Selective reflection combined with Fabry-Perot effects from two-level atoms confined between two dielectric walls

The coefficient of selective reflection at oblique incidence from two-level atoms confined between two dielectric walls is calculated in this paper. It is found to be related to the transient behaviour of atoms after colliding with the wall and the distribution of the field inside the vapour corresponds to L/λ, with L the thickness of the film and λ the incident wavelength. We find that the sub-Doppler structure is manifest both for normal incidence and small angle oblique incidence, It is feasible to detect the real part of selective reflection in several cases that have not been achieved before.

Excitation Dependence of Dipole-Dipole Broadening in Selective Reflection Spectroscopy

We investigate the dipole-dipole broadened selective reflection spectrum with the Cs atomic aensity of 10^14- 10^15 cm^-3. The dipole-dipole broadening is reduced and the hyperfine splitting is well resolved when the ground state atoms are excited by a detuned pump beam. The dependences of dipoleMipole broadening of Cs atoms in the 6S1/2（F= 3） → 6P3/2（F＇= 4） hyperfine transition line on atomic density and the excitation factor are studied. It is found that the reduction of the dipole-dipole broadening is dependent on the pump beam power and is independent of the atomic density in this density range. These results are useful for understanding of the dynamical process in this range of atomic density.

Measurement of the wavelength modulation indices with selective reflection spectroscopy

The wavelength modulation indices are measured based on harmonic amplitude ratio of 4famp/6famp (4famp and 6famp are the 4- and 6-th harmonic central peak amplitudes correspondingly) with the Doppler-free selective reflection modulation spectroscopy. The experiments for the 6S1/2(F = 4) → 6P3/2(F' = 5) transition of cesium D2 line with 30-MHz linewidth were carried out. The 4f- and 6f-harmonic signals were detected with two digital lock-in amplifiers separately. The maximum error for modulation indices measurement was ±0.1 within the range of m from 3 to 6. The non-linear modulation behaviour of an external cavity diode laser induced by voltage tuning was studied with this method. The method for modulation indices measurement does not require a solid etalon as usual for measuring the wavelength modulation depth and the absorption linewidth correspondingly.

Naphthylethyne based liquid crystals with high birefringence and characteristics of selective reflection

A series of high birefringence liquid crystalline molecules with cyano, isothiocyanato and trifluoromethyl terminal compounds based on naphthylethyne core was successfully synthesized and characterized. The molecular structures of the intermediates and resulting compounds were confirmed by Fourier transform infrared （FT-IR）, nuclear magnetic resonance （NMR）, mass spectrometry （MS）, and elemental analysis （EA）. Their thermal stability, transition temperatures, and phase sequences were investigated by simultaneous thermal analyzer polarized （STA）, optical microscopy （POM） and differential scanning calorimetry （DSC）. The birefringence was measured by using an Abbe refractometer. In addition, the selective reflection characteristics with naphthylethyne compounds were also studied.

PREPARATION AND PROPERTIES OF ETHYL-CYANOETHYL CELLULOSE/POLYACRYLIC ACID COMPOSITE FILMS WITH REFLECTION COLORS

Ethyl-cyanoethyl cellulose [(E-CE)C]/acrylic acid (AA) becomes a cholesteric liquid crystalline solution withvivid colors when the (E-CE)C concentration is 42 wt%～52 wt%. (E-CE)C/polyacrylic acid (PAA) composites withcholesteric structure were prepared by polymerzing AA in (E-CE)C/AA liquid crystalline solutions. The layers of orderedpolymer chains in the cholesteric phase were inclined during polymerization and the degree of the inclination depended onthe polymerization temperature and the concentration of the solution before polymerization. The cholesteric structure in thecomposites could not be changed when temperature was lower than 100℃. Cross-linking of the PAA in compositesimproved their water-resistance. The cholesteric order of the composites without cross-linking was destroyed when theywhere immersed in water. The color derived from the selective reflection of the cholesteric phase of the cross-linkedcomposites turned from blue to red after the composites absorbed water. The color of the composites could be returned to theoriginal one when the absorbed water was removed from the swollen composites.

Superelastic Radiative Cooling Metafabric for Comfortable Epidermal Electrophysiological Monitoring

Epidermal electronics with superb passive-cooling capabilities are of great value for both daytime outdoor dressing comfort and low-carbon economy. Herein, a multifunctional and skinattachable electronic is rationally developed on a porous all-elastomer metafabric for efficient passive daytime radiative cooling(PDRC) and human electrophysiological monitoring. The cooling characteristics are realized through the homogeneous impregnation of polytetrafluoroethylene microparticles in the styrene–ethylene–butylene–styrene fibers, and the rational regulation of microporosity in SEBS/PTFE metafabrics, thus synergistically backscatter ultraviolet–visible–near-infrared light(maximum reflectance over 98.0%) to minimize heat absorption while efficiently emit human-body midinfrared radiation to the sky. As a result, the developed PDRC metafabric achieves approximately 17℃ cooling effects in an outdoor daytime environment and completely retains its passive cooling performance even under 50% stretching. Further, high-fidelity electrophysiological monitoring capability is also implemented in the breathable and skin-conformal metafabric through liquid metal printing, enabling the accurate acquisition of human electrocardiograph, surface electromyogram, and electroencephalograph signals for comfortable and lengthy health regulation. Hence, the fabricated superelastic PDRC metafabric opens a new avenue for the development of body-comfortable electronics and low-carbon wearing technologies.

Facile synthesis and characterization of novel thermo-chromism cholesteryl-containing hydrogen-bonded liquid crystals

Two series of novel cholesteryl-containing H-bonded liquid crystals were prepared through facile self-assembly between cholesteryl isonicotinate （proton acceptor） exhibiting a monotropic cholesteric phase, and the 4-alkoxy-benzoic acid or 4-alkoxy cinnamic acid （proton donor）. It was found that the increase of the conjugate length as well as the terminal length can contribute to enhance the interaction of molecules and thus significantly influenced the thermal behaviors of H-bonded LCs. The cholesteric reflection spectra of the induced mesogenic complexes were located in the visible region with the color tuneable thermo-sensitivity, which could be used for display application.

Optically Ambidextrous Reflection and Luminescence in Self-Organized Left-Handed Chiral Nematic Cellulose Nanocrystal Films

Defect-embedded chiral nematic organizations are attractive due to their light manipulation ability that is crucial for photonic applications.Self-assembly of cellulose nanocrystals(CNC)forms a left-handed chiral nematic structure,which makes simultaneous reflection of left-handed circularly polarized(LCP)and right-handed circularly polarized(RCP)light a challenging task.Herein,we present unprecedented evidence that self-organized CNC films with left-handed helical sense and photonic bandgaps(PBG)display ambidextrous CP light reflection with peak reflectivity up to 68%and transform spontaneous photoluminescence to RCP and LCP luminescence with respective|glum|values up to 0.796 and 0.120.These ambidextrous chiroptical properties originate from a left-handed chiral nematic structure consisting of a nematic-like phase,acting as a half-wave retarder,sandwiched between two PBG layers.The latter are spontaneously intercalated into the left-handed helicoids by rapid gelation of CNC colloidal suspensions.We demonstrate that the ambidextrous chiroptical properties can be manipulated by changes in evaporation temperatures,concentrations,and characteristics of CNC suspensions.We showcase the potential of defect-embedded chiral nematic CNC films for the sustainable and scalable development of anti-counterfeiting optical labels.

Chiral Nematic Cellulose Nanocrystals-Magnetite Nanocomposite Films Displaying Magnet-modulated Circular Dichroism Activity

Chirality is omnipresent among biological materials,such as amino acids,sugars,and DNA[1].It plays a vital role in wide-ranging applications including biomedicine,nonlinear optics,and negative index metamaterials[2-4].The chiral structures of molecules and supramolecular systems may cause differential absorption of left-and right-handed circularly polarized light leading to circular dichroism(CD)activity.

A Double Layer Laminated Film of Cellulose Nanocrystals and Dye Displaying Vibrant Circularly Polarized Light

Circularly polarized(CP)light is a circularly polarized electromagnetic wave and is of significance for applications,such as information storage and encryption,3D display and sensing due to its unique optical properties including optical information storage capacity and chiral specificity11-61.In order to produce circularly polarized light,chirality and light including spontaneous luminescence and incident light are necessary.

Does Selectivity in Passenger Pickup Reflect Wisdom or a Moral Crisis?

Zang Qin, 42, a taxi driver in Shanghai, came into the media spotlight because of a blog posting, and has now become a household name in China. It all started from a conversation between Zang and Liu Run, a department manager for Microsoft (China) Corp., when Liu took Zang’s taxi in the middle of March. Liu posted an article on his blog noting how Zang had a monthly income of 8,000 yuan (almost twice the average income of local taxi drivers) by choosing the time he works, his customers and routes to control costs. Zang said he is a happy driver, good at finding pleasure in work. Liu’s article was later linked to other websites and caused a sensation. According to Beijing Youth Daily, Liu invited Zang to Microsoft to give a lecture to some 50 employees. The 45-minute speech was interrupted eight times by hearty applause.