The cloning of a contiguous segment encompassing this region would directly address these issues. We have utilized a cloned segment of the human protamine P1 gene to isolate a human cosmid clone which contains the genes for protamines P1 and P2 and transition protein TP2. Sequence and hybridization analysis of this cosmid showed that the TP2 gene resided 3' of the P2 gene at a distance of approximately 7 kilobases (kb). This establishes the order of this gene cluster within a 13-kb region of 16p13.13-16p13.2 to be P1-->P2-->TP2. Similar to their spatial order, comparative computer-assisted sequence analysis predicts an identical relative rank order of emergence. Accordingly we propose that this gene cluster may have arisen from the P1 gene through a series of gene duplication events.

Doppler-Free Spectrum of the Barium 1S0−1P1 Transition by Degenerate Four-Wave Mixing Using an Air/Acetylene Flame

Doppler-free flame spectrometry based on resonant degenerate four-wave mixing (D4WM) is shown to be an effective analytical tool for the determination of barium at high spectral resolution. Optical phase conjugation is produced in an air/acetylene flame, resulting in an optical signal that is a coherent time-reversed replica of the probe beam. The degenerate four-wave mixing spectrum of barium for the 6 s21 S0-6 s6 p1 P1 transition at 18,060.19 cm−1 is collected with a linewidth of 0.08 cm−1 (FWHM) with the use of a convenient continuously flowing atmospheric-pressure flame atomizer. A preliminary detection limit of 5 μg/mL barium, while a Doppler-free linewidth is maintained at 0.08 cm−1, is reported.