Search

Diffraction gratings that can be used to convert the Hermite--Laguerre--Gaussian (HLG) mode into the Gaussian mode were obtained; these modes are space modes of light beams. The HLG mode is intermediate between the Hermite--Gaussian and the Laguerre--Gaussian modes. Generally, gratings produced from interfering two beams as holograms contain information of not only the phase modulation factor but also the amplitude modulation factor. Thus, they cannot be expected to provide high conversion efficiency. To produce high-efficiency gratings, the interference equation is divided into two factors. The gratings produced by considering only the phase factors act as phase converters. [c] 2010 Optical Society of America OCIS codes: 050.1950, 050.4865, 120.5060, 140.3300.

A fiber-optic mirror magneto-optical trap (mirror-MOT) that uses a pair of circularly polarized light-emitting optical fibers as an optical access is demonstrated. The fiber is fabricated so that a length of birefringence fiber, designed to be a quarter wave retarder at both wavelengths of 780 and 852 nm, is attached directly onto a polarization-maintaining normal fiber. The polarization states of light emitted from the fibers are sufficiently circular for the operation of a mirror-MOT with [sup.87]Rb atoms. The mirror-MOT is able to capture approximately the same number of atoms obtainable with a conventional mirror-MOT. The technique makes it possible to fabricate a compact MOT apparatus by introducing the optical fibers directly into an ultrahigh-vacuum chamber. OCIS codes: 060.2420, 260.1440, 260.5430, 140.3320, 020.7010.

A surface plasmon resonance (SPR) sodium ion sensor using an ion optode membrane film was experimentally and theoretically described based on an absorption-based SPR principle proposed in our previous article (Kurihara, K.; Suzuki, K. Anal. Chem. 2002, 74, 696-701). The sodium ion concentrations from [10.sup.-6] to [10.sup.-1] have been successfully, determined not only by the resonance angle diagnosis of the SPR curve but also by the minimum reflectance one. The ion optode film was plasticized poly-(vinyl chloride) including a neutral sodium ionophore, a pH-sensitive cationic dye, and an anionic additive. Its optical absorption intensity changed with the sodium ion concentrations. The SPR ion sensor physically measured the complex refractive index caused by the absorption in the ion optode film. We have exhaustively investigated the experimental response behavior of the SPR curve relative to the sodium ion concentrations by comparison with numerically simulated SPR curves using a three-layer Fresnel equation including experimental values for the sodium ion optode membrane film. As predicted by the absorption-based SPR principle, the SPR curve behavior of the SPR ion sensors depended on two factors: one was the relation between the excitation frequency of the light source and the absorption maximum frequency in the ion optode film while the other was the gold metamc thickness in the Kretchmann configuration. The concept and practical theory of an absorption-based SPR sensor not only have been proved by the experimental results of the SPR sodium ion sensor but also have successfully allowed flexible ion sensing in an SPR sensor, which would be very difficult without the absorption mechanism in the ion optode film.

Two new types of surface plasmon resonance (SPR) sensors that can determine the concentration of ammonium cations and urea were realized based on the previously reported theory of the absorption-based SPR measurement method. The change of the dielectric constant caused by the change of the light absorption characteristics of dyes incorporated in a sensing membrane phase is utilized in these SPR sensors. The determination of ions using the SPR sensor was realized by detecting the SPR signals of the minimum reflectance related to the change of absorption spectra of the dye in the ion optode membrane consisting of an ammonium-selective ionophore (TD19C6) and a lipophilic cationic dye (KD-M11) that shows absorption spectral changes due to protonation and deprotonation. A SPR enzyme sensor that can determine the concentration of urea was prepared by the combination of this ion optode membrane and an enzyme membrane based on urease. With the newly developed SPR sensors, the intensity changes of the reflectance at the fixed SPR resonance angle are monitored, which is different from conventional SPR sensors where usually the change of the SPR resonance angles is detected. In a continuous-flow experiment using the SPR ion sensor for N[H.sub.4.sup.+] ion determination, a dynamic measurement range from [10.sup.-5] to [10.sup.-2] M was achieved. In the case of the enzyme-based SPR urea sensor, a dynamic range from [10.sup.-4] to [10.sup.-1] M was observed in a stopped-flow batch arrangement. It is expected that this sensing technique can be applied for the SPR-based detection of a wide range of low molecular weight analytes.

An optical-absorption-based surface plasmon resonance (SPR) sensor is proposed, and its theoretical aspects are discussed in terms of mathematical descriptions and numerical simulations of the SPR curve. The response theory of the absorption-based SPR sensing is based on the expansion of Kretchmann's SPR theory into the case in which optical absorption in the sensing layer is expressed by the Lorentz model. The numerical simulations were performed using a three-layer Fresnel equation of p-polarization. It was found that SPR curve behavior of the absorption-based SPR sensor depends on the frequency relation between the light source and the optical absorption and the thickness of the metal layer. The SPR curve behavior is divided into three types according to the large, small, and equal relations between excitation and absorption frequencies. Each type of behavior is further divided into two types that are due to thin and thick metal layers. The theory of this new type of sensor based on optical absorption was explained and demonstrated by the simulation of the SPR curves using optical parameters relating to a silver-metal-based SPR sensor.

The preparation and response features of a micrometer-sized sodium ion-selective fiber optode based on a liquid membrane were described. The sensing membrane is a plasticized poly(vinyl chloride)-based copolymer with a neutral sodium ionophore and an anionic dye. To fabricate a micrometer-sized fiber optode, a 'micropipet fabrication method' was proposed to fix a liquid membrane-based optode on the small tip of an optical fiber probe, in which the optode size can be varied from [approximately] 1 [[micro]meter] to more than 10 [[micro]meter]. Our first optode incorporated a 16-crown-5 derivative as the neutral sodium ionophore and a dibromofluorescein derivative as the single-emission anionic dye. The sensor response was monitored by measuring the fluorescence intensity under a time-resolved photoncounting method. At the first stage of the investigation, it was found that the ionophore including a sodium ion in its cavity leached from the membrane phase. However, we have discovered that the problem can be resolved by using a 'tailed' ionophore, which is an ionophore possessing a lipophilic long alkyl chain. The 'tail' of the ionophore functions as an 'anchor' that prevents leaching of the ionophore from the membrane phase into the water phase. The anchor effect of the tailed ionophore was clearly demonstrated with 6-[[micro]meter]-sized sodium ion-selective optodes. Using a 3-[[micro]meter]-sized optode, the sensor response was examined and successfully explained by the response theory. The size limitation of the optode was also examined using the response features of a 1.5-[[micro]meter]-sized fiber optode. The second optode incorporated a tailed 16-crown-5 derivative as the neutral sodium ionophore and a coumarin derivative as the dual-emission anionic dye. The second optode is more practical than the first optode because the problem of fluorescence distortion due to photobleaching and solvent effect is resolved by ratiometric calibration where the sensor response is monitored by the spectral shift of the dual-emission fluorescence. The sensor response of an 8-[[micro]meter]-sized fiber optode having ratiometric calibration was examined and successfully explained by the response theory.