Near-field Optical Fiber Probe Research Articles

Nondestructive Temperature Measurement Method for Living Cells Based on Near-Field Optical Fiber Probe

Nondestructive Temperature Measurement Method for Living Cells Based on Near-Field Optical Fiber Probe

Nanoscale optical thermometry using a time-correlated single-photon counting in an illumination-collection mode

A nanoscale thermometry method called fluorescence near-field optics thermal nanoscopy (Fluor-NOTN) has been developed using near-field fluorescence imaging. This method can detect local temperature distributions with a nanoscale spatial resolution by measuring the fluorescence lifetimes of Cd/Se quantum dots (QDs) as a temperature probe. To increase the sensitivity of Fluor-NOTN, time-correlated single-photon counting (TCSPC) was introduced with a triple-tapered fusion-spliced near-field (TFN) optical fiber probe. This highly sensitive technique for measuring the fluorescence lifetime of QDs enabled the detection of low-level light signals with a picosecond time resolution at high-precision in an illumination-collection mode for Fluor-NOTN. The feasibility of this proposed method was experimentally verified by measuring the temperature dependence of the fluorescence lifetimes of the QDs by Fluor-NOTN using TCSPC with a TFN optical fiber probe with an aperture of 70 nm.

Numerical analysis of the temperature dependence of near-field polarization for nanoscale thermometry using a triple-tapered near-field optical fiber probe

A novel nanoscale temperature measurement method using near-field polarization, namely polarized near-field optics thermal nanoscopy (P-NOTN), has been developed. This method is performed in illumination–collection mode (I–C mode) using an Au-coated near-field fiber probe, and enables non-contact and nanoscale temperature measurement. The polarization change of the near-field light due to temperature change in the I–C mode is complicated. In order to confirm and understand the temperature dependence of the near-field polarization, and assess the validity of the temperature measurement by P-NOTN, numerical investigations were performed by the finite-difference time-domain (FDTD) method, which numerically solves Maxwell’s equations. Three-dimensional models of the Au-coated near-field fiber probe and the one-dimensional nanostructure as a sample (i.e. Au nanorod) were produced. The electromagnetic field between the probe tip and the nanoscale sample was calculated by the FDTD method in order to evaluate the polarization change in the I–C mode. The calculation results showed that the polarization plane in the near field changes as a function of the refractive index of the sample, which in turn is temperature-dependent. These calculation results verified the capability of P-NOTN to achieve nanoscale temperature measurement by detecting the temperature-dependent polarization rotation change in the near field.

Plasmon Polariton Imaging Characteristics of Near-Field Optical Fiber Probes

The influence of different near-field optical (near-field scanning optical microscopy) probes on the imaging of surface plasmon polaritons propagating on thin metal films is investigated. Metal-coated fiber probes exhibit a suppression of the measured plasmon signal close to the metal film surface and increased local scattering of the plasmon field. Purely dielectric fiber probes are shown to be largely free of these effects.

FDTD Analysis of Nanoscale Temperature Distribution Induced by Near-Field Photothermal Effect

We have developed a novel nanoscale patterning method of self-assembled monolayer (SAM) using near-field light. This method utilizes the thermal desorption of constituent molecules of a SAM (e.g. the desorption temperature of Octadecanethiol on Au is 130～230 °C) through the irradiation with near-field light, which can make noncontact and noncontaminating patterning of the SAM at nanoscale. In this paper, the near-field photothermal effect is numerically analyzed by the finite difference time domain (FDTD) method, and the electromagnetic field intensity and temperature distributions are estimated. The sample consists of Au thin film as a bonding layer with thiolated molecules of SAM, Ti thin film as an adhesion layer for Au, and SiO2 substrate. In the analysis, the shape of the near-field optical fiber probe and the thickness of the thin film layer are considered. In the case of the thick Au layer with a double-tapered near-field optical fiber probe, the temperature of the fiber-tip becomes higher than that of Au surface. The strong heating of the probe tip causes a fatal damage of the coating metal of the fiber, therefore it is difficult to couple the high intensity laser into the near-field optical fiber probe in order to reach the desorption temperature. On the other hand, the desorption temperature can be achieved with the 10 nm-thick Au thin film. Moreover, in order to gain high optical intensity enhancements, the triple-tapered near-field optical fiber probe is utilized. Our simulations confirm extremely high temperature distribution on the sample surface by using the triple-tapered near-field optical fiber probe with 10 nm-thick Au thin film layer on 50 nm-thick Ti membrane.

Near-field fluorescence thermometry using highly efficient triple-tapered near-field optical fiber probe

A novel local temperature measurement method using fluorescence near-field optics thermal nanoscopy (Fluor-NOTN) has been developed. Fluor-NOTN enables nanoscale temperature measurement in situ by detecting the temperature-dependent fluorescence lifetime of CdSe quantum dots (QDs). In this paper, we report a novel triple-tapered near-field optical fiber probe that can increase the temperature measurement sensitivity of Fluor-NOTN. The performance of the proposed probe was numerically evaluated by the finite difference time domain method. Due to improvements in both the throughput and collection efficiency of near-field light, the sensitivity of the proposed probe was 1.9 times greater than that of typical double-tapered probe. The proposed shape of the triple-tapered core was successfully fabricated utilizing a geometrical model. The detected signal intensity of dried layers of QDs was greater by more than two orders than that of auto-fluorescence from the fiber core. In addition, the near-field fluorescence lifetime of the QDs and its temperature dependence were successfully measured by the fabricated triple-tapered near-field optical fiber probe. These measurement results verified the capability of the proposed triple-tapered near-field optical fiber probe to improve the collection efficiency of near-field fluorescence.

A Fusion-Spliced Near-Field Optical Fiber Probe Using Photonic Crystal Fiber for Nanoscale Thermometry Based on Fluorescence-Lifetime Measurement of Quantum Dots

We have developed a novel nanoscale temperature-measurement method using fluorescence in the near-field called Fluorescence Near-field Optics Thermal Nanoscopy (Fluor-NOTN). Fluor-NOTN enables the temperature distributions of nanoscale materials to be measured in vivo/in situ. The proposed method measures temperature by detecting the temperature dependent fluorescence lifetimes of Cd/Se Quantum Dots (QDs). For a high-sensitivity temperature measurement, the auto-fluorescence generated from a fiber probe should be reduced. In order to decrease the noise, we have fabricated a novel near-field optical-fiber probe by fusion-splicing a photonic crystal fiber (PCF) and a conventional single-mode fiber (SMF). The validity of the novel fiber probe was assessed experimentally by evaluating the auto-fluorescence spectra of the PCF. Due to the decrease of auto-fluorescence, a six- to ten-fold increase of S/N in the near-field fluorescence lifetime detection was achieved with the newly fabricated fusion-spliced near-field optical fiber probe. Additionally, the near-field fluorescence lifetime of the quantum dots was successfully measured by the fabricated fusion-spliced near-field optical fiber probe at room temperature, and was estimated to be 10.0 ns.

Nanoscale Two-Photon Induced Polymerization of Diacetylene Langmuir−Blodgett Film by Near-Field Photoirradiation

We have succeeded in nanoscale polymerization of Langmuir−Blodgett (LB) films of cadmium 10,12-pentacosadiynoate (CdPA) by near-field two-photon excitation with femtosecond pulses. The LB films of CdPA were excited locally through an aperture of a near-field optical fiber probe by femtosecond-pulsed near-infrared radiation. The formation of polydiacetylene (PDA) films has been confirmed by two-photon induced and ordinary (linear) luminescence and Raman measurements by using a scanning near-field optical microscope. The polymerization of CdPA to PDA was induced by the femtosecond-pulsed near-infrared radiation but not by continuous wave radiation. This result confirms that the polymerization was not induced by heat arising from the near-field irradiation. The number of photons involved in the polymerization reaction was estimated to be 2 from the dependence of photoluminescence intensities of PDA on the power of incident light for polymerization.

Nano-manipulation performance with enhanced evanescent field close to near-field optical probes

Recently, interest in nano-manipulation using the evanescent wave generated by nano-objects has been growing, but the analyses of manipulation flexibility and performance haven't been solved. In this paper the near-field optical trap utilizing a tapered metalized probe used in NSOM is described in detail. By employing a generalization of the conservation law for momentum using three-dimensional FDTD method, rigorous calculations of field distributions and trapping forces in near-field region are conducted. Calculations show that the particle with radius larger than the aperture is pushed away from the metal-coated fiber probe, while it tends to be trapped in larger effective region as its radius becoming smaller. The particle that is placed very near the aperture and around two field peaks intends to be dragged to the aperture edge, while the particle placed at other position tends to be attracted to the center surface of the probe tip. Furthermore, a preferable method using the combination of the near-field optical fiber probe and the AFM metallic probe is proposed, for more efficient non-contact manipulation and better observation of one single nano-particle. The analyses of trapping potential along the probe axis and the near-field distribution show the possibility of particle trapping.

Direct observation of below-diffraction-limited optical spot induced by nonlinear saturable absorption of Ag-doped Si nanofilms

In this work, using the scanning near-field optical fiber probe method, we carry out a direct observation of below-diffraction-limited optical spot induced by nonlinear saturable absorption characteristic of Ag-doped Si nanofilms. The experimental results indicate that the squeezed spot size decreases with laser power increase, and the smallest spot can be squeezed to 68% of the diffraction-limited focusing spot size, which is very useful and can be applied to superresolution optical recording, optical lithography, and optical imaging.

偏光した近接場光を用いたナノスケール温度測定手法の開発(<小特集>第1回マイクロ・ナノ工学シンポジウム)

Measurement of temperature distribution at nanometer scale is important for the thermal design of high integrated devices. However, in conventional optical measurement techniques, the spatial resolution is limited by the diffraction limit of light, which is approximately half of the wavelength of the optical beam. Therefore, we have developed a novel optical temperature measurement method in nanometer scale using near-field microscope technique. We newly employed the polarization of light into the measurement principle, since the near-field polarization has a high sensitivity for the refraction index of the sample, which varies with temperature. In this method, the near-field optical fiber probe which can maintain the polarization state is necessary for increasing the measurement sensitivity. Hence, we have newly fabricated the single mode near-field optical fiber probe. In this paper, we report the verification of the new measurement principle and the comparison of the measurement sensitivity with the results using temperature dependence of reflectance.

M3-6 偏光した近接場光を用いたナノスケール温度・熱物性測定手法の開発(M3 熱流体デバイス)

Measurement of temperature distribution at nanoscale is absolutely important for the thermal design of high integrated devices. However, in conventional optical measurement techniques, the spatial resolution is limited by the diffraction limit of light, which is approximately half of the wavelength of the optical beam. Therefore, we have developed a novel optical nanoscale temperature measurement method using near-field microscope technique. We newly employed the polarization of light into the measurement principle, since the near-field polarization has a high sensitivity for the refraction index of the sample, which varies with temperature. In this method, highly polarization maintaining near-field optical fiber probe is necessary for increasing the measurement sensitivity. Hence, we have newly fabricated the single mode near-field optical fiber probe. In this paper, we report the verification of the new measurement principle and the comparison of the measurement sensitivity with the results using temperature dependence of reflectance.

Ultrasonically induced Effects in Electroless Nickel Plating to Fabricate a Near-Field Optical Fiber Probe

We have studied the submicron size dependence of electroless nickel plating under ultrasonic irradiation with a frequency of 1 MHz to fabricate a near-field apertured probe. Using a new ultrasonic bath with a small water depth of 80 mm, we found that a nickel film with a hollow structure is coated on the flat clad end of a fiber probe. The diameter of the hollow is 12 µm much smaller than the ultrasonic wavelength in water.

Fluorescence correlation spectroscopy at 100 nM concentrations using near‐field scanning optical microscopic (NSOM) geometries and highly diffracting force sensing fiber probes

AbstractA tapered cantilevered optical fiber probe is introduced for fluorescence correlation spectroscopy (FCS). The probe has an aperture that is coated with metal and its dimension can be very well defined. Its design is based on cantilevered near‐field optical fiber probes that allow for on‐line atomic force feedback. This permits unprecedented stability in FCS measurements. Even such probes that have large diameters are below the cutoff wavelength of light propagation in optical fibers. Such large diameter probes produce bright spots of light that are highly diffracting. Therefore, only the fluence of light very close to the surface of the glass probe aperture is sufficient to exhibit a high probability of fluorescence excitation. From the results presented in this paper the z extent of such probes seems comparable to what can be obtained from prism‐based evanescent wave methods, but with much more flexibility and including force sensing capability. In agreement with theoretical results on prism evanescent field‐based excitation, it is shown that even with large xy dimensions for the fiber probes in this paper, fluorescence correlation spectra from 100 nM fluorophore concentrations can be recorded. This is 10 times larger than the concentrations generally required for conventional confocal FCS. The results suggest that such an approach has considerable potential for applications of FCS in membrane, near‐membrane, solution, and even within‐cell environments. The latter is achieved through atomic force feedback controlled penetration of tapered cantilevered metal‐coated glass fibers into cells, and this is also reported in this paper.

Fabrication of a Brush-Shaped Bent Fiber Probe for Near-Field Optics by Heated Pulling Combined with Chemical Etching

We developed a method to fabricate bent fiber probe: heated pulling combined with chemical etching. Based on sampling theory, the resolving power of SNOM relates to the size of the probe tip. If the apex of the probe is smaller, the resolution ability of SNOM is higher. At the same time it can collect more near-field information through bigger cone angle of probe. Through improving the operation and optimizing the parameters of the heated-pulling instrument, we can obtain the probe with bent angle fiber varying from 120-150 degree, the cone angle varying from 40-90 degree and the apex diameter less than 100nm. With this new brush shape of probe, the collecting efficiency for near-field light is improved. That is to say that more near-field information is obtained. The successful ratio of the produce is more than 70%.

2-09P-46 Plating method with ultrasonic agitation to fabricate a near-field optical fiber probe(Poster session 2)

2-09P-46 Plating method with ultrasonic agitation to fabricate a near-field optical fiber probe(Poster session 2)

Synthesis of nanocrystals in KNb(Ge,Si)O 5 glasses and chemical etching of nanocrystallized glass fibers

The nanocrystallization behavior of 25K 2O−25Nb 2O 5–(50− x)GeO 2– xSiO 2 glasses with x = 0 , 25 , and 50 (i.e., KNb(Ge,Si)O 5 glasses) and the chemical etching behavior of transparent nanocrystallized glass fibers have been examined. All glasses show nanocrystallization, and the degree of transparency of the glasses studied depends on the heat treatment temperature. Transparent nanocrystallized glasses can be obtained if the glasses are heat treated at the first crystallization peak temperature. Transparent nanocrystallized glass fibers with a diameter of about 100 μm in 25K 2O–25Nb 2O 5–50GeO 2 are fabricated, and fibers with sharpened tips (e.g., the taper length is about 450 μm and the tip angle is about 12°) are obtained using a meniscus chemical etching method, in which etching solutions of 10 wt%-HF/hexane and 10 M-NaOH/hexane are used. Although the tip (aperture size) has not a nanoscaled size, the present study suggests that KNb(Ge,Si)O 5 nanocrystallized glass fibers have a potential for new near-field optical fiber probes with high refractive indices of around n = 1.8 and high dielectric constants of around ε = 58 (1 kHz, room temperature).

Tip-Shape Reconstruction for a Laterally Vibrating SPM Probe

This study is concerned with the tip-shape reconstruction for the shear-force scanning probe microscope and the near-field scanning optical microscope, in which the probe executes lateral vibrations. The spatial resolution of the microscopes is directly dependent on the tip radius. A reconstruction method is proposed that employs specially designed test structures and is based on deconvolution. The method is used to generate images of tungsten and nickel wire probes, fabricated by electrochemical etching, and near-field optical-fiber probes. The results are verified by TEM imaging of the probes. By the same approach, correlation is revealed between reconstructed probe aperture and resolution for the near-field optical microscope.

Observation of tip-to-sample heat transfer in near-field optical microscopy using metal-coated fiber probes

Metal-coated scanning near-field optical microscopy fiber probes can undergo significant heating due to partial absorption of the coupled light by the metallic film covering the apical zone. In this letter we report experimental evidence of tip-to-sample heat transfer on a 7,7′,8,8′-tetracyanoquinodimethane molecular crystal. Local melting is observed at nanometric tip–sample distances, when increasing the laser power injected into the fiber above a threshold of 8.8mW. Hole formation and material displacement are observed, as well as failure of the shear-force-based imaging process, due to partial sticking of the melted material to the probe.

Intermode conversion in a near-field optical fiber probe

The propagation of light in metal-coated fiber probes used in scanning near-field optical microscopy is studied computationally by means of the cross-section method. In contrast to previous work focusing on the behavior of the HE11 mode in the vicinity of the end aperture of the probe, we trace the propagation of the incident fundamental mode of the optical fiber through the tapered probe. The transformation of the fiber mode into the probe modes, intermode conversion, and modes cutoff are consistently calculated. In particular, it is shown that in the conventional gradual tapered probe only a few percent of the input power are transformed into the HE11 mode which has the smallest cutoff radius. In addition, an easily manufacturable modification of the shape of the probe’s tip that can provide a tenfold enhancement in optical near-field intensity has been proposed.